Engine driven pumps

[Boo2]

Hi,

I came across these engine drive bilge pumps and they have the useful feature that they don't need the prop shaft removed to fit.

I do have a question though, which is that s*ds' law dictates that when you need your engine driven pump the most there will be a line tangled round the prop. So ideally you'd want a clutch between engine and prop shaft, but with a typical engine / gearbox layout wouldn't that imply both or neither the pump and prop running ? One way round it would be to split the prop shaft and put a clutch between the part attached to the engine and the part attached to the prop, but I'm just curious whether that would be "normal" ?

Or if not, how would it be done ?

Boo2

 

[theoldsalt]

Perhaps useful with variable pitch/feathering prop where the shaft could be driven without propulsion. Handy as a boat washdown pump as well as a bilge pump. However very expensive at $600.

Pumps driven by an engine front-end pulley and belt would be much cheaper and could be used with gearbox in neutral if required similar to cooling water circulation pump. A clutch could also be incorporated if required.

 

[prv]

Those propshaft pumps are not as clever as they look, for several reasons that get brought up here from time to time. Partly to do with not shifting as much water in real life as they claim to in lab conditions, and partly to do with the inadvisability of motoring around at max chat when you have a hole in (probably the front of) the hull. I'm sure someone will be along shortly with the details.

Personally if I was fitting out a rugged and self-sufficient boat for long-distance use, I'd instead have a big Jabsco pump with its own built-in clutch run off a belt from the front of the engine.

(My fantasy boat design includes a small diesel donkey engine in the forepeak, so I'd have another pump on that and probably pack a petrol portable as well.)

Pete

 

[pvb]

I came across these engine drive bilge pumps and they have the useful feature that they don't need the prop shaft removed to fit.

They're basically not practical for most boats. From time to time, people suggest these pumps (often called "Ericson"), but never consider the implications. 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 my 35ft yacht.

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”.

So, if you could fit one in, and if you could open up your bilges right through the boat, and if you thought that motoring flat out with a hole in the hull (and a lot of water sloshing around inside) wouldn’t be a problem, then an Ericson might shift 8000 gallons an hour. And it costs about £600. Why not get 3 big 12volt bilge pumps (say 3000 gallons an hour each) instead? They’d be cheaper, they’d work as soon as water got in, they’d chuck out at least as much water, and you wouldn’t need to be motoring flat out in order for them to work.

 

[vyv_cox]

If ordering one, make sure you don't confuse the part number with one from the Penis Erectile Pump lower down the page. That might make your eyes water!

 

[fisherman]

Just buy the belt driven Jabsco bilge/deckwash pump, with electric clutch. Mine is on just about all the time, 6000 hours or more since fitting, at 500-2000 revs, have not yet changed the impeller. As big as you can. Drive it off a large pulley to get the revs up, 2000 is good. Then fit a simple manifold to connect it to any part of the bilge, or the seacock for deck wash, or have a long inlet hose that you can poke anywhere or over the side, it is self priming. Useful as an emergency engine raw water pump, I have used it for this and also to back flush the engine when the oil cooler pipe stacks got thoroughly jammed with shredded weed.

 

[Boo2]

Just buy the belt driven Jabsco bilge/deckwash pump, with electric clutch.

Do you mean these ones ? They do look useful.

Thanks for all the replies and the warnings about practicalities. The Jabsco ones above with the built in electric clutches do look like a better bet than the ones I originally posted.

Boo2

 

[fisherman]

Do you mean these ones ? They do look useful.

Thanks for all the replies and the warnings about practicalities. The Jabsco ones above with the built in electric clutches do look like a better bet than the ones I originally posted.

Boo2

That's the one. 2" is quite big, mine is 1", about half that money at the time, 2001. It chucks a 1" bore of water about 15 feet. Mount it on a slotted or hinged plate to tension the belt.