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)