"Now let's examine the studies findings on vessels that sank while underway.
The single most critical reason boats are flooded on open water has to do
with transom height. Thirteen of the 15 boats in this category were
outboard-powered and the engine cutouts were often only inches above the
water. The motor wells in some cases were too low, too shallow, and too slow
to drain. The lack of freeboard aft allowed seas to board, "pooping" the
boat as water came over the stern. Slow draining wells caused the boat to
sit lower on her lines due to the weight of the water, further compounding
the problem of low transom height. Another contributing factor is typically
weight distribution. The addition of trolling motors, large coolers, and
bait wells, among other things, decrease buoyancy aft and trim the vessel
down by the stern, in turn decreasing freeboard aft."

Excerpted from "Why do boats sink" by Ocean Marine Services Marine
Surveyors.

http://www.oceanmarineservices.com/w...boats_sink.htm