Things that go bump in the night - Repairing water tank baffles

The first clue we had that our water tank baffles were giving issues was having things go “bump” in the night. We had a mysterious knocking in the forward starboard side that we just couldn’t find – I initially thought it would be a stray can of beer or bottle of rum but no matter how hard I looked I couldn’t find anything that was going “bump”. We looked inside and out but the bump continued, months passed… We were also seeing glass fibre strands and gel coat chips in the water strainers - at the time I thought it was probably debris from the original build.

When checking the water tank by chance a boat went past and the wake caused the bump and I saw the baffle move – it had become detached along its aft edge. There are three baffles in the tank but you can really only see the first one and even that is hard.

After consultation with KYC they provided a repair procedure and some great diagrams to help us understand what needed to be done. We found a GRP specialist yard to effect the repair, the correct materials were sourced and shipped in (food grade resins and flow coat), the work dock was booked.
There is no easy way to access the baffles, it’s impossible to work through the round inspection hatch.

So following the process we had been given, the angle grinder came out and the top of the tank was cut out.

Both of the main baffles were partially detached – so the tank was dried, cleaned ground back – and the baffles re-bonded and fixed in place with GRP tape and resin. After it had all been allowed to cure it was re-painted with food grade flow coat.
The top of the tank was then reattached with tape and resin then flow coated to match. We took the opportunity to add a second inspection hatch so we can now access the 2nd compartment of the tank as well as the first.

The yard “Raiatea Marine” (in French Polynesia) who normally build the local tourist boats did a fantastic job. They even gave us the best job report at the end of the works that we have had from any marine supplier anywhere in the world!
Thanks must also go to KYC for being very supportive and helping us with the process to effect this repair.

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Hi Ian. Thanks for a great and thorough post. This was an interesting post for me as I had the same issue two years ago but not as nearly as dramatic as yours. My middle baffle detached on the top left corner … I filmed it moving with my Oscilloscope (what a handy tool this has been to have on the yacht!!) … anyway to keep the story short … I cut out the same size hole (as per your new hatches) and managed to bond two L shaped gussets (supplied by KYC) to reattach it with West Systems epoxy and let it cure with a lamp for two weeks and only refilled the tank after two months (we were at a dock at the Chesapeake Yacht club for hurricane season) so it had plenty of time to cure properly. West systems would not give a firm answer on the toxicity of the epoxy but after letting it cure for that length of time I felt comfortable … the repair has held firm including a crossing from the southern end of the Bahamas to Spain via Bermuda and the Azores with some sporty conditions! I fitted a clear hatch cover which has been useful when filling up and keeping an eye on the tank without having to open it.