As a nation, we've never had so many garages, but we're using them less and less to keep our cars in. Cars are seen as disposable products, and modern paints, coatings and plastics will protect them from the worst ravages of the weather and keep them looking reasonably neat for most of their short lives. The idea of keeping one in the garage so it doesn't rust is seen as quaintly old-fashioned.

Boats could hardly be more different. They are kept in a damp, usually salty environment, which does nothing either for the intricate electronics and plush fabrics inside, or for the moving parts left open to the elements outside. They remain unused, unvisited and untouched for weeks or months at a time, and yet are expected to repay the substantial initial outlay with a long operational life.

Glassfibre isn't immortal, but it's safe to say that a modern FRP (fibre-reinforced plastic) hull and deck will usually outlast most of the other components installed within them. Secondhand values don't have to follow the depreciation curve that used car prices do, which is short, steep and largely based on age: a prospective boat buyer is likely to be more interested in its condition than in the number of years since it came out of the factory. So the best way to protect your investment in a boat is to keep it well-oiled, functional and gleaming.

Hull and superstructure

Modern composites are considerably more durable than their predecessors, with isophthalic resins offering greater water resistance and tensile strength and techniques such as performance matching giving a better bond between the gelcoat and the skin coat beneath. But even the strongest carbon fibre and epoxy laminate can still be chipped, dented, scratched or cracked.

Repairing damage to FRP laminates is important for structural as well as cosmetic reasons. Thanks to advances in composites technology, there is now less likelihood of a boat developing osmosis, but any breach of the gelcoat must be viewed as potentially letting water into the substrate, which could ultimately lead to delamination of the hull or deck. This is particularly important with sandwich construction on older boats, where to keep the laminate light but strong the builders included a reinforcing layer of plywood. If water is allowed to soak into the ply, it can swell up and eventually split the laminate.

Crazing of the laminate can be found on almost any older boat, particularly around highly-stressed areas of the deck such as stanchion bases. If the crazing is below the surface, the gelcoat integrity is probably unaffected, but keep an eye on the problem, and if it starts to spread think about repair.

Glassfibre is not difficult to repair using proprietary kits, but repairing more advanced FRP laminates will need careful matching of materials.

If you do find signs of osmotic blistering on the hull, get professional advice so that you know how far the problem extends. Unless it's very local, you will probably need to call in the experts to deal with it.

Wooden and steel boats should be protected from water by an impermeable skin of paint or plastic, so if the skin is chipped, rubbed or flaked off it ought to be repaired as soon as possible.

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