(snip) Top speed is MAYBE 9 knots through the water. Cruise around 7. Think that would create a suction? (endsnip) I think it could . . . but I am shooting from the hip here . . . hull dynamics really is not my field, and wiser heads with experience here may reply. The drains I was referring to were on a SNARK, and were about a 3/4 clam shell over a 1" hole (with one-way flapper valve). The opening in the clamshell faced directly aft, and the holes were about 6 inches from the stern. You did not have to get very fast before you would hear the valve "pop" and then all the water would suck out of the boat. You could hear it gurgle/suck anytime you were moving about what I would call 1/4 speed. Since I crashed/swamped/flipped this thing alot I got a chance to regularly test this feature. I have absolutely no idea how fast it was . . . I expect top speed could have approached 9 knots . . . it is an 11 foot open boat with a lateen rig. For what it is worth, all the (large numbers) of intake through-hulls removed from my project have bronze half clamshells (with slots on the "open" part as a sort of strainer). They all faced downward . . . CUAgain, Daniel Meyer http://cuagain.manilasites.com