[bolger] Re: leeboards and hull shapes?

> Is it hull shapes or sail plans?

The issue is the flow of water where the hull and leeboard are close
together. If the hull side is greatly curved (as seen from above), and
the leeboard is much farther from the hull at the leading edge than at
a point farther aft, then the board can act as a sort of scoop, causing
a lot of drag. Therefore, boats designed for leeboards will have
somewhat straight sides where the leeboard mounts.

For many boats which were not designed for leeboards, the sides are
'toed in' whre the leeboards would be mounted. They would have the
problem described above.

I'm not sure of the exact properties that are attributed to forward
raking foils, but they are not a new idea. One characteristic is that
if the board twists under pressure, it will increase the angle of
attack - a sort of jibing centerboard.

For an example of a boat with forward-raked daggerboards, look at
design #946, SeaShell, at www.tantonyachts.com. (This is NOT the design
that caused a firestorm on this list a little while ago.) SeaShell is
designed for about the same use as the AS-29, but is perhaps a 50%
bigger progect.

Peter

Re: leeboards and hull shapes.
Is it hull shapes or sail plans? The way I understand it a centerboard
may be placed anywhere in the sole of the hull, whereas a leeboard needs
to be mounted at the point of greatest beam of the hull. Sail plan must
then be positioned for appropriate balance. Any comments?
David

ed haile wrote:

>
> Simon,

Take it from a Martha Jane man, leeboards are great in nearly all
respects. One big drawback however is that, whereas centerboards work
on any hull, leeboards only work on certain hull shapes. Bolger's
Chebacco is not designed for leeboards, is it? Make sure the Chebacco
boat has the right hull shape.

But it seems like the world is divided in half between the CBs that
always work perfectly and those that constantly stick. Try once more
and maybe you'll get lucky. No, I hate CBs for just the reasons you
cite.

In one respect the leeboard is at a disadvantage. It is a free foil, so
in effect a leeboard makes your boat a multihull. It pierces the water
surface, hence turbulence, cavitation, etc., meaning loss of
efficiency. It's why multihulls aren't faster than they are. On the
other hand, a centerboard is fully immersed (unless you sail with me).
Now, a cruising cat man told me the way you calm the seas again & get
rid of your little mini-bow wave and wake, and restore full efficiency
to a leeboard is to present a leading edge raked aft, i e the top of
the board's leading edge aft the bottom, or at least aft where the
board breaks the water. I have never seen where Bolger discusses any of
this. And I have not done any tests on my Martha Jane.

Ed Haile

> After a childhood spent dealing and helping to deal with stuck and

sticky

> centreboards I refuse to spend my adult years doing the same ,

consequently

> i am putting leeboards on my chebacco 25 ... reasons?
> 1) easily removed and fixed.
>

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