Re: 18' open bow bilge pump total capacity
After almost losing my 22' open bow boat due to the shift cable bellows pulling loose, I went to 2 totally redundent automatic pumps on separate electrical systems and batteries (the original 750 GPH and an additional 1500 GPH). They are also both wired to a manual switch. Doesn't take much of a leak to put you on the bottom if you're not aware of it. I've personally seen 2 boats sunk because the drain plug was left out and the owner tied the boat to the dock and walked away for a few minutes. Nobody was in them, so nobody realized they were sinking until they disappeared under the water!
My shift cable bellows and outdrive bellows had been replaced 2 weeks previously and I had watched carefully for leaks on the 2 previous outings. The boat stayed perfectly dry, no water at all. After being on the water for several hours on the 3rd outing I was luckily sitting on the dock and heard it when the automatic bilge pump came on. Good thing that the 4 year old (never maintained!!) original automatic pump worked. If it hadn't I wouldn't have known the boat was filling with water until it disappeared! Turned out the shift cable bellows had pulled loose. If the automatic pump hadn't worked the boat would have been on the bottom of the lake.
Bilge pumps are cheap compared to getting your boat back off the bottom. You can get a big automatic pump for well less than $100. I plan to replace my original 750 GPH pump with another 1500 GPH pump this spring.
A 1 inch hole will let in about 25 gallons/min, which is 1500 gallons/hour. Water weighs about 8 lbs/gallon. So if your boat is rated for 1600 pounds, around 200 gallons of water will probably sink it. That's less than 10 minutes with that 1 inch hole. And the smaller your boat is, the quicker it will sink if the water starts coming in!
The recommendations below are from a David Pascoe article (
http://www.yachtsurvey.com/bilge_pumps.htm)
Boat Length___No. Pumps__Total Capacity - GPH
16 - 20 _________2_________2500
21 - 26 _________2_________3000 - 3500
27 - 35 _________3_________3500 - 4500
36 - 42 _________3_________6000
43 - 49 _________3 - 4______8000
50 - 59 _________4 - 5______9000 - 10,000
60 - 60 _________4 - 5______10,000+
There are two factors which must be considered, the capacity of pumps and the number of pumps. The number of pumps is important from the stand point that bilge pumps are not reliable because they are electrical devices submerged in water. Contrary to common belief, the pumps themselves rarely fail; its the electrical system from which they operate that is usually the cause of the failure. Because of this, one way to improve reliability is with redundancy, or increasing the number of pumps to decrease the odds of complete loss of pumping ability.
