Bilge hose - important difference!

[rhody98]

And the head difference matters too - height from pump to discharge. I dont know your setup Father, but the relative elevation of the pump and the water levels in the two tanks will impact the results. I would expect you would get higher flow rates if the 600 gal tank is topped off versus the water level just above the pumps with a garden hose keeping the water level static. So your results for both hoses are probably even better than actual conditions in a boat where the lift is, say 18" (2'?).

I came across results from pump tests Rule financed in 1997, all with a 3' head (lift).
Attwood 500, smooth hose = 302 gph, corrugated hose = 242 gph.
Rule 1100, smooth hose = 682 gph, corrugated =530 gph.
Rule 2000, smooth hose =1,052 gph, corrugated = 880 gph.

So in a boat where a bilge pump is lifting water 18" (or whatever), can we guess that actual results may be somewhere between Fthr Franks #'s and the Rule test #'s? In any case it should be apparent that pumping at the manufact. rated output is unlikely to happen.

Also, interesting to compare these to flooding rates: a hole 1 ft below waterline, 1" in dia. lets in 20 gpm - that's gal per minute which is 1,200 gph! A 2" hole 1' below the waterline is 79 gpm, or 4,740 gph. I will stop now before I convince myself not to launch this Spring...

I should list my source, its a book my wife got me for Christmas, Boatowner's Mech and Elec Manual.....spent more time with it than the socks.

[Fr. Frank]

One thing we can all learn here - the single 500 or 800 gph pump just isn't enough under any circumstances.

I have friends who snicker at me because I have three 1200 gph pumps in a 19'8" boat. I later snickered at one of them when he "sank" his V20' Wellcraft while he was grounded on a sandbar. The waves washing over the transom and down through the cable access were more than his little 500 gph West Marine pump could keep up with and he came back to find saltwater had filled his bilge completely and was over the deck - all while his little pump was working as hard as it could. His boat was sitting hard on the motor's lower unit and the hull bottom, and canted over as the tide continued to fall.

Fortunately for him, he had a SeaTow card in his wallet. They could have called it salvage, not assistance, and he would have been out his $1k insurance deductible. As a member, they loaned him a gas-powered 20,000 gph pump, and pumped him out in a few minutes. He was then able to get off at high tide. As it was he had to completely rewire the boat.

More pumps, more gph is better, smooth wall hose is important.