My keel is an 8,750 pound bulb/fin. It is sort of a compromise. One of
my criteria was good up wind and light air performance. When John Fox
started work on my design he had been building flat out racing boats so
the first proposal had a 9' draft wing. We compromised with a 7' draft
beavertail bulb. Beavertails count mightily against you in most
handicapping systems but that was not a concern for me.

As I said, the advantage of the bulb besides reducing draft for the same
RM is the end plate effect and the beavertail is supposed to split up
the remaining vortex.

I talked to Mars about casting it for me but their price was a little
over $1.40/pound plus some extra charges for waste disposal and
transportation if I provided the plugs and bolt frame. That was 5 years
ago. Being me, I set about collecting wheel weights and cast the bulb
myself a couple of years ago. I have finally built up the nerve again
and will be casting the fin just after Christmas. I figure to have
about 40 cents/pound in the finished keel. OTOH, the backyard may end
up with a Superfund designation some day. :-)

Mars does sell a bolt on winglet set for shortening keels but it takes
some design work to figure out the weight and location so that your RM
does not change much. There has to be a careful balance of added weight
and higher center of gravity. Also if the keel has a large dihedral
shortening the keel will shift the lateral center of force forward which
might make the boat a bit squirrley and hard to trim out. I would call
Mars and see what they say. They have already done the engineering and
have patterns for many different hulls. No matter what they say, ask
for references for boats similar to the one you are contemplating
modifying and check with the owner for actual results.

Keel design is a balancing act between stability, performance and
comfort. Production boat designers spend a lot of time and money trying
to arrive at a happy compromise that is best for the market the boat is
intended to compete in. Ssmall changes below the waterline can make big
changes in the way the boat sails. Some can be good but more can be bad.

Personally I would not consider a complete re-keeling of any boat. It
would be outrageously expensive and you run the risk of changing the
sailing characteristics of the boat in unpredictable ways.

Skip Gundlach wrote:

Hi, Glenn, and thanks for your input (crossposted to RBB). I've left the
original thread attached to bring the RBBs up to speed.

Since you're building one, and have done extensive research on all aspects
of your boat, I'm interested to know what you'll do about a keel for RUTU
(apologies if it's been covered already some time in the past - I don't get
over to 'building' very often).

I'm also interested in your opinion, if you have one, of Mars Metals'
approaches to afterfits, and, if you've had any exposure to the
modifications I'm speaking of. Anecdotal experience suggests that it's a
neutral effect, or, worse, frequently, a negative effect. Of course,
perhaps the add-ons already identified were homegrown, and Mars Metals'
approach is engineered, which, of course, would make a tremendous
difference.

Thanks.

L8R

Skip


--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com