"News f2s" wrote in message
...
No, I meant stable! Take the top weight of the mast off, and the centre
of gravity of the boat drops down, so the righting moment goes up.

Add to that the fact that the mast's inertia has gone, and the boat now
reacts very much more quickly to any disturbance - then rolls back and
forth, one cycle every couple of seconds.

"Capt. JG" wrote in message
...
Nope. It doesn't work like that. You would think it would, but it
doesn't. We had a dismasting on the bay (one of my students). It was
caused by a hairline crack. They were pounding up to the Golden Gate area
from Alcatraz on a typical 20-25 knot day in 3-4 foot chop. After the
mast came down, the boat was almost uncontrollable as it drifted back
down hill. Finally, after they cut away the mast, they were able to motor
back to the slip, and according to the crew who we interviewed, it was
the worst part of the trip. The boat was so unstable a couple of people
got sea sick.

You said it yourself in your final paragraph... that is the definition of
instability.

For clarity, I'm only talking about the rolling stability. There are two
types of roll stability we're perhaps confusing here.

First, static stability is the tendency of a boat to right itself once it
has been heeled over. After a single disturbance the boat will rock side
to side a couple of times until the motion dies off. If static stability
decreases, the boat will right more slowly after a disturbance. If
statically unstable, the boat will roll upside down. If, on the other
hand, static stability increases, the boat tries to right itself more
quickly than before. The rocking motion will speed up.

If the rocking motion dies away, you have dynamic stability too.

Dynamic instability is when an oscillation builds up instead, until either
something breaks or there's a breakdown in the circumstances. The best
example of this is the 'death roll' enjoyed by a downwind boat with too
much sail up for the wind. Our relevant example is when the wave frequency
disturbing a dismasted boat is the same as the (quicker) tendency to rock
back and forth. The rocking amplitude will then increase (instead of dying
away) until it reaches some peak value, when there's usually some hiatus
before the whole lot starts off again.

Incredibly uncomfortable. Dynamic instability, caused by excessive static
stability raising the boat's natural rocking frequency to match the wave
frequency.

JimB

Ah, well, then for the other kind of stability, you should get a multi. :-)

--
"j" ganz @@
www.sailnow.com