This got me thinking about something - when a catamaran heels (or is
tipped in some way) does the masthead go up, or does it go down?

A few minutes on the calculator reveals the answer (assuming I did the
trig right): tipping the 50 foot mast of a boat 10, 20, and 30 degrees
reduces its height by 0.76, 3, and 6.7 feet respectively. However,
assuming a 20 foot beam, the center of the boat is raised 1.74, 3.4,
and and 5 feet respectively. The other factor to be considered is
that shifting the weight entirely to one hull will lower that hull
(and the entire boat) by some amount, roughly .5 to 1.2 feet on this
hypothetical cat.

Thus, the answer is that tipping a cat will raise the masthead until
it reaches a point somewhere between 5 and 20 degrees, depending on
the geometry.

BTW, the polar charts for my boat don't normally have a heel angle
greater the 5 degrees, but it does go up to 8 degrees when carrying a
spinnaker on a beam reach in 20 knots of true wind. Boat speed is
around 17 knots. I can honestly say I have no intention of verifying
these numbers, although the folks at the factory claim they have.


Jeff wrote:
Duh!
This is a catamaran! Tipping it to lower the masthead is not a very
bright idea.


Solo Thesailor wrote:
wrote:
The boat is about 21' wide with a bridge clearance of 56'6"
but I can remove the mast if I have to.
.....

For any possibility of mast-bridge problem, in this case or in future,
you might be interested to check out how the Volvo Round-the-World
70-foot yachts "limbo'ed" under a bridge in Melbourne, Australia,
during their stop-over with their masts intact. It was a sight to
behold. Apparently they:
1) used water bags to weigh the top of the mast downward, or for some
boats,
2) attached a halyard to another motor boat alongside and winched.

Solo Thesailor
http://sailingstoriesandtips.blogspot.com



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