Boat Bilge Pump, Right Size It

[Electronics Guru]

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Our 25' Contender test boat came from the factory with only one bilge pump. And even though a bilge pump is not marine electronics per se it is still an extremely important piece of marine electrical gear that we cover in our reports.



After much research we determined this single pump approach was inadequate for a boat of this size and use.

The Contender bilge is a single compartment and the original pump was properly located just forward of the transom.

Still, with mostly offshore usage in mind and large diameter through-hull fittings to service the boat's in-deck bait tank the need for more pumping capacity was indicated.

To remedy the inadequate pumping capacity we elected to replace the original bilge pump and add a second.

The additional pump provides a backup pump and increased capacity in the event of a single pump failure or emergency.
Testing Bilge Pump Capacity

This reevaluation of our test boat led us to run a full review of bilge pumps currently on the market. First, we devised a test procedure, then we divided the pumps into groups based on their advertised capacity.

Test results let us pick the best pair of pumps for our Contender. We planned for a total installed pumping capacity in the 2000 to 3000 gallons per hour range. Adding a second pump required fitting another pump outlet, in addition to the one already installed.

We finally settled on a total capacity figure of 3000 GPH based on the size of the seacocks installed in the boat. If one happened to break clean off and start flooding the bilge with water, the two pumps together should be big enough to keep up with the incoming water long enough to give us time to find the hole and plug the leak.

A smaller main pump backed up by a larger secondary pump minimizes our everyday electrical power usage yet yielded our desired combined GPH rating.
Bigger Boat, Bigger Pumps

In a larger vessel with bulkheaded compartments, each separate area should have both a primary and backup pump installed.

Any retrofit or replacement pumps must be properly sized for both the vessel and the bilge compartment they will drain.

Power consumption, GPH rating, outlet pipe diameter, and physical pump size must all be taken into consideration when selecting a pump.

[jawz12]

let me add to this a little:


additional bilge pumps,excellent idea-never seen a contender with one bilge pump ??
anyway,it's good practice to seperate the power source to the bilge pumps,2 batteries,2 pumps-this way,in the event of a dead battery,you still have a hot pump.the addition of a "high bilge water" alarm is priceless.in my opinion,every boat that runs offshore should have a high water alarm on it...also,every boat should carry tapered hard wood plugs in various sizes to fit the thru hulls-in the even a thru hull is broken off,hammer a plug in...while on thru hulls,if you have nylon thru hulls,you really need to repalce them with either bronze,stainless steel,or marelon-the nylon can and will break at the most inopportune time...
and for saftey sake,the batteries on your boat,they should be seperated and electrically isolated from each other...

last point,bilge pumps:
do not believe a 2000gph pump will pump 2000gph thru a hose-this is called a "head",these pumps are tested using no head...use only smooth wall "sanitation" hose for bilge outlet,do not use the cheap corrogated bilge hose,it becomes brittle and it will break,anything that's not smooth will impede water flow-common sense...be sure the connections are done with heat shrink waterproof connections only,anything else will fail in short order...

[Storm]

This all sounds so complicated. I simply installed two 3800 gpm Rule pumps in the boat - one with a float switch and alarm. Alarm switch on the secondary pump is slightly higher than the primary pump float switch.

Then there's two smaller pumps in the aft lazarette.

In the event the four pumps quit, I installed a "Tee" fitting and ball valve on my Rule 3800 gpm general purpose pump (lobster tank drain pump).

In the event the five pumps quit, I have a Tee, ball valve, hose, and strainer plumbed to the sea cock intake for the lobster tank pump (2" hydraulic Pacer pump).

If all else fails, I can pump directly through the engine intake.

If the five electric pumps, hydraulic Pacer pump, and engine intake can't keep up, I keep a couple spare pumps onboard as well as a 12 volt power pack (battery jumper pack).

The steering lazarette is watertight and I keep an assortment of wooden plugs on standby in the event the driveshaft falls out, etc. My main concern is the wet exhaust outlet. If that goes, I'm chum.

[JD5652]

Originally Posted by jawz12

ch other...

last point,bilge pumps:
do not believe a 2000gph pump will pump 2000gph thru a hose-this is called a "head",these pumps are tested using no head....

This is a great point.....attached is a independent test report on the most widely available bilge pumps....also attached is actual data and how they faired with rating versus actual pumping capacity....