Bilge Pump Installation and Maintenance Tips

Posted by Frank Lanier at 12:25AM - Comments: (9)



The low-capacity bilge pumps we tested included 10 models from Shurflo, Johnson Pumps, Rule/ITT, and Attwood.

The best bilge pump in the world won’t keep your boat dry if it’s not properly installed and maintained. While bilge pump installations are fairly straightforward—and definitely within the scope of DIY projects—there are several factors to consider (capacity, wire size, hose diameter, fuse size) before you begin, and there are some good rules of thumb to follow.

CHOOSING AN ELECTRIC PUMP

The first step is selecting the right bilge pump(s) for the job. We recommend installing two electric centrifugal pumps (preferably one with automatic water level sensor): a smaller pump mounted at the belly of the bilge to handle the incidental bilge water (rain, stuffing box drips, etc.) using minimum power and another pump mounted a few inches higher to handle bigger jobs. There are several reasons for this; the main one being that a back-up is always installed should one pump fail.

• Capacity: For most mid-sized boats (30-35 feet in length), we’d recommend a 1,000-1,500 gallon-per-hour (GPH) pump for the primary and one with a capacity of about 2,000 GPH for the backup. The American Bureau of Shipping recommends one 24-gallon-per-minute pump (roughly 1,440 GPH) plus one 12-GPM (720 GPH) pump for boats shorter than 65 feet.

When comparing output specs on multiple pumps, be sure the rating criteria are the same. New standards set by the American Boat and Yacht Council (ABYC) require that compliant makers rate pump capacities so that they reflect real-world usage. The ABYC stipulates that pumps be rated with a head height (also called vertical lift) of 1 meter and a hose length of 3 meters, and with a head height of 2 meters and hose length of 6 meters. Head height is the vertical height of the hose outlet above the pump outlet. Head pressure (also referred to as static head) is the resistance that a pump has to overcome when pumping water up and out of the boat. It includes the resistance generated by the vertical distance the pump has to move the water up (vertical lift) and any resistance generated by the discharge plumbing (hose kinks, ribbed hose, fittings, and bends). Some ratings also will be given at 13.6 volts, rather than the more realistic 12.2 volts (for a 12-volt system). The latter will more accurately reflect capacity in real-world conditions.

• Key features: An automatic pump will rely on a water-level sensor such as a float switch to activate the pump. This can be a separate unit or one that is integral to the pump. This sensor should resist fouling and be easy to test for proper operation. Common float switches should be in a housing, otherwise they are more prone to fouling by debris in the bilge. An easy-to-access strainer (or strum box) is also important, as are long wire leads, which help keep connections out of the wet bilge area.

Regina Gallant
Regina Gallant

When installing two electric pumps, the lower-capacity pump should have a built-in float switch, be mounted at the lowest point of the bilge, and be wired straight to the battery through a fuse. The higher-capacity pump is installed a few inches higher, but not directly above the smaller pump.

INSTALLATION

The illustration above shows one recommended setup for automatic bilge pump installation.

• Location: According to the ABYC, the pump inlet must be positioned so that bilge water can be removed when the boat is in a static position and when it is at maximum heel (ABYC H-22). The mounting location also should make it easy to service the pumps and to clean them, particularly their strainers.

The discharge outlet (thru-hull) must be above the maximum angle of heel so that water outside the boat is not siphoned inside the boat. According to ABYC H22, if you can’t position the discharge this way, a vented loop (installed above the heeled waterline) and a properly installed seacock must be included in the setup. (Check valves should not be used in this scenario.)

When installing two electric pumps, the lower-capacity pump should have a built-in float switch, be mounted at the lowest point of the bilge, and be wired straight to the battery through a fuse. The higher-capacity pump is installed a few inches higher, but not directly above the smaller pump. As the illustration shows, you can mount the larger pump to a piece of plywood that’s bonded to the bilge sides. It should be wired to a dedicated breaker, which can be used as a switch, or it should also be wired to a dedicated, clearly marked toggle switch.

• Plumbing: When plumbing an electric bilge pump, be sure the setup is designed to reduce head pressure as much as possible to maximize discharge capacity: use smooth hose sized to meet maker recommendations; keep hose runs as short as possible; and try to avoid bends, turns, and elbow fittings in the run. In terms of adding resistance, using a 90-degree bend in a 1-inch-diameter discharge hose is the equivalent of adding 3 feet of hose to the line, which is like a 3,000 GPH pump being reduced to a 2,000 GPH pump, if the battery is fully charged. According to pump maker ITT/Rule, small electric submersible pumps are rarely useful with more than 4 feet of vertical discharge head and medium/large submersibles are similarly ineffective with more than 7 feet of head.

The discharge line should rise steadily to the through-hull or loop. If there are any low spots in the run, water will pool there once the pump cycles off. This can create an airlock when the pump is activated again, and the pump likely will stall. Hose connections, as recommended by the ABYC, should be made with non-corrosive clamps and should be airtight.

• Wiring: Use correct size wire and fuses: The proper wire size reduces voltage drop and properly fused wiring reduces risk of a locked rotor (a motor that’s trying to turn, but can’t) causing an overcurrent situation and potential fire hazard.

Consult the American Wire Gauge 3% voltage drop table (www.marinco.com/page/three-percent-voltage) to be sure you’re using large enough wire. Remember that the run length given in wire-gauge tables is the sum of the positive and negative legs of the circuit; a pump 10 feet from the battery will be referenced as having a 20-foot wire run.

For the fuse size, simply go by the pump maker’s recommendation, and you should be set. The fuse, per ABYC standards, should be installed within 7 inches of the power source.

If the pump’s leads are too short, extend them carefully. Use oversized tinned marine wire and adhesive heat-shrink connections. ABYC standards recommend using a length of water-resistant electrical cable, sealed at the pump connection, so all electrical connections can be made above the max bilge water level.

• Accessories: A few accessories to consider adding to the bilge pump system include a visual/audible bilge alarm, bilge switch, and a cycle counter. ABYC standards require an alarm on boats with enclosed berths. Be sure that the alarm is loud enough to be heard over engine noise while underway and ideally by passersby or marina personnel when docked.

Automatic pumps should always be fitted with a readily accessible and clearly marked manual switch so that even if the owner isn’t around, anyone (crew, marina neighbors, or passersby) can locate and activate the switch when the need arises. Switches also should offer visual indication that the pump has power supplied to it. Our top pick for mercury-free bilge switches, reviewed in the January 2006 issue, is the electronic Water Witch 230.

If the larger-capacity pump has a float switch, we highly recommend connecting it to a bilge alarm (and alarm cut-off switch). That way, hopefully, the horn will get someone’s attention before the constant cycling of the pump drains your batteries. We reviewed the Aqua Vigil Alarm in the May 15, 2001 issue, and deemed it “simple but quirky.” We plan to revisit bilge alarms and cycle counters, including combo units like the Aqua Alarm pump monitor, alarm, and counter.

Two good references on bilge pumps and installing them are “This Old Boat” by Don Casey and Nigel Calder’s “Boatowner’s Mechanical and Electrical Manual.”

MAINTENANCE

Regular and frequent inspections of your bilge pumps are a must and should be included in the vessel’s overall preventative maintenance program. This helps you know when to replace worn or damaged components (bad float switches, deteriorated  hoses) before they fail. Before you set sail, it’s always a good idea to make sure the pump has power and is working properly, keeping in mind that testing should verify the actual pumping of water overboard, rather than (in the case of electric pumps) simply switching the pump on and listening for motor operation.

Keeping your bilge clean can be a hassle, but it doesn’t compare to the headache of a locked rotor or an impotent bilge pump in an emergency. 

For more details on specific pumps, check out our most recent tests of high capacity bilge pumps of greater than 1,500 GPH, and and smaller pumps rated at 1,500 GPH.

For more comprehensive guidance in carrying out an upgrade of your boat’s essential systems, check out our 5-volume ebook series on Marine Electrical Systems at http://www.practical-sailor.com/books.

Capt. Frank Lanier is a long time PS contributor and an accredited marine surveyor with over 30 years of experience in the marine industry. His website is www.captfklanier.com.

Comments (9)

I recently had to replace the "sump pump" in a rental house and began to think about the use of one of these for a bilge pump. They are relatively inexpensive compared to marine pumps and move a lot of water very quickly...and I might add, they move it vertically. Of course they are 120V so they would only be good for those boats with an inverter and your engine would have to be running. They are not designed for marine use and ABYC would never approve, of course...but I'm just thinking of it as your last ditch effort to stay afloat.

~ ~ _/) ~ ~ Mike

Posted by: MJH | December 1, 2017 1:36 PM    Report this comment

Some of my C34 colleagues have had success with the backflow issue by installing a vented loop in the discharge hose under the galley sink.

Posted by: Ejs | December 1, 2017 12:06 PM    Report this comment

I had a bilge pump failure that was traced back to the Rule Float Switch. Ends up that Rule makes several float switches that appear extremely similar (virtually identical) but have extremely different costs. One of my switches (the one that failed) was a lower cost switch that had very small wires (approx. 18 gauge) and what failed was the wire ROTTED OUT near the switch ( only 5 years old). I replaced it with their more expensive switch that had much heavier wire (approx. 12 gauge). In almost 30 years of sailboat ownership - this was the only such failure I encountered. Moral of the story - you get what you pay for.

Posted by: aschoenberg | December 1, 2017 5:20 AM    Report this comment

I had a bilge pump failure that was traced back to the Rule Float Switch. Ends up that Rule makes several float switches that appear extremely similar (virtually identical) but have extremely different costs. One of my switches (the one that failed) was a lower cost switch that had very small wires (approx. 18 gauge) and what failed was the wire ROTTED OUT near the switch ( only 5 years old). I replaced it with their more expensive switch that had much heavier wire (approx. 12 gauge). In almost 30 years of sailboat ownership - this was the only such failure I encountered. Moral of the story - you get what you pay for.

Posted by: aschoenberg | December 1, 2017 5:19 AM    Report this comment

Serious offshore cruisers need beefy pumps with backups. Rule 3500 GPH are the standard with 10,000 hour run time. Anything less are toy pumps used for showers.
Then add several 5000 GPH 110 heavy duty pumps with lots of portable hose. Several commercial bilge alarms. Plus an emergency gas driven Honda trash pump rated at 5 to 10,000 GPH. Total cost about $2500 for all the above. Will keep you afloat. It's the "package" used by commercial fish boats the world over. The task is to stay afloat under all conditions. That means being able to move huge amounts of water to effect repairs.
Total cost is about the same as a life raft. We speak from some experience.

Peter I Berman
Nowalk, CT

Author: "Outfitting the Offshore Cruising Sailboat" ParCay Pub.

Posted by: Piberman | November 30, 2017 2:21 PM    Report this comment

Since most sailboat have deep narrow bilges why do most pumps have a discharge parallel to the sole which usually requires a 90 degree bend immediately after discharge port?

All of the pumps pictured above have this design.

Would it not be better if the pump came with another fitting (even at extra cost) that created slow, smooth transition to vertical?

Posted by: Jack Buba | November 30, 2017 2:05 PM    Report this comment

I have the same issue as MJH and JDS with a tall narrow bilge and a hose run that's long enough that the backflow will re-trigger a traditional float switch indefinitely. Don't install a check valve though. Instead install a float switch with a time delay like the Water Witch or Whale BE9006. Place the float switch a little higher relative to the pump than you normally would. On my boat putting the switch at the height of the middle of the pump body works well. When the float switch triggers it will keep the pump on for an additional 8-30 seconds after the water drops below the switch. So it continues to reduce the water level in the bilge. When the pump shuts off and the water in the hose flows back into the bilge it shouldn't be nearly high enough to re-trigger the bilge pump.

Posted by: toro | November 30, 2017 12:30 PM    Report this comment

I have the same problem as MJH, very deep bilge with long exhaust hose run. When tied to dock during a blow and I'm not there the pump might cycle 6-700 times, I have a counter in the pump wiring system. Tired of playing with switch elevation in bilge and going to install a check valve and accept the risk of clogging and failure. I do have a large backup pump on a switch for emergency, j

Posted by: JDS | November 30, 2017 11:01 AM    Report this comment

When I replaced my bilge pumps a few years ago (Rule 3700 and Rule-Mate 750) I followed the Bible and didn't put in check valves. I soon discovered that due to the very deep bilge of my boat and necessary hose length (6-7') from bilge to vented loop, the backflow carried enough water to cause the Rule-Mate 750 automated pump to cycle even with the small 3/4" hose. So, take the hose length backflow for your system into consideration. Also, the best orientation of your float switch should be along the longitudinal line of the boat with the movable part aft so that healing and forward thrust doesn't adversely affect it. This can be problematic to achieve with engine, transmission, and shaft along that same longitudinal line requiring some forethought.

~ ~ _/) ~ ~ MJH

Posted by: MJH | November 29, 2017 1:27 PM    Report this comment

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