The Boat Tinkerer: Episode 53 Corner Blocks

This was probably the most complex piece of wood-working I have carried out on my Cygnet 20.

I had previously made up some corner-blocks, which worked well in some respects, and not well in others. The starboard block broke and, rather than repair it, I decided to replace both blocks with a new design.

The blocks serve two purposes. The first, and most important, is to mount a socket for the pin for the tiller-pilot. The tiller-pilot is a Raymarine Autohelm 800 (inherited from a previous boat) that engages a pin on the rudder at one end and a vertical socket on the other. It has an internal ram that moves the tiller and an internal compass and electronics to move the ram as the boat moves off its compass bearing. The socket has to be mounted securely for the tiller-pilot to push and pull against as it tries to keep the boat on a steady course. The second purpose is to provide sockets for the mast crutch for on-road transport. The Cygnet 20 does not come out of the boat shed with sockets; the mast crutch is simply held in place in the corners at the transom with a bit of carpet as padding. I was beginning to lose the bits of carpet on various trips, and wanted something a little more robust. The corner-blocks presented an opportunity to formalize the arrangement.

The thing that worked well with the original block was the basic operation of the tiller pilot on the starboard side. I had tested this on a couple of day-sails. It provided the relief of being able to let go of the tiller to go and do something like go forward to retrieve the fenders, get a snack or have a pee. However, I could not use the port side because the tiller-pilot collided with the outboard engine. Also, the rudimentary sockets were not aligned, so the mast crutch was not well supported. Finally, the starboard block got broken by the tiller pilot splitting the timber along the grain, which told me that some reinforcement was needed.

The first set of corner blocks were made from standard pine from the Big Green Shed. My mate, Naman (who is interestingly pedantic with his joinery) berated me for using such crappy timber, so I hit him up for some offcuts of decent timber from his pile. He couldn't find lumps that were big enough for the whole block, but he did find some pieces that could be joined together.

Having got the pieces, I set about cutting them to fit into the corners. This is where things got complicated. All the angles were compound angles. Nothing was square or at right-angles. Having a drop-saw that can cut compound angles was an advantage, but it was a three-dimensional puzzle in which each cut took considerable planning. To make things even more complex, the compound angles limited the options for clamping the small pieces down, or gripping them in a vice. Only the upper and lower faces remained parallel.

Then, there was the issue of drilling the holes for the bolts that would hold the blocks to the boat. I have a policy of drilling as few holes into my lovely Cygnet 20 as possible, so wanted to re-use the holes I had previously drilled for the old blocks. I could mark the locations of the holes on the blocks by fumbling with a pencil on the inside of the boat moudling, but this was only the start. I had to figure out a way to drill through the blocks in an inside-out direction, at right angles to the sloping inside face of the combings. This is where I could have done with a drill-press or pillar-drill, but I only had hand tools. I found a piece of scrap aluminium angle that I could use to create a guide at 90 degrees, gritted my teeth and applied my extra-long drill bit. Thankfully, the drill bit emerged from the visible face of the blocks in almost the right locations. The end result was that the blocks could be secured by bolts at 90 degrees to the faces of the combings which, of course, was not 90 degrees to the visible faces of the blocks.

One niggle I had about the previous blocks was that the bolts were not set at 90 degrees to the faces of the combings, so tightening them levered the blocks away from the corners. The new angles pushed the new blocks securely into the corners. The problem here was not structural integrity, but rather keeping the blocks secured so that the Sikaflex bedding would not be worked, allowing water to get into the joints.

To prevent the tiller-pilot splitting the timber again, I added some stainless steel straps, cut from a 0.9mm plate. Cutting, drilling and bending the straps was done with hand tools, which lack the precision of machined parts. I sorely needed a centre-punch to stop the drill bit from wandering in its initial cuts. The imperfections are visible, if you look hard enough, but the overall effect is good enough for me. I secured the straps by bedding them on epoxy and drilling in 50mm screws. Further 3D puzzles arose from ensuring that the hardware inside the blocks (including the tiller-pilot sockets and holding-bolts) did not clash.

The blocks are now bolted in place and bedded on Sikaflex. The port side is now operational, should I ever need to swap the tiller-pilot over from the starboard side. The tiller pilot squeezes nicely between the outboard engine and the locker lid. By bringing the socket further forward a few inches, I have also reduced the angle to the tiller, which reduces the force required to move the tiller. The sockets for the mast crutch line up, making them more secure (the crutch itself is currently getting adjusted and re-varnished). I have also improved my varnishing skills.

I am quite pleased with the result.