On Sat, 21 Feb 2009 17:15:04 -0500, "Roger Long"
wrote:

"IanM" wrote

You *are* missed.

Well, thank you. OK, I'll throw something into the pot. Here's a first
draft of something I may come back to later. A discussion along the same
lines got started here quite a while ago and disolved into the usual flame
war. I brought it up over at the high class bar where I hang out now and
another RBC refugee complained that I never finished my explanation here and
was I going to leave them hanging over there as well? It's winter and there
are only so many hours a day I can work on my boat so I whipped this up:

http://www.rogerlongboats.com/Stability.htm

Sorry, Virginia, buoyancy is imaginary.

Roger, welcome back, your expertise is missed.

We once had a discussion about anti-roll tanks and how to design them.
Some where in that discussion or in a stability discussion, the
subject of roll period came up, ie, the time for a complete roll, over
and back. My recollection is that I estimated the roll period for
our GB49 trawler to be about 3 seconds, and that some discussion
ensued about whether or not that was impossibly fast. I have since
then taken more recent measurements and come up with a more accurate
figure by averaging a number of rolls. It came out to about 3.2
seconds, quite close to my original estimate. Perhaps you could
comment on the implications of that as it relates to stability.

The GB49 is a ballasted, full length keel, semi-displacement trawler
with hard chines, a displacement of about 70,000 lbs and a draft of 5
1/2 ft.