: I found last night that I have made some unexpected modifications to the
: plywood walrus hull that shortened it up by 8" DON'T LAUGH!!! My dad
: always said measure twice and cut once...whatever... stupid cumulative
: error when placing forms.

If you have shortened it by only 8 inches your center of bouyancy is going to be no more than 8 inches from the design point (and probably within 4 inches) so your on-water testing should be fairly rapid -- you won't have to shift any weight very far forward or back.

Since the construction materials are fairly even in size from front to back, If the boat is fairly symmetrical you can only hope to approximate the center of bouyancy by balancing on a board. But, a few extra floorboards or ribs in the bow will not affect displacement anywhere near as much as they will affect your balancing attempt. By the same token, your displacement is affected by the width.

Consider two parallel boards balanced on your dowel rod. If these defined the shape of your boat then the balance point would be the center of bouyancy. But, take those same tow boards and now turn them a bit so that one end of each board -- let's say the left ends -- comes toward the other board. If you move them far enough, they will touch each other, forming a wedge. While they will stay in balance, if you had a boat built in this shape, the left side would obviously displace far less than the right side.

Now, if this was a solid, wedge shaped, board you would find the center ofbalance would be much further to the right, and again, you might come close to approximating the center of bouyancy. but htis too has too many potential errors -- rocker for example will throw you off, as will any equipment bolted on, or reinforcing added around a cockpit.

So, best solution is what has been recommnded: try it out.

PGJ