How Do You Determine What Size Bilge Pump You Need

How do you know what GPH pump you need?

Simple for me, the biggest you can afford that will fit in the space.

There is no right answer beyond one bigger than your biggest leak...whatever and whenever it is.

It is a complex risk management decision that only the boat owner can rubber stamp.

There are rules of thumb that I find a folly, yet you can feel satisfied by being reasonable then multiplting by 3.

Like mentioned biggest but it should at least be able to pump the biggest water intake volume you can face in case of something breaks like a raw water hose. Of course this does not apply to major structural damage as I don't think any pump will support a 4 square feet hole

I inadvertently tested earlier this year that my 2000gal/h is correctly sized

L

I always have thought this article has some good basic info, a bit dated but still quite relevant as to the issues. :

ALL ABOUT BILGE PUMPS - Boats, Yachts Maintenance and Troubleshooting

kartracer said:

How do you know what GPH pump you need?

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Don't feel bad about adding a second bilge pump if you wish.
I added a second bilge pump on my Nordhavn and set the discharge to the opposite side of the first pump.

At least one bilge pump in each bilge area. Some compartments are not totally water tight.

"There is no right answer beyond one bigger than your biggest leak...whatever and whenever it is."


That is what I thought also !!!!

Also consider that the installed capacity is seldom what is advertised. There are several quick switches for raw water intake from bilge that can add emergency capacity and might be worth considering based on cruising style.

Let's face it, you get a high water alarm, you will go find out why. If it's a hose, you will shut the hull valve.
If you holded the hull, you have more important things to do, launching the dingy and or survival raft, gathering up the UHF radios and food and water.

Do more boats flood/sink at the dock than while underway?

Lou_tribal said:

I inadvertently tested earlier this year that my 2000gal/h is correctly sized

L

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Sooo, tell us about the 'inadvertently"????

Yup, centrifugal bilge pumps are pretty good at sucking but the discharging can be a problem.... That is why I had suggested, if you put in a second bilge pump, discharge it to the opposite side. Seldom do boats sink 'flat' when underway.

menzies said:

Simple for me, the biggest you can afford that will fit in the space.

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And for us, two more further up with float switches at different heights
And two more of same in the spares locker
And two submersible 240v ones that can be moved around as required
And a spout and valve off the raw water in before the strainer that can be used to suck bilge as main engine runs.

I have a spare bilge pump with a long discharge hose and powered by long 12vt battery clamps.

OldDan1943 said:

Sooo, tell us about the 'inadvertently"????



Yup, centrifugal bilge pumps are pretty good at sucking but the discharging can be a problem.... That is why I had suggested, if you put in a second bilge pump, discharge it to the opposite side. Seldom do boats sink 'flat' when underway.

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Well last spring when we departed from our dock for a 1 month trip we had a "little incident", the main raw water hose connected to the exhaust manifold popped out and the engine was pumping water in the ER directly.
To make it short first thing I did when I notice the 2 feet of water in the ER is to force the main pump on and turn back to the dock. The pump was strong enough to keep up with the flow of water coming in while we were underway. ( before any comment yes I could have reconnected the hose and solve the issue but under the stress of the situation I did not notice the disconnected hose and was just thinking not to sink in the middle of the river )

L

Lou_tribal said:

To make it short first thing I did when I notice the 2 feet of water in the ER is to force the main pump on and turn back to the dock. The pump was strong enough to keep up with the flow of water coming in while we were underway.

L

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2 feet of water? You ER must be bigger than mine. 2ft of water in my ER would be catastrophic. It would overtop the bilge pump.
What diameter a hose was it?

2 ft? Time to set the float switch and high water alarm lower in the bilge.

OldDan1943 said:

2 feet of water? You ER must be bigger than mine. 2ft of water in my ER would be catastrophic. It would overtop the bilge pump.

What diameter a hose was it?

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I think the hose size is 2 inches and yes the pump was submerged water was half way the engine and I took it at the right moment few inches more and it would have reached the air filter
Good thing is that it cleaned my engine bottom and ER lol Better laugh about it now!
L

Lou_tribal said:

Good thing is that it cleaned my engine bottom and ER lol Better laugh about it now!
L

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And lots of fresh water used to hose out the salt too.
That is one way to clean the bilge but, I would not recommend it.
Glad you were able to recover.

Lou_tribal said:

I think the hose size is 2 inches and yes the pump was submerged water was half way the engine and I took it at the right moment few inches more and it would have reached the air filter
Good thing is that it cleaned my engine bottom and ER lol Better laugh about it now!
L

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Scary and no fun at all.

But you had what I knew in the USCG as a self correcting sinking.

When the engine quits, the inflow of water most of the time stops too.

Respnded to several vessels where just that happened.

Not a good way to save the boat....

Any way one can recover from a sinking is a good way. It may not be "pretty" but if it works who cares.

Bigger is better. On my 32' boat I have three electric bilge pumps. On either side of the keel I have a 2,000 gph pump and I have a 4,000 gph pump on top of the keel. Each pump has its own float switch. The switch for the 4,000 gph pump is located above those for the 2,000 gph pumps. So far the 4,000 gph pump has never run (except in tests). Another consideration is the electric draw of your pumps and how that relates to your battery capacity. My 2,000 gph pumps draw 7 amps and the 4,000 draws 20 amps. Needless to say, the 4,000 gph pump would flat my batteries if it was running and the boat was unattended for 24 hours. Fortunately at the end of the season my smaller pumps were only running for 8 seconds a day so I was drawing a trivial amount from my batteries which my solar replaced within minutes.

Mainship 30 pilot came with 3 sump pumps - forward, mid, and aft. Plus a 4000 gph emergency pump.

Yup, once the batteries are dead or shorted out, time to be beached.

Dockside , with a power cord most any 1-1/2 inch discharge unit will do fine.

Big DC pumps require big DC power , which can kill the batts very rapidly.

A 2 inch clutched bilge pump is probably a good choice if you ever go in blue water.

IF you have a noisemaker a house sump pump of 2 inch is not too costly.

Mystic Blue said:

Mainship 30 pilot came with 3 sump pumps - forward, mid, and aft. Plus a 4000 gph emergency pump.

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come with a 400 gph pump? Hmmm, I wonder why. Loss of faith in their equipments?

The American tug comes with 1 bilge pump. I added 4 more plus the moveable bilge pump. I have no excuses for sinking the boat. LOL

OldDan1943 said:

And lots of fresh water used to hose out the salt too.

That is one way to clean the bilge but, I would not recommend it.

Glad you were able to recover.

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Fortunately enough I am in fresh water so no salt crust

L

psneeld said:

Scary and no fun at all.

But you had what I knew in the USCG as a self correcting sinking.

When the engine quits, the inflow of water most of the time stops too.

Respnded to several vessels where just that happened.

Not a good way to save the boat....

Click to expand...

Indeed it was very scary and very stressful at the moment. Like you said when we reached the dock and cut the engine problem was solved but at that time I thought I would sink at the dock lol I was lucky that I thought to go to the dock slowly to keep the exhaust not to hot ( as it was not getting any water), if I would have been full speed not sure the pump would have been able to cope with the inbound water flow.

L

I've read articles that recommend pump sizes based on boat size. They invariably recommend larger pumps for larger boats.

This seems ass backward to my way of thinking. To me a bilge pump is there to buy you time to fix the leak. Since a small boat will sink faster than a large boat with the same size leak, the smaller boat needs a bigger pump to give you the same time to stop the leak.

In the real world just put as many and as big pumps as you feel is reasonable. To me a reasonable number is always more than one for a boat that lives in the water.

Some guys will add a very large bilge pump but then the hose and thru Hull are too small to handle the water flow. If you sink you didn’t have enough.

Lou_tribal said:

Well last spring when we departed from our dock for a 1 month trip we had a "little incident", the main raw water hose connected to the exhaust manifold popped out and the engine was pumping water in the ER directly.
To make it short first thing I did when I notice the 2 feet of water in the ER is to force the main pump on and turn back to the dock. The pump was strong enough to keep up with the flow of water coming in while we were underway. ( before any comment yes I could have reconnected the hose and solve the issue but under the stress of the situation I did not notice the disconnected hose and was just thinking not to sink in the middle of the river )

L

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Hey Lou, Your story sounds all too familiar.

A couple years ago I had noticed that my bilge pump switch was sticking. I thought I better keep a close eye on it until I could replace it, so I removed the plywood cover over the bilge so I could easily check for any water in the bilge. About and hour out, I opened the hatch to check on things and saw water half way up the engine. PANIC! The muffler was under water so I couldn't see the source of the incoming water. It took me a minute or two to calm down and just switch the bilge pump from auto to manual, and the bilge drained fairly quickly.

With the water level down, I saw the disconnected exhaust hose. The plywood cover that I removed to keep an eye on the bilge, also kept the muffler snug in its place. Removing it allowed the water muffler to move slightly in rough seas and work itself off the end of the hose.

When I got home I installed another bilge pump slightly higher, tied to an alarm. I also ended up replacing the starter motor, which I didn't flush the salt out of well enough and it failed a week later.
Lots of lessons learned. It's of no use getting older if you are not getting wiser.

My high water alarm is a 4 inch bell that will wake the dead.