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Written by Staff of Quadrant Marine Institute
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Q. I have a small area of rot (a few inches square) in the main teak ply cabin bulkhead, under one of my chain plates. Removing the chain plate should be easy enough, but is there a simple way of removing and scarfing in a new section of wood. How would someone without fancy woodworking tools or a great deal of carpentry experience go about this?
A. Keeping freshwater from leaking into the interior woodwork can be the most challenging aspect of owning a boat, especially here on the “wet” coast. Jobs like the one you are facing often grow and take on new proportions once you start disassembling and analyzing the situation; be prepared for this to become much more complicated than you expected!
The first thing to understand about rot is that there is generally far more of it than is immediately visible. A good way to think about rot is that the crumbling, decayed wood you can see is what’s left after the fungus has taken what it needs for sustenance and moved on. It is currently most active in the apparently sound material that is in the immediate vicinity. This is why chopping out the visible signs of rot and inserting graving pieces is rarely a successful strategy in the long term.
The old rule for rot removal in solid wood is to go three feet down the grain in either direction from the last visible sign. In practical terms, this means the proper course of action when dealing with an infected member in a boat is usually to take out the whole piece, frame, plank, stem—whatever it is. Economics often dictate such action impossible, in which case we must be as ruthless as our wallet and the value of the vessel will permit.
In your case, you are dealing with a structural bulkhead with a high point loading at the chain plate itself. Most likely, you will be better off replacing the entire structure or at least a major portion of it. There may be a natural place to cut back to without removing the whole bulkhead, but this will depend on the arrangement of the interior joinery.
“Chopping out the visible signs of rot and inserting graving
pieces is rarely a successful strategy in the long term.”
In any case, take apart any joinery in the way, cut out the glass tabbing with an angle grinder and remove the old plywood. Before you do that, be sure to seal off the rest of the interior with plastic sheeting and tape to contain dust. Grind out all secondary fibreglass bonding, clean and vacuum in preparation for the new bulkhead.
If the damaged ply comes out in one piece, it can be used as a template for the new one; otherwise, take an accurate pattern of the shape using strips of plywood and a hot glue gun. (You may want to check your pattern before removing the bulkhead and make sure that the new bulkhead will fit through the companionway!) Make and fit the new piece and glass it into place with tapered laminates to match the original spec as closely as possible.
After replacement of the bulkhead is complete, be certain that you have solved the original source of trouble—the freshwater leak in the deck—by properly bedding the chain plate and, in particular, the cover plate where it penetrates the deck. It would also be a good plan to seal the plywood well with epoxy resin in the area where the chain plate will be fastened. Do this before installing the chain plate, but after boring for the fastenings.
There is no easy fix for this one. Replacing a rotted bulkhead, or even part of one, is a serious repair job and most boat owners would find it beyond their skill level. If the repair becomes more than you are willing to tackle, seek professional assistance. Failure of a chain plate or its supporting structure is likely to bring the whole rig down—a catastrophic event by anyone’s reckoning.
One last word: It really pays to keep an eye out for leaks on thru-deck fittings, especially chain plates. At the first sign, do something! Re-sealing and bedding these fittings is a simple job, whereas the repair described above is a major and expensive undertaking.
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