Shipbuilding and repair

The construction of each of the large merchant ships, ocean liners and warships built during the 1990s swallowed up tons of steel and aluminum and used a host of materials ranging from the most common to the most rare. . All carry in their sides hundreds, even thousands of kilometers of pipes and cables, as well as very sophisticated electrical and electronic equipment. To carry out the missions entrusted to them without difficulty, they must be able to face the most hostile environments while ensuring the comfort and safety of crews and passengers.

Shipbuilding and ship repair are among the most dangerous industries in the world. The US Bureau of Labor Statistics, for example, ranks this industry among the three industries with the highest accident rates. Even if the materials, methods, tools and machinery used have changed a great deal over time and continue to evolve and if, thanks to the training of personnel and the importance given to safety and health issues , the lot of workers in shipyards has greatly improved, the fact remains that every year throughout the world, many workers die or are victims of serious accidents on these yards while they are employed in the construction, maintenance or repair of ships.

Despite technical progress, many of the tasks involved in building, launching, maintaining and repairing ships today are much the same as when the first keel was laid, there are thousands of years; the same applies to working conditions. The size and shape of the parts that make up a ship and the complexity of their assembly and armament prohibit, to a large extent, the use of any form of automated process. A certain degree of automation has, however, been made possible thanks to technical progress, with the exception of repair work which hardly lends itself to it. Shipbuilding requires a large and highly skilled workforce capable of working in a harsh and physically demanding environment.

The environment in which shipbuilding work is carried out is in itself a challenge. Apart from a few shipyards where the construction and repair of ships takes place under cover, this work generally takes place in the open. Ships are built in all latitudes. While construction workers in the Far North have to face the rigors of winter (which forces them to work on surfaces made slippery by ice or snow, during days when daylight is scarce, and at physical exertion that is all the more strenuous as they have to spend long hours on icy steel surfaces and in often uncomfortable positions), those in more southern regions have to endure the stresses of heat, the risk of sunburn , working on surfaces so hot that food could be cooked on them, insect bites and even snake bites. Work is generally carried out above or around a body of water, in water or even under water. Often, the wind whips up the tidal currents and causes the surface on which the workers have to perform difficult tasks to roll or sway in all sorts of dangerous positions and using equipment capable of causing serious injury. The wind, which is often unpredictable, is a force that must be taken into account when positioning or moving parts frequently weighing more than 1,000 tonnes, especially if the operation is done using coupled cranes. The challenges presented by the natural environment are manifold and offer a seemingly endless combination of situations for which safety and health professionals must design ad hoc preventive measures. It is obviously essential that the workforce be properly informed and trained.

From the installation of the first steel plates that make up the keel, the shipyard is constantly changing and its growing complexity is accompanied by a whole series of potentially dangerous and ever new situations which require that not only precise procedures be established for getting the job done, but also the means to recognize and resolve the myriad unpredictable situations that will inevitably arise during construction. As it progresses, the scaffoldings are added to each other to allow access to all points of the hull. Constructing strong scaffolding is inherently a very specialized job that can expose workers to increasing risks as the vessel rises above the ground or water. As the hull begins to take shape, the interior of the boat also falls into place thanks to modern construction methods which allow large sub-assemblies to be assembled, thus creating enclosed or confined spaces.

It is at this stage that the high density of labor that characterizes this sector of activity is most evident, underlining the importance of good coordination of safety and health measures and of taking awareness of workers in all matters relating to their own safety and that of their co-workers.

Each space within the hull is designed for a very specific purpose. The hull can be a void that will contain the ballast, but it can also contain tanks, cargo holds or berths, or even house a highly sophisticated military operations control center. Be that as it may, its construction will require the intervention of teams of specialists who will have to work side by side. Thus we can find, in the same place and at the same time, pipe fitters mounting valves on pipes, electricians pulling on cables or installing circuits, painters doing touch-ups, welders assembling bridge plates, carpenters, installers of insulating materials or even a team responsible for checking the proper functioning of a system. Such situations, and others even more complex, arise every day and throughout the day, in changing patterns dictated by technical or planning requirements, staff availability and even weather conditions.

The application of coatings presents several risks. Spray painting often has to be done in confined spaces with volatile paints and solvents or with a range of epoxy type coatings known for their toxic effects.

Considerable progress has certainly been made over the years in terms of safety and health thanks to better-designed construction methods and materials, safer installations and great efforts to train the workforce. work. However, most of the progress made to date and what remains to be done is and will be due to the attention paid to the worker as an individual and to the behaviors that are at the origin of the accidents. This is no doubt true for the majority of branches of activity, but the high density of labor which characterizes shipbuilding yards makes this aspect of the problem particularly important. This new design of safety and health programs involving workers more directly and taking their opinions more into account not only has the advantage of making them aware of the risks inherent in their work and the means of avoiding them, but also gives them a feeling ownership of the prevention program. Yet it is precisely this feeling that is the key to success in this area.

Shipbuilding.

Building a ship is a complex, highly technical process. It requires the close collaboration of many qualified personnel and a contract labor force which generally works under the direction of a main contractor. Boats are built for commercial or military purposes. It is an activity of an international nature, where a few large shipyards are fighting to conquer their share of a relatively small market.

Since the end of the 1980s, profound changes have marked this branch of activity. In the past, building a ship was mostly done inside a building or in drydock, and almost piece by piece, from keel to masts. Thanks to technical progress and more advanced planning, it is now possible to build a ship in sub-assemblies or using relatively easy to assemble modules, already equipped with integrated installations and systems. This way of proceeding is faster and less costly and facilitates quality control. In addition, it is more amenable to automation and robotization, which not only saves money, but also reduces worker exposure to chemical or physical hazards.

The main stages of building a ship

This begins with the study of the project. The elements taken into consideration at this stage vary according to the type of ship considered. A ship is generally designed to primarily transport materials or people. It can be a freighter or an ocean liner, a surface ship or a submarine, a warship, a coaster or a ferry; it can be conventional or nuclear powered. It is important, from the design office stage, to consider not only the usual construction parameters, but also the health and safety risks inherent in the construction or repair process, as well as their possible effects on the environment.

The basic material of shipbuilding is sheet steel. The sheets are cut, shaped, bent or shaped to give them the desired dimensions and shape (see figures 92.2 and 92.3). In general, sheet metal is cut by gas oxycutting. The resulting members are then welded to form I-, T- or L-joists and other chords.

The sheet metal plates are then sent to the manufacturing workshops where they are assembled into different units and different sub-assemblies (see figure 92.5). It is at this stage that the piping, electrical circuits and other distribution circuits are put in place and integrated into the units. These are assembled by automatic or manual welding, or by a combination of the two techniques. Several welding processes are used, the most common being arc welding with a coated fusible electrode as the filler metal. Other arc welding processes use an inert protective atmosphere or even refractory electrodes that withstand very high temperatures.Figure 92.5 Work on a vessel subassembly.

Units or sub-assemblies are usually transferred to outdoor assembly areas where they are deposited awaiting assembly into larger assemblies (see figure 92.6). We then proceed to additional welding and adjustment operations. These assemblies and more specifically their weld beads are subjected to quality controls and tests by radiography or ultrasound as well as, where appropriate, to destructive or non-destructive tests. Defective welds are removed by grinding, flame cutting or gouging, then redone. The elements are then abrasive blasted, if necessary, to make them fit, before receiving one or more coats of paint (see figure 92.7). This is applied by brush, roller or, most often, by spray gun. In some cases, it may be flammable or toxic paint that poses a risk to workers and the environment. Stripping and painting operations must be accompanied by the required safety measures.

Once completed, the large units are transported to dry dock, dry dock or to the final assembly area where they are assembled to form the ship (see figure 92.8), which calls for further welding and fitting operations. . With the hull structures thus assembled and its watertightness verified, the ship is launched. The launch can be done either by sliding it along an inclined plane until it is afloat, or by flooding the dry dock, or by lowering the hull to the water. These launches are almost always the occasion for festivities.

Once launched, the ship enters the arming phase; this requires a lot of time and significant equipment. This involves laying cables and pipes, fitting out the galleys and crew quarters, fixing the insulation, installing the electronic equipment and navigation aids and setting up the propulsion and the governing bodies. Many trades are involved.

At the end of the outfitting phase, the ship undergoes trials in the basin and at sea, during which all the systems are tested to ensure that they operate correctly. It is only once all the necessary tests and adjustments have been carried out that the vessel is delivered to the client.

Manufacture of steel parts.

The various phases of this manufacture are briefly described below.

The cutting

The "assembly line" of a shipyard starts from the steel storage area, where large sheets of various qualities and sizes are stored and prepared for processing. The steel is then stripped to receive a base coat which will ensure its anti-corrosion protection throughout the various phases of construction. The sheets are then transported to a manufacturing area where they are cut to the desired dimensions by flame cutting; this operation is automated. The strips thus obtained are assembled by welding to form the structural elements of the ship.

Welding

The framework of most ships is made of steels of various qualities, which range from mild steel to high tensile steel. Steel has the qualities of ductility, machinability and weldability, as well as the resistance essential to any ocean-going vessel. Aluminum and non-ferrous materials are also used for certain superstructures (for example deckhouses) and for other specific parts of the ship. Other materials stainless steel, galvanized steel, cupro-nickel alloys are also used to meet various corrosion resistance requirements and to improve the solidity of the whole. However, steels are still widely used more than non-ferrous materials. In general, less common materials are reserved for ventilation installations, military operations control centers, navigation systems and piping. These materials fulfill a large number of functions, whether for propulsion machinery, emergency electrical circuits, galleys, fuel pumping stations or combat systems.

Three types of steel are used in shipbuilding: mild steel, high strength steel and high alloy steel. Mild steels have remarkable properties and are easy to produce, shape and weld. High-strength steels are low-alloy in order to give them mechanical properties superior to those of mild steels. Finally, very high-strength steels have been specially developed for shipbuilding. In general, high strength, high yield strength steels are designated HY-80, HY-100 or HY-130. Their strength is greater than that of commercial high-strength steels. They require more complex welding processes if their properties are to be avoided: special welding electrodes, joint preheating, etc. High alloy steels contain relatively large amounts of alloying elements such as nickel, chromium and manganese. These steels, including stainless steel, offer high resistance to corrosion and also require special welding processes.

Steel is an excellent shipbuilding material; a judicious choice of welding electrodes is essential, whatever the type of welding to be carried out. The general objective is to obtain a weld with the same resistance characteristics as the base metal. Since any welding operation can present minor defects, the processes and the electrodes used are chosen so that the quality of the welds obtained is superior to that of the base metal.

Aluminum is increasingly used in shipbuilding due to a better strength to weight ratio than steel. While it is still little used for hulls, it is increasingly used in the superstructures of merchant ships and warships. Ships that are made solely of aluminum are mostly small-sized vessels, such as fishing boats, pleasure boats, small ocean liners, rowboats and hydrofoils. The aluminum used in shipbuilding and repair is usually alloyed with manganese, magnesium, silicon or zinc. These alloys offer high strength and good weldability and corrosion resistance.

Welding, more specifically fusion welding, is done almost everywhere in a shipyard. The operation consists of assembling metals by bringing contiguous surfaces to extremely high temperatures in order to join them by fusion using a filler metal itself in fusion. A heat source is used to heat the two edges to be welded, allowing them to bond with the filler metal (electrode, wire or rod). The necessary heat is usually generated by an electric arc or a gas flame. The welding process is chosen in each case according to the specifications drawn up by the customer, production rates and a certain number of operating constraints, in particular official standards. These are generally stricter for warships than for merchant ships.One of the important factors in arc welding processes is the protection of the weld pool. The temperature of the weld bed is considerably higher than the melting point of the metals to be welded. At extremely high temperatures, reaction with oxygen and nitrogen in the air occurs rapidly and can compromise the strength of the weld. If atmospheric oxygen and nitrogen are caught in the weld metal or molten rod, the weld zone is weakened. This defect and the good quality of the weld can only be avoided by protecting it from the atmosphere. In most welding processes, this protection is done by adding a flux (flux), a gas or both at the same time. With the flux, the gases produced by vaporization and chemical reaction at the end of the electrode form, by combination with the gas and the flux, a protection which prevents the weld from capturing nitrogen and oxygen. This issue is covered in more detail in the sections below on specific welding techniques.

In electric arc welding, a circuit is created between the workpiece and an electrode or wire. If the electrode or wire is held in close proximity to the workpiece, a high temperature arc will form. This arc generates sufficient heat to melt the edges of the workpieces and cause the end of the electrode or wire to produce a fusion weld system. There are many electric arc welding processes that can be applied in shipbuilding; all require protection of the area to be welded from the atmosphere. They can be subdivided into two categories: flux protection and gas protection.

According to manufacturers of welding equipment and related products, arc welding with fusible electrodes is the most widely used technique.

Gas-shielded arc welding with coated fusible electrodes (Shielded Metal Arc Welding SMAW)

Electric arc welding processes with flux protection are mainly distinguished by their manual or semi-automatic nature and by the type of fusible electrode used. In the SMAW technique, a fusible electrode (30 to 46 cm long) with a dry flux coating is used, held in an electrode holder and brought to the welder by the welder. The electrode is composed of a core or core of solid filler metal obtained by drawing or rolling and coated with a sheath of metal powders. SMAW is also often referred to as "stick welding". The electrode metal is surrounded by a flux which gradually melts, coating the deposited molten metal with slag and enveloping the nearby area in an atmosphere of shielding gas. The manual SMAW can be used for floor (flat), horizontal, vertical and overhead welding. It can also be used semi-automatically using a rotary welder. Rotary welders take advantage of the weight of the electrode and backing to move the weld work along the workpiece.

Submerged Arc Welding SAW

This alternative arc welding process with flux shielding is used in many shipyards. The technique consists of depositing a layer of granulated flux on the part to be welded, then using a consumable electrode of bare metal. Usually the electrode is used as filler metal, although in some cases metal granules are added to the flux. The arc is submerged in a powdered flux, part of which melts, covering the weld with a layer of slag. A high concentration of heat allows heavy solder deposits at relatively high speeds. After welding, the molten metal is protected by a layer of molten flux, which is subsequently removed and can be recovered. This welding process must be carried out on the ground and is perfectly suited for the butt welding of sheets. In general, the SAW technique is completely automated, with the equipment mounted on a mobile cart or on a self-propelled platform overlooking the parts to be welded. Most of the time is spent aligning the joints under the machine. Since the arc operates under a layer of granulated flux, the rate of smoke production is low and remains so throughout operations, provided the flux layer is sufficient.

Gas shielded arc welding with fusible electrode wire (Gas Metal Arc Welding GMAW). Another important class of electric arc welding processes are those that use shielding gas. In these processes, recourse is had to electrodes which are generally bare wires. The shielding gas which can be inert, active, or both envelopes the electrode. GMAW, also commonly called MIG (Metal Inert Gas) welding, uses a consumable electrode which consists of a bare wire of small diameter, pushed automatically into a contact tip, and a shielding gas. This technique is the result of long research aimed at perfecting a method allowing continuous welding without having to stop to change electrodes. It requires an automatic wire feeder. A wire feeder delivers wire as it melts, either at constant speed or at variable speed depending on the voltages required, in this case regulated by a variable speed drive. When the arc strikes between the wire and the piece to be welded, a gas shield is created around the electrode by blowing in argon or helium using a torch. The combination of CO 2 and an inert gas has proven useful for steel welding, reducing production costs and improving the quality of welds.

TIG welding (Gas Tungsten Arc Welding GTAW)

Another gas-shielded welding process is refractory tungsten arc welding, sometimes referred to by the brand name Heliarc because in the beginning helium was used as the inert gas. This was the first of the "new" welding processes, which succeeded filler rod welding some 25 years later. The arc is struck between the workpiece and a refractory tungsten electrode. An inert gas, usually argon or helium, serves as a shielding gas and makes the process a clean, low fume technique. Also, the arc in this case does not transfer the filler metal, but simply melts the workpiece and the wire, resulting in a cleaner weld. The TIG process is most often used in shipyards for welding aluminum, sheet metal and small diameter pipe, or for depositing the root pass of a multipass bead when welding heavy duty pipe. larger diameter or larger parts.

Flux Core Arc Welding (FCAW) uses the same type of equipment as MIG welding in that the arc is fed with continuous wire. The main difference is that the electrode in the FCAW process is a tubular wire and contains a flux in its core which contributes to localized protection in the weld zone. Although some wires of this type provide sufficient protection thanks to their single core, many FCAW processes used in shipbuilding require additional gaseous protection in order to meet the requirements of the industry.

The FCAW process makes it possible to produce high quality welds with higher production rates and efficiency than those obtained by the conventional SMAW method. It can meet a variety of production requirements, such as overhead welding and vertical welding. FCAW electrodes tend to be slightly more expensive than SMAW electrodes, but the improved quality and productivity often justify the investment.

Plasma arc welding, or plasma welding (Plasma-arc Welding PAW)

The most recent of the gas-shielded welding processes is inert gas plasma welding. The PAW process is very similar to the GTAW process, the only difference residing in the constraint imposed on the arc to undergo a constriction in a plasma gas before reaching the part to be welded. This results in an extremely hot and fast plasma jet. The plasma is an ionizing jet of gas carrying the arc, generated by the constriction imposed to pass through a small orifice of the torch. The PAW process makes it possible to obtain a denser arc, at high temperature, which allows faster welding. Apart from the use of an orifice to accelerate the gas, the PAW and GTAW processes are identical and both use a refractory tungsten electrode and inert gas shielding. PAW is generally manual and very little used in shipyards, although it is sometimes used for flame spraying applications. In shipyards, it is mainly used for cutting steel.

Plasma cutting of sheet metal underwater

Gas welding, hard soldering and soft soldering. Gas welding uses the heat produced by the combustion of a gas or several combustible gases with an oxidizing gas (usually oxygen); he usually uses a rod for the filler metal. The most traditional fuel is acetylene, used in combination with oxygen (oxyacetylene welding). A hand-held torch directs the flame toward the workpiece, while melting the filler metal that is deposited in the contact area. The surface of the work piece melts to form a molten crater, with filler material used to fill in the voids or grooves. Molten metal, primarily filler metal, solidifies as the torch travels along the workpiece. Gas welding is comparatively slow and not suitable for automatic or semi-automatic equipment. As a result, it is rarely used as a common welding technique in shipyards. The equipment is however compact and portable, and it can be useful for welding thin sheets (up to about 7 mm), as well as for small diameter pipes, boxes for heating, ventilation and air conditioning, conduits for electrical cables and for soldering. The same or similar material is used for flame cutting.

Hard soldering and soft soldering are techniques intended to join two metal surfaces without melting the base metal. A filler metal or alloy is poured in the liquid state until the space which separates the two surfaces to be joined is filled, then it is solidified. When the temperature of the filler metal is below 450°C, the process is called brazing; when it is above 450°C, it is called hard soldering. Soft soldering is usually done using heat from a soldering iron, flame, resistor or electric induction coil. Brazing uses the heat of a flame or that produced by a resistor or an induction coil. It can also be done by immersing the parts in a bath. Brazed joints do not have the strength of welded joints. Also, hard solder and soft solder have limited applications in shipbuilding and ship repair, with the exception of joining small diameter tubes or sheet metal, or maintenance work.

Other welding processes

There are other welding techniques that may be used in a shipyard in small quantities, for a number of reasons. Vertical electroslag welding consists of transferring heat by means of a bath of molten slag which melts the edges to be welded and the filler metal. Although the material used is similar to that used for arc welding, the slag is kept in a molten state by the resistance it offers to the current which passes from the electrode to the piece to be welded. It is therefore a form of resistance welding. Chilled pads placed behind the workpiece are often used to contain the crater. Electrogas welding is a gas shielded arc welding process that uses a fusible electrode wire to feed the weld pool and CO 2 as shielding gas. These processes are both very effective for automatically producing vertical butt welds and are of undeniable interest in the case of thick sheets. They should find much wider applications in shipbuilding.

Thermite welding uses a superheated liquid metal to melt the parts to be welded and the filler metal. The heat required for welding is provided by the exothermic reaction of a mixture of metal oxides and aluminum powder. The liquid metal which constitutes the filler material is poured into the cavity which separates the parts to be welded and which is surrounded by a mold of sand. Thermite welding is reminiscent of foundry casting and is mainly used to repair parts from the foundry or forge or to weld frame elements such as the stern frame.

Laser beam welding is a new technique that uses a laser beam to melt and join the parts to be welded. Although the feasibility of this process has been proven, its high cost has so far hampered its commercial exploitation. However, its ability to produce high quality welds should make it an important technique in the future.Another relatively recent welding technique is electron beam welding, obtained by the melting of the base metal under the impact of a focused beam of electrons which bombard the part to be welded, which is placed in a inert gas envelope. Since the method does not depend on the thermal conductivity of the material under consideration, it has major advantages due to its relatively low energy requirements and its limited effects on the metal. As with laser beam welding, the major problem is the high cost of the equipment required.

Stud welding is a form of arc welding in which metal studs act as electrodes. A special gun holds the stud while the arc forms. The plate and the end of the stud melt, the gun presses the stud against the plate and welds them together. Security is provided by a protective ceramic ferrule that surrounds the stud. The process, semi-automatic, is commonly used in shipbuilding to facilitate the installation of non-metallic materials (such as insulation materials) on steel surfaces.

Painting and finishing coats

Painting work is carried out in almost all the workshops of the shipyard. The nature of shipbuilding and repair requires several types of paint, each of which serves different purposes. The paint needed for a certain type of application can range from a water based product to a high performance epoxy filler; the choice depends on the environment to which the coating will be exposed. As for painting equipment, it ranges from simple brushes and rollers to airless spray guns and automatic machines. As a general rule, the following parts of a vessel require painting:

below the waterline (underwater works, hull);
waterline; topsides superstructures;
interior spaces and cisterns;
upper bridge;
mobile equipment.

There are different types of paint for each of these parts. Many considerations come into play when choosing paints, such as industrial hygiene standards, the severity of environmental hazards, drying times, equipment available and application processes. Many shipyards have special facilities and areas reserved for painting work. Closed painting facilities are expensive, but provide higher quality and output. Painting work carried out in the open air generally has a lower transfer efficiency and can only be carried out if the atmospheric conditions are favourable.

Types of coatings used in shipyards

On a ship, paints are applied in many places and for various purposes. No paint can perform all the desired functions (eg protection against rust, dirt antifouling paints , alkalinity, acidity). Paints contain three main ingredients: a pigment, a binder and a solvent. Pigments are small caliber particles that generally determine the color as well as the many properties associated with the coating. Examples of pigments are zinc oxide, talc, carbon, coal tar, lead, mica, aluminum and zinc filings. The binder can be considered as a glue that consolidates the pigments of the paint. Many paints are designated according to their type of binder (epoxy, alkyd, urethane, vinyl, phenolic). The binder also plays a very important role in determining the performance of the coating (including flexibility, chemical resistance, durability and appearance). As for the solvent, its role is to thin the paint and allow its easy application; it evaporates during drying. Common solvents are based on acetone, mineral spirits, xylene, methyl ethyl ketone and water. Anti-corrosion and anti-fouling paints are the two main types of paint usually used on ship hulls. Anti-corrosion paints are available either as vinyl, lacquer or urethane-based products, or as more recent epoxy-based products which are widely used today and which offer all the qualities required in the marine environment. . Antifouling paints are used to prevent the proliferation and attachment of marine organisms to the hull of ships.They are often copper-based and release toxic substances in minute quantities in the immediate vicinity of the hull. The colors are obtained by adding carbon black, red iron oxide or titanium dioxide (white).

Primers in shipyards

The first coat of paint applied to raw steel sheets and parts is generally a base coat, sometimes called a "shop primer". It is essential if you want to preserve the good condition of the part throughout the construction process. It is applied to steel sheets, profiles, pipe sections and ventilation ducts. The primer has two important functions: 1) to protect the steel throughout construction; and 2) facilitate subsequent work. Most primers are rich in zinc and contain organic or inorganic binders. Zinc silicate fillers are the most used among inorganic binders. Zinc provides roughly equivalent protection to galvanizing. If the steel is coated with a zinc-based primer, the oxygen, in contact with this metal, produces zinc oxide which forms an airtight layer, thus avoiding any contact between the steel and the metal. in air or with water.

Application equipment

There are many types of materials used for painting in the shipbuilding industry. Air guns and airless guns are two common devices. Compressed air systems blast both air and paint, causing some paint to atomize and dry quickly before it reaches the intended surface. The transfer efficiency of pneumatic guns can vary between 65 and 80%; this relatively low transfer efficiency is primarily due to overspray, drift, or gun defects. These devices tend to become obsolete due to their low transfer capacity.

The airless spray gun has become the most widely used device for applying paint in the shipbuilding industry. In this device, a hydraulic pump brings the paint to a nozzle placed at the end of the gun. The paint is thus projected under the effect of hydrostatic pressure and no longer of pneumatic pressure. To reduce overspray and accidental spillage, shipyards are maximizing the use of airless spray paint. This device is also cleaner to use and has fewer leakage problems than the air gun because it requires less pressure. Airless guns have a transfer efficiency close to 90%, depending on the working conditions. A new technique, called “high volume, low pressure” (HVLP) allows the airless gun to achieve even better transfer efficiency in some cases. Transfer efficiency is measured by estimation; it takes into account the accidental flows and spills that may occur during the work.

Hot metallization, also known as spray metallization or flame metallization, consists in applying a coating of aluminum or zinc to the steel to ensure its long-term protection against corrosion. This coating technique finds multiple military and commercial applications. The special equipment it requires and the relatively slow production rates make it a technique radically different from traditional coating processes. There are two main categories of hot metallization machines, depending on whether the combustion of a wire or an electric arc is used. In the first case, combustible gases and a flame are used, as well as a yarn distribution regulator. The combustible gases cause the metal projected on the parts to melt. In contrast, the electric arc spray machine uses the energy of an arc to melt the projected metal onto the base material. It includes a compressor, an air filter, an electric arc supply and regulation system as well as a metallization gun. Base surfaces must be suitably prepared to ensure good adhesion of sprayed metals. The most commonly used technique for preparing the surface to be treated is shot blasting (projection of a jet of shot, for example aluminum oxide). The initial cost of hot metallization is usually high compared to that of painting; however, hot metallization becomes more attractive from an economic point of view if the life cycle of the metal is taken into account. Many shipyards have their own plating facilities, while others prefer to outsource their work. Spray metallization can be carried out both in a workshop and on board the ship.

Painting methods

Painting methods vary considerably from process to process. Mixing is done both manually and mechanically, usually in an area surrounded by berms and which may be covered. In shipyards, painting work takes place both indoors and outdoors. Thin metal sheets or sheets of plastic or fabric are often put in place to catch the excess paint projected, to shelter from the wind or to retain paint particles. New techniques contribute to the reduction of the quantity of airborne particles. By reducing the amount of excess paint projected, the overall amount of paint used is also reduced, and savings are thus achieved.

Base surface preparation and painting

The techniques used in surface preparation and painting in shipbuilding and ship repair can be illustrated by considering five main parts of ships.

Painting of the hull. Hull painting is practiced both for ships under repair and for new ships. The preparation of the base surface and the application of paint to the hull of vessels under repair are normally carried out while the vessel is fully refitted, ie laid up in drydock. For ships under construction, the hull is prepared and painted in the build position using one of the techniques described above. Blasting air or water containing shot from platforms or lifting gear are the most common methods used for hull preparation. Guns and special means of access are used to reach high surfaces (elevators, lifting tables, mobile scaffolding). The number of coats of paint required varies from case to case.

Painting of superstructures. A ship's superstructures include weather decks, deckhouses and other structures above the main deck. Scaffolding is often used to access antennas or other overhead installations. If paint or spilled materials are in danger of falling into nearby waters, protection will be put in place. On ships under repair, the ship's superstructures are mostly painted when docked. Base surfaces are prepared using hand tools or high pressure jets. Once the surface is ready, painting can begin. The paint is usually applied using airless spray guns. The painters access the superstructures by scaffolding, ladders and the various lifting devices already borrowed during the preparation of the surfaces. The protections installed to prevent the projection of abrasion products will be maintained to deal with any paint splashes.

Painting of tanks and interior compartments

Tanks and interior compartments of ships must be repainted constantly. Tanks on ships under repair require extensive surface preparation before they can be repainted. The majority of them are located at hull level (eg ballast tanks, bilges, fuel tanks). Tank preparation requires the use of solvents and detergents to remove accumulated grease and oil; these must be treated and disposed of appropriately. After drying, the interior walls are shot-blasted; it is necessary to set up a recirculation of the air and to recover the shot by suction, which is done by means of a liquid ring vacuum pump or a rotary screw pump. These pumps must be very powerful to be able to rid the tank of the shot it contains. Vacuum and ventilation installations are generally placed on the surface of the dry dock and access to the tanks is through openings in the hull. Once the surface has been stripped and the grit removed, the paint job can begin. Sufficient ventilation and suitable breathing apparatus are essential for all work carried out in interior compartments and tanks, ie in closed or confined spaces.

Stripping of surfaces to be painted and painting at the construction stage. Once the blocks or multiple units leave the assembly area, they are often transported to a stripping area where the entire block undergoes preparation before being painted. The parts are generally completely stripped to a bare metal state, the primer applied at the construction stage being removed (see figure 92.7). The most frequently used blasting method uses a high pressure air blast. For painting, painters generally use airless spray guns and work on a platform. Once the parts are painted, they are transported to an arming area.

Painting small parts

Many parts of a ships construction must be coated before installation (hose reels, ventilation ducts and doors, for example). Small parts are generally prepared in a shipyard workshop specifically designed for this purpose. They can be painted in the area of the site that best meets production constraints. Some parts are painted in different workshops, while others are painted in a place under the control of the department in charge of the painting work.

Surface preparation and painting on block and on board

Finishing coats are done on board and touch-up paint is often done on site (see figure 92.10). Block paint touch-ups are necessary in many cases. The paint may have been damaged, which requires a new preparation of the base material; in other cases, the wrong paint was used and must be replaced. Block painting involves stripping and painting using portable equipment that is moved into the outfitting areas. Onboard painting includes both the preparation and painting of connecting sections between building blocks and the painting of areas damaged by welding, rework, fitting or other circumstances. Surfaces can be prepared by hand (sandblasting, brushing, cleaning with solvents) or by any other suitable technique. The paint is applied using airless spray guns, rollers or brushes.

Armament

Arming the building blocks before they are assembled is the method currently used by all manufacturers who want to be competitive around the world. The process consists of installing the required parts (piping, ventilation ducts, electrical components, etc.) on the blocks before they are assembled, which allows the shipyard to adopt an "assembly line" type approach.".

At each stage of construction, fitting out is planned so that it takes place continuously and regularly throughout the site. Once the steel structure of the block is assembled, we can, for simplicity, divide the armament into three main stages:

arming the unit;
arming on block;
armament on board.

The armament of units is the stage during which the accessories, parts, machines and other armament materials are mounted autonomously; in other words, the units are prepared away from the structural steel blocks, allowing workers to assemble their components on the ground where they can easily access machinery and workshops. The units are then installed during one or the other construction stage, on block or on board. These units can vary greatly in size, shape and complexity. In some cases, a unit is nothing more than a fan connected to a plenum. Large complex units are mainly found in engine rooms, boiler rooms, pump rooms or other hard to reach compartments of the ship. The engine rooms have intensive armament. Arming on the ground increases safety and efficiency as man hours are saved that would otherwise be spent arming on block or on board in tight spaces where work is more difficult.

In block arming, most of the arming hardware is installed on the blocks. This equipment consists of ventilation circuits, ducts, doors, lighting installations, ladders, railings, electrical installations, etc. Many units are also placed during the arm on block step. Throughout this stage, a block can be lifted, rotated and moved to facilitate the installation of armament equipment on ceilings, partitions and floors. All the workshops and services on the site must remain in communication during the assembly stage on the block in order to guarantee the installation of the equipment in the desired location and at the appropriate time.

Fitting on board takes place after the blocks have been hoisted onto the ship under construction (ie after their assembly). At this precise moment, the ship is on a construction area or docked. The arming of the blocks is already well advanced, but there is still a lot of work to be done before the ship is operational. Onboard armament includes the installation on board of large units and blocks. It involves lifting and placing large blocks and units on board the new vessel and welding or bolting them in place. Onboard equipment also includes the interconnection of onboard systems (piping, ventilation system, electrical circuits, etc.). It is during the fitting out stage on board that all the wiring is put in place throughout the vessel.

Trials and Trials

These tests and tests (known as acceptance or reception) are intended to verify the proper functioning of the elements and systems installed. If their results are inconclusive for any reason, the defects found must be corrected and the system tested until it is in full working order. All the pipes on board will be pressurized in order to locate any leaks. Tanks are also tested by filling them with liquid (eg salt or fresh water), inspecting them and testing their structural integrity. Ventilation circuits, electrical circuits and many other systems are also checked. Most trials and trials are carried out while the ship is at berth; however, there is an increasing tendency to practice them at earlier stages of construction (for example, in production workshops). Carrying out tests during the earlier stages of construction allows better repair of technical failures thanks to easier access to the systems under test, although the complete testing of the systems should always be carried out on board. Once all the preliminary tests have been completed at the quay, the ship is subjected to a series of complete operational tests at sea before being delivered to the shipowner.

Ship repair

Steel vessel repair practices and processes.Ship repair generally includes all maintenance programs, alterations, refitting after survey, as well as the repair of major damage and minor repairs to equipment. Ship repair is a very important sector of maritime transport. In most private shipyards, about 25% of the workforce is employed in repair and conversion tasks. Currently, many ships require modernization to meet safety and environmental standards. Shipping companies are strained by the high cost of new ships and aging fleets worldwide. In American shipyards, conversion and repair work is generally more profitable than the construction of new buildings. In yards building new ships, repair, refurbishment or conversion contracts help to stabilize the workforce during the limited construction periods of new buildings; on the other hand, new construction increases the workload of repair crews. This is not significantly different from shipbuilding except that the work is generally done on a smaller scale and at a faster rate. Repair work requires more precise coordination and a more dynamic tendering policy. The clientele requiring repair work generally includes the navy, shipowners owning commercial vessels and owners of other vessels.

The customer usually provides contractual specifications, sketches and standard items. There may be contracts at firm and definitive prices (Firm Fixed Price (FFP)), at firm and definitive prices plus merit fees (Firm Fixed Price Award Fee (FFPAF)), at cost plus fixed fees (Cost Plus Fixed Fee ( CPFF)), cost plus merit fees (Cost Plus Award Fee (CPAF)) or urgent repair contracts. The process begins in the marketing department when the shipyard receives a Request for Proposal (RFP) or an Invitation for Bid (IFB). The lowest-priced bidder generally wins an IFB type contract, while an RFP can be won on criteria other than price itself. The repair assessment team prepares a cost estimate and a repair contract proposal. The bid estimate typically includes man-hours and rates of pay, materials, overhead, special service costs, subcontractor payment, overtime and shift premiums, other fees, the money rent of the installations and, finally, the estimated contract price based on all these elements. Once the contract has been signed, a work program must be drawn up and approved.

Planning, technical organization and execution of repair work

Although some planning takes place prior to tender submission, careful planning is required if the work is to be completed on time; it is a heavy task. You must read and assimilate the entire specification, classify the work by category, integrate it into a logical production plan and determine the critical path. The departments responsible for planning, design office, materials, subcontracts and the execution of the repair work must work in close collaboration in order to meet deadlines and achieve the best possible performance in terms of materials. of profitability. Piping, ventilation installations, electrical and electronic equipment and certain mechanical installations are often manufactured or prepared before the ships arrival. The pre-arming and pre-conditioning of equipment requires close collaboration with the production workshops.

The most common repair work

Ships are similar to other types of machinery in that they require regular maintenance and sometimes complete overhaul to remain in service. Many shipyards have maintenance contracts with shipping companies. Examples of repair and maintenance tasks include:

stripping and painting the ship's hull, freeboard, superstructures and interior tanks;
machinery overhaul (eg diesel engines, turbines, generators, pumps);
maintenance and rehabilitation of facilities (eg, washdown, pipe testing);
the installation of a new system, the addition of new equipment, the replacement of obsolete systems (navigation systems, combat systems, communication systems);
the repair and adjustment of propulsion and steering apparatus;
the creation of spaces to receive new machines (cutting of existing steel structures, addition of new partitions, stiffeners, pillars and frames).

Repair work is frequently driven by an emergency situation and therefore involves little or no notice, making ship repair a very changing and unpredictable environment. Vessels undergoing routine repairs will be able to stay at dock or in a dry dock between three days and two months, while major repairs and alterations may last a year or even longer.

Major repair and transformation projects

Major overhaul and major conversion contracts are common in the ship repair industry. Most of this work is carried out by shipyards which are also equipped to build ships.

Most major repairs and conversions require a great deal of planning effort and significant technical resources. They will most often involve a number of operations on steel parts (for example, the cutting out of large portions of the existing structure and the installation of new structures). These projects can be subdivided into four main stages: demolition, construction of a new structure, fitting out and testing. It is necessary to use sub-contractors for most major and minor repair and alteration work. Subcontractors bring their expertise in particular areas and help distribute the workload in the shipyard. Here are some of the tasks performed by subcontractors:

assistance in the repair of the ship;
combat systems installations;
reconstruction of boilers, replacement of tubes;
overhaul of compressors;
deflocking and disposal of asbestos; tank cleaning;
stripping and painting;
rehabilitation of pumps;
manufacture of small structures;
overhaul of winches;
modifications to the main steam circuit;
miscellaneous fabrications (piping, ventilation system, foundations, etc.).

As with new builds, all installed devices and systems must be tested and function properly before the vessel is handed over to the owner. Testing requirements are usually specified in the contract, although specific clauses from other sources exist. The tests must be programmed, monitored to ensure that they are carried out correctly and supervised by the competent services (internal quality of the site, commissioning control, government agencies, shipowners, etc.).There are many analogies between shipbuilding and ship repair. Both processes use essentially identical practices, manufacturing techniques, facilities and workshops. They both require a highly specialized workforce, because for many processes the possibilities of automation remain limited (especially in the field of ship repair). Both repair and construction require excellent planning, engineering design and interdepartmental communication. While in many respects ship repair is similar to shipbuilding, the latter requires a more advanced organization due to the importance of the hired labor and the workload, the number of parts and the complexity of the communications (execution plans and production schedules, in particular) which characterize all the operations.

The dangers and precautions

Shipbuilding and ship repair are among the most dangerous industries. Indeed, the work must be carried out most of the time in very exposed situations, in confined spaces or at considerable heights. A significant proportion of manual work is carried out with heavy equipment and materials. The various tasks are so intertwined and are carried out in such promiscuity that an operation or a process that goes wrong can endanger the workers involved in another operation or another process. In addition, a large part of the work is carried out outdoors and extreme weather conditions can lead to a dangerous situation or aggravate already dangerous working conditions. The use of chemicals, paints and solvents, in particular, can pose considerable risks to workers.

Health risks

Chemical hazards include:

dust produced by sandblasting;
exposure to asbestos and mineral fibers in insulation work;
fumes from paints, solvents and thinners;
fumes from welding, burning and brazing operations;
exposure to gases used in various welding, burning and heating processes;
exposure to toxic substances found in epoxy resins, organic copper and tin based antifouling paints, lead based paints, oils, greases, pigments and the like.

Physical risks include:

extreme temperature variations and climatic differences in outdoor work;
electrical hazards;
problems related to the frequent handling of heavy and bulky equipment;
ionizing and non-ionizing radiation;
noise and vibration;
the risk of lack of oxygen and other risks associated with confined spaces, tanks, double bottoms, etc.;
level falls and falls from heights.

Prevention measures

Although shipbuilding and repair is a very dangerous industry, hazards to personnel can and should be minimized. This essentially requires the establishment of a solid safety and health program based on close cooperation between management, unions and workers.Once the risks have been identified, there are many methods that can eliminate or reduce them. These methods can be roughly grouped into several strategies.

Technical prevention measures are implemented to exclude or mitigate risks at source. They should have a priority character, because they are very reliable:

Substitution or elimination. Where possible, processes that create hazards or produce toxic materials should be eliminated or replaced with less hazardous processes or materials. This form of prevention remains the most effective. An example is the use of non-carcinogenic insulation materials instead of asbestos. Using lifting platforms to handle heavy loads, rather than manual lifting, is another. It is often possible to replace paints that contain solvents with water-based coatings. Finally, automation and robotics can be used to eliminate human intervention in certain operations. Protection by distance. It is sometimes possible to keep workers away from processes that present risks that are difficult to control otherwise. Often, sources of intense noise or radiation can be relocated to provide sufficient distance between them and workers. Work in confined spaces. Operations or personnel may also be placed in an enclosed space to eliminate or at least reduce hazardous exposures. Thus, machine operators can be placed in cabins to protect themselves from noise, heat, cold and even chemical risks. The operations themselves can also be carried out in isolation. Paint spray booths or welding booths are examples of facilities that reduce exposure to toxic agents. Exhaust or exhaust ventilation. Processes that give rise to toxic substances can be coupled with artificial ventilation in order to capture these substances at source. This technique is widely used in shipbuilding yards, especially to control fumes, vapors and other fumes. Fans and blowers are often installed on the decks of ships to draw in air and expel it outside, or to blow clean air into confined spaces so as to maintain a sufficient oxygen content.

Administrative measures can also be used to limit the exposure of personnel placed in potentially dangerous situations. It is possible, for example, to provide for a rotation of personnel from high-risk positions to less dangerous positions, or even to limit the duration of work in the event of particularly dangerous exposures.

In the first case, the method has drawbacks, since the workers all have to spend a certain amount of time at the positions at risk, which doubles the number of exposed workers.

Individual protection. Shipyard workers must make extensive use of various personal protective equipment. Indeed, the nature of the operations does not lend itself well to traditional technical means of prevention. A ship is made up of a host of very confined spaces that are difficult to access. A submarine has one to three hatches 75 cm in diameter through which the workers in charge of its maintenance and the essential equipment must pass. It is difficult to introduce ventilation ducts of sufficient size and in sufficient number. Similarly, on large ships, the work is done deep inside the building and, although moderate ventilation can be blown to the various workstations, its effects are limited. In addition, the fans are generally placed outdoors, usually on a main deck, and have relatively low power.Shipbuilding and ship repair do not take place on an assembly line, but in separate and mobile workplaces, so that fixed technical means are hardly practicable. A ship may only be under repair for a few days, and again the scope of the technical measures can only be limited. Under these conditions, personal protective equipment is called upon to play a major role.

Here are the main applications of personal protective equipment in shipyards:

Welding, cutting and grinding. The essential operations of shipbuilding and repair are the cutting, shaping and assembly of parts of steel and other metals. They give rise to fumes and particles of metal and other materials. Although ventilation can sometimes be put in place, most often welders must wear respirators to protect themselves from the particles and fumes generated by welding. They must also be equipped with effective eye protection against ultraviolet and infrared radiation and flying fragments. These protections will be supplemented by gloves and long-sleeved work suits intended to prevent sparks and particles of molten metal.

Abrasive blasting and painting. Before receiving their base coat, the parts must be blasted with a powerful jet made up of abrasives of the appropriate caliber to ensure good adhesion.

Pickling of small parts can be done in a closed vessel (glove box, for example). Larger pieces are pickled by hand. Operations can take place either in the open air, or in large cabins designed for this purpose, or even inside ships or sections of ships. In all cases, personnel performing this work should use full body protection, including hearing protection and fresh air breathing apparatus. It must be supplied with breathable air at a sufficient flow rate.

In some countries, the use of crystalline silica has been banned in pickling work. In any event, its use is strongly discouraged. If materials containing silica are nevertheless used, strict protective measures must be adopted.

After stripping, the parts must be painted quickly in order to prevent the formation of “rust bloom” on the surface. Although mercury, arsenic and other very toxic metals no longer enter into the composition of paints, those used in shipyards generally contain solvents as well as pigments such as zinc. Many paints are of the epoxy type. Painters using such products must be protected and wear full suits, gloves, special shoes, eye protection and a compressed air line breathing apparatus. Sometimes painting operations must be carried out in confined or enclosed spaces. In these cases, fresh air supplied respirator and full body protection should be used. It is also necessary to take special measures, adapted to confined spaces, and to provide work permits.

Falling objects. Due to the large number of cranes and the mass of work carried out at height, wearing a helmet is generally required throughout the perimeter of a shipyard.

Installation of insulating materials. The pipes and certain components must be insulated in order to stabilize their temperature and reduce the heat inside the ship; in some cases, insulation is also required to attenuate noise. In ship repair, the insulation in place must be removed to allow access to the pipes and ducts in question; in these cases, asbestos may still be present. In shipbuilding, on the other hand, fiberglass or mineral fibers are most often used. In either case, appropriate respiratory protection and full body protection are required.

Sources of noise.

Everyone knows how noisy shipyard work is. Most of the operations involve metal parts and are accompanied by sound levels exceeding the permissible limits. Given that not all noise pollution can be contained below these limits by means of technical prevention, appropriate personal protection is essential.

Foot protection.

Shipyards involve a certain number of operations which present risks of accidents to the feet. Since it is difficult and impractical to separate the work site into two zones, those which are at risk for the feet of others, it is usual to require the wearing of safety boots or shoes throughout the work area a shipyard.

Eye protection.

There are many sources of risk of eye damage in shipyards: ultraviolet and infrared radiation (welding and flame cutting), dust and splinters produced during metal shaping or pickling, pickling baths, caustic substances, paint pistol, etc. Given the ubiquitous nature of these hazards, the wearing of safety glasses is frequently required in all work areas of a shipyard for the sake of practical and administrative simplification. Of course, each specific task requires appropriate eye protection.

Lead.

For years, lead-based primers and coatings have been widely used in shipbuilding. Although their use is rather rare at the present time, a significant quantity of elemental lead is present on shipyards that build nuclear-powered ships where this heavy metal is used as a shielding material against ionizing radiation. In addition, ship repair work frequently involves the removal of old paint layers which often contain lead. It should be noted in this respect that any ship repair operation requires a good knowledge of the materials previously used and the precautions they call for. Thus, any work presenting a risk of lead poisoning requires full personal protection including coveralls, gloves, helmet, shoes with insulating soles and appropriate respiratory protection.

Boat building

In some respects, boats can be considered light ships in that the processes used for their construction and repair are very similar to those used for ships, but on a smaller scale. In general, boat hulls are made of steel, wood or composite materials. Composites typically include materials such as fiber-reinforced metals, fiber-reinforced cement, reinforced concrete, fiber-reinforced plastics, and glass-reinforced plastics (GRP). Reinforced plastics are also called reinforced plastics. The development, at the beginning of the 1950s, of manufacturing techniques combining the manual placement of layers of traditional materials and thermosetting polyester resins reinforced with glass led to a very rapid extension of this method of construction, from 4% in the fifties to more than 80% in the eighties and even more today.On boats over 40 m long, the replacement of wood by steel is the main alternative to the use of reinforced plastics. Below a length of 20 m, a steel hull is generally not profitable. Small steel boats also tend to be too heavy due to the need for extra thickness for corrosion protection. However, for boats over 40m, the lower cost of welded steel construction is normally a considerable advantage. It seems unlikely that reinforced plastics are more advantageous than steel structures when it comes to building boats over 40m in length. However, special circumstances (for example, the transport of bulk cargoes of frozen materials or corrosive products, which requires a non-magnetic hull, or the need to lighten the vessel as much as possible for performance reasons) may require the installation of using other materials for hull construction.

Reinforced plastics are currently finding a wide variety of uses in the construction of speedboats, ocean-going yachts, coasters, service vessels, pilot boats, passenger launches and fishing boats. Their success with fishing boats, for which wood was the traditional material, is attributable to the following factors:

an advantageous initial cost, especially when many hulls are made according to the same plan, and also because of the increase in the price of wood and the shortage of qualified carpenters;
good performance, low maintenance costs (due to the watertight qualities of the hull, the absence of rotting and resistance to marine borers) and the lower cost of repairs;
the ease with which complex shapes required for hydrodynamic or structural needs or for aesthetic reasons can be achieved.

Manufacturing methods

The most common method of fabrication for the planking, decks and bulkheads of small and large reinforced plastic hulls uses monolithic laminates reinforced where necessary with stiffeners. Various manufacturing methods are employed in the construction of monolithic or sandwich hulls.

Cast molding. This process is the most used for monolithic reinforced plastic hulls of all sizes. It consists of pouring the material in the liquid state into an open or female mold and solidifying it by the action of a hardening agent or heat, without pressure.

Preparing the mold is the first step in the process. For small to medium sized hulls, the molds are usually made of reinforced plastics, in which case a male mould, usually wood with reinforced plastic finishes, is first assembled. Its outer surface precisely defines the shape of the shell. The preparation of the mold generally ends with a polishing with wax and the application of a layer of polyvinyl alcohol or an equivalent curing agent. Lamination or stratification usually begins with the application of a gel coat made of a good quality resin. The stratification continues, before the complete hardening of this coating, by one of the following processes:

Projection. Fiberglass rovings and polyester resin are sprayed simultaneously from a gun, the resin being mixed in the gun with a curing agent and an accelerator. Manual layering. The resin mixed with a curing agent and an accelerator is generously deposited on the gel coat or on a preliminary reinforcing layer applied by brush, roller or spray gun.

By the cast molding process, very heavy reinforcements can be made (a basis weight of 4000 g/m 2 has been used successfully, although 1500 2000 g/m 2 has been preferred for high volume production). scale) by combining a fast lamination rate with low labor costs. A similar process can be applied for the rapid construction of flat or nearly flat decks and bulkhead panels. It takes 10 weeks per hull for the execution in small series of certain 49 m hulls, including the installation of decks and bulkheads. Compression molding. Compression molding involves loading material into an open, heated mold and then compressing it. It increases fiber content and reduces voids by pressing out excess resin and blowholes.

Vacuum bag molding. This process, which can be considered a refinement of cast molding, consists of placing a flexible membrane on the rigid mold, separated from the uncured laminate by a layer of polyvinyl alcohol, polyethylene or an equivalent material, and seal the edges by creating a vacuum under the membrane until the laminate is subjected to a pressure not exceeding 1 bar. Curing can be accelerated by placing the bagged component in an oven or by using a heated mold.

Autoclave molding. By carrying out the bag molding in an autoclave (with pressures of the order of 5 to 15 bars and at a high temperature), higher fiber contents and hence better mechanical properties can be obtained.

Two-part molding. The uncured molding material, which in the case of a structure as large as a boat hull probably consists of a premix (mixture of resin, reinforcements and fillers) is compressed between two paired molds , male and female, usually metallic and heated if necessary. Due to the high initial cost of the moulds, this process is only advantageous for large series.

Filament winding. In this process, the reinforced plastic product is obtained by winding a continuous base wire (roving) and a resin-coated reinforcing material on a mandrel or a mold under controlled tension and in a determined arrangement. .

Sandwich construction. Sandwich hulls, decks and bulkheads can be made by the cast molding method using room temperature curing polyester resins, much the same way as monolithic structures. An external reinforced plastic skin is first placed on the female mould. Strips made of the core material are then placed on a layer of polyester or epoxy resin. Manufacturing ends with the fitting of an internal reinforced plastic skin.

Polyester and epoxy resins. Unsaturated polyester resins are by far the most commonly used matrices for marine laminates. This is due to their moderate cost, their ease of implementation by different manufacturing processes (manual lamination or spraying) and their behavior in the marine environment. Three main types of these resins are used in shipbuilding:

Orthophthalic polyester, made from the combination of phthalic and maleic anhydrides with a glycol (usually propylene glycol), is the least expensive material both for making dies and for making the hulls of small boats. Isophthalic polyester, which contains isophthalic acid instead of phthalic anhydride, is more expensive; it has somewhat superior mechanical properties, is more resistant to sea water and is generally specially indicated for the construction of more efficient boats and for the preparation of marine gel coats. Bisphenol-based epoxy resins, in which the phthalic acid or anhydride are partially or completely replaced by bisphenol A, offer (at a significantly higher cost) much better resistance to chemicals and water.

Health and safety risks

Many of the chemical, physical and biological hazards encountered in boat building are identical to those found in ship building. However, exposure to solvent vapors and epoxy dust is a major concern. Uncontrolled exposure to these agents may cause central nervous system disorders, liver and kidney damage or sensitization reactions. The preventive measures to be put in place are, for the most part, the same as those described above in the section devoted to the construction and repair of ships, whether technical preventive measures, administrative or personal protection.The regulations relating to emissions into the air, discharge into waters and waste have the primary objective of protecting public health and ensuring the general well-being of the population. In general, the term "population" means all the individuals who live or work in the area where the site in question is located. However, winds can transport air pollutants from one area to another even beyond national borders; spills into waters may also travel into territorial or extraterritorial waters; and the waste can be transported by ship across the country or around the world.

Shipyards carry out a large number of operations during the process of building or repairing ships and boats. Many of them emit pollutants for water and air whose harmful effects on human beings are known or suspected and which manifest themselves in direct physiological or metabolic damage, such as cancer or lead poisoning. Pollutants can also act indirectly as mutagens (affecting future generations by impairing reproductive biochemistry) or as teratogens (affecting the fetus after conception).

Both air and water pollutants are likely to have side effects on humans. Air pollutants can fall back into water, affect the quality of receiving waters or crops, with all the consequences that this can have for the consumer. Pollutants discharged directly into the waters can degrade the quality of the water to such an extent that it is not safe to drink or swim in it. Pollution of water, soil and air by spillage of pollutants can also contaminate marine life and ultimately affect human health.

Air quality

Virtually all operations relating to the construction, maintenance and repair of ships and boats can produce emissions into the air. Among the air pollutants that are subject to regulation in many countries, we can cite sulfur oxides, nitrogen oxides, carbon monoxide, various particles (smoke, soot, dust, etc.) .), lead and volatile organic compounds. Shipbuilding and repair activities responsible for oxide-based pollutants include combustion sources such as boilers and heat sources for metal processing, generators and fireplaces. The particles come from combustion smoke, as well as dust produced during woodworking, sandblasting or shot-blasting, grinding and polishing.

In some cases, lead ingots must be partially melted down before being reshaped for radiation shielding on nuclear powered ships. Paint stripped from ships being refitted or repaired may also contain lead dust.Hazardous air pollutants are chemical compounds known or suspected to be harmful to humans. They are produced during many operations carried out in shipyards, such as foundry or electroplating operations, which can give off fumes of chromium and other metallic compounds.

Certain volatile organic compounds, such as naphtha and alcohol, used as paint solvents, thinners and cleaners, or in many adhesives and glues are not hazardous. On the other hand, other solvents used mainly in painting operations, such as xylene and toluene, as well as certain chloride compounds used most often as solvents and cleaners, in particular trichloroethylene, methylene chloride and 1,1 ,1-trichloroethane, are dangerous air pollutants.

Water quality

As ships and boats are built on waterways, shipyards are required to comply with water quality criteria specified in permits required by regulation for all industrial wastewater discharging into nearby waters. For example, most US shipyards operate a program called "Best Management Practices", which is considered one of the best reference documents for the techniques shipyards must apply to satisfy under the conditions required by the load-shedding permits. Another control technique used in shipyards with dry docks is the boom and baffle system: the boom prevents solids from reaching the sump and then being discharged into surrounding waters, and the baffle system prevents oil and floating debris from reaching the sump.

Stormwater monitoring is another requirement that has been added to many site permits. Facilities should have a stormwater pollution prevention plan that implements various control techniques to prevent pollutants from entering nearby waters whenever it rains.

Many shipyards also dump part of their industrial wastewater into the sewers. They are then required to comply with the water quality criteria imposed by local regulations regarding the disposal of waste water. Some shipyards choose to build their own preliminary wastewater treatment plants that meet local water quality criteria. There are two types; one is mainly intended to eliminate toxic metals, the other, essentially petroleum derivatives.

Waste Management

Each stage of the shipbuilding process produces its own types of waste that must be disposed of in accordance with regulations. Steel cutting and forming generates wastes such as scrap metal produced during cutting and forming of steel sheets, paint and solvents during steel coating , and used abrasive resulting from the removal of oxidation or superfluous coatings. Scrap metal presents no inherent risk to the environment and can be recycled. On the other hand, waste paint and solvents are flammable and the used abrasive can be toxic depending on the characteristics of the abraded coating.During the fabrication of the steel modules, all the piping is added. Preparing the piping for the modules generates wastes such as acidic and caustic wastewater from pipe cleaning operations. This wastewater requires special treatment to rid it of its corrosive properties and to remove pollutants such as oil and impurities.

The elements that make up the electrical circuits, machinery, piping and ventilation for the ship's outfitting are prepared at the same time as the steel fabrication. This weapon preparation phase also generates waste such as lubricants and coolants used during metal cutting, degreasing substances and waste water from electroplating. All of these products must be treated to remove impurities and oils before being discharged. Electroplating wastewater is toxic and may contain cyanide compounds which require special treatment.

Ships in need of repairs usually have to unload waste accumulated during their cruise. Sewage bilge water should be treated to remove oil. Sanitary waste water must be discharged into a special disposal system for biological treatment. Even garbage and other waste may also be subject to special treatment to comply with regulations intended to prevent the introduction of foreign plants and animals.