On 24 Aug 2004 13:34:07 GMT, William R. Watt wrote:

Morgan Ohlson ) writes:
On 23 Aug 2004 12:04:28 GMT, William R. Watt wrote:

On a dingy the centre of effort should be above the centre of lateral
resistance. I'd get some books on designing and building small sailboats
out of the public library and read up on the subject. You might also
seaarch the Internet on "dingy cruising".

In practise, doesn't the real center of effort move depending on how well
the captain stears?

...and should the theoretical center of effort (side view) the be exactly
above centre of lateral resistance or slightly behind or in front?

the theoretical or desinged centre of effort on a dingy where the sailor
can shift weight to adjust sail balance should be directly above the
centre of lateral resistance, ecept on a boat with no rudder when I've
found putting a daggerboard almost under the back edge (leech) of the sail
is good. I also found that putting the daggerboard in at an angle gives
more flexibility in adjusting sail balance. I originally put my
daggerbords in at an angle to avoid breaking them on obstructions and to
part weeds in the shallow lakes and rivers where I sail. The improvment in
adjusting sail balance was accidental.


Does a jib sail improve sailing up against the wind?

what improves sailing up against the wind (close hauled) is
height-to-width (high aspect ratio) which is why tall marconi rigs are on
race courses. you'll notice that the Olympic Finn and Laser boats do not
have jibs (headsails).

I'm not certain about this but I don't think headsails make any difference
over cat rigs (main sail only) on small boats. There is a difference of
opinion over this based on theoretical handwaving. Jibs complicate single
handed sailing but give a second person in the boat something to do and
train sailors for bigger boats where headsails are useful.

as for different sailing rigs for small craft, JA Marchaj did wind tunnel
tests for the UN for fishing boats for poor natives who can't afford
motors and fuel and found little difference among the different rigs
except a low aspect latteen sail is noticably worse, and the marconi rig
had a slight advantage sailing upwind. the most powerful sail was the crab
claw sail which uses the same priciple as a kite (edge turbulence) instead
of the airfoil principle. the problems with the crabclaw sail are the
difficulty tacking and the difficulty adjustign the size of teh sail to
different wind strengths (reefing). I think the crab claw sail is best
suited to ocean sailing where the winds are steady and tacking or reefing
are not done very often. I tried and experimental crab claw sail I called
a bear paw sail and put photos on my website. try
www.ncf.ca/~ag384/BearPawSail.htm or look under
www.ncf.ca/~ag384/Boats.htm. there was also and article on it at
www.duckworksmagazine.com which may be available in their online archives.
an Interent search on "bear paw sail" should provide access to the
article.

one thing which does make a difference is a mast sleeve. it reduces mast
turbulence at the critical leadign edge of the sail. Marchaj describes teh
effect in one of his boats on sail perfromance. I've borrowed a couple of his
books from the Ottawa public library.

when chosing a sail for a non-racing dingy I mostly consider cost and ease
of handling. I've used odd shaped sprit sails so far, except for the last
one which was better desinged based on information I've gathered and put
it in a file on my website at www.ncf.ca/~ag384/SpritSail.htm. I think
that's what I called it. It can be found under www.ncf.ca/~ag384/Boats.htm

hope that helps.

What plus and minus do they have?

Are all suited for unstayed mast?

_Classical:_
gaff yawl
gunter
bermuda = marconi ?
cat ketch
Cat gaff

_Non traditional_
crab claw
bear paw

Morgan O.