Roger Long wrote:
Well, if that's the case, it's a good example of what Winston
Churchill said about being divided by a common language and an apology
(from this end) is in order.


Roger, I'll apologize and start all over as well.


I've encountered so much confusion over the years on this point, (even
from Coast Guard officers with naval architectural degrees engaged in
writing regulations) that I'm probably primed to expect it.


Could be... one reason why I'mn a bit frustrated is that you
don't seem to be reading my posts. For example, what Wayne B
was talking about is exactly what I meant.

Since we have managed to so thoroughly confuse each other, I'm sure
almost everyone else is lost as well. For their benefit and not to
talk down to you:

Let's look at the simplest case, a catboat with an un-stayed mast. The
hull and ballast are a given and you now want to figure out how bit to
make the mast. You determine the maximum righting moment which will be
in the 35 - 45 degree range for this kind of boat. The mast is a
simple lever and maximum material stress will be at the deck. The
bending moment will exactly equal the righting moment. Once you know
the material properties, it's a quick calculation to determine the
required diameter, with a proper safety factor applied.

Now, you decide your catboat is a little slow so you decide to double
the sail area. Do you need to make the mast bigger? No. The righting
moment, which limits the force on the mast will be the same. The only
difference is that the boat can be heeled to any particular angle in
much less wind. The force on the mast will be the same at any
particular heel angle as it was before the sail increase.


Exactly so. And the benefit to the boat's performance will
be in lighter air, and perhaps downwind (depending on a lot
of factors). The power developed by the rig has to be
counteracted by the boat's righting moment... more power
means more heeling... and once the boat is heeled past it's
most efficient sailing angle, the boat ain't goin' one lick
faster. However, it will go faster in lighter air and reach
it's maximum developed power sooner.


Actually, because you have added the weight of longer mast, boom, and
gaff, as well as more sail material, the center of gravity will be
slightly higher. This reduces the righting moment. This is within the
fuzzy factor of the calculations as used in the real world but, if you
were to compulsively design to exact loads, stresses, and safety
factors, you would find that the boat with the larger sail plan could
paradoxically have a slightly smaller mast.


heh heh reduced windage, greater efficiency... a snowball
effect... at what point can you have infinitely large sails
with no mast at all?

Fresh Breezes- Doug King