replacing steel cb with alum.

[PAComet]

Hi all

Restoring a wooden Comet from the '30's in PA. Two centerboard options were originally available- galvanized steel or bronze (for only 15 more bucks!). Mine came with steel- and is heavily rusted. I'm considering replacing with 5052 aluminum or 6061. I'm told its 1/3 the weight. Opinions on whether to go with 5052 or 6061 (60 is more expensive but stronger). Opinions on whether the loss of ballast weight will be significant?

Thanks!
Matt

[Ian McColgin]

For that small boat, the weight loss could matter, but really most of holding her up is what you and your crew do on the rail and hiking out, so I'd not worry about that so much. For many boats, the total displacement really matters to bring the boat down to her marks, but with the Comet shape, I don't see how lighter could be a problem.

Two problems:

Aluminum is fairly ductile and seems to me more easily bent than steel or bronze of similar thickness. This matters if you sail in shallow waters and risk scraping the plate, especially on a beat where it's easy (I've done it) to bend a metal board thus jamming it down.

The Comet class association may have weight rules that would disallow such an easy way to shed a few hundred pounds. If you want historical accuracy, in short if you mean by restoration something faithful, better stick with steel.

If you don't want a new board, it's not really that big a deal to rent a sand blaster to clean it up and then fair up with epoxy.

G'luck

[Thorne]

Also consider getting either galvanized steel or SS - the latter you'll have to epoxy several layers together to get a decent thickness at an affordable cost.

[PAComet]

Thanks guys! I'd probably shed around 30 pounds. The rust is up past the pivot hole, so cheapest route would be to cut, weld, fair, and re-dip. But there would be a concern about warping with the heat of the torch. In terms of faithful restoration, or class rules, she's too old for competitiveness, and basically I want pretty bright cedar topsides and functionality. Thorne- had no idea you could epoxy SS sheet together! Thanks again.

[Thorne]

Well, you'd have to cover it with more fiberglass and epoxy, but it would be one way for a dry-sailed boat to have a non-rusting mostly metal CB -- I thought about that as my wife works for a stainless fab outfit but can only get thin sheets. Really the stock galvanized steel one would be a better choice, particularly if you sail shallow rocky waters.

[Canoeyawl]

Just cut a new one out of steel and take it to the galvanizer.
Any one with a good bandsaw, a water jet or plasma cutter can cut it. None of those methods will warp it.

Or, you can cut aluminum yourself on a wood bandsaw - the difference in righting moment is not calculable.

[Woxbox]

So how thick is this board? If not too thick, Ian's right about the risk of bending it. If you flip the boat, you'll want to be able to stand on it. I'd sandblast it and fair the old one with thickened epoxy, too. Paint it up and it will be like new.

[PAComet]

1/4 inch plate. I think it'd be strong enough to stand on... I would work with cab0sil but the hole where the thing pivots is thin enough to shave with, if you didn't mind tetnus