Jeff wrote:

This is nonsense. It may be true that the particular design used in the
12's wouldn't be appropriate for a cruiser, but the basic concept is
valid and quite useful. Simply put, the water that flows under the tip
of the keel reduces the effectiveness of the bottom foot or so of the
keel. The wing keel prevents this flow and keeps the last foot of the
keel effective. This permits reducing the draft by roughly a foot in
many cases. In addition, the ballasted wings are essentially a bulb.
It should be noted that the primary purpose is to reduce draft; the deep
keel will normally be more effective overall.

After the America's Cup where the winged keel appeared, a lot of shoal
draft winged keels appeared on cruising yachts.

Winged keels are actually very HARD to get right. The added weight
down low helps, but the extra wetted surface and drag are
considerable. You have to get the angle of the wings right and
without doing studies in a tank, that's hard to do.

My copy of Principals of Yacht Design has an interesting study of
shoal keels. Delft University researchers used a VPP to compare keel
shapes. Results of sailing an Olympic trial course in the computer.

Times are in decimal hours:

Deep Fin keel 3.96
Shallow keel + centerboard 4.06
plain shoal draft keel 4.13
Scheel keel 4.10
Winglet keel 4.04
(short wings, aft swept leading edge)
Winged keel 4.01
(wide wings, reverse taper)
Deep Elliptical keel 3.96

So a good winged keel can be nearly as fast as a deep fin keel. But a
bad one (as many were) can be quite slow upwind due to extra drag.


If your husband is a ME then adding a simple bolt on lead bulb is the
best bet to keep performance reasonable. I'd try to keep the bending
moment on keel root the same as the original keel. I'd also use a
body of revolution using a 64 series NACA foil to define the bulb
shape. He can use Profili to get foil sections in DXF format, export
into Autocad or any 3D modeler, and revolve to get a bulb shape with
the correct volume. Then plot out full size cross sections and make
templates to form the bulb. Make a bulb plug in foam or wood. Get
somebody else to cast it for you or DIY. Glenn Ashmore's RUTU site
has a good description of keel casting.

I don't like Sponberg's "beavertail" keel. I think there's a lot of
drag in the tail that isn't justified as an endplate astern of the foil.

Evan Gatehouse
(also a naval architect and ME)

Wayne.B wrote:
....
The whole wing keel concept was really applicable only to the old
style 12 meter Americas Cup boats because of a design quirk in the
rating rule. ...

The Oz II keel had a lot of things going on including inverse taper,
and very thick winglets cum bulbs and, as a whole, it could only have
worked well on Oz II. When we saw it I think most of us though, "wow,
that keel is on upside down!" It is the upside down or inverse taper
part of that keel that was most notable and is least transferable to
non-meter designs. There is a theory that the inverse taper on the Oz
II keel smoothed out the spanwise lift for the entire boat including
its deep, narrow canoe body. If true, this would only work on oddly
shaped boats like late generation 12 meters and so, I think it's
reasonable to say that upside down keels are only applicable to 12
meters because of the rating rule.

Winglets and bulbs are a whole other kettle of fish, and they can work
well on many designs.

Anyway, for the OP, let me second the opinion that
http://www.marsmetal.com/newpages/torpedobulbs.html is worth a look.

-- Tom.

I also believe that some of the posts are making this a little too
complicated. It's unlikely minor differences in keel shape will be
noticeable cruising - I bet a new sail or two would have a much bigger
impact. The Carter 33 was a very fast boat in it's time.

I am not a naval architect and you do the following at your own risk.
I'm also assuming you don't care about resale value - since you got the
boat for almost nothing. What I would do is a low cost test. Cut 9"
off the keel for a 4' 8" draft (wear a respirator) and chock the cut
off piece in the bottom of the bilge. The whole boat only displaces
8000lb so the last 9" of this fin keel isn't going to be very heavy-
you could cut it into smaller pieces so you don't hurt your back or so
it fits better in the very shallow bilge space in this boat. Then see
how the boat sails - she will be more tender -- so start off with a
reef in the main and a small jib. Get a good feel for any stability
changes. If it's too tender, you'll need to find a way to put more lead
at the bottom of the keel - but you may feel it's fine for your
purposes. Forget this whole plan if you ever think will do real
offshore work and tell any future buyer what you did!

Another plan - and safer - is to call Bob Perry. He worked with Dick
Carter when your boat was designed (as did a lot of other now famous
designers). He should know the boat and might have some creative
thoughts. Or he'll tell you it's a big mistake. Either way it won't
cost you much and you'll learn a lot of things about your boat besides
the keel.

Here's a link:

http://www.perryboat.com/page/consult

And enjoy the Carter 33. It's a great boat.

Carl