Anode Bolts in Wooden Boats

I thought this might be of interest.

There are many thoughts about the fitting of anodes onto wooden boats, which I have no desire to replicate; there is plenty of information available on the Internet.

The problem is that whenever wood and metal come into contact, a chemical reaction takes place that sometimes cause denaturing of the wood, and eventual structural breakdown in the wood fibres.

The wooden boat I work on has had such problems. The boat was fitted with 2 anodes, 1 for the seacocks, 1 for engine and shaft. We noticed the area around the anode bolts inside the hull showing a white powdery substance and the darkening of the wood in the area.

After consultation with a wooden boat surveyor, we removed the anode for the seacocks, drilling out the holes to find good wood and gluing in tapered hardwood plugs. However, I was reticent to remove the one protecting the engine and shaft.

This season, I again noticed the white powder forming around the anode bolt in the inside of the hull. As the anode is part decomposed it would appear it is doing its job and therefore I feel we still need to keep an anode on the hull to protect engine and shaft.

Once the boat was hauled ashore for the winter I removed the bolts and checked the condition of the wood, which luckily was still in good condition. I have heard of washing the area with vinegar to neutralise the presumably alkaline deposits. There seemed no harm in doing this.

I debated the idea of enlarging the holes and sleeving them with plastic piping to isolate the metal bolts from the hull, however, a wooden boat builder suggested sleeving the bolts with heat shrink.

The above photo should show the finished product. I have made plastic washers that fit both sides of the bolt where it touches the hull. The bottom square one I have glued into position to ensure it doesn’t move when I put the bolts back. Having then heat shrunk the sleeve into place; I sealed the join with a glue gun. The top plastic washer simply sits next to the wooden hull before the metal washer is fitted 

I will still liberally coat the entire bolt in sikaflex prior to fitting to ensure a watertight fit and further insulation between the wood and metal.

Only time will show whether this will work or not. It will certainly do no harm.