I have some 3/16 aluminum plate, and I need another fin or two, so I was thinking that if the fin was made of metal, then you could decrease the amount of ballast (keel bulb) at the bottom, right?
thx
Yes, but do you want too?
The problem is that you want the the fin to be as light as possible so that the lead is as heavy as possible. You want the lowest possible CG. Doing what you propose would raise the GC and make the boat more tender for the same total weight.
Yes, although the weight would not be positioned in the ideal place. Ideally you want all your ballast as low as possible, to increase the righting moment. That is why keel bulbs are used instead of sandbags in the bilge – to keep the weight low, together, and balanced. That said, an aluminum fin probably won’t weigh so much that you will throw your ballast too much out of wack… although, that may in itself defeat your purpose of trying to cut the amount of ballast. Your other option – if you are simply trying to cut down on bulb size – would be to cast a keel entirely out of lead, or part of a keel. It could be argued that doing so would cut down on drag at the end of the keel as well, however, once again, if you look at any racing keelboat today, they all have bulbs… there’s a reason for that.
oops, hiljoball beat me to the punch… ah well, it bears saying twice!
It seems to work on the solings, which are pretty much solid lead top to bottom.
But that’s not a good analogy. The Soling has a balasted fin keel. Your boat has a fin and bulb.
You want the weight as low as possible.
^^ What the man said ^^