Friday, December 10, 2010

Building ‘Sharpy’ Part 35

Comparative size of keel

Both pieces

I have tried cutting aluminium when I have made gimbals and fire shields for galleys, but with the limited tools in my possession, I was not very adept at it. If you are cutting a straight edge, you can do it well with a suitable guillotine, but try doing it with a hand saw, then the result will be nowhere near as good. Cutting irregular shapes in sheet aluminium requires a skill that I do not possess.

Since the keel is made from a sandwich of two pieces of aluminium on the outside and a piece of plywood between them, I opted to have the metal cut to shape by a professional. He used a laser cutter to do the job and came up with a first-class finish. Because he hadn’t read the plans correctly, he made the holes at the bottom for the ballast retaining pins too large. The solution was either to make another two pieces or infill the holes with welded aluminium and re-cut the holes to the correct size. This appears to have been done successfully.

Now that I have the aluminium parts cut to shape and to size I can get on with making the plywood infill. There’s nothing to stop me from cutting and assembling the lead ballast laminates when I obtain the flashing, and I can go ahead with the keel box. All I need is for the weather to improve so that the temperature is OK for working out of doors. The forecasters predict cold weather for the middle of next week, so the prospects are not promising. I’ll have to be patient.

The photo gives a pretty good idea of the size of the keel. The length from top to bottom is 42 inches, and it has been cut from 3 millimetre aluminium, which is half a millimetre thicker than the plan specifies, but my plywood is 9 millimetres thick instead of being 10 millimetres as per plan; therefore the nominal thickness of the keel will be the required 15 millimetres, plus a little more for the thickness of the adhesive.

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