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does anyone know if there is a "rule of thumb" for bilge pump output per boat length?

my boat is 18' and I plan on installing a big manual pump. Seems like electric ones go bad and clog often etc. Plus I dont want to rely on electricity as my boat is not new. I'm going to mount what I think is somewhere between a 600 and 900 gpm pump in my transom and it can double as a washdown. if it is 900 then no problem but if it is 600 im not sure it will be enough in an emergency. I really don't want to give the abandon ship order!
 

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Get the biggest pump you can fit in the space allowed. Bilge pumps NEVER pump at the rated flow. Lets say you start with a 1000GPH pump. For every foot of elevation the pump has to move the water,they lose about 20% of their rating. If your pump is in the bottom of the boat and it has to pump water to a thru-hull fitting 2' above the pump,you now have a 600GPH pump.

If you use the cheesy corrugated hose most guys use,you lose another 20% of the pumps capacity.

I have a 2000GPH AND a 1200GPH pump in my boat. Even with those two pumps,a sizeable hole in the hull will overwhelm the pumps.

1000GPH seems like alot,but thats only 16 gallons per minute.
 

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I second the notion of getting the biggest pump you can fit. Back in early october while out bm fishing I got tangled on a crab pot and took several waves of water over the back of my alumaweld. After cutting the downrigger wire and putting the boat in forward momentom it took a good 40+ minutes for the pump to run out of water to pump. I sure would have liked it to work a little faster. Even after the water has stopped comming in it is still a little nerve racking to be ankle deep. A larger bilge pump is definatly on my to upgrade list.
 

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If your Alumaweld is an inboard, you may as well go buy a new starter now. A couple of years ago I had a Duckworth inboard jet, and I forgot to close the inline T valve in the cooling system after flushing the motor the previous trip. A half hour into fishing I noticed I was standing in an inch of water and immediately turned the bilge on. It cleaned out in 10 minutes, but was very scary having that much water in the boat. To get to the point, the bilge didn't have a float switch and the starter was submerged. The starter worked for the next couple of trips and then went out while I was boondogging on the Cowlitz at Blue Creek. I got to boondog all the way to Mission Bar, and a good friend got to drive down from Puyallup to give me a ride back to my truck.
 

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What Duro said, I have two on my boat I want to bump the gph up on both of them.One is a manual the other is an auto w/o a float switch what it does is cycle on every so often to check for water, so it comes on even when there is no water present,When I sleep on the boat it annoys the shiat out of me as you can hear it cycling on and off. So I will be putting a pump w/float set up in it's place.I just sleep better knowing there is a pump ready to run if need be.
 

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Don't overlook the need for the old tried and true manual bilge pump after installing the largest electric pump. wink:
Be redundant and have a backup for any emergency. Give it to the most panic stricken member on the vessel and watch how fast a bilge will empty, even with the electrical unit running. clown:
 
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