On Thu, 03 Jul 2008 14:34:39 -0100, David dh@. wrote:

I've got an old boat very much like this one:

http://www.warnersdock.com/images/Fr...fores15yel.JPG

that I'm trying to make into a mini-houseboat,
sort of like a camper. I only expect to have
about 200-300 pounds in the roof and walls,
and the roof will only be about 48" above
the gunwale. The hull will weigh a *lot* more
than what is added, so shouldn't that alone
be enough to keep it from being top heavy
and flipping over? If I add weight, like a
couple hundred pound bags of sand down
in the hull to counterballance, shouldn't
that take care of it? If so, should they
be placed on the sides, or in the center?

That hull doesn't weigh as much as you think it does. Plus, it's
essentially flat which, while counter-intuitive, makes it less stable.

Alll boats and ships obey two laws of physics - center of buoyancy
(CB) which is the center of the underwater volume of the vessel and
center of gravity (CG) which is where all the mass would be
concentrated if it had to be compressed to a single point. To float
properly on the design waterline, then the CG must be in line
vertically with the CB.

Once you start messing around with CG (which is essentially what you
are doing), it throws off the CB (because they are interrelated) and
you are constantly playing catch-up to keep it properly oriented (dry
side up and wet side down). Even adding 300 pounds isn't going to
affect anything much because your CB, which is not a constant and can
change depending on any number of factors, is out of whack.

Additionally, you have to worry about beam - it ain't got none to
speak of.

You can figure it all out if you really want to.

http://www.johnsboatstuff.com/Articles/estimati.htm

Good luck.