> It has to be airtight in order to use the huge weightless foot pump
> idea!!!!!

> (I would vent it of course w/ up and down tubes thru the bulkhead)

> -mick

Not to worry.

Since you are relying on the pressure in that area to force out the water, additional venting is not needed. The exit pipe from your pump handles it nicely. If pressure builds up through heat, then anything in the bilge is pushed out of the boat,and you just have to pump a little bit less to pressurize the area.

The problem might occur if the boat cools, and sucks in water, but that should not be very much, and you can eject it easily by using your diaphragm-in-a-bulkhead weightless pump idea. Just give it a few pumps to add air to replace that which condenses with the drop in temperature.

For the diaphragm mechanism may I suggest using half of a rubber playground ball. These are the size and shape of cheap basketballs, or soccer balls and are designed to be used by kids. They are pretty durable, and may have a smooth exterior which could be easier to seal.

hope this helps

Paul G. Jacobson