"Wayne.B" wrote

Thanks for that analysis, interesting. Supposedly the boat does
have some ballast in the keel,

That would be consistent with the short roll period and high GM.

we got rolled a lot and started thinking about ways to slow it down, hence
the interest in an anti-roll tank which we would fill only when
needed.

The problem with anti - roll tanks is that their effectiveness is a function
of the initial stability, of which you have a lot. You would therefore need
a large tank. With the noise, weight, and space taken up, I don't think you
would find enough improvement to end up happy with it. The simplest tank is
just a rectangular box. The speed of the sloshing when the tank is about
1/4 full is governed by the water depth. It works when you get exactly the
right water depth and makes things worse when you have it wrong. It can add
just as much to the roll as it reduces it. You could build a simple plywood
box and experiment but I'll be surprised if you end up making it permanent.

Slowing your roll will put you in tune in larger waves that have more
energy. You probably don't want to do that. Slowing the roll with weight
up high will increase the amplitude (angle) of the roll so G forces will
come out much the same and it will be visually worse. If you did want to
slow it, the best solution from the comfort standpoint would be a lot of
weight down about main deck level and distributed outboard as much as
possible. Maybe a set of cast lead guard rails I know of one boat that
had 1 - 2 inch "tiles" of cast lead laid over much of her deck but she was a
defective design. They did do a nice job on machinery noise though.

--
Roger Long