Bilge Pump: Unsunk Heroes of Boating Equipment

WARNING: Bilge pumps, both electric and manual, are NOT designed to keep a leaking boat from sinking. Their ultimate value in emergency situations is in the precious time they buy boaters in identifying, slowing the leak, and returning to a safe harbor where a permanent fix can be made. Please do not rely on a bilge pump to keep your boat afloat long-term if it has a known leak.

Who needs a bilge pump?

A better question may be, who doesn’t? Any boat that is stored in the water should be equipped with a bilge pump and a means to power it consistently while the boat is unattended. There is no feeling quite so sinking as returning to your boat on a mooring to find its waterline has disappeared and there’s knee-deep water in the cabin.

Where should the bilge pump be located?

The bilge pump should be installed in a fixed location at the lowest point in the bilge, where all the water will accumulate. For larger boats, several bilge pumps may be required for all compartments capable of collecting water. If you’re unsure about whether other compartments in your boat require pumps, take a look:

• Do the walls between them have limber holes at the bottom for drainage or are they watertight?
• Does your boat have a shallow bilge from bow to stern?
• Is your boat a powerboat that will drain toward the stern when it’s operating at speed?

Knowing about your boat’s drainage system and bilge layout before starting your bilge pump shopping will save you time, headaches, and surprises. (Like when your shower sump pump quits working and you find two inches of water in the bow section of your boat…)

There are two common types of bilge pumps for recreational and small-medium-sized commercial vessels: diaphragm and centrifugal.

A diaphragm pump has two internal rubber membranes in the pump housing connected by a shaft that moves back and forth when power is applied to the pump. The one side of the membrane when pulled to the center of the body creates suction which allows water into the pump body via the intake side. When the shaft moves the membrane back into place, the water then shifts to the discharge side of the pump and forces it out the other side with the second membrane as more water is sucked in the intake side.

Some of the benefits of using a diaphragm pump for removal of nuisance water:

• They are self-priming, meaning they do not need to be submerged in a liquid in order to operate— they can be run “dry.”
• They can be remotely mounted— making them ideal for tighter bilge spaces where the body of the pump can not fit and for ease of installation and maintenance.

Some drawbacks of an electric diaphragm pump for a bilge pump are that their intake is typically a small-diameter hose which is run to the lowest point in the bilge. Its capacity is much lower than an electric centrifugal pump and its manual diaphragm pump counterparts, averaging closer to 3-5 gallons per minute (GPM) compared with a manual diaphragm pump’s 28 GPM. These types of pumps are better used for the complete removal of water in the bilge after the primary bilge pump has done its work and a small bit of water still remains.

Manual diaphragm pumps are the recommended option for backup emergency dewatering on vessels that make coastal and offshore passages.

For the purposes of this article and product review, we focused on specifically electric centrifugal bilge pumps designed for 12 volt battery systems.

Centrifugal pumps operate with a motor powered by a 12 Volt battery, which spins a rigid impeller (typically made of hard plastic) creating suction and lift. The liquid is essentially pulled up into the body of the pump and sent out the discharge end of the pump through a hose that is led overboard and above the boat’s waterline.

These pumps are submersible and while most are not self-priming, some can be run dry for short periods.

What size bilge pump do you need for your boat?

Bilge pump sizes are rated by the pump’s maximum discharge capacity— how much water they can pump, usually given in gallons per hour (GPH) or liters per hour (LPH). Manufacturers measure this number with the pump being supplied by a full battery (13.6V) and at the pump’s immediate discharge location. This assumes there is no distance and no vertical lift that the pump is required to move the bilge water. This distance is also called head height.

Since the pump will rarely be operating in such ideal conditions, it’s best to look at the pump’s capacity and know that in reality it will be somewhat less than advertised.

While there are no regulations governing the size of bilge pumps required for recreational boats of varying sizes, there are some recommendations. Given that the purpose of the bilge pump is to buy time and keep the boat’s stability intact, bigger is better.

Generally speaking, opt for a pump with a capacity of AT LEAST 1,000 GPH or greater. Keep in mind that these systems aren’t JUST being used for draining the rainwater out of your skiff boat while it’s in the trailer in your back yard and when deciding on what bilge equipment you’re installing, the cost is less of a concern.

How many bilge pumps do you need?

As the saying goes, “two is one and one is none.” There are huge benefits to having redundancy in any system you have on a boat you plan to do any serious traveling in, but the bilge system is one that should NOT be overlooked.

A good setup to consider is this:

• Have a smaller capacity pump at the lowest point in the bilge. This one’s task will be to take care of the normal nuisance water. It has a low power draw and moves a decent amount of water.
• Have a second large capacity pump for emergencies, mounted higher in the bilge, but low enough to kick in before the rising water can damage any critical equipment (such as engine starters, and battery banks) While this pump will draw much more power, the idea is that in an emergency you will start the engine which will charge your batteries to keep that pump going.

Bilge Pump Safety and Environmental Compliance Accessories

Many bilge pumps often come as “non-automatic,” meaning they would need to be manually activated whenever there is water in the bilge. To ensure your bilge pump is removing water when you are not present to manually activate the pump, the following bilge system add-ons are needed:

• An external float switch
• A three-way rocker or toggle switch
• An external audible/visual high water bilge alarm (this is required for any boats with an enclosed cabin if your boat is kept to American Boat and Yacht Council or ABYC standards)
• Inline filtration system to the discharge line from your bilge pump to filter out any oil or petrol products that have accidentally found their way into the bilge. (It is against the law to discharge oil into the water) These filtration systems will reduce your bilge pumps output capacity.

Rule 33ALA – Marine High Water Bilge Alarm

SEACHOICE 19401 Universal Series Bilge Pump Automatic Marine Float Switch

Installing an electric bilge pump

Installing an electric bilge pump can seem like an intimidating task, but in reality, it’s quite simple. In fact, often the most difficult part (depending on the style of the boat) is gaining access to the space in which you will be mounting the pump. But, with a little determination and planning, installing a bilge pump yourself is well within the scope of even newbie boat project DIY-ers.

Materials you will need:

• Your new bilge pump, external float switch, and rocker switch (if your pump model does not already have an internal float switch)
• 14-AWG marine-grade tinned copper wire. Red and black wire insulation is the standard color code for your negative and positive wire leads, so it’s best to go with these colors. Making sure the wire you select is tinned copper is important because it has a greater resistance to the corrosion experienced in harsh environments–like your bilge.
• A wire terminal bar. This is for connecting the float switch to the pump itself, and then to the power source. When the float is lifted by collecting water, it closes the circuit between the power source and the pump, letting it know that it’s time to work.
  You could also splice the connections using your butt connectors, but the terminal bar makes it easy to remove and clean the pump when necessary, without cutting and reconnecting wires.
• Heat shrink butt connectors. These go hand-in-hand with the above in sealing out the elements from your electrical wire connections and preserving the internal wires so they keep the electrical current flowing. It’s not a perfect system but will help in prolonging the life of your wires. Extra credit to those who use a covered terminal box in addition to heat shrink connections. When it comes to getting to the electrical connections, accurately measure the path from your pump to the batteries to ensure you have enough cable to reduce the number of connections required. When in doubt, a cable that is too long is better than too short.
• Smooth hose of the same diameter as your pump’s discharge port. This hose should be reinforced (non-collapsible) and non-ribbed. Ribbed hose increases the resistance the pump experiences when moving the liquid from the bilge out to the overboard discharge location–all factors to consider when installing a pump to ensure you maximize its efficiency and lifespan.

• Stainless steel hose clamps. These clamps should be in the size range of your hose diameter, and while stainless steel is more expensive, it is recommended for saltwater applications as it will again be more resistant to corrosion.
• 12V battery or battery bank.

How to Install a Bilge Pump

The following step-by-step instructions for setting up and installing a bilge pump is for an electric model with a float and rocker switch. While it can be easily done when following these instructions, it might also seem overwhelming.

When confronted with the option of having a bilge pump or waiting, a quick version of directly connecting a bilge pump with a built-in float switch to the battery is doable. Some of the bilge pumps in this list include the pump, the float as well as the necessary wires to hook up to a battery.

But for best, long terms results follow these steps.

STEP 1. Determine your bilge pump’s mounting position. Again, this should be at a low point in the bilge where water will collect, and for larger vessels, any compartment where water is likely to collect.

When mounting, the suction end of the pump should be mounted so that the majority of its face is accessible to nuisance water at different angles of the vessel heel (i.e. the pump should be mounted upright, near the boat’s centerline so it is effective even as the boat is in motion).

The float switch should be mounted in a nearby location and at a height equal to the pump suction where it will be activated by accumulating water, but not allow the pump to run dry.

STEP 2. Determine and measure the path from the pump location to the point of discharge and run the length of the hose from the discharge point to the pump before cutting the hose to that length. This path should be as direct as possible, avoiding excessive and sharp angle turns where possible, as this reduces the pump’s efficiency. Attach the hose to pump discharge using the hose clamps. Attach the hose to the discharge through-hull fitting using the hose clamps. ( NOTE: This bilge pump installation guide assumes the replacement of a previous pump system and the presence of an existing discharge through-hull.

Ensure you have the correct hose diameter. It is recommended that any creation of a new through-hull be conducted or inspected by a professional. A new through-hull for the purpose of bilge water discharge should be at a sufficient height above the waterline so as to prevent seawater from back flowing into the hose)

STEP 3. Wiring the pump to batteries.
While your boat may be equipped with a breaker panel that can be isolated from the battery bank, it is recommended to wire your bilge pump directly to the battery via a separate switch. This allows your bilge pump to maintain a power supply when the boat is left unattended for longer periods of time with the breaker panel and all its consumers in the “OFF” position. The peace of mind this affords is priceless.

Blue Sea Systems 300 Amp m-Series Battery Switches

Most bilge pumps are equipped with about 2 feet of wire already attached. For many vessels that would require an electric bilge pump, this length of wire is not enough to reach your batteries or circuit breaker from the bilge.

Determine where you will be mounting your rocker switch. Measure the distance for the run of your electrical wire from the pump to the rocker switch, and the rocker switch to the battery.

Ensure you have the appropriate gauge of wire for the job. Too small a wire size creates resistance and reduces the efficiency of your pump. 14-AWG wire should be sufficient for this purpose if the distance between the battery and the pump is no more than 20 feet.

BNTECHGO 14 Gauge Silicone Wire Spool red and Black Each 25ft Flexible 14 AWG Stranded Copper Wire

Connect the wires from the bilge pump to the wire terminal bar. The positive wires from both the float switch and the pump itself should be connected to the terminal with the outgoing positive (+) wire leading back to the positive (+) on the rocker switch, which is also led to the fuse on the circuit breaker and then to the positive (+) on the battery terminal itself.

An audible/visual alarm can be spliced into the positive (+) wires before the toggle switch to give boaters a “heads up” any time the bilge pump is running.

The negative (-) on the pump and the float switch should then be led to the negative (-) on the rocker switch and the battery and then grounded to the engine block.

Most modern toggle switches will come with a fuse included. If not, a fuse should be placed between the battery’s positive (+) terminal and the positive (+) wire leading to the pump. This way, if the pump is malfunctioning and drawing more amperes (amps) than the fuse is rated for, the fuse will blow, opening the circuit and preventing further damage or a fire hazard.

For appropriate fuze sizes, follow the pump manufacturer’s guidelines and you’re golden.

General Maintenance Practices and Pre-Departure Checks

“An ounce of prevention is worth a pound of cure” -Benjamin Franklin

Frequently checking the bilge daily (if cruising) is a good habit for any boater to practice. Knowing what’s going on below the deck plates can alert you to situations that have the potential to become a serious problem later on.

After installation and every time before leaving port, test your bilge pump and float switch.

• Check the pump in “manual” using the rocker switch.
• Set the bilge pump switch to “AUTO.”
• Check your float switch lifting the float switch with your finger, or a dowel or screwdriver if your float switch is out of arm’s length. Ensure that the pump comes on when the switch is in the lifted position. Ensure that it turns off with the float switch in the down position. Have someone look overboard to make sure there is actually water being discharged.

Most bilges are dingy, dirty places, and things like paint chips, hair, food crumbs, sunscreen and other debris can all make their way down there and have the potential to clog or significantly reduce your pump’s capacity. Make sure clean cleaning your pump’s inlet and strainer is a part of your routine maintenance schedule, as well as cleaning your bilge. Adding a strainer basket around your pump to supplement the built-in strainer is a good way to help prevent debris from getting caught in the pump’s impeller.

Routinely haul your boat out of the water and look at the hull. Check all your through-hull fittings and replace them when necessary.

Check and replace as necessary all hoses leading to and from the hull. This includes the engine exhaust—if that guy springs a leak, you’ll be literally pumping hot seawater into your boat.

Remember, you don’t get what you expect, you get what you INSPECT!

FAQ – Frequently asked questions about Bilge Pumps