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Bilge pump


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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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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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The current plan.

Bear in mind that we are sitting in the suburbs of Rotterdam with only limited tools on board, so the installation needs to be kept simple.

Attached, the plan for comments please.20180523_090906.jpg

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You haven't said why you want to install a bilge pump, have you?

Does the boat not have one at the moment?

I'm under the vague impression steel boats don't get wet inside, because A) they don't leak, and B.) water inside causes major issues with the steel.

 

But to answer your question on the 'current plan', where does the deck wash pump go after the deck, is it just a hole in the deck?

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Fish, the bilges are dusty dry and this whole bilge pump installation is an exercise in futility.

In order to get to France we need to sail 3-4 days through Belgium, the home of stupid heavily invasive beaureaurocy. The water police have a nasty habit of checking boats for compliance, hence the need for a bilge pump. I also need to have on board a 10 foot oar for each person,at least 3 mooring lines a minimum of 20 metres each, a red flag with a white centre to fly when underway - apparently they can't tell if a boats underway or not without a flag - and the silliness list goes on and on..

Thankfully it's only Belgium. Holland, France, Germany etc are far more relaxed in their regulations.

In answer to your other question, the deck wash hose has a nifty fitting on the end that enables it to connect to the deck outlet.

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I'm going with your suggestion in the meantime BP.

When I came to plumb up the pump I discovered that water can't flow out of the deck wash fitting unless the hose is attached. Joke kindly pointed out the fact that I should have checked this before hand. She's right of course but don't you just hate it when people point out the obvious after the event?

I'm just so over this bilge pump business.

But having invested in a pump, float switch and wired the whole thing up to a master switch and indicator light in the wheelhouse, i want it to work.

So in the meantime I will tuck the end of the discharge bilge line behind the water boiler and it will look the business if we are inspected. I have bought a skin fitting and no doubt we'll eventually meet up with another canal boater with a drill and 25mm bit on board that I can borrow to poke a hole through the topside.

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Sounds like you have a plan

I’d install the float switch in the bilge hooked to an alarm then have the pump on a long hose that if or when you ever need it you can poke the hose outside

Then you have the piece of mind of knowing that if water did get in the alarm would let you know and the pump is ready if needed ?

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