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Old 17-01-2011, 20:39   #1
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Bilge Question

My bilge outlet is below the water line when boat lists in the marina due to wind from off side so I close the gate valve problem is auto bilge pump cant pump out.My question is if I loop the outlet pipe up above the water level by a foot or more it should stop the ingress of water through the bilge pump I think??? I'm also going to install a non-return valve in the manual pump line am I doing the righ thing???
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Old 17-01-2011, 20:51   #2
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The "normal installation" of a bilge line is to have the pump outflow run thru a loop that tops out above the waterline under all conditions, and then down to a through-hull just above the waterline. In your case where wind might put your through-hull below the water line occasionally it would protect you without needing a check valve.
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Old 17-01-2011, 20:53   #3
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i have done this and it worked fine
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Old 17-01-2011, 21:08   #4
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A further thought:
Putting a check valve in the bilde pump discharge line can be problematic. They can get sticky which may be a bigger risk assuming that an adequate loop above the waterline is installed. A safer means of achieving this is to use and anti-siphon loop. Here is an example: Fisheries - Product Detail. You will want to find one that matches the hose diameter that fits your pump.
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Old 17-01-2011, 21:11   #5
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This is a surprisingly dangerous situation as the below waterline outlet makes a siphon quite possible even with a loop of hose. This can and does sink boats.

While a check valve should work, they can easily stick open without showing any sign of trouble making the siphon again possible.

Loop the hose up as you plan but put a vented loop at the top of the hose (which should be higher than the water level when the boat is at maximum heel. These vents are readily available.

Carl
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Old 17-01-2011, 23:31   #6
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In the case of a bilge pump, a check valve would normally be in the closed position, and could corrode in that position, which would be the worst case because it would render the bilge pump ineffective if a hull leak also should occur.

The subject situaltion is not terribly dangerous because the through-hull is above the waterline except when wind would heel it over. Also with a proper loop installed the vertical the line should drain from the loop downward to the through-hull even without an anti siphon loop fitted. If one is fitted, any doubt should be removed.
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Old 19-01-2011, 07:31   #7
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Did he say "Gate Valve"....Im hoping your through hull fitting is not using a gate valve. These corrode and can cause all sorts of issues. Ball valve would be more suitable.
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Old 21-01-2011, 23:32   #8
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yep I did say gate valve there a few things previously in this boat I'm chainging andsfrom responses here vented loop is the way to go without relocating the outlet. The boat was built in 1976 and has had lot of upgrades like wheel saeering raised cockpit with extencive fiborglass and timber and fully fitted out with teak interia proably add a tonn or so but they didn't think about extra weight.
Thanks eveybody feedback is good.
Laurie
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Old 21-01-2011, 23:49   #9
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check the literature that came with your pump. Many pump manufacturers will specifically discourage the use of check valves with their equipment.

Think of it this way: a frozen check valve could result in a sunken vessel.
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