One of my pet peeves has to do with the ever increasing level of junk being
placed above the center of gravity on most boats. For instance: the boat
before had a too large dinghy and crane placed on the stb side. The boat
lists to stb, naturally. All this is placed about 10 feet above the CG.  If
it weighs 1500 pounds, that is equivalent to 15,000 pounds of moment placed
one foot above the CG. The boat was also equipped with stabilizers. Not
that they were put on to compensate for the dink. On the other hand, what
is a fellow to do if he gets into rough water and has to slow down which
lowers the effect of the stabilizers, which is all that is keeping the boat
from rolling excessively?

Then there was the 120 footer in the Carib last month, that had 10,000
pounds of boats, gym equipment and LIFTING weights placed about 15 feet
above the CG. That's 150,000 pounds of moment placed one foot above the CG.
It too had stabilizers. Does anyone think that stabilizers are the solution
to excess rolling?

Any boat set up this way, is not a good candidate for being out in the open
in rough conditions or a storm.

Then there is the client with the 63' steel trawler, about 25 years old. It
rolls excessively and has NO stabilizers.  Over the years the boat has been
modified repeatededly. Most likely without benefit of a naval architect
analysing the effect of all the changes of mass and it's effect on the CG.

The list of these kinds of problems is almost endless.

Take a good look at your own situation. Bet you haven't thought about this
creeping kind of problem on your boat, recently. If you get to sea in a big
storm, I bet you will before you get to safety.

Regards,
Mike

Capt. Mike Maurice
Near Portland Oregon.

Captain Hal wrote, "Increasing the roll moment makes the roll period longer,
and thus the boat less "tender".  If a boat has an excessively fast roll
period it will quickly respond to, for example, a beam sea.  A longer roll
period can allow beam seas to pass under the boat before a roll can have a
chance to develop. The solution to a problem with too quick a roll period?
Increase it by adding weight away from the roll axis."

However roll inertia is a double edged sword. Although higher roll inertia
slows the roll response it also increases the energy storage, so once the
vessel does roll it takes longer to dampen out. In vessels the size we are
talking about it is impossible to increase the natural roll frequency to a
value higher than the natural frequency of waves, so while you might make it
better for one wave frequency it will be worse for longer wave lengths,
closer to the new natural roll frequency, and the range of motion will be
higher. If your Naval Architect did his job right, he will have optimized
the roll inertia for your application. If it is optimized, then anything you
do to change it will only make it worse. If your Naval Architect didn't do
his job right it will take a better Naval Architect to fix it. I doubt you
will improve it for all conditions by trial and errors.

Sincerely;
Mike Schooley
Trailerable Trawler wannabe