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  #1  
Old 06-19-2013
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Question Pumps do not do what you think

So I did some real world tests and calculations on my pumps.

Four pumps will net me about 160GPH

A one inch hole lets in 2,400GPH

Nowhere near enough for even a relatively small hole. Basically all pumps are useful for is open windows and children's dribble?

I made a video, the math is at the end, can this be right?

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Old 06-19-2013
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Re: Pumps do not do what you think

bilge pumps are almost never big enough to "save" a boat.
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Old 06-19-2013
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Re: Pumps do not do what you think

That's funny.
I did the exact same math with my boat shortly after we bought it and discovered that the gunnel would be underwater in less than 17 minutes with a 1 1/2" hole.
I wanted to have an idea of how much time I would have to abandon ship in the event that was unable to keep up with a leak.
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Old 06-19-2013
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Re: Pumps do not do what you think

I think that's where the beezwax toilet ring and similar "stuff" can come in VERY handy. Staunch the flow, then use the pump to start getting rid of what's already come aboard or to deal with what little continues to come in.

Yachting Monthly did an interesting set of tests that might be helpful as you think this through:

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Old 06-19-2013
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Re: Pumps do not do what you think

Your best bet is to reduce the "head" that the pump has to push through, as much as possible, and have simple damage control equipment onboard that can quickly reduce a 1.5 inch hole to a trickle that the pumps can keep up with.

In addition to various wooden and foam plugs, I recommned Marine-Tex underwater putty and creating a 1'X1' heavy duty plastic or vinyl mat with grommet holes around the perimeter to act as a "belly band" for large holes.
Slap it on, tie it in place around the hull, and you can also put Marine Tex around the perimeter to seal things up.

This is all extreme, worst case of course. 99% of us will never need anything other than a wooden or foam plug.
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Old 06-19-2013
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Re: Pumps do not do what you think

I have an appropriate sized wooden plug for each through hull. I hope I never have to use any of them.
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Re: Pumps do not do what you think

Jim, that was a great video! But I wonder how calm anyone would be without the boat hanging in the slings. Especially if you consider all the ways a boat could get holed - usually in unfavorable conditions. All the various methods demonstrated in the video would be much more difficult to execute in a pitching seaway. Just finding the source of the leak can be a challenge in itself.
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Old 06-19-2013
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Re: Pumps do not do what you think

I am hoping my setup would buy me some time. I have a 500GPH and a 2000GPH pump in the bilge along with a hand operated pump from the cockpit. I also have a valve that is upstream of the engine raw water intake seacock that would allow my engine to pump bilge water. In a pinch I could also plumb the fresh water pump and the wash-down pump for temporary duty.

A big problem that is often discovered when it is too late is that the bilges in many boats have debris that clogs pumps when you need them the most.
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Old 06-19-2013
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Re: Pumps do not do what you think

I've developed a slight obsession with bilge pumps ever since I've managed to flood my boat on hard the first winter we've had her . So I've got three electric pumps (2400 gph x2, 500gph gx1) and the hand operated whale gulper that I've modified so that I can basically now reach any place inside with a hose to suck it dry. I know, it's sheer OCD ... What I never understood, though, is, why in the name of safety do we drill new holes into the sides of our boats for through hulls that will potentially fail and flood the boat. Shouldn't the pumps let out on the highest possible point, i.e. on deck ? I yet have to find a reasonably "standard" bilge pump, that can provide enough lift/head to allow that.
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Old 06-19-2013
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Re: Pumps do not do what you think

Commercially available "bilge" pumps won't, but if you want to continue your OCD then buy a pump like the ones the Coast Guard uses when they go to rescue folks.
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