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If you suspect a hull-to-deck joint has failed, then being absolutely sure where the actual leak is occurring is of prime importance. Areas to check are near the deck fittings, where the decks may be put under considerable stress by the rigging and the continued flexing of the hull. Another area to check is where mooring cleats have been subjected to excessive strain or when a boat has been left tied alongside with insufficient fenders in place.

Hull-to-deck joints are designed not to come apart, so they are permanently bonded, often covered up and some are even glassed in. This can make repairing them very challenging:

  • Getting access – hull-to-deck joints are usually fastened with bolts from above and nuts below. Others are fastened by screws and others by rivets. Getting access to the underside of the fastenings usually entails stripping away the headlinings or panels. So the first thing to do is check what type of fastenings you have on your boat and then work out how you are going to get access to them and remove them.
  • Loosen the rigging – before you begin to unfasten things, it is a good idea to slacken off the rigging to ease the tension acting along the length of the joint.
  • Removing the rail – back on the outside, it is common for the joint to be protected by a rubber fender or toerail, which may be constructed either from aluminium or wood. The rail invariably needs to be removed first. Metal rails might be bolted, screwed or riveted. Wooden rails will be bolted or screwed.
  • With the rail removed – closely examine the joint and get a better idea of where the problem lies. It might be that there are only a few places where leaks are occurring, meaning that a localised repair is all that is required. A thorough inspection at this stage will help you decide.

  • Unfasten the joint – remove the fasteners holding the joint in place around where the problem lies. The reason for this is that you need to open up the joint in order to apply new sealant for the repair. Alternatively you may choose to re-bond the entire length.
  • Remove the old bedding compound – before new sealant can be added, all the old bedding compound must be removed, using a reefing iron or similar to scrape out the old material. Use wedges to separate out the joint flanges enough to get access for the repair.
  • Fill the joint with new sealant – with the old joint cleaned out as well as possible, fill the joint with polyurethane sealant, ensuring there is sufficient to reach well into the joint beyond the fastening holes. Once the sealant has been applied then remove any wedges and where possible clamp the joint to ensure there will be a good seal along its length.
  • Re-fasten the flange – re-fasten the flange with through-bolt fittings if possible , but if not use self-tapping stainless steel screws. Apply extra sealant beneath the heads of the bolts or screws, but leave the nuts beneath clear of sealant to make it easier for the joint to be undone in the future. Clean up any excess sealant before it cures.
  • Re-fasten the rail – re-fasten the rail, bedding it with polyurethane sealant and bolts or screws. Re-attach the fender strip if there is one.

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