new bulb keel

[mod flod]

Hi everybody,
need a little advice here. I have a 37' IOR racing design sloop from the early 80's that I'm converting to cruising. These boats are not positively stable enough to my taste (ballast in the bilge) and I have an exposed rudder issue with the sabre daggerboard. I talked to a very competent architect that suggested strongly to put a bulb-keel under the boat, that would also have the advantage of getting rid of the trunk in the cabin. He said that it would make it sail even better.
Considering that it's a big decision and mui dineros for me, I would feel more at peace with having outside opinions on certain matters before I start sending checks...
-Better sailing with a modern bulb keel that with the daggerboard
-What's a ballpark for what I should pay for the design of both the 8000pounds keel and the modification of the bottom of the hull to receive it

Thanks much

[fredrosse]

What is the construction material of your hull?

[mod flod]

fiberglass, airex core

[tspeer]

More stability means more stress on the rig. So you might end up spending money there, too.

Instead of spending a lot of money on making this boat into something it's not, have you considered selling it and buying what you really want? The net cost could be cheaper.

[mod flod]

good point Tspeer, but i got the boat dirt cheap and realistically, with a good keeljob done, it would still have cost me less than half of a typical boat this size (and I'm being conservative in figures). One thing that I'm curious about is the rigging issue. Are we talking new shrouds or spar and all?

[mod flod]

another side of this is that french architects have not stopped designing "deriveur integral", by that I mean ballast at the bottom of the hull, no keel and sabre daggerboard so it must not be such a bad design right. With the notable exception that most of the ones I see are twin rudders. I'm not an architect but I guess two rudders= smaller rudders so that could solve my exposed rudder problem...

[dionysis]

8000 lbs in a bulb is a very large increase in stability. Maybe you do not need such a big increase - just enough to make the boat self righting may be all you need. Putting that much mass at the bottom of your keel will change the sailing characteristics of the boat - the pitching moment will increase e.g..

[Skippy]

Originally Posted by dionysis

Maybe you do not need such a big increase

That's a good point. Tom, how bad would it be to put on a small bulb, just enough to increase the loads slightly but reduce the boat's weight?

[tspeer]

I don't think one can answer that question with no more information than you've provided. And I think there area others on this site that are much more qualified to answer it in any case.

One approach might be to remove the internal ballast and substitute a bulb that provided the same righting moment at the same heel angle as the existing boat's maximum righting moment. Then it ought to provide positive stability over a wider range, but have similar stability over the normal range.

However, just reducing the displacement will change things. The boat will sit higher in the water, so it will have less waterplane area, and be more tender initially. So there's not a simple answer - you are changing one of the fundamental design aspects of the boat, and it's going to have some impact on just about everything.

You really need to go to your friendly neighborhood NA and have the change designed right.