REPAIRING DRY ROT IN A KEEL
Dry rot isn’t dry, it’s soft. If your fingernail or the end of a screwdriver can easily penetrate wood, it’s likely to be as a result of dry rot.
If not removed dry rot will continue to spread either side of a seam or along the weakest grain. The only solution is complete removal, back to hard wood, leaving nothing at all. This is a daunting challenge especially when it’s in a vintage boat keel.
Early signs of trouble had been a ‘tear line’, like an elephant in musk, originating half way down the keel. Ignoring it was no longer possible, the softness of the wood was an indication of dry rot. It had to be cut out or the whole keel would need replacing before long. It was near the prop-shaft tube where integrity is critical.
I took a deep breath and started to drill through the keel at the margins of the soft wood. The wood just crumbled as I used my fingers to pull it out. This was a stinkwood keel, shaped in 1934, that I was destroying. The pile of crumbling wood on the floor reassured me there was no alternative and no stopping either.
The resulting gap in the keel resembled the shape of a key and revealed the cause of the problem. An early technique to build a keel, was to insert the ‘bolt’ end into a hole in the existing keel, onto which the bottom keel piece could be lifted and bolted in place. The hole around this bolt had been filled, but presented a weak spot for water. Gradually salt water started to rust the bolt allowing in more water.
The rot had worked its way along the seam and the damage was extensive!
I was going to cut out the healthy wood along my pencil line above, to make a regular shape that a large rectangular plank could fill. This would be inserted sideways after removing the offending bolt. This was to avoid using two or possibly three separate pieces of wood.
Fortunately a visiting boatbuilder friend advised me to leave the ‘lock and key’ shape. He held the new stinkwood piece I had in stock (known for it’s bug repellency properties) to the opposite side of the hole while I drew the unique shape onto it. Cutting out the replacement, I was careful to leave plenty of wood outside the pencil line. Then the piece was shaped until it fitted snugly. It could only be put in from one side and the locking nature of the shape held the wood firmly in place. The dry fit was successful.
A gap extending towards the prop area between that retaining metal strap was filled with a mixture of thickened epoxy and micro bubbles. Then the replacement stinkwood and the periphery of the hole were liberally applied plenty of thickened epoxy. The ‘key’, once firmly inserted in place, was secured with clamps and the excess epoxy removed.
The next day I took a belt sander to the keel and smoothed down any protruding wood and epoxy, sealed the area with regular epoxy and a day later primed and anti fouled the area. The insert shape had not only replaced diseased wood, but also added sideways rigidity to the keel. Although clearly visible in this photo, at a top speed of 6 or 7 knots, the insert would not slow the progress of the boat at all.