Using engine as a bilge pump?

[pvb]

This is what you need! http://www.yachtwork.com/bilge-pump.htm

That shaft-mounted Ericson pump isn't a very good idea. Yes, even the smallest size has a huge pumping capacity (but, crucially, not in a boat). The pump's theoretically rated at over 40,000 gallons an hour. But - and this is a big but - this rated capacity is at 3500rpm (pump revs). The average 30-40ft cruising yacht has a small diesel which will do maybe 3000rpm flat out, connected typically to a reduction gearbox (say 2.4:1 ratio), meaning that the prop shaft (which the Ericson pump is clamped around) is only turning at a maximum speed of around 1250rpm. At this slower shaft speed, the output is much less, maybe only 8000 gallons an hour (the Ericson data is surprisingly a bit woolly on this).



Next problem: the Ericson pump is huge - the smallest model is about 10” diameter and about 5” front to back. There’s no way it will fit in many yachts.



Next problem: before it will pump efficiently, the aperture around the prop shaft must be fully submerged. So there needs to be a hell of a lot of water in the boat before the Ericson will start working properly. This would affect the boat’s stability somewhat (understatement!).



Next problem: it’s most likely that a dramatic leak will occur in the front part of the boat, and the Ericson is much further back. For it to work, it will be necessary to have a virtually open bilge right through the boat. With modern boat construction, stiffening ribs, etc, this is difficult to achieve.



Biggest problem: the pump only works well when the boat is flat out in forward gear. As “Motor Boat & Yachting” pointed out in its review of the Ericson pump “it is probably the case that most collisions involving breaches of the hull would damage the vessel's forward sections. In this case, driving the boat forward would tend to fill her and negate the usefulness of the pump”.


 

[prv]

Next problem: it’s most likely that a dramatic leak will occur in the front part of the boat, and the Ericson is much further back. For it to work, it will be necessary to have a virtually open bilge right through the boat. With modern boat construction, stiffening ribs, etc, this is difficult to achieve.



One small plus point - once the boat has enough water in it for the pump to start working, it will be flowing freely over most internal rib structures anyway.

Everything else though - what you said

Pete

 

[ghostlymoron]

This topic has come up several times before and the conclusion has always been the same.

 

[ottow]

I've always fitted a T-valve on my engine inlet in my boats, as that makes it much more easier to winterize. Just start the engine, put the suction hose in a bucket with antifreeze mix and then flip the valve. Just remember to flip it back to "normal" position afterwards or you may forget it come spring and overheat...
I find the possible use of the engine as a (albeit of low capacity) emergency pump more of a bonus which I hope I will never need.

 

[fisherman]

I've always fitted a T-valve on my engine inlet in my boats, as that makes it much more easier to winterize. Just start the engine, put the suction hose in a bucket with antifreeze mix and then flip the valve. Just remember to flip it back to "normal" position afterwards or you may forget it come spring and overheat...
I find the possible use of the engine as a (albeit of low capacity) emergency pump more of a bonus which I hope I will never need.

You could just close the valve, take the top off the strainer and pour in from a watering can, or use a hose.

 

[jamie N]

Interesting, though lapsed thread! On my Renault Couach RC8D, the belt driven water pump has 2 chambers, one for the raw water cooling, and a separate one for the bilge. No outside action is required in switching, as the pumps are both 'live' at all times. To ensure that the bilge pump doesn't run dry, the 2 chambers are linked, or rather not sealed from each other, which lubricates the bilge side with a small amount of splash. The bilge pump side of it works well in draining the bilge, nor has there ever been a problem with flooding the engine, as the engine must be running to power it, and it pumps out through the same fitting on the exhaust manifold; a very clever bit of engineering! Another advantage is that there's always a spare pump. Should the raw water side of it fail, then it's simplicity to swap over to the other chamber. The downside is that it's prone to syphoning (ask me how I know), so one's got to remember to close the sea-cock, unless confidence in the non-return valve is high!
I've come to this thread as I've fitted an electric coolant pump onto the engine, that circulates a non-water based 'glycol' coolant around, through a small heat exchanger, through which the raw water from the usual pump also flows. After the good engineering on the pump, the engine doesn't have any provision for an anode, or CP of any sort, and are "prone to corrosion", to quote the supplier!