High volume electric pump

oldbilbo

oldbilbo

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I anticipate carrying a small genset, rated about 800-1000w, which can provide 12v at around 100W and 8.3A, according to labelling, with the main purpose of recharging batteries now and then. While I have 2 normal 12v bilge pumps installed ( 500gph, low and high levels ), I'm wondering about a higher capacity pump which could be driven 'in extremis' - should there be a ruptured through hull fitting, for example - from the little genset.

What might be practicable, and what needed? Any experience to share?
 
Plenty of mains submersible pumps about.
Of course sloshing seawater about is not a comfortable mix with mains generators, particularly a portable one sat on a wet deck.
If you promise to only attempt to sink in calm conditions, I'm sure it would be OK.
 
Talking about the 12v output specs make it sound like you're planning to run the pump off the 12v side. Don't do that, 8.3A is buggerall for a bilge pump, probably less than what your existing ones draw.

Pete
 
prv said:
Talking about the 12v output specs make it sound like you're planning to run the pump off the 12v side. Don't do that, 8.3A is buggerall for a bilge pump, probably less than what your existing ones draw.

Pete
Click to expand...

8.3A would be a fairly big Rule centrifugal pump(s).
 
Firstly, I think you're being excessively cautious. However, if you're seriously interested in an emergency pump, you should go for the biggest flow rate your genny will power. I'd suggest you look at the Machine Mart range of mains submersible pumps. These are good, hefty pumps. For reasons I won't go into, I have one of their 2" stainless steel pumps permanently mounted in an inspection chamber in my garden, operating as needed on a float switch. It's been there for years and continues to work efficiently. I have another one which I use on odd occasions when we suffer flooding. For emergency use in a boat, don't get one with a float switch - it needs too great a depth of water before it turns on.

You need to consider how you would get the water from the pump to the sea. Presumably you're not considering permanently installing it (although this would be the best way, because it's not a quick process to rig it in an emergency). You must use proper circular pipe. If you use the convenient, layflat hose, it will kink at every bend and greatly reduce the flow rate. So you might also need to find stowage for a few metres of pipe.

The quoted flow rates of submersible pumps are based on free-flow, no pipe, no head, so actual flow rates will be much much less.

A better bet for an emergency pump would be a petrol-driven 2" pump, something like this one. At £200, it's not much more than a mains submersible, and it's likely to shift more water and probably be easier to rig in an emergency.

Just to put this pump issue into perspective, a 1.5" hole in the boat, say 2ft underwater, will allow about 250 litres a minute to leak in. Sobering thought.
 
I have a mahoosive Johnson pump with a length of 2" pipe with croc clips which I plan to connect direct to the battery (with engine running) in the event of a serious problem. It's all separate from anything so I can just dump the pump in the bilge, connect up and hopefully not sink! It sits behind the companionway.

Ask me why I bought it..
 
I've come to exactly the same conclusion. Petrol pumps are hard to store, maintain, fuel, and be sure they will start. I would rather bet on my daily used diesel genset. I will buy the Honda submersible trash pump and folding (fire truck style) discharge hose. Important to specify a TRASH pump, which will deal with the floating **** which will appear in any flooding incident (no matter how clean you keep your bilges) and which will no doubt disable your regular bilge pumps early in the incident.
 
oldbilbo said:
I anticipate carrying a small genset, rated about 800-1000w, which can provide 12v at around 100W and 8.3A, according to labelling, with the main purpose of recharging batteries now and then. While I have 2 normal 12v bilge pumps installed ( 500gph, low and high levels ), I'm wondering about a higher capacity pump which could be driven 'in extremis' - should there be a ruptured through hull fitting, for example - from the little genset.

What might be practicable, and what needed? Any experience to share?
Click to expand...
Big bucket and some adrenaline.

Virtually no practical small-boat pump setup will cope with serious flooding. The priorities are to stuff something in the hole to reduce flow - you don't need to totally seal it, then pump. If lots of water then bucket it. Once water level down a bit try and improve the seal.

Through-hulls failing under way should not be a problem as you should be able to get to them. A bigger problem could be a hull penetration from impact somewhere there is an inner moulding. On my boat (typical AWB) there is an area of hull under the heads/shower flooring that is virtually impossible to reach unless you have a well-trained small monkey with four foot long arms.

Also, an open seacock looks terrible, but it will actually take quite a long time to sink a boat. As the hull gets lower the inflow pressure reduces.
 
Much of the above I'm familiar with, thankee. As I'm considering carrying a small genset anyway, I'm wondering if a simple 'bolt-on' could have it serve extra duty should I - or someone else - ever need a hefty-capacity water pump. :)
 
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