Materials knowledge
Materials in the maritime environment are exposed to particular stresses. Moisture, salt, UV radiation and mechanical strain have a lasting effect on metals, woods, plastics and textile materials. Knowledge of their properties facilitates the selection of suitable products and supports proper processing.
The following sections provide an overview of central materials in the ship and shipyard sector, their typical areas of application and material-related special features.
Metals
Metals are among the central materials in the ship and shipyard sector. They are used for fittings, connecting elements, hull components, installations and numerous structural details. In the maritime environment, they are permanently exposed to moisture, salt and electrochemical processes.
Decisive for the choice of material are corrosion behavior, strength, machinability and compatibility with other materials. Contact corrosion in particular can occur when different metals are combined with one another. A coordinated selection and proper installation help to ensure function and service life.
Depending on the area of application, different metal alloys are used. The following sections explain typical properties and areas of application.
Bronze
Bronze is a copper alloy whose properties vary depending on its composition. In the maritime environment, it is used due to its good corrosion resistance to seawater as well as its mechanical load-bearing capacity. It is suitable for permanently exposed components on deck and in the underwater area.
Typical applications are fittings, valves, hull penetrations, propeller components or highly stressed connecting elements. Bronze shows stable behavior toward electrochemical influences, especially when it is combined with suitable materials. Compared with pure brass, it is generally more resistant in salty environments.
The surface can remain untreated and develops a patina over time. Alternatively, ground or polished versions are possible, depending on design or functional requirements.
Brass
Brass is a copper-zinc alloy with good machinability and versatile application possibilities. In the ship and shipyard sector, it is used for fittings, valves, screws, electrical components and decorative elements. Strength and corrosion behavior differ depending on the alloy composition.
In salty environments, unsuitable alloys can undergo what is known as dezincification. In this process, zinc is dissolved out of the alloy, causing the material to lose strength. For applications in the maritime environment, dezincification-resistant or specially adapted alloys are therefore used.
Brass is mechanically easy to form and can be turned, milled or polished. Untreated surfaces change under the influence of weathering and develop a darker shade or patina over time.
Stainless steel (V2A and V4A)
Stainless steels are used in the maritime sector for fittings, railings, connecting elements, shafts, tanks and numerous structural components. They are characterized by good strength, dimensional stability and a resistant surface.
In the ship and shipyard sector, the material groups V2A and V4A in particular are common:
- V2A (e.g. material 1.4301)
Contains chromium and nickel. It is corrosion-resistant to moisture and many environmental influences, but only has limited resistance to chloride-containing media such as seawater. For protected areas or freshwater environments, V2A is often sufficient.
- V4A (e.g. material 1.4401 or 1.4571)
Also contains molybdenum. This increases resistance to chloride-containing environments and reduces the risk of pitting corrosion. For permanently exposed areas on deck or in direct contact with seawater, V4A is generally more suitable.
The corrosion resistance of stainless steels is based on a thin, self-healing passive layer of chromium oxide. This forms on the surface when there is sufficient contact with oxygen. Mechanical processing, welding work or contamination by foreign metals can impair the passive layer. In such cases, targeted cleaning and passivation may be required in order to restore the protective effect.
Regardless of the material, surface quality, proper processing and regular cleaning are decisive for durability. Flash rust can occur when iron-containing foreign particles are deposited on the surface.
Copper
Copper is a highly conductive, comparatively soft metal with high resistance to atmospheric corrosion. In the maritime sector, it is used among other things for electrical cables, pipework, fittings and lamps as well as for special applications in the underwater area.
In moist or salty environments, copper forms a protective oxide layer, which can develop over time into a characteristic patina. This layer inhibits corrosion and contributes to the durability of the material.
Due to its electrochemical properties, copper also plays a role in connection with galvanic processes. In combination with other metals, potential differences can arise, leading to contact corrosion. A coordinated choice of materials and suitable insulation measures must therefore be taken into account in mixed installations.
Copper is easy to form and can be soldered, bent and processed. Its conductivity makes it a central material, particularly in the area of electrical installations.
Aluminium
Aluminum is a comparatively lightweight metal with good strength at low weight. In the ship and shipyard sector, it is used among other things for masts, profiles, fittings, deck components and structural components. Its good machinability enables milling, drilling and profiling with low material use.
A thin oxide layer forms on the surface of aluminum, protecting the underlying material from further corrosion. This protective layer is self-healing, provided that sufficient oxygen is present. In salty environments, however, pitting corrosion can occur, especially if the surface is damaged or aggressive media are present.
Due to its electrochemical potential, aluminum reacts sensitively to direct contact with more noble metals such as stainless steel or bronze. Without suitable separation, galvanic processes can occur, leading to material removal. Insulation measures, suitable connecting elements and coordinated material combinations must therefore be taken into account during installation.
Depending on the area of application, aluminum is used untreated, anodized or coated in order to improve corrosion behavior and surface resistance.
Galvanized steel
Steel has high strength and is used in the ship and shipyard sector for load-bearing and heavily stressed components. Without protection, however, unalloyed steel reacts sensitively to moisture and salty environments. To improve corrosion resistance, it is therefore often galvanized.
During galvanizing, a layer of zinc is applied to the steel surface, usually by hot-dip galvanizing. This layer has a dual effect: it forms a physical barrier against environmental influences and additionally provides cathodic corrosion protection. If the surface is damaged, the surrounding zinc can continue to protect the steel by corroding preferentially.
In the maritime sector, galvanized steel is used for chains, shackles, anchor accessories, wire ropes, fittings and structural elements. Especially with anchor chains, galvanizing is decisive for service life under changing loads and in direct contact with seawater.
The protective effect depends on the layer thickness, mechanical stress and environmental influences. Through abrasion or long-term corrosion, the zinc layer can be worn away over time. In such cases, re-galvanizing or replacement of the component should be considered.
When combined with more noble metals such as stainless steel or bronze, galvanic processes can occur, especially when large-area material differences exist. A coordinated choice of materials and structural separation help to avoid undesirable corrosion phenomena.
Quality, standards and documentation
For galvanized steel products, durability and safety depend less on the country of origin than on defined specifications and traceable testing and manufacturing standards. Above all, material identification, quality grade, dimensional and shape tolerances as well as documented tests are meaningful.
Products that are manufactured and tested according to standards or quality grades are generally easier to compare because requirements for material, processing and testing methods are defined. In galvanizing, for example, defined layer structure and execution requirements are relevant.
For goods without clear quality classification or without reliable documentation, assessment is more difficult. Typical differences then tend to show in uniform galvanizing quality, dimensional accuracy, surface condition, batch consistency and traceable provenance rather than in the label “Made in …”.
Cast iron
Cast iron is an iron-based alloy with a high carbon content, characterized by good castability and high compressive strength. In the ship and shipyard sector, it is used primarily for dimensionally stable components where dimensional accuracy and mass play a role, such as stoves, housings, pump components or certain fittings.
Compared with steel, cast iron is more brittle and has lower tensile strength, but it has high wear resistance and good damping properties. The casting process allows complex shapes to be produced economically.
Untreated cast iron is susceptible to corrosion and must be protected in the maritime environment by coatings, paint finishes or regular care. Surface rust can form quickly, especially in moist and salty environments. Corrosion protection is therefore decisive for durability.
Depending on the version, a distinction is made between gray cast iron, ductile cast iron or other cast qualities, which differ in strength and fracture behavior. For load-bearing or safety-relevant applications, the corresponding material specifications and requirements must be observed.
Lead
Lead is a very dense, soft and easily formable metal with high corrosion resistance to many environmental influences. Due to its high mass at low volume, it is used in the ship and shipyard sector in particular as ballast material, for example in keel structures or as a counterweight.
In addition, lead is used in certain sealing applications, as shielding material or in the form of lead strips and sheets for adjusting weights. Its good formability enables easy adaptation to different geometries.
In moist environments, lead forms a protective oxide layer that protects the underlying material from further corrosion. Mechanically, however, lead is comparatively soft and is not suitable for highly stressed load-bearing components.
During processing and use, the applicable regulations for handling lead must be observed. Suitable protective measures must be taken, especially during grinding or machining work.
Wood and modified woods
Wood is a central material in both traditional and modern shipbuilding. It is used for decks, superstructures, interior fittings, masts, strips, handrails and numerous structural details. In addition to mechanical load-bearing capacity, moisture behavior, dimensional stability and durability are particularly decisive in the maritime environment.
Wood reacts to changing humidity and temperature by swelling and shrinking. A suitable choice of wood, proper construction and coordinated surface treatment are therefore crucial for service life and dimensional stability. Different types of wood have clearly different properties with regard to hardness, natural resistance and machinability.
In addition to classic precious woods, modified woods such as Kebony are also used today, whose properties have been specifically improved through technical processes.
Teak
Teak is a tropical hardwood with high natural durability and good resistance to moisture. It contains natural oils and substances that make the wood resistant to rot and pests. Due to its slip resistance even when wet, it is traditionally used for decks, handrails, gratings and heavily stressed exterior areas.
Teak has comparatively high dimensional stability, but like any wood, it reacts to changing moisture by swelling and shrinking. Untreated surfaces turn gray under UV exposure. Regular cleaning and, if necessary, oil treatment influence the appearance, but are not structurally mandatory.
Today, ecological aspects and availability in particular are viewed critically. Origin, certification and sustainable management are playing an increasing role in material selection. In addition, costs and quality differences between plantation teak and old-growth teak are clearly noticeable.
Against this background, alternatives are used in certain applications. These include modified woods, cork products or special plastics with slip-resistant surfaces. These materials aim to reduce maintenance effort or take ecological requirements into account. Depending on the area of application, mechanical load-bearing capacity, temperature behavior and long-term stability must be checked.
Mahagony
Mahogany refers to various tropical hardwoods with a reddish-brown color and uniform structure. In the ship and shipyard sector, it is traditionally used for superstructures, coamings, strips, doors, interior fittings and shaping components. It can be easily processed, milled and sanded and provides a stable basis for paint systems.
Compared with teak, mahogany has lower natural oil content and is therefore more dependent on structural wood protection and suitable coating systems. Proper sealing with varnish or oil is decisive in order to limit moisture ingress and UV-related aging.
Different types of wood are traded under the term mahogany, differing in density, durability and structure. Origin and quality influence strength, grain and resistance. Suitable surface systems and regular maintenance are required for heavily exposed exterior areas.
Mahogany is often used in visible areas, especially when a uniform surface and a high-quality varnish build-up are desired. Its dimensional stability and good machinability make it suitable for precise woodworking.
Marine plywood
Marine plywood consists of several cross-glued veneer layers. This multi-layer structure reduces stresses and significantly reduces swelling and shrinking compared with solid wood. In the ship and shipyard sector, it is used for interior fittings, bulkheads, furniture, deck substructures and dimensionally stable components.
The cross-gluing ensures high dimensional accuracy and good dimensional stability. Compared with solid wood, plywood works less under changing moisture conditions, but remains a hygroscopic material. Edges and cut surfaces must be sealed particularly carefully in order to prevent moisture ingress.
Marine plywood is generally manufactured with waterproof glues. Quality and durability depend on the veneer quality, the gluing and the bonding of the layers. Suitable gluing standards and a uniform veneer structure are decisive for maritime use.
Due to its dimensional stability, plywood is suitable for high-quality coating systems, including 2-component paint systems. The lower movement compared with solid wood reduces the risk of stress cracks in the paint film. Proper surface preparation, where necessary a suitable primer, and a completely closed coating system are prerequisites.
Plywood can be sawn, milled and sanded. Clean cut edges, suitable tools and careful edge sealing contribute to durability.
Kebony
The “thermowood” Kebony has established itself as an alternative to teak wood. This is not a separate type of wood, but the softwood of the radiata pine (Pinus radiata, Radiata Pine, Monterey Pine), which is refined through a patented process. Kebony was developed in Oslo. The manufacturer Kebony Global has its headquarters in the Norwegian capital.
The radiata pine is a soft coniferous wood that was originally native to western California and northern Mexico. A mature tree reaches a height of up to 40 meters. Due to rapid growth in cultivation on plantations, annual rings several centimeters wide are formed. Today, radiata pines mostly come from FSC-certified plantations in Australia, Chile, New Zealand or Spain.
The wood modification, also called furfurylation, consists of the following work steps
- The starting product is the untreated wood of the radiata pine
- This is impregnated with furfuryl alcohol
- This by-product from sugar production is pressed under pressure into the cell walls of the wood
- By heating, the curing of the alcohol then takes place: the furfuryl monomer polymerizes inside the cell walls
- As a result, the cell walls become approximately 50 percent thicker and therefore harder, more stable and more durable than the untreated wood
- Hardness, durability and dimensional stability are now comparable with the properties of tropical hardwoods
Properties of Kebony
- high durability (often durability class 1)
- improved dimensional stability (less swelling/shrinking)
- high resistance to rot, mold, insects
- natural wood appearance. Initially chocolate-like brown shade, after approx. 1 year weathered silver-gray like teak
- if the wood is sanded, sawn or planed (all possible without problems), the original brown color shade reappears
- low maintenance effort: adequately maintained with salt water or with soft soap or green soap
- treatment with varnish or (teak wood) oil is possible
- fully recyclable or disposable like “normal” wood
The ecological footprint of the modified softwood Kebony is significantly better than that of teak wood. The significantly lower biodiversity in radiata pine plantations compared with natural forests as well as the sometimes long transport distances (e.g. from New Zealand to Europe) of the source wood must be noted critically. The modification is also energy-intensive.
Why is a substitute for teak necessary?
Within the EU, teak wood may only still be used if it comes from legal, sustainable sources (plantations), which is proven, for example, by an FSC certificate. Thus, according to the EU Timber Regulation (EUTR) / EU Regulation on deforestation-free products (EUDR), teak wood from Myanmar (formerly Burma) is de facto prohibited because it is practically impossible to verify whether it was legally harvested. Illegal logging and unclear supply chains have existed in the country for decades. The human rights situation in the country has been disastrous for years.
Rope and textile fibers
Ropework performs load-bearing, guiding and securing functions on board. It is used for mooring lines, halyards, sheets, tackles, lifting operations and securing. In the maritime environment, breaking load, elongation behavior, abrasion resistance, UV resistance and water absorption are particularly decisive.
The choice of suitable material depends on load, duration of use, handling and environmental conditions. A basic distinction is made between natural fibers and synthetic fibers, which differ significantly in their properties.
Natural fibers
Natural fiber ropework is traditionally made from hemp, manila or cotton. It is characterized by good grip, a natural appearance and comparatively high friction. It continues to be used in classic shipbuilding, on historic ships or in decorative applications.
Natural fibers absorb moisture, are more susceptible to rot and have lower breaking loads compared with synthetic materials. Regular care and dry storage are decisive for durability.
Traditionally, natural ropework is treated for preservation with agents such as Stockholm tar or pine tar. These penetrate into the fibers, have a water-repellent effect and delay biological decomposition. At the same time, they change the color and surface of the ropework and increase resistance to weathering influences. The treatment is particularly common for ropework permanently exposed outdoors.
Synthetic fibers
Synthetic ropework is made from synthetic fibers such as polyester, polyamide or polypropylene. These materials offer higher breaking loads at a smaller diameter, are rot-resistant and more resistant to moisture.
Polyester is characterized by low elongation under load, good UV resistance and high abrasion resistance. It is frequently used for halyards, sheets and mooring lines.
Polyamide (nylon) has higher elongation capacity and has a shock-absorbing effect. It is particularly suitable for mooring lines where dynamic loads occur.
Polypropylene is lightweight and buoyant, but has lower UV resistance and abrasion resistance. It is frequently used for auxiliary lines or marking purposes.
HMPE / Dyneema
High-modulus polyethylene (HMPE), known under trade names such as Dyneema, offers very high breaking loads at low weight and minimal elongation. It is used for highly loaded applications such as adjusters, halyards, shroud replacement or special rigging.
HMPE fibers are characterized by high tensile strength and low water absorption. Due to the low elongation, precise dimensioning is required. The material has a low melting temperature compared with polyester, which is why friction and heat loads at deflections must be taken into account.
Dyneema is frequently used as a core in braided lines, combined with a protective cover made of polyester or other abrasion-resistant fibers.
Plastics and Composite Materials
Plastics perform a wide range of tasks in the ship and shipyard sector. They are used for fittings, housings, panes, lines, seals, bearings, insulation and structural components. Decisive for the choice of material are mechanical load-bearing capacity, UV resistance, temperature behavior, water absorption and chemical resistance.
Unlike metals, plastics are not electrically conductive and do not corrode in the classic sense. However, they can become brittle, deform under load or age due to UV radiation. Suitability therefore depends strongly on the respective type of plastic and area of application.
PVC (polyvinyl chloride)
PVC is used for hoses, profiles, coatings and protective sheathing. It is weather-resistant, dimensionally stable and easy to process. Soft PVC contains plasticizers and is flexible, while rigid PVC has higher stiffness.
Under UV exposure, PVC can become brittle in the long term unless it is appropriately stabilized.
Polyethylene (PE)
Polyethylene is a tough, impact-resistant plastic with very low water absorption. It is used for tanks, sheets, sliding strips or robust components. PE is chemically resistant and shows good sliding properties, but has limited suitability for bonding and painting.
Polyamid (PA)
Acrylic glass (PMMA)
FRP (fiberglass-reinforced plastic)
FRP is a composite material made of glass fibers and synthetic resin. It is used in boatbuilding for hulls, superstructures, decks and structural components. The glass fibers absorb the tensile forces, while the resin matrix ensures shape and stability.
FRP is corrosion-resistant and dimensionally stable, but can be affected by UV radiation or osmotic processes. Repairs are usually carried out by laminating and suitable coating systems.
CFRP (carbon fiber-reinforced plastic)
CFRP is a composite material made of carbon fibers and a polymer resin matrix. The carbon fibers absorb the tensile forces, while the resin stabilizes the shape and bonds the fibers together. The material is characterized by very high strength at low weight.
In the maritime sector, CFRP is used for highly stressed and weight-sensitive components, such as masts, spars, rudder systems or structural reinforcements. Through the targeted alignment of the fibers, mechanical properties can be adapted to the respective load direction.
CFRP is corrosion-resistant in the classical sense, but is electrically conductive. In combination with metals, electrochemical effects can occur, especially in direct contact with aluminum. Structural separation and suitable insulation measures must therefore be taken into account.
Compared to GRP, CFRP has higher stiffness and lower elongation, but is more cost-intensive and more demanding to repair. Machining and laminating work require suitable protective measures, as carbon dust can be relevant to health.
Coatings and protective systems
Coatings take on a central protective function in the maritime environment. They separate materials from moisture, oxygen, UV radiation and mechanical stress. Depending on the substrate and area of application, they serve corrosion protection, impregnation, sealing or fouling inhibition.
The effectiveness of a system depends on the coordinated structure: substrate preparation, suitable primer, compatible intermediate and top coats as well as correct layer thicknesses are decisive. Errors in processing or insufficient adhesion can significantly reduce the protective effect.
Impregnations
Impregnations primarily serve the preventive protection of materials against moisture, dirt, or biological influences. They penetrate into the material without forming a closed film on the surface. The aim is to reduce water absorption and increase durability without visibly changing the material structure.
In the wood sector, impregnations are used to delay the penetration of moisture and thereby reduce swelling and shrinkage movements as well as risks of rot. They often form the basis for subsequent coatings or are used as independent protection on surfaces that are not subject to heavy stress.
Unlike oils, impregnation focuses less on the visual effect and more on technical protection. Compared with varnishes, no protective surface film is formed. The protective effect therefore depends on penetration depth, substrate condition, and regular refreshing.
Impregnation products are applied, depending on the system, to dry, clean substrates and can be part of a coordinated coating structure.
Varnish oils
Varnish oils combine properties of oil and varnish systems. They penetrate into the wood like an oil, but additionally form a thin, open-pored protective layer on the surface. This creates a more resistant structure than with pure oils, without producing a completely closed varnish film.
Compared with classic varnishes, varnish oils are more flexible and react less sensitively to wood movements. They therefore tend less often to crack or flake on working substrates. At the same time, they offer more surface protection than pure oils, particularly against moisture and soiling.
Application is generally less complex than with multi-layer varnish structures. Damaged areas can be locally sanded and treated afterwards without rebuilding entire surfaces. For areas subject to heavy mechanical stress, however, classic varnish systems are often more resistant.
Varnish oils are particularly suitable for components where a natural appearance is to be preserved while increased protection against weathering influences is desired.
Varnishes
Varnishes form closed surface films and protect wood, metal, or GRP against moisture and UV radiation. A distinction is made, among other things, between one-component and two-component systems.
Two-component varnishes cure chemically and form particularly resistant, hard surfaces. They place higher demands on the substrate, mixing ratio, and application. One-component varnishes are easier to apply, but are mechanically and chemically less durable.
Oils
Primers
Antifouling
Antifouling coatings are used in underwater areas to reduce fouling. Depending on the system, the principle of action, service life, and application requirements differ. Selection and structure depend on cruising area, speed, and existing coating.
A detailed overview of system differences and application is presented in the Antifouling Guide.
Sealants and adhesives
Selection and application in context
The suitability of a material does not result in isolation, but in interaction with construction, load, and environmental conditions. Material combinations, surface treatment, and professional processing significantly influence function and service life.
Careful selection taking into account corrosion behavior, moisture absorption, mechanical stress, and maintenance effort helps to meet technical requirements permanently.
For specific questions about material combinations or system structures, the TOPLICHT team supports classification and selection of suitable products.
