Water-borne vessels are constructed of various materials, ie steel, aluminium, wood, glass reinforced plastics (GRP). Steel is used for large vessels. Aluminium is used for very small craft and for on-board structures, ie minor bulkheads, deck houses, guardrail and awning stanchions, non-watertight doors and furniture. Wood is used for pleasure craft, yachts, small to medium fishing boats and for mine countermeasure vessels. GRP is used for small vessels such as pleasure craft and yachts and for mine countermeasure vessels.

Steel.

Advantages. Steel is used mainly because:

1. it has great strength;
2. it is relatively easy to “join” (ie weld);
3. it is relatively cheap;
4. it is impervious to marine organisms such as wood borer.

Disadvantages. Steel has a number of shortcomings:

1. it is susceptible to corrosion (rust);
2. it requires a fair amount of maintenance;
3. it has an adverse effect on the magnetic compass (it causes deviation);
4. because of its magnetic field, it could trigger magnetic mines during wartime.

Wood.

Advantages. Wood is suitable for smaller craft because:

1. it is fairly easy to work with;
2. it is fairly robust (strong);
3. it is non-magnetic;
4. the material itself is buoyant.

Disadvantages. The shortcomings of wood are:

1. it can be very expensive;
2. it requires much maintenance;
3. it is susceptible to marine organisms such as wood borer.

Aluminium.

Advantages. Aluminium is used in ship construction where weight is a bigger consideration than
Strength, ie the superstructure on passenger vessels..

1. it is very light;
2. it is very flexible;
3. it is impervious to marine organisms such as wood borer;
4. it is non-magnetic.

Disadvantages.

1. it does not have great strength;
2. it corrodes in salt water;
3. it is very expensive;
4. it is suitable for the construction of small vessels only and for structures such as
   superstructure and internal bulkheads and fittings aboard vessels.

Glass Reinforced Plastic (GRP)

Advantages. Again GRP is used for the construction of small vessels.

1. GRP is stronger than wood;
2. it is non-corroding (almost maintenance free);
3. it is impervious to marine organisms such as wood borer;
4. it is easily formed into complex shapes;
5. it is non-magnetic (it is ideal for mine countermeasure vessels).

Disadvantages. It is not feasible for GRP to be used for the construction of large vessels.

1. the manufacturing process is unsuitable (moulds have to be made to shape the GRP for whatever is envisaged and temperature control is vital);
2. it does not possess the strength to take the stresses and strains which large vessels are subjected to;
3. it is susceptible to long term exposure to ultra-violet radiation.