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post #1 of 19 Old 12-30-2007 Thread Starter
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Redundant bilge pump

My electric bilge pump has a manual back up. I'm considering adding a completely redundant electric bilge pump. I'm thinking of a second bilge pump, switch, strainer and suction hose tied into the existing discharge. I'm wondering how many people out there have such an arrangement or is it overkill?
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post #2 of 19 Old 12-30-2007
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I have 2 one is near the engine and the other is mid ship. It doesn't cost a lot to do. I used a T fitting to tie in to the existing hose.

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post #3 of 19 Old 12-30-2007
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I wouldn't plumb it into the existing discharge, unless you have some sort of high loop in the line going to each pump. Otherwise, the water could easily back up and then flow back into the bilge via the other hose and pump. You could also use a check valve in each line, but I'm not a big fan of check valves since they reduce the pump's output somewhat.

Having multiple electric bilge pumps is usually a good idea. My preferred setup is having two separate switches and two outlets....with the one switch set as low as possible and the second a few inches higher than the first.

The first switch is connected to a very small pump, with a narrow hose. This is the "maintenance" pump, and keeps the bilge dry of any water that occurs as the result of normal operation of the boat, including drips from the stuffing box and such. The smaller pump and hose reduce the electrical load and how much water can back flush in to the bilge when the pump shuts off. This one has a bilge pump counter on it... so the rate of leakage over time can be checked.

The second pump is a much higher capacity pump with a much larger diameter hose. This is the "emergency" bilge pump and is for helping deal with larger leaks. This pump should have redundant backups IMHO, including, ideally, two manual ones—one in the cabin of the boat, and one operable from the cockpit of the boat.

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post #4 of 19 Old 12-30-2007
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Its a good idea. I have 3 on my boat. However, using a common discharge would require the use of check valves to stop pumping back into the standby pump. That's a bad idea. Bilge pumps loose pumping capacity quickly with just a small amout of added pumping resistance, known as head or pressure drop. Install a separate discharge hose and fitting.
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post #5 of 19 Old 12-30-2007
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Coincidently, today I was attempting to install a second bilge pump and tried plumbing the discharge into the drain of my sink bit I found out real fast that this was not a good idea. The discharge was under the waterline and siphoned back in. I'm now looking for an alternate solution. Where do you suggest plumbing the extra bilge pump?

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post #6 of 19 Old 12-31-2007
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I think it makes a lot of sense, our new boat has three bilge pumps. We have two electric and one manual. There are any number of reasons for a bilge pump to not operate correctly when you really need it, so a redundant electric makes a lot of sense to me. The manual is the last resort if all else fails. One electric is plumbed through the manual's discharge which I am not sure is a good idea, but seems to work fine. I think I am going to plumb it with it's own discharge to reduce any flow restriction(long way down on major refit list).

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post #7 of 19 Old 12-31-2007
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Redundancy is good when it comes to keeping the wet stuff outside.

Consider a different kind of pump, though. I liek staged pumps. Stage one is a standard little impellor pump form a generic marine store. Set 20mm in the bilge higher is an electrical diaphram pump that pushes way more water, has its own float switch and can cope with larger particles in the water that would clog the little impellor pump...Scale up through as many pumps as you see neccassary.

Simply duplicating impellor pumps is not the best option. If the first one clogs due to stuff in the bilges...the second one will about ten seconds later, and then what is the point?

Think in terms of if X kills pump A, what sort of pump do I need so it won't die too.

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post #8 of 19 Old 12-31-2007
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We have 2 seperate electric and one manual They have seperate discharges.

You might also want to consider this. I attached a brass fitting to the thru hull which draws the raw water to my engine. ( I have a FWC engine with raw water exchanger.

This fitting is "T" ed to 1) the hose to the raw water pump to the engine and 2) a separate threaded opening which I have put a threaded plug in. I have a 10 foot length of hose in my spare parts attached by c claps to a barb with the other end threaded which can be screwed into the "T" fitting after pulling the threaded plug out.

This arrangement allows me to easily winterize my engine for one but also serves as an emergency "bilge system" which if necessary would allow me to use the engine raw water pump to pump out the bilge by simply sticking the hose in the bilge after attaching to the "T" fitting. This is a redundancy of bilge pumping which does not necessarily rely on the electrical system

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post #9 of 19 Old 12-31-2007
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The one caveat I have for the engine cooling line as a dewatering device is that doing so can easily make a bad situation worse... You're much better off IMHO putting in several electric larger high-capacity diagphragm pumps and not futzing with the engine cooling system. If you futz with the engine cooling system, you might get debris in it...that would cause it to stop working properly—and that would kill the engine just when you may need it most.

Also, most engine cooling systems don't draw all that much water...so they aren't really all that useful as a dewatering pump.

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post #10 of 19 Old 12-31-2007
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Completly agree with the above DO NOT USE YOUR ENGINE RAW WATER INTAKE ASA BILGE PUMP! You will move very little water even if it works perfectly. You will endanger your engine to a perilous degree when you need it most, and the impellor will really only take up water if it is primed or at positive pressure...Which means you need to artifically inject water into the hose to get it going, or the engine has to be half submerged by the water in the bilges before it works. All this for less then ten gallons PER HOUR on most 20HP engines.

Running your engine when you need serious bilge pumping is a good idea. It keeps your batteries charged when you are using electric pumps and if you are smart and worried about such possibilities you can fit a high volume pump running off a pulley on your engine which can be engaged at will. This will move up to 3000gallons per hour and will not much care if it sucks up a cat by way of debris....

But trying to make the very small engine coolent pump drain your boat is nine kinds of stupid.
Oh yeah...the other advantage of running the engine in those circumstances...It improves your chances of running for shore somewhere!

Nothing beats solving the mystery hunt for the big hole around the bits of yacht interior you can check, like getting to a travel lift, dock with serious craneage or even a soft gradual sandy beach. Then you can check theproblem from the outside (You'll find it, water from your bilges will be pouring out of the hole!)


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