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Bilge pump

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Guest 000

I want to Install an automatic bilge pump without drilling any holes - firstly because the boat is steel and secondly because I don't have the neccessary tools with me.

Is it permissible to have the bilge pump discharging through an unused water intake pipe? Can a small electric bilge pump force the water out against the water pressure of an underwater skin fitting?

If so then the plan is to take the bilge discharge line in a high, above the waterline loop, put in a non-return return valve and then down again to the skin fitting.

Possible?

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Not ideal but doable

Make sure you put a siphon brake in the top of the loop

Non return valves don’t work well with bilge water I’ve found as anything your pump picks up can block them open

Effectively this is how most heads work

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Yes Chris. As Jon said. The water will always sit in the pipe to the level of the outside water level.
I have non return valves and they are prone to debris, but 99% of the time they work OK.

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Guest 000

Yes, not crazy about the idea. Will look for alternatives and use the water inlet option as a last resort.

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Or as I jokingly said to a water taxi operator once, who had come in onto the slipway in an emergency with a leak in the hull some where. " in emergency situations like that, just drill anothe3r hole slightly below the leak to let the water out" . He had that vacant look on his face as the gears were turning thinking about it before it clicked and he laughed.

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Hole saw, drill just above waterline, fit quality plastic skin fitting, 1 hour all done. If still feeling insecure fit appropriate v/v. and tail for hose. + syphon break for just in case. otherwise tap (tee) into an existing skin fitting. How old is the boat and how long has it managed without said Mod?? I know, I'm a belt and braces man, but sometimes (often) I over think things.

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 Can a small electric bilge pump force the water out against the water pressure of an underwater skin fitting?

 

From a hydraulic point of view, it will make no difference. The total head the pump sees is made up of static head and dynamic (or friction) head. 

The static head is the difference between how low in the boat the pump is, and the highest point on the discharge pipe. If the pump were to go straight out to the through hull, then the pump would see the static head of the depth of water (distance pump is under the water line). Obviously you need a siphon break, so the static head will be the height difference between the top of the pipe and the pump.

 

If, for example, you put it out to the cockpit, and the cockpit was 1 m above the waterline, you'd actually substantially increase the static head...

For friction head, this is a function of the size of pipe, length of pipe and number of fittings like elbows and check valves. It is possible that if you ran the discharge line a long distance to the stern, the total head would be higher than just chucking it out a through hull. Especially if your pipe was a tad small (higher friction losses).

 

If you are either concerned or interested about it, get a pump that actually has a pump curve. A graph of flow verse head. Most shitty bilge pumps have flat head curves, i.e. flow drops off fast with head. A good pump will have a steeper curve, giving more flow at higher head, but these will draw more current....

 

This online calculator can be used for determining head losses. This website will have enough info to work everything out if you feel like getting all techo on it....

https://www.engineeringtoolbox.com/hazen-williams-water-d_797.html

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Rough as guts?....so your not and overtinker?

 

I drilled mine just clear of deck fillet and installed valve. No siphon break obviously.

Never turned it off, and hasn't let water back when we've been on our ear.

Dunno why.

 

Nother thing, whilst we're on our ear, damn diesel tank vent pipe gets diesel init and upsets

the relative pressures in sight glass fuel gauge. Gotta put that on the todo. 

It is hard to check your fuel tho, when on said ear. :wtf:

 

If you don't at first succeed, try another tack.

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