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