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Random Quote: If you dont stand for something..youll fall for anything!!"
Reading another thread made me think about this. On the subject of bilge pumps. Now don't get me wrong. I have three in my boat and i always inspect them for proper operation. But are bilge pumps to keep you from sinking or just to get rid of a little unwanted water and keep the bildge dry. Lets say you have a 2000gph pump. With any amount of hose attached the volume of that pump is reduced pretty quickly. Anyway, that pump is SUPPOSED to pump 33gpm. Thats without any backpressure. SO, just how much does that pump really put out in the real world? A wave breaking over the bow will put that much water in the boat in a hurry. In a few seconds. And then here comes another one. I'm not saying bilge pumps are useless. I'm just saying that maybe some people put too much faith in these pumps that could get them into trouble.
I wouldnt have anything smaller than 3-2000 gph pumps in any boat going offshore. And then this may not be adequate. If you take a big wave over the bow or stern its going to take those pumps a while to get rid of that water. As far as the 500gph pumps. I dont know where they have any place in a offshore boat. But i guess they are better than nothing.
I could just see it now. T-nut and his buddy are fishing. Buddy, "hey T-nut, we just took a wave over the bow and here comes another one." T-nut, "dont worry sha, we have a 500gph bilge pump in this vessle. Well do just fine." And thats the end of T-nuts fishing trip. And boat
Bottom line, They may give some a false sense of security.
PBR [PowerBoat Reports] did a good write up on diffrent pump's a while ago. It had the imfo your asking about. 0 lift output and then something like 3ft lift output.
With the use of foam, one can increase the hull's swamped flotation and also reduce the size of the bilge so that even when filled, this amount of water will never put you in danger, even if the pump fails.
So I always determine pump size in terms of bilge size and recovery time. A 500 gph bilge pump is large enough for a bilge that measures 3 cubic feet, holding up to 23 gallons, or 175 lbs of water on a 19´hull IMO, as it will start to pump as she fills.
More important is the scupper size as this is a gravity flow system that is your first defense with and without power, and a length of line will not hang them up either.
Why not make them into a rectangle measuring 6" wide by 1.5" tall so that they are 10 times as efficient as what comes standard,. Two of these will drain about 300 gallons in a minute, or one 55 gallon drum of water in 10 seconds.
Using standard 3/4" hose, anything over 1000 gph is really overkill as the orfice size will limit the low head centrifugal pump performance anyway.
Diaphram pumps will create more pressure and pump more water through smaller fittings.
Water that comes over the bow shouldn't end up in the bilge because all offshore boats should be self bailing.
Of course not all self bailing boats will continue to drain water out the scuppers when you eat a large greenie because of the weight of all that water in the cockpit may lower the scuppers below the waterline. Oh well.
""Why not make them into a rectangle measuring 6" wide by 1.5" tall so that they are 10 times as efficient as what comes standard,. Two of these will drain about 300 gallons in a minute, or one 55 gallon drum of water in 10 seconds.""
If this issue is a concern (and I'm not trying to imply that it isn't) then it is imperative that outboards be dispensed with and switch to inboard engines where you can have a manual set up to use the engine intake pumps so that large amounts of water can be bailed in an emergency.
SeaJay - 6/29/2005 3:28 PMIf this issue is a concern (and I'm not trying to imply that it isn't) then it is imperative that outboards be dispensed with and switch to inboard engines where you can have a manual set up to use the engine intake pumps so that large amounts of water can be bailed in an emergency.
Actually its not a concern with me. I was just bringing it up. In the boat i have now the only bilge area is 4'X4'X20" deep. The rest of the bilge is sealed and filled with foam. If my cockpit is filled with a rouge wave i will just open the transom door. If i can?
SeaJay - 6/29/2005 3:28 PMIf this issue is a concern (and I'm not trying to imply that it isn't) then it is imperative that outboards be dispensed with and switch to inboard engines where you can have a manual set up to use the engine intake pumps so that large amounts of water can be bailed in an emergency.
Actually its not a concern with me. I was just bringing it up. In the boat i have now the only bilge area is 4'X4'X20" deep. The rest of the bilge is sealed and filled with foam. If my cockpit is filled with a rouge wave i will just open the transom door. If i can?
Quantify again
4x4x1.6x7.45 = 200 gallons x 8.36 lbs per gallon = 1772 lbs.This a lot of weight IMHO.
200gal/14 gpm = 15 minutes to pump it out, with one pump through a 3/4" hose.
I really think most fishing boats are pretty well covered for taking waves with the self bailing cockpits. Even the full transom boats, my bay boat has two 1-1/4" maybe 1-1/2" drains. I punched a wave with it, put about 6" in it, drained off pretty quickly, only water that made it to the bilge would be thru the console door (not much). Take a I/O ski/cruise boat that doesn't have self bailing.. Different story.
Bilge pumps are like doctors and lawyers, when you need one, you want a good one. Have to admit, I haven't needed it yet, and I haven't paid attention to it. I carry a spare livewell pump on board now, does that count?
a 1.5" hole below the waterline will emit 70 gallons of water a MINUTE into your boat, or 4,200 gallons an hour. If anyone is expecting your bilge pumps to keep you afloat if you punch a hole in your boat, you are nuts. Even two 2000 gph pumps won't get near close enough to keep you from taking on water very quickly. A 2000 gph pump on most of our boats, with hose bends etc, might get you 1400 gph effective, or 2800 gph. That still leaves a negative of about 1400 gallons, or 8000 plus pounds an hour....AKA sinking.
You better find it and confirm that auto float switch is operational!!! Open every deck hatch/plate/access panel. Even follow the hose back from the thru-hull fitting. Get a mirror, attach it to a yard stick and look around your bilge.
scott-hydra24 - 6/30/2005 11:31 AMa 1.5" hole below the waterline will emit 70 gallons of water a MINUTE into your boat, or 4,200 gallons an hour. If anyone is expecting your bilge pumps to keep you afloat if you punch a hole in your boat, you are nuts. Even two 2000 gph pumps won't get near close enough to keep you from taking on water very quickly. A 2000 gph pump on most of our boats, with hose bends etc, might get you 1400 gph effective, or 2800 gph. That still leaves a negative of about 1400 gallons, or 8000 plus pounds an hour....AKA sinking.
Very good point. This is all i was trying to piont out. I guess if its your day to sink no amount of bilge pumps will help.
Very good point. This is all i was trying to piont out. I guess if its your day to sink no amount of bilge pumps will help.
Everyone have a happy fourth.
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And a good point to make. We almost bought the farm a few weeks ago on a return trip from the Bahamas. The pumps worked fine and the scuppers drained nicely.
We were still 30 seconds from our first liferaft/ EPIRB deployment.
Too much faith in bilge pumps 
