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Installing a Bilge Pump

A deep keel sump makes things difficult

by Jim Hebert,

The Problem

When Voyager III was first delivered, the only bilge pump aboard was a manually operated pump, located in the cockpit. Since the boat is an internal-ballast/keel design, there aren't any keel bolts to leak, and, if hull integrity is maintained, there should not be much water coming aboard, save for the dripping from the prop shaft. Of course, even a slow drip from a prop shaft can accumulate considerable water over time.

The keel sump in Voyager III is quite deep, extending four feet below the cabin sole, and about five feet below the waterline. This is a nice feature. Any water that does come aboard is contained in this deep sump, and it doesn't slosh around the cabin--at least not until you've collected many, many gallons of it in the sump.

Early in her career with the Voyager Sailing Program Voyager III had an electric bilge pump installed deep in her keep sump. Well, I should put quotes around the word "installed", because all that was really done was to lower a small submersible pump into the keel sump, where it was left loose to bang and slosh around with the bilge water.

The pump was a centrifugal-type pump, with an enormous rating for output in terms of gallons-per-hour. I never could understand how that little pump was going to push all that water up through the 0.75-inch-ID outlet hose fitting. It would clear the keel sump, but it would take a minute or two to pump a gallon or so of water out. Since the pump was loose in the keel sump, it could land upside down--it frequently did--which meant that it would leave six inches of water in the sump after its intake was exposed. So it would never really get the sump dry.

The submersible did have a few things going for it, however, namely:

  1. cheap
  2. easy to "drop" in place
  3. very low power drain
  4. quiet operation
  5. actually did pump water out from the sump.

It did the job for about ten years, but finally gave up in 1996. I suspect that reason no. 4 (quiet operation) is what did it in. The pump made so little noise that you could barely tell it was running, so it was very common to leave it on. You'd come aboard, clear the bilge of water with the pump, start the engine--making enough noise that the pump was totally inaudible now--and leave the pump running for hours, until you finally shut the engine off and heard the pump running dry. Ten years of that type of abuse ultimately killed the thing, not to mention ten years of being submerged in oily bilge water.

When the pump died, the boat was up in the North Channel on charter. A new pump was purchased and taken up by the next charterer, and when "installed" (note the quotes this time), it proved the equal of the original, with the exception of item no. 5. This pump would not actually pump water out of the sump. Oh, it ran and made a try at it, but the buyer of the pump had overlooked one critical specification: HEAD capacity. He'd purchased a pump that claimed a zillion gallons per hour of output, but only if the path was all downhill from the pump. In Voyager III , the submersible pump has to lift its output water almost seven feet. There's the five or so feet to get out of the bilge sump itself, then a couple of feet more to come up to the cockpit deck level and join the cockpit scupper lines to exhaust the water overboard. Seven feet of head on the pump was way more than it could manage. About all the pump could do was maintain water in the first five feet of output line, but it could not quite pump the last couple of feet to get it out of the boat. To make matters worse, the pump exhausted into corrugated flexible hose, whose inside was filled with hundreds of little ridges from the corrugation, making resistance to flow higher.

Better Bilge Pump

I'd been wanting to install a real bilge pump on Voyager III for a long time. Now was my chance! I'd never liked the submersible pump for one simple reason: it seemed wrong to put an electrical motor under water to operate. There was not a compelling reason to submerge the pump, and most things-electrical would prefer to operate high and dry, not underwater. The new bilge pump would be one of those big, ugly, noisy, diaphragm pumps that could mount in the cockpit locker, well above the oily water of the bilge sump. When you think about it, every one of those attributes is an advantage:

Advantage of Diaphragm Type Bilge Pumps


It would be nice if the best solution was also the cheapest. This is seldom achieved, especially if the word "marine" is involved. So it is with bilge pumps. The "cheap" factor is not an option with the diaphragm-type pump. It is more expensive, by quite a bit. The parts for my install ran about $250, as follows:


Installing the new pump was pretty straightforward. The worse part of the job was cleaning out the cockpit locker so I could get down below to work. When finally emptied of all their junk, cockpit lockers always seem to have a bottom layer of perpetual dirt. The whole locker had to be swabbed down before I could crawl in to work.

I wish I had a very tall but skinny assistant. Working below is not a picnic for me, as I am not as svelte as I used to be. Fortunately, Voyager III has a beautifully large locker that I can sit in. The ideal spot for mounting the new pump was right behind the fuel tank, on a nice plywood platform that used to house the old electric water heater, since removed. Using a battery-powered drill to make pilot holes, and then switching to a phillip-screwdriver bit to drive the stainless-steel pan-head screws, it was easy to mount the pump to the plywood. After this pre-mounting, the pump was then unfastened to make the wiring and plumbing installation easier. Having all the holes pre-drilled and screws pre-set made the final mounting easier.

The wires for powering the old bilge pump in the keel sump were, amazingly, just long enough to reach the new pump, so there was no additional fuss in the electrical end of the installation. One thing that threw me was a lack of polarity shown on the motor leads. They were both black and unmarked. I looked at the pump's reciprocating design and concluded that the pump part could not tell which way the motor was running, anyways. The motor just actuates an arm up-and-down, and the pump transforms that mechanical motion into pumping of water from intake to exhaust fitting. So, as far as I could tell, polarity did not matter. I tested it once, before making the connections final, just to be sure that it pumped out, not in! Here, again, the new installation seemed much better because these electrical splices from the breaker panel wires to the motor wires were being made above water, whereas in the old submersible design, they were often under water (when a lot water was in the sump).

The plumbing was very simple. The hose was easily cut (perhaps a little too easily!) by a "gingsu" knife from the galley, and the Slip-On hose fittings were simple to work with. A hose clamp was installed at each connection to secure everything. And, with my luck running strong, the 3/4-inch-ID hose was the same as used previously when joining the cockpit scupper exhaust lines, so no additional fittings were needed to adapt the new pump discharge line to the overboard exhaust. Sadly, that whole part of the plumbing is a little "Rube Goldberg", and it needs some attention--maybe next spring.

The intake line is held in place in the sump by the weight of the bronze strainer fitting, which--if you cut the hose to the right length-- lies right on the bottom of the keel sump. The fitting has a coarse strainer built in, allowing material to pass through 1/4-inch-diameter holes on the way to the pump. A second strainer is mounted ahead of the pump, this one with a screen that prevents material larger than about 1/16-inch from getting to the pump. This strainer is mounted to a bulkhead alongside the engine, and it is accessible from the cabin's quarter berth. It can be inspected and cleared without special tools by unscrewing the see-thru cover. (Don't loose the gasket!).


With everything installed, it was time to test the new pump. A peek in the bilge showed some water above the stainer's intake. When the circuit breaker panel supplied power to the pump, water immediately was drawn up the intake line to the pump. Once the pump was primed, the water began exploding out the overboard drain! The bilge was cleared of water in a matter of seconds! It was so fun to watch that I got a couple of buckets of lake water and poured them into the bilge, just to have some more liquid to pump overboard. The performance was vastly better than the old pump, even though the rated capacity of this pump was lower. JABSCO only claimed 8-gallons-per-minute, or 480-gallons-per-hour(GPH), compared with the old pump's rating of almost 1,000 GPH. What was the difference?


When a pump is rated for discharge volume, there are two important factors to consider: lift and head. They affect the rated discharge quite a bit.

Lift is the height that the pump must raise its intake water. In the case of the old submersible pump, lift was about zero, as the pump was in the water it was trying to move and depended on gravity to feed the water to it. With the new diaphragm-type pump, the lift was about five feet, the vertical distance the pump was located above the intake strainer. The pump must prime itself by sucking the water up its intake hose.

Head is the height the pump must raise its discharge water. In the case of the old submersible, this was about seven feet. This large head was the cause of the poor performance of the pump. The larger the head, the less output volume the submersible pump was capable of producing. At some point, the pump was not able to lift the water completely out of the boat, and it ceased to be a bilge bump. The new diaphragm-type pump has less than two feet of head, that is, it only has to pump the water about 18-inches vertically from the pump to get it out of the boat. It has no problem doing that, and the water comes out the cockpit drain in high pressure bursts as the pump cycles between intake and discharge.

For every type of pump, there will be a certain amount of lift and head involved in a particular installation. The actual volume of water a pump will produce in a particular installation will be affected by these dimension. Another consideration is the combined lift and head. The JABSCO diaphragm bilge pump is rated for a maximum lift of 10-feet and a maximum head of 10-feet, but only a combined lift and head of 15-feet. There is always some derating of output volume as lift or head increase.

A Dry Bilge is a Good Bilge

With the new installation finished, the bilge is really dried out in a hurry when the pump is run. I was very satisfied with the pump output, and it seems to be built like a battleship. It's covered by a one-year warranty, and replacement kits are available for the drive belt, rubber gaskets, and other moving parts. Now if I can get the packing nut on the prop shaft adjusted just right, there won't be any water in the bilge...but that's another story.


                           Diaphragm Design Allows Dry Running
                           Quiet Operation
                           Built-In Hydraulic Pulsation Damper
                           Permanently Lubricated Ball-Bearings on Shaft and Connecting Rod
                           Large Vibration Absorbing Pads
                           Corrosive Resistant Materials Throughout for Sea Water Service
                           Meets USCG Electrical Specifications
Open Flow..................8.0 GPM
Vert. Dry Suction Lift.....10 feet (3.0 m)
Ports......................3/4-inch Slip-On Hose
Weight.....................11 lbs.
Power (by Model)...........12 Vdc: 11 Amp
                           24 Vdc: 5.5 Amp
                           32 Vdc: 4.0 Amp                           
                           115 Vac; 1.0 Amp

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Copyright © 1997 - 1999 by James W. Hebert.

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