Engine Bilge Pump

[Fishbone 1]

Correction... Vane style, Not impeller!

[ottow]

I've installed this on my VP 2002, a simple 3-way valve which allows me to select either the intake on the saildrive leg or pull from a 2m hose with a strainer on the end.
Primarily to make winterizing easier, but also as an emergency bilge pump.


This summer there was an incident with a sinking sailboat mentioned in the local press here, the SAR team was quoted saying it was a good thing the owner had such a setup as it helped keep the boat afloat until they arrived.
I suppose a small capacity pump is better than no pump in an emergency. Or as a complement to the main pumps.

[HopCar]

Originally Posted by Fishbone 1

how about a impeller style pump on the drive shaft. I have seen pumps used on military Duck boats that have an impeller inside a closely fitted housing around the prop shaft. They draw water in around both sides of the shaft to a vane style pump and discharge overboard above the water line. No friction or seals to worry about and they only pump when submerged. I guess that they probably move a little air when not submerged. I saw a demo and i think that these were moving many thousands of gallons an hour

There is a link to what you’re describing in post #2. I think it’s a great idea but I see two problems.

First it’s not cheap. Second the prop shaft has to be turning so the boat is moving for it to work. Depending on where the leak is, you might not want the boat moving.

[skipperpete]

Originally Posted by Fishbone 1

how about a impeller style pump on the drive shaft. I have seen pumps used on military Duck boats that have an impeller inside a closely fitted housing around the prop shaft. They draw water in around both sides of the shaft to a vane style pump and discharge overboard above the water line. No friction or seals to worry about and they only pump when submerged. I guess that they probably move a little air when not submerged. I saw a demo and i think that these were moving many thousands of gallons an hour

Bowman yachts offered this propeller shaft pump as an add on accessory. It was a fairly large housing around a big impeller that acted as an engine room blower under normal circumstances but as a huge volume bilge pump should catastrophic flooding occur. On the one I had dealings with it had a 2½" overboard hose and a very substantial impeller. It made my job of doing an engine alignment far more difficult than it would normally be.

[Uncle Bob]

Originally Posted by HopCar

There is a link to what you’re describing in post #2. I think it’s a great idea but I see two problems.

First it’s not cheap. Second the prop shaft has to be turning so the boat is moving for it to work. Depending on where the leak is, you might not want the boat moving.

Couldn't agree more, if there is a catastrophic leak that requires such a high volume pump I wouldn't want the boat to be powering on probably making it worse.
I guess it would be great for ventilation though.

[a64pilot]

Depends on where you are etc.
They claim 24,000 gals an hour at 2000 shaft RPM, now if I do the math right, that 400 gallons per minute.
That’s one massive leak, and surely just a thru hull or similar is less than that, so you could pump it down enough to find the leak and plug it.
Remember you don’t turn it on, it doesn’t hurt to dry run it, as soon as water is there, it pumps it out. You could be motoring along and notice the stream of water flying out the side of the boat, nothing electric, no float switches to fail, but the engine has to be able to run of course.

Good Lord a 400 gpm pump takes over a three inch hose, that is a tremendous amount of water.

So far as making an engine alignment tough, it shouldn’t because you always are moving the engine to align to the shaft, not the other way around, or put a Sigma drive on and forget about alignment.
I considered one, it’s not but maybe $1,000 installed if you do the work yourself, then finally I guess just decided that not everything is survivable, and that maybe that was carrying things just too far.
However if I was the type that sailed where there in no help coming, no USCG helicopter etc. I may think differently.

Even if it were only 200 gallons a minute, that’s still one heck of a pump.

The engine coolant pump idea is not going to keep up with any kind of a leak, it’s only real use if if your bilge pumps are gone and eventually the bilge fills from the stern gland leak and you need a way to dewater.

[Simi 60]

This is the type I was mentioning earlier
230 gallons/minute

https://www.absolutewaterpumps.com/p...oylXT_PXapCF3w

As used here

https://mvdirona.com/2017/04/fighting-water-ingress/

[skipperpete]

Originally Posted by admiralslater

Personally I am not worried,I have pumps in each engine room , I was just thinking about a little redundancy. It seems a simple way to get a bit extra with the advantage of running through the night etc .
Does anyone think there is a down side other than those I brought up .

Assuming that the suction is properly filtered and no bilge rubbish can make it up to the heat exchanger at oil cooler then the only real downside would be that you would have to sit and watch the bilge level because if the engine pump runs dry, the impeller has not long to live.... even a globe impeller..... then you lose an engine until a new impeller is fitted.

[cal40john]

Originally Posted by admiralslater

That is interesting, It would be a substantial % increase to most of the pumps used for this

Sounds like you're saying the 3GM pumps a lot. It is less than the smallest Rule centrifugal pump.

[FPNC]

A modern small diesel engine should pump around 6 gallons per minute / 360 gallons per hour at speed. That's not bad if you don't have a big hole in your boat. If you have a big hole, not many bilge pumps will save you anyway.

Remember that when a bilge pump company rates the flow of their pumps, it is normally in ideal conditions. I.E., Max rated operating voltage, horizontal flow with no head pressure and no hose restrictions from type of hose and bends. After installation, you may be lucky to pump 250 gph from a 500 gph rated pump.

A bilge pump is just that. Don't rely on it to keep a vessel afloat if you have a breach shipping a large amount of water.