: We need to source a good quality thick walled rubber ball so no spring is
: needed and this pump could be made light weight, quickly and at low cost!

: This bulletin board is great isn't it!?

This bulletin board is, in fact, great. So are the laws of hydronamics or physics or whatever I was fighting last year, trying to do something not nearly as enterprising as what y'all are trying now. For what it's worth, I tried converting an old, deck-mounted Henderson "Chimp" pump into a footpump, emulating the design that Henderson uses to make its own footpump, the "Lexus" of footpumps --- at least using pricing as a guide. Finding several stainless steel springs which might work was surprisingly easy, although the fact that I live not far from Baltimore, with its wide array of machine shops catering to "old economy" and maritime industries, including two large spring winding plants, might have been a major advantage (these places keep scrap bins of overruns and reject parts, and an astute buyer can usually leave with a brown paper bag of five or ten springs for a few dollars!). However, finding a spring sized properly to handle the diaphragm of a Henderson pump was significantly more difficult. It takes an incredibly large amount of stored mechanical energy to extend that diaphragm, even in the relatively small cavity (4.5" diameter, 1.25" deep, plus the volume expanded by the spring-extended diaphragm) of the Henderson body (the same body, valves and diaphragm are used by Henderson in the deck-mounted pumps and footpumps) when it has to pull water up as little as three inches from the bilge. The idea that you'll find a ball or other rubber hemisphere with enough memory --- and the physical capability to use that memory while sucking in bilge water --- seems very unlikely, unfortunately. The spring in the stock Henderson footpump (slightly conical, about 3.5" extended, about 2.5" diameter at the base and about 2.0" at the point where it sits on a disk attached to the backing plate which extends the diaphragm), is very difficult to compress by hand. Dunno the rating, but it's significant.

I wound up buying a second Henderson footpump when I built the North Bay because all my work in rebuilding a Chimp pump resulted in non-functioning or suboptimal pumps, with the spring being the only significant problem. (No, Henderson won't sell a spring! I tried that, too.) The Bosworth Guzzler is a good option, but it's bigger, and, I understand, has even more stored energy in its spring.

All this should also indicate the amount of strain that you're going to be putting on your bulkhead --- which is, of course, what this thread was supposed to be about in the first place --- so plan accordingly. It takes a lot of foot and leg power to pump out even a low volume boat like my Pintail.

Jack Martin