On Sat, 21 Aug 2004 05:18:01 -0400, Ron wrote:
[re-arranged text to appear in chronological order]
"Mac" wrote in message
news
On Fri, 20 Aug 2004 21:18:49 -0400, Ron wrote:
"Stephen Baker" wrote in message
...
Ron,
Maybe some hints as to what your canoe does would help. Is it a
question
of
balance? Will it simply not move to windward at all?
Give us a hint. ;-)
Steve
Stephen C. Baker - Yacht Designer
http://members.aol.com/SailDesign/pr...cbweb/home.htm
[top-posting fixed]
It's a 161/2 foot Appleby aluminum flat bottom canoe with a 3/4 keel. I
have been setting the sail about 5' from the front and the leeboard
about 2'
behind. I need to use a paddle strongly on the lee side to go straight
even
down wind. If I don't use the paddle i turn into the wind.
I have to admit I had it loaded with five kids and the wind was not
steady
the last time we sailed. But even by myself I have had trouble into the
wind. I clamp on the mast step and leeboard (10" by 3/4" plywood with
about 3' in the lake.) The sail is about 44 square feet.
What you describe is called weather helm. Two things contribute to it:
center of pressure on sail too far aft (compared to leeboard), or too much
heel.
So, move your leeboard aft, or your sail forward, or try to keep the boat
more upright.
Oh, also do you have a rudder? A rudder would help if you don't have one.
Also, your leeboard will probably work much better if it is faired into a
hydrodynamic shape. At least in theory. I don't have any experience with
the type of leeboard you describe.
--Mac
I have been moving the sail forward and that has helped. I will try moving
it even more. The boat is not really heeling much as the sail is small.
The leeboard is just a piece of 3/4" hardboard siding. Would a better
shaped board make a significant difference?
I can't say from experience that a proper foil-shaped leeboard would make
a big difference, but from what I understand of aero- and hydrodynamic
theory, which may not be much, it could make a big difference under some
circumstances.
In order for a leeboard to function, it has to provide lift. It can only
provide lift if it has an angle of attack. Put another way, when the
boat experiences a force to leeward, there will always be a little bit
of slippage. If you consider the slippage, then it is clear that the water
is flowing over the leeboard at an angle. This angle is called the angle
of attack.
The aerodynamics of a flat-plate (which is what your leeboard is, AFAICS)
are OK as long as the angle of attack is very small (i.e., the boat
doesn't make much leeway), but they rapidly go to pot when there is a
large angle of attack. By "go to pot" I mean that the drag forces become
very large, which will keep you from making good headway.
I think it is a good idea to get the boat more or less balanced first,
then try playing with a foiled leeboard if you desire.
Another variable with the leeboard is size. I'm not really sure what a
good ratio is of sail area to leeboard area, but I don't think your
leeboard is too small, off the top of my head. Still if you feel like the
boat is slipping to leeward almost as fast as it is going forward, you can
try a leeboard with more surface area.
It sounds as though you are steering with a paddle as a rudder, which
should work fine once you get the boat more balanced. (I base this on
another poster's testimony, not on personal experience!)
Good luck!
--Mac