Raw water pump as emergency pump

[pcatterall]

The stories about flooding due to skin fittings and the near loss of that charter boat has made me think about this idea again, especially as I am trying to 'refit' my 'new' boat.
It seems like a good idea ( any views) and looks fairly easy in my boat. I think I could just insert a Tee into the hose ( between inlet and engine) with a valve and a hose section going down to a few inches of the bilges.
The important thing would seem to be able to open the fitted valve quickly and then shut off the sea water sea cock. ( and brief crew accordingly!)
Would I have to mount the T and the valve on something solid or could they hang on the pipe?
Will the bilge pipe be able to suck up the water as it will be dry until water flows?
Any other issues/ filter thing etc?

 

[pvb]

It's really not worth the trouble, as the flow of cooling water isn't that great usually.

 

[nimbusgb]

Don't bother. Even a big raw water pump only gets through a few gallons of water and you'd need the engine running pretty hard to get a decent flow. Also if the inlet gets blocked and you screw up the impeller you are now in a boat with a semi crippled engine AND a leak!

If you insist however ....
Use a changeover valve so no need to shut off the skin intake side.
Yes the engine inlet will 'lift' the bilgewater easily.

If you have a Perkins 4108 give me a shout I have a stacked, dual rotored, dual pumping raw water pump that was rigged to do a similar thing. rear one for engine raw water, front one for bilges. looks like Original equipment.

 

[VicS]

As pvb suggests the capacity of the raw water pump is not likely to be large enough to be really useful.

How about a proper engine driven bilge pump? With suitable change over valves etc it could also be used as deck wash pump!

 

[Goldie]

How about a proper engine driven bilge pump? With suitable change over valves etc it could also be used as deck wash pump!

Exactly what we have - a changeover valve gives the option of sucking water in from bilge or a separate raw intake; another changeover valve selects the option of through the side (for bilge out) or deck hose (for raw out). Works a treat for cleaning the muddiest anchor! 'Default' setting is 'Bilge in - Bilge Out' with the deckwash being selected when required. That way the bilge pump is instantly available. Pump has electro-magnetic clutch activated by a switch at the helm.

 

[pcatterall]

Ahh thanks. It was the maib report on the fishing boat that nearly sank that started my chain of thought. I thought that the either recommended this adaption or said that it had worked well and saved the day. I will re-read.
Thanks Nimbusgb; I had thought that a grill on the end and sucking up from not right down in the bilges would avoid bits being drawn in but your point about sinking and enginless is taken !!; it is a 4108, is the pump you refer to just bolted on to replace the existing water pump ( two pumps one drive?) I wonder what the output is? There is only a hand pump on the boat at the moment so I am going to have to sort something. I guess that as long as the engine runs,( and charges!) a powerful electric pump may be the simpler option.

 

[prv]

Ahh thanks. It was the maib report on the fishing boat that nearly sank that started my chain of thought. I thought that the either recommended this adaption or said that it had worked well and saved the day. I will re-read.

I think they did say that, but note that they were also using an electric pump and a manual one at the same time. I doubt anyone actually measured how much help the engine cooling pump was adding.

Note also that this was a 32-foot motor boat, which presumably has a substantial engine whose cooling pump shifts a fair bit of water. A 32 foot yacht can have the same amount of water to get rid of, but the engine pump will be far smaller.

Pete

 

[westhinder]

My cooling water intake is fitted with a cylinder which houses the strainer and which has a lid that can be screwed off. That way, if needed, I can close the valve, open the cylinder and the engine will suck water from the bilge.
This arrangement was fitted from new on my Perkins Perama in 1988, but it has never been used in earnest and I hope to keep it that way. The volume used by the engine is limited, and debris blocking the strainer would be a constant worry.

 

[PCUK]

Depends on the pump size. The Sherwood on my 300hp Cummins moves several hundred gallons an hour. Same as a clutch pump of the same size (obviously!)

 

[Deleted member 36384]

Rig it up as an emergency pump. It could make the difference. Just be aware of the additional risks and have controls / procedures to address them if they happen as others have stated: engine temperature, frequent listening and visual check on the exhaust outlet for water flow. A blockage should be detectable soon enough to prevent engine damage.

If you can fit a larger pump on a pulley and bracket that would be a better solution. Also an electric bilge pump may be quite easy to install and give you more pump capacity than the the raw water pump.

The raw water inlet as a poor boy additional pump is still a viable option though. I have sailed on a few boats that had this system. One boat was just a loose copper pipe extending into the bilge with a hose tail to slip over the raw water pump suction side. The copper pipe and hose tail sat snugly in the engine bay, next to the raw water pump, ready to fit. A very simple solution with little additional risk when not in use. Others had change over valves.

 

[Deleted member 36384]

... it is a 4108 ....

The 4108 raw water pump has a relatively high flow rate. On older 4108 engines there was a manual choke to restrict the flow rate as the engine never got up to temperature due to the high flow rate. You are not likely to have this as temperature is controlled by the thermostat now.

I have checked two manuals, the 4108 and 4236, and neither state the raw water flow rate. Having used both these engines the flow rate from the exhaust looks substantial enough to me to warrant using the raw water pump as an emergency addition to save the boat from sinking.

As I said above it could make all the difference i.e. achieving a rendezvous with a lifeboat that has a large flow rate pump, or sinking as you notice the lifeboat on the horizon. Its a no brainer in my opinion.

 

[Salty John]

14 gpm and 21 gpm according to Jabsco. Influx from a seacock half a meter down is around 60 gpm.

I think the ability to get at all seacocks and tranducers, even when they are underwater, and plug them is extremely important. If you rely on a pump to keep up with the influx you're fighting a losing battle - you have to get at the hole and plug it, at least partially.

Some say using the engine cooling water pump puts you in danger of creating a second problem just when you don't need it but others will be pleased to have the option.

 

[Ex-SolentBoy]

14 gpm and 21 gpm according to Jabsco. Influx from a seacock half a meter down is around 60 gpm.

I think the ability to get at all seacocks and tranducers, even when they are underwater, and plug them is extremely important. If you rely on a pump to keep up with the influx you're fighting a losing battle - you have to get at the hole and plug it, at least partially.

Some say using the engine cooling water pump puts you in danger of creating a second problem just when you don't need it but others will be pleased to have the option.

60 gpm - no problem. Fit an Ericson safety pump to the back of the engine.

Even the smallest one does 180gpm!

 

[PCUK]

As I keep saying, don't forget your fothering sheet as well!

 

[pvb]

60 gpm - no problem. Fit an Ericson safety pump to the back of the engine.

Even the smallest one does 180gpm!

Really can't agree with you. From time to time, people suggest the Ericson pump, 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.

 

[DaveS]

Whilst I would agree with those who point out the relatively low capacity of a typical yacht auxiliary raw water pump versus possible leak rates, I do use this arrangement myself. The "alternative" suction line consists of a couple of metres of hose coiled neatly in the bilge. It's never been used as an emergency pump, but it's extremely handy for putting in a bucket of first fresh water then antifreeze mix for winter lay up. (Avoids all the business of disconnecting hoses etc.)

 

[Babylon]

1. Locate and plug the leak - if its a skinfitting leak use a bung, or stuff cushions into, batten over and add a sail outer bandage over any big holes in the hull - but if its a failed stern-gland then I don't know what you'd do.
2. Use buckets to remove the majority of water - add a dose of fear to up the discharge rate.
3. Fit a manual bilge pump - your electrics might be flooded.

However, surely a makeshift raw-water bilge-pump can be achieved simply by removing the inlet hose from the seacock tail; lengthen it by stuffing a length of copper pipe or similar into the hose end. Presumably the inlet strainer will still be doing its job, so small debris will be filtered out before the water enters the impeller pump.

 

[prv]

if its a failed stern-gland then I don't know what you'd do.

In my grandad's case, cut a strip of rubber out of a seaboot and bind it round the gland and shaft with a few hose-clamps. Then, set out to cross the Atlantic. Not "continue", mind you, but "set out". He wasn't the most mechanical of chaps

However, surely a makeshift raw-water bilge-pump can be achieved simply by removing the inlet hose from the seacock tail; lengthen it by stuffing a length of copper pipe or similar into the hose end.

Yes it can - the point is that, with the average small yacht engine, it won't then do terribly much. Look at the water spluttering out of your exhaust next time - if I was trying to empty the boat, I'd want to see water going overboard a lot faster than that.

Pete

 

[jwilson]

The stories about flooding due to skin fittings and the near loss of that charter boat has made me think about this idea again, especially as I am trying to 'refit' my 'new' boat.
It seems like a good idea ( any views) and looks fairly easy in my boat. I think I could just insert a Tee into the hose ( between inlet and engine) with a valve and a hose section going down to a few inches of the bilges.
The important thing would seem to be able to open the fitted valve quickly and then shut off the sea water sea cock. ( and brief crew accordingly!)
Would I have to mount the T and the valve on something solid or could they hang on the pipe?
Will the bilge pipe be able to suck up the water as it will be dry until water flows?
Any other issues/ filter thing etc?

No-one in their right mind would let a charter boat they owned have a setup that would allow a choice of the engine pumping from an empty bilge, or depending on whether you teed or Y-valved, possibly filling the boat from the sea..

 

[pcatterall]

This was a skippered charter fishing boat and as I said crew must be briefed.