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The whole structure of a boat at sea is rocked and twisted as it pitches, yaws and rolls through the waves. This motion exerts considerable stresses on the hull, decks and superstructure as anyone will appreciate who has experienced the continuous slamming of a boat through rough weather at sea.

The deck and superstructure are often overlooked as structural components but they need to be checked over on a regular basis. When inspecting their boat’s deck it helps an owner if they are aware of how these parts of their boat have been designed and constructed. What goes on beneath the smooth flowing lines of their pride and joy? Does the deck have a foam core, or is it balsa or plywood? How is it supported, where has it been strengthened, how is it joined to the hull?

The deck and superstructure of a medium sized GRP yacht commonly consists of a deck, coachroof and cockpit in one moulding. The deck, coachroof walk area and cockpit seats are usually stiffened by glassed-in members and areas of load are backed with plywood plates. Down below, structural bulkheads are built in to provide strength and reduce flexing. The whole deck moulding is attached to the hull via a hull deck joint.

Not all boats are built to the same design standards. For example an inshore motor cruiser is not designed to cope with 10 metre waves while an ocean going tug most definitely will be. This may seem obvious, but it is important to be aware of a boat’s limitations and not to subject it to conditions it was not designed for.

If a boat owner is not sure how their boat is constructed, it will be a good idea to find out, so that nothing is left to guesswork. The first thing to do is try and get hold of plans, then get in touch with other owners of the same class of boat, join class associations and forums. If in doubt, then asking a surveyor should clarify things.

Deck and superstructure inspection

 A deck and superstructure inspection can be done at any time, but adding it to a to-do list of jobs to be done immediately the boat comes ashore for winter storage is a good plan. You don’t want to delay carrying out an inspection and then discover there are things that need fixing the week before the boat is due to be re-launched.

The deck of a boat is constantly exposed to the elements and should be inspected on an annual basis. Particular attention needs to be given to the overall condition of deck fittings such as the stanchions, cleats and chainplates.

Here are some checks to carry out:

Walk around the deck and test for any signs of flexing, which can indicate degradation of the core caused by rot. If the deck remains firm this is a good sign.

  • Look for stress cracks around the deck fittings.
  • Check for any loose fittings which could be the cause of deck leaks.
  • Check through-bolts for tightness. Note that fastenings are not always easy to inspect as they can be hidden behind cabin panelling or may be glassed in.
  • Inspect all the windows, checking them for secureness, signs of leaks, stress cracks and the condition of the seals.
  • Check the secureness of guardrails, stanchions and handrails. Also look out for stress cracks where they meet the deck.
  • Check that the lifelines are in good condition and well secured.
  • Look around the mast foot for any signs of cracking or damage.
  • Check all hatches are watertight. Also check the condition of their seals, hinges and fastenings.
  • Inspect for any holes left by old deck fittings or fastenings that have been removed.

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