Bilge pump sizing?

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burgundyben

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Er..there was an ingress of water into the boat a few days ago, nothing major, plumbing error on my part....

I had about 8 inches of water in the bilge, it took an age to pump out, I have no idea how many gallons an hour it is, just a cheapo chandlery job, has 1" bore hose, 12 volt, I dunno, maybe £30.

I have a manual pump too, a man, no matter how frightened, was going to make much difference.

The spurt of water coming out the side of the boat was pathetic, fine if you've hosed the cockpit, or let some water in while cleaning the impellor, but in the event of any kind of trauma it wasn't going to be of any use at all.

It made me consider installing a BFO pump, but how big to be of use?

What do others have?
 
Hmm. This one is tricky Ben. You can google flow rate tables based on diameter of hole and head of water. I did this for my boat and was shocked how much GPM you get with say a 3 inch hole (my biggest seacocks) and 1.3m head. There was no way the plastic bilge pumps would do the job, even if £130 not £30 and even if you have 5 of them as I do. Some people have valves to use the engine raw pumps but that is total BS because the flow rates on those babies are nothing like enough.

So I bought a BFO pump from the Clarke catalogue. It needs 230v so if my gensets both fail I'm dead, but I reckon there are plenty of scenarios when that wont happen. I also carry a dedicated "emergency leak response" bag with bungs for seacocks and a 2m x 3m canvas sheet with cringles all the way around the edge and read-to-go hanks of cord, so I can swim under the boat and patch/throttle a hole using that tied over the hole

I feel much more comfortable carrying the BFO pump and 10m of 2 inch roll-up discharge hose

The BFO pump works nicely in reverse if there is a fire and I want to spray the inside of my boat with sea water (before the fire brigade come and do it for me)

Edit - here is the one I bought http://www.machinemart.co.uk/shop/product/details/gse2-2in-hduty-ind-stainless-steel-pump Remember with these centrifugal pumps the flow rate is VERY dependent on head. The manufacturers publish tables
And note that this, which is at the heavier end of what you'd want to handle, is nominally "only" 500LPM, but with 4 foot of head (2psi) water does something like 600LPM through a 1.5inch hole and 3000LPM thru a 3 inch hole (all those numbers are ballparkish and rough but serve to make the point. I could try to find better data)
 
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jfm said:
Some people have valves to use the engine raw pumps but that is total BS because the flow rates on those babies are nothing like enough.
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Although in this particular case that exactly how the water got in...ahem...I was surprised at how much got in with the engine just at idle for a few mins.

As you highlight, a Clarke BFO pump would be fine, but its only a 28ft boat and a cockpit half full of Machinemart's finest wouldn't put visitors at ease.

It is tricky to see the right solution. I can see a way of fitting something fairly hefty in the back of the bilge with an outlet through the transom.

This question always make me wonder why I don't have a lifejacket for the boat, displacement is 4000kgs, but much of it is wood which floats, I reckon about 2.5mtrs cubed of air bag would keep her afloat come what may. A BFO air bag and cylinder in the cabin would be the perfect thing to keep her afloat.
 
The largest practical pump with a 25mm hose is a 1100 gph nominal capacity. However for your size boat a 30mm hose which will allow a pump up to 2000gph is better. My 37 footer has a Rule 2000 which costs around £110. Being a good Bavaria it does not leak a drop so the original pump seized through lack of use! However I tested the new one by filling the bilge to wash it and the pump really shifted water. You can get it with an automatic switch as well.
 
petem said:
What's your take on shaft driven pumps like this...

http://www.yachtwork.com/product-bilge.htm

24,000gph!
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that looks a superb bit of kit!

just to add, we have 2 auto bilge pumps on floats, both 12v johnsons units, forward one is a submersible, aft one (main unit) is one of these with a pressure switch, http://www.asap-supplies.com/marine/motor-bilge-pumps-with-flexible-impeller-12v/504322-johnson-pump its nothing like the BFO LPM rating, but having washed out the bilges a few weeks ago it nearly keeps up with the hoses at Mercury... but not quite.

also have a manual pump. & I have bungs tied to all our seacocks...
 
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petem said:
What's your take on shaft driven pumps like this...

http://www.yachtwork.com/product-bilge.htm

24,000gph!
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I like that Petem. They're misguided thinking the shaft will do 2000rpm (there is 2:1 reduction) but nevertheless they are nice things and it's a clever concept. I don't think I can fit one in but I'll take a look

The idea of using the engine is interesting though. I'm thinking of an extra valve and pair of hoses on my already big hydraulic pack, running a hydraulic motor driving a big centrifugal bilge pump. Just flick a dashboard switch and the solenoid valve opens, and you have a 10 hp pump. AND you can run it in with engine in neutral, which is handy if you are dealing with other aspects of the emergency and don't want to be charging around at 20 knots
 
that is a good point..... it only works if props turning. ... if shaft/s mashed this pump becomes irrelevant, quite a bit of water ingress situations can be because you have run into something that either has holed the boat and you are in shallow water or bent/ ripped out shafts....
 
Firefly625 said:
that is a good point..... it only works if props turning. ... if shaft/s mashed this pump becomes irrelevant, quite a bit of water ingress situations can be because you have run into something that either has holed the boat and you are in shallow water or bent/ ripped out shafts....
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Yup, good point there. You definitely want to be able to take power from the engine while gearbox is in neutral
I'm going to investigate the hydraulic route. Many engines have a facility to add a hydraulic PTO. These are quite small things, and then you have complete freedom over routing the hydraulic hoses, so you can mount the motor and BFO pump wherever convenient
 
Need to do the math but I think BB might need to be a bit careful that a big enough airbag to make a difference didn't provide sufficient lift to rip the deck off. Mind you, if the choice is the boat sinks or the boat breaks and also sinks then I guess it's a fine distinction.
 
benjenbav said:
Need to do the math but I think BB might need to be a bit careful that a big enough airbag to make a difference didn't provide sufficient lift to rip the deck off. Mind you, if the choice is the boat sinks or the boat breaks and also sinks then I guess it's a fine distinction.
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That point isn't lost on me.

I'm thinking of a multi pronged approach to this (although not sure why after 12 years I'm looking at it now).

A 4000 GPH pump in the rear of the boat with a 1.5" discharge.

A 3000 ltr air bag in the cabin, kept in a valise, 2 straps which fasten onto strong point with snap shackles when required, gas inflated.

The pump could keep up with anything except the biggest trauma, if that failed, the air bag would prevent sinking.
 
Manual and Electric clutch pumps have been around for years and assuming the engine is running(!) will give a better head/flow pressure curve than any centrifugal. As the are flexible impeller pumps try not to run dry although there are run dry versions available.

Jon
 
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