One feature of this project is that it is not possible to keep trying things on for size. You do not know if it all fits together until the new guide plates etc are attached to the keel and it is put back in the boat. When it’s back in the boat it is impossible to see how well the guide plates fit in the keel box and how well they mate up with the bottom of the boat when the keel is down.
Another feature is that I knew the new guide plates and front pad must be different sizes from the existing ones, so could not just copy the old ones.
I was concerned that I might make the new guide plates the wrong size or shape and wanted a way that I could try them on, so I made a "dummy keel". This was initially a wooden dummy of the top part of the keel (to which the guide plates attach). I then attached the original guide plates to the wooden dummy. This was not completely successful as I could not work accurately enough to make the dummy exactly the same as the original part of the keel. This was caused by my own lack of skill and also because the bolt holes in the keel for securing the guide plates were not true.
I then made a "mark 2 dummy keel" which included wooden replicas of the guide plates. Using car body filler I took a cast of the inside of the bottom of the boat (where the plate rests) on the end of the dummy keel. This then gave a reasonable idea of the shape that the new guide plates should be (the old ones did not fit the boat accurately). In order to measure the inside of the keel box I made a simple measuring stick which would just fit inside the keel box (when held at right angles to the axis of the keel). This made it easy to express measurements as "stick+2mm" etc. I also made a thin plywood template with handles on it which just fitted inside the keel box. It was shaped to replicate the way the guide plates bear on the inside of the keel box. Using this template I then made 2 wooden templates which would just fit round it and therefore represent the keel box itself. If my keel with its new guide plates would fit inside these templates then it would fit inside the keel box.
New Guide Plates
It was then time to make the new guide plates. The old ones were 21mm thick, which seemed odd. However it seems that the acetal / delrin is normally supplied a bit oversize. I was relieved to find that the stuff I ordered as 20mm arrived as 21mm. The order of fitting the guide plates was:
- Cut slightly oversize with circular saw
- Plane bevels on the inside to match the shape of the main part of the keel
- Drill fixing holes, counter-bore the fixing holes and fit to the keel. Drilling had to be done through the keel so that the hole in the delrin matched the wonkiness of the hole in the keel.
- Plane front and back to the correct dimensions (checked using the templates described above)
- Shape the bottom ends to match the boat
- Round the outside corners
- Put a bit of West epoxy in the bolt holes to make them more waterproof and discourage water penetration into the core of the keel. Wait for it to set.
- Bolt on, bedded in a layer of silicone sealant
- Measure again, followed by a little more planing.
New Front Pad
This required thicker material than the guide plates. The space available was 35mm, the existing pad was 25mm, so I ordered material 30mm thick, intending to use washers to fill the gap. Using the existing pad as a guide I cut the material to the correct angle to match the keel using the circular saw. I then shaped the edge which would bear on the keel using a small coarse halfround file and sandpaper, using plywood guides to keep the file straight. This took ages but seemed to give the right result. The other end of the block was left oversize pending careful measurement. The new pad did not quite fill the 35mm available, so I made some thin shims so that it was a snug fit in the bracket.
New hold-up strap
The metal strap which is used to hold the keel up is made of galvanised steel on my boat (however some later ones are stainless) and was quite badly rusted. I removed it and took it to a steel fabricator for his opinion. He did not have the right size of stainless steel in stock and said re-galvanising was not simple as the old galvanising had to be removed, so he made me a replacement in mild steel. This was not exactly the correct angle where it mated with the keel, so I took it back together with a wooden block which had a mould of plastic padding on it showing the exact shape of the old strap. He modified it – I should have made up the mould at the start as it only took a few minutes. I got the strap galvanised at a different place which makes boat cradles. I fitted the new strap bedded in a layer of West epoxy with milled glass filler, so that it was in contact with the keel all the way along. I used new bolts and put a bit of Duralac where the bolts went through the holes – it is supposed to reduce corrosion when fixing dissimilar metals.
New top roller
After the new hold-up strap was fitted it became apparent that the old top roller would not bear on the back of the keel box, so I turned a new slightly larger one from a piece of Delrin rod.
Just before fitting the whole thing back in the boat, Fred Larkman reminded me that the cables were worn out and needed replacing. He soon made up new ones.
I think there had been a little leakage from the hydraulic cylinder, so I took it to Ipswich Hydraulics for overhaul on the principle of doing everything possible to get the keel in good order. They fitted new seals throughout. The keel tends to very slowly go down when left up and held only by the hydraulics. I am not sure if this is caused by leakage at the cylinder or some other part of the system. So I also installed a valve in the aft locker at the start of the main pipe run to the keel cylinder. Closing this valve will stop the keel from slowly falling unless the cause is the cylinder itself.