Bilge Pumps

[PinHead]

I have been doing some reading on some articles regarding bilge pumps.
My boat has a self draining deck which is sealed from the bilge area. There is a 1100gph pump in the stern and a 750 gph up front. What capacity do these actually pump when taking into account the head the pumps have to push...is it 80% of rating or 50% or ?????
I guess I should work out the volume of the bilge and of course there are many variables such as size of hole in boat for water to ingress.

the 1100 gph equates to 1.375l/s and the smaller pump 0.94l/s.

Would both these pumps be sufficient in an 18 1/2' boat as a general rule of thumb?

[Mad-One]

You have alot more than most people. I suppose you can never have to many pumps

Phil

[garman1]

After reading "boat ramp mishaps", the biggest problem seems to be forgotten bungs. I wondered if my bilge pump would cope with the inflow of water from two forgotten bungs????? It is a quintrex 4.3 mtr with two "standard" bungs, the bilge pump doesn't look that large a model.

I think putting in a large bilge pump may be prudent. The other thing is the outlets are only a "standard" size too, would they cope with the xtra output from the pump?????

Anyone have any input to add to the "boat ramp mishaps"........???? re bilge pumps...............??

Maybe this is a question that "all" of us should be asking ourselves, before the event.

[TheRealAndy]

After reading "boat ramp mishaps", the biggest problem seems to be forgotten bungs. I wondered if my bilge pump would cope with the inflow of water from two forgotten bungs????? It is a quintrex 4.3 mtr with two "standard" bungs, the bilge pump doesn't look that large a model.

I think putting in a large bilge pump may be prudent. The other thing is the outlets are only a "standard" size too, would they cope with the xtra output from the pump?????

Anyone have any input to add to the "boat ramp mishaps"........???? re bilge pumps...............??

Maybe this is a question that "all" of us should be asking ourselves, before the event.

Test it out. Keep bungs out, reverse boat in deep enough whilst still in trailer and let the water in. Turn on pump and see if it can keep up.

[Midnight]

Gday,
Pinhead, should be plenty with a self draining deck. Do you have float switches on them?

Garman1, If you forget the bungs, just put it into gear and keep moving forward and it will self drain through the bungs while the bilge pumps do their bit. But yeah, try it out as Andy suggested, it would be interesting to find out.

When I was a young bloke, we regularly came across the bay in tinnies on crappy days with both bungs out to get rid of the water that was coming over the side.

Cheers,
Myles

P.s I have a 1500gph, 1000gph and a 750gph in my Bertram 25. The 1500gph sure pumps the water out when you turn it on!

[ToXiCFiSH79]

when i was a teen, three of us in a tinny in botany required regular "debunging" manevours to drain the boat. two of us would go ashore and the remaining person would do happy laps until the boat was drained again thru the bungs...

[FNQCairns]

I have been doing some reading on some articles regarding bilge pumps.
My boat has a self draining deck which is sealed from the bilge area. There is a 1100gph pump in the stern and a 750 gph up front. What capacity do these actually pump when taking into account the head the pumps have to push...is it 80% of rating or 50% or ?????
I guess I should work out the volume of the bilge and of course there are many variables such as size of hole in boat for water to ingress.

the 1100 gph equates to 1.375l/s and the smaller pump 0.94l/s.

Would both these pumps be sufficient in an 18 1/2' boat as a general rule of thumb?

There was a site ages ago that did a comparo with a few pumps, only one actually met the gph claimed. Off the top of my head the claimed GPH is without even a hose attached and running well better than 12v hence when a hose is attached with say 500mm head or more.....I would consider myself lucky if I ended up with 60-70% of the stated flow.

Easy to check by timing a 10/15L bucket full with water straight from the thru hull, i too have the 1100 and a fair flow comes from it, my other one is a 650 I think. I assume these two would buy me valuable time in bung out situations but not save me from a good swamping if I shipped enough water to turn turtle it will probably happen before the pumps could clear enough to stabilise.

Realistically a sealed deck boat will turn turtle before an unsealed deck hull will (apples to apples) from shipped water but probably not from a bung out situation.

IMO stick another 1100 beside the back one to feel a little better, if just for the redundancy.

cheers fnq

[garman1]

Now if i have an "accident" at the boat ramp ie:forgot to put bungs in, I can just say "nah mate didn't forget the bungs, just trying the pump eh". That almost sounds like being a responsible thing to do and not just a cock-up. Thanks Andy appreciate the tip off for a good answer, ya never know when you might need that line.

Now for an excuse for dropping the boat on the boat ramp, before it's in the water..mmmmmmmmmmmmmm shock testing the bilge pump before you get it in the water without the bungs in, so you can then test the bilge pump...............

[on-one]

Not sure if you've read this article but he suggests it could be less than 50% of the stated capacity http://www.yachtsurvey.com/bilge_pumps.htm, there's also a 6 page article on bilge pumps in the latest passagemaker magazine

[cormorant]

Is graphs on the sides of boxes and websites show head and flow but they are optimistic and best case. many outlets are too small so well worth using the correct size pipe and largest free flowing outlet as many are restrictive. Some really hate lower than normal voltage as they have no torque on cheaper motors. Testing on the boat is teh only way just stick the hose up a bung and see how quickly your existing will fill a bucket

Can never have enough capacity and larger pumps are built a lot more duarable and don't clog as easily - just remember the battery capacity to run it.