Bilge Pumps

If you’re a boat owner, you know how important it is to keep your vessel in top condition. One of the most crucial components of any boat is the bilge pump. This device plays a vital role in keeping your boat afloat by removing excess water from the bilge area. Without a functioning bilge pump, your boat could be at risk of sinking.

It’s important to note that the bilge pump fitted to your boat was never designed to keep you afloat in the event of a collision and a large hole in the hull, rather its purpose is to deal with nuisance water from rain, spray and a small leak. You may well want to beef up your bilge pumping system to cope with a more significant volume of water.

Understanding bilge pumps is essential for any boat owner. Several types of bilge pumps are available, including hand operated and automatic models. Choosing the right bilge pump for your boat depends on several factors, such as the size of your vessel, the amount of water that needs to be removed, and your budget. Once you’ve selected the appropriate bilge pump, it’s crucial to install it correctly and perform regular maintenance to ensure that it functions correctly when you need it most.

Key Takeaways

  • Bilge pumps are a critical component of any boat, and their proper functioning is essential for keeping your vessel afloat.
  • The pump(s) which came with your boat were not designed to cope with a hull breach.
  • Choosing the right bilge pumps depends on several factors, including the size of your boat and the amount of water that may need to be removed.
  • Proper installation and maintenance of your bilge pumps are essential to ensure it functions correctly when required.

Understanding Bilge Pumps

The Role of Bilge Pumps

Bilge pumps are an essential component of any boat’s safety equipment. They are designed to remove water accumulating in the bilge, the lowest part of the boat’s hull. The bilge is where water collects when it enters the boat, either from rain, waves, or leaks. Without a bilge pump, the water in the bilge can cause damage to the boat’s structure, electrical systems, and equipment, and ultimately swamp the vessel so that is capsizes or sinks.

The primary function of a bilge pump is to remove water from the bilge. However, bilge pumps can also perform two additional functions. The first is to remove nuisance water, such as rainwater or packing gland drips. The second is to assist emergency pumps during a flooding situation. Bilge pumps come in various sizes and capacities to handle different volumes of water.

Types of Bilge Pumps

There are two main types of bilge pumps for smaller boats: centrifugal and diaphragm pumps. Piston pumps, also known as reciprocating bilge pumps, are generally found on larger vessels. Manual pumps are operated by hand, while electric pumps are powered by a battery or the boat’s electrical system.

Centrifugal pumps are the most common type of bilge pump. They work by using an impeller to create a flow of water, which is then pumped out of the boat. Centrifugal pumps are usually electrically powered and may be submersible – so they can be fitted in the lowest part of the bilge – or remotely situated.

Diaphragm pumps use a flexible diaphragm to create a vacuum that draws water into the pump. The diaphragm then compresses, forcing the water out of the pump. Diaphragm pumps are typically more expensive than centrifugal pumps but are also more reliable and require less maintenance. Most hand operated bilge pumps are diaphragm pumps, although they can also be electrically powered.

Both types of pump may be fitted with an automatic switch, triggered by a rising water level. This switch may be integral to the pump or fitted separately.

Self Priming Pumps

Self-priming pumps are designed to automatically remove air from the pump casing and suction line, allowing the pump to start pumping fluid without manual intervention. This feature is particularly valuable in applications where the pump may frequently run dry or where the suction conditions are challenging.

A self-priming pump has a chamber that retains fluid after the pump is initially primed. When the pump is restarted, this retained fluid is mixed with incoming air to create a mixture that is easily pushed through the pump. As the air is expelled, the pump becomes fully primed, and normal pumping resumes.

Centrifugal pumps are often not self priming and need a non-return valve in the hose close to the pump to help them create a head of water. Diaphragm pumps are usually self-priming.

The Bilge Pump System

The components of a bilge pump system include:

  • A bilge pump
  • Hose sized to the pump
  • A skin fitting for above the waterline sized for the hose
  • Hose clamps sized for the hose
Hand & electric bilge pump system
Whale Systems – Electric pump with a hand operated back-up pump

Optional additional components include:

  • A Y valve to use a single skin fitting for more than one outlet
  • A strainer or strum box for remote mounted pumps
  • A non-return valve sized to the hose
  • A power source for an electric pump
  • A remotely mounted switch for an electric bilge pump
  • A bilge pump switch triggered by a rising water level for pumps that are not triggered automatically
  • A bilge alarm system to advise when a pump is operating, and to sound an alarm when water reaches a high enough level indicating a more serious problem

Choosing the Right Bilge Pump

When choosing the right bilge pump for your boat, there are a few things you need to consider. In this section, we’ll go over some of the key factors you should keep in mind.

Choose a Reputable Brand

As with everything these days, most manufacturing takes place in China, but it’s worth noting that several brand names have been manufacturing pumps for marine use for decades. These companies have a reputation to uphold, an established quality control process and good follow-up customer service. Whilst the brand name does not guarantee that your pump won’t fail you at the worst possible moment, I’d rather buy from an established and reputable company for such an essential safety item.

Below is a table showing many of the brands of bilge pumps for boats, the date the brand was started and the country where the company is based. 

BrandDate StartedCountry of Origin
Whale1810Northern Ireland
Jabsco1938United Kingdom
Johnson Pump1968Sweden
Amarine MadeUnknownChina

Manual vs Electric vs Automatic Bilge Pumps

Another factor to consider is whether you want a manual or electric/automatic bilge pump. Manual pumps require you to manually pump the water from the bilge, electric pumps may be switched on and off using a manual switch, while automatic pumps will turn on and off automatically as water enters the bilge.

Hand pumps are less expensive and can be a good option for smaller boats or boats that spend less time on the water. Automatic pumps are more costly but can provide added peace of mind since they’ll turn on and off automatically as needed.

Size Considerations

One of the most important things to consider when choosing a bilge pump is the size of your boat. The size of your boat will determine how much water your bilge pump needs to be able to handle. As a general rule of thumb, you should choose a bilge pump that can handle at least twice the amount of water your boat’s bilge can hold.

The size of a bilge pump needed for a boat depends on several factors, including the boat’s size, design, intended use, and the likelihood of taking on water. Here’s a general guide to help you determine the correct size bilge pump for your boat:

Boat Size: As a general rule, the larger the boat, the larger the bilge pump required. A small dinghy might only need a pump with a capacity of 500 GPH (gallons per hour), while a large yacht might require a pump of 2000 GPH or more.

Water Ingress Risk: Consider the likelihood of water getting into the bilge. A larger pump may be needed if the boat is used in rough waters or has many openings that could allow water in.

Manual vs Automatic: Automatic bilge pumps can be smaller as they operate continuously, while manual pumps might need to be larger to handle water quickly when needed.

Redundancy: Many boaters choose to install more than one bilge pump. A typical setup is to have a smaller automatic pump for regular use and a larger manual pump for emergencies.

Legal Requirements: Some jurisdictions require bilge pump capacity based on the boat’s size or type. The US Coast Guard, for instance, have requirements in place for all commercial vessels. Always check local regulations to ensure compliance.

Manufacturer’s Recommendations: Boat manufacturers often provide recommendations for bilge pump size based on the boat’s specific design and intended use.

General Guidelines

  • Boats under 18 feet: 500-800 GPH
  • Boats 18 to 22 feet: 800-1100 GPH
  • Boats 22 to 25 feet: 1100-1500 GPH
  • Boats over 25 feet: 1500 GPH or more, possibly with multiple pumps

Remember, these are general guidelines (provided by West Marine Boating Store), and the specific needs of your boat may vary. Consulting with a marine professional or the boat’s manufacturer can provide tailored advice for your situation. It’s always better to err on the side of caution and choose a pump with a slightly higher capacity than you think you need.

For several reasons, its very likely that your pump cannot actually pump the full rated volumes indicated on the pump specifications. Read this article to find out more.

Power Source

Finally, you’ll need to consider the power source for your bilge pump. Bilge pumps can be powered by either AC or DC power or your boat’s battery. DC pumps are popular since your boat’s battery can power them. You’ll need to ensure that your battery is in good condition and that you have a backup plan in case your battery dies.

AC pumps are another option, but they require you to have access to shore voltages. If you have an onboard generator, this may be a good option for you.

Maintenance and Troubleshooting

Regular Maintenance & Routine Checks

To ensure that your bilge pump works properly, it’s essential to perform regular maintenance. This includes inspecting and cleaning the pump and its components, checking the wiring and connections, and testing the pump to make sure it works. Regular maintenance can help prevent pump failure and ensure your boat stays afloat.

Here are some steps you can take to maintain your bilge pump:

  • Check the float switch: The float switch is responsible for turning the pump on and off. Make sure it is not stuck or obstructed by debris. You can also test it by manually lifting it to see if the pump turns on.
  • Inspect the pump and hoses: Check the pump and hoses for any signs of damage or wear. Look for cracks, leaks, or loose connections. Replace any damaged components immediately.
  • Clean the pump and strainer: Remove any debris or sediment from the pump and strainer. This will prevent clogs and ensure that the pump is working efficiently.
  • Test the pump: Test the pump periodically to ensure it works correctly. You can do this by pouring water into the bilge and observing if the pump turns on and removes the water.

Common Problems and Solutions

Despite routine maintenance, bilge pumps may encounter problems. Here are some common problems and solutions:

Pump does not turn onCheck the fuse and wiring connections. If they are intact, the pump or pump motor may be faulty and need to be replaced.
Pump turns on but does not remove waterCheck the hoses and discharge outlet for clogs or obstructions. Make sure the pump is properly installed and positioned.
Pump runs continuouslyCheck the float switch for obstructions or damage. If the switch is working properly, the pump may be undersized for the amount of water in the bilge.
Pump is noisyCheck the impeller for damage or debris. Clean or replace the impeller if necessary.

Safety Measures

When it comes to boating, safety should always be your top priority. Bilge pumps are an essential piece of safety equipment that can help prevent your boat from sinking. However, additional safety measures are necessary to ensure you and your passengers stay safe on the water.


Having a backup bilge pump is a good idea in case your primary pump fails. Consider installing a secondary pump that operates on a separate power source, such as a battery or manual pump. This redundancy can provide an extra layer of protection against flooding.

Automatic Switch

An automatic bilge pump switch can help ensure your pump turns on when needed most. The switch detects when water levels rise and activates the pump, even if you’re not on board. This can help prevent flooding and give you peace of mind when you’re away from your boat.

Bilge Alarm

A bilge alarm system will alert you when a pump is running, and also trigger an alarm when something more serious is happening, such as a pump not working or a more serious leak that the pumps are not keeping up with. This is a useful addition for people voyaging offshore or spending longer periods of time aboard.

Regular Checks

In addition to regular maintenance, it’s important to check your bilge pump regularly to make sure it’s working correctly. This includes checking for any signs of damage or wear, ensuring the pump is properly secured, and testing the pump to ensure it works. Regular checks can help you catch any issues before they become major problems.

Emergency Procedures

Even with a functioning bilge pump, it’s essential to know what to do in case of an emergency. Ensure you and your passengers know how to use the pump and any other emergency equipment on board. Have a plan in place for what to do in case of flooding or other emergencies, and practice the plan with your passengers. Being prepared can help keep everyone safe in case of an emergency.

By following these safety measures, you can help ensure that your bilge pump works properly and that you and your passengers stay safe on the water. Remember, safety should always come first when boating.

Environmental Impact

Bilge pumps play a crucial role in keeping your boat afloat but can also impact the environment. It is important to be aware of the potential environmental impact of bilge pumps and take steps to minimise it.

Oil Discharge

One of the biggest environmental concerns associated with bilge pumps is the discharge of oily water into the waterways. When the bilge pump pumps out water, it may contain oil, fuel, and other pollutants that can harm marine life and the environment.

To prevent this, you could use a bilge pump with a filter to remove oil and other pollutants from the water before it is discharged. There are also oil-absorbing towels and bilge socks available that can be used to clean up any spills or leaks.

Noise Pollution

Another environmental concern in certain areas is the noise pollution caused by bilge pumps. The sound of a pump can disturb marine life and disrupt its natural behaviour. If this is a concern where you are boating, install a noise-reducing cover over the bilge pump or use a quieter pump to minimise the impact of noise pollution.

By taking these steps, you can minimise the environmental impact of your bilge pump and help protect the marine environment for future generations.


In conclusion, a bilge pump is an essential piece of equipment for any boat owner. Removing excess water from the bilge is vital in keeping your vessel afloat in case of a leak.

When selecting a bilge pump for your boat, look at the different types available, their components, and their functions. Centrifugal pumps are commonly used and effectively remove large amounts of water quickly. Diaphragm pumps are another, usually manual, option that can be mounted away from the corrosive environment of the bilge, increasing ease of maintenance and longevity.

The American Bureau of Shipping recommends one 24-gallon-per-minute (gpm) pump and one 12-gpm (720 gph) pump for boats under 65 feet. However, it is important to note that bigger is better within reason. Select a pump that can handle the burden of pumping out as many gallons of water as fast as possible.

In addition to selecting the right pump for your boat, it is essential to maintain and use it properly. Regularly inspect the pump and its components, and replace any damaged or worn parts. Test the pump periodically to ensure it is functioning correctly.

By understanding the importance of a bilge pump, selecting the right type for your boat, and properly maintaining and using it, you can ensure the safety and longevity of your vessel.

Frequently Asked Questions

How do I know what size bilge pump I need?

To determine the size of the bilge pump you need, consider the size of your boat’s bilge, the amount of water it can hold, and the type of boating you plan to do. As a general rule of thumb, you should have a bilge pump that can move at least 500 gallons of water per hour. You can consult with a professional or refer to the manufacturer’s recommendations to determine the most appropriate size of bilge pump for your boat.

Should I leave the bilge pump on while boating?

It is generally recommended that you leave your bilge pump on while boating, especially if you are in rough waters or if there is a chance of taking on water. This will help ensure that any water that enters the bilge is quickly pumped out, reducing the risk of flooding or sinking.

How long will a boat battery run a bilge pump?

The amount of time a boat battery will run a bilge pump depends on the capacity of the battery and the size of the bilge pump. A fully charged marine battery can typically run a 500 GPH bilge pump for approximately 5-6 hours before needing to be recharged.

What are the benefits of an automatic bilge pump?

Automatic bilge pumps are designed to turn on automatically when water enters the bilge without the need for manual intervention. This can be beneficial in emergencies where you may not be able to turn on the bilge pump manually. Additionally, automatic bilge pumps can help prevent damage to your boat by quickly removing any water that enters the bilge.

What are the differences between a manual and automatic bilge pump?

Manual bilge pumps require manual intervention to turn on and pump out water from the bilge. In contrast, automatic bilge pumps turn on when water enters the bilge. Automatic bilge pumps are typically more expensive than manual bilge pumps, but they offer greater convenience and peace of mind.

How many bilge pumps do I need?

The number of bilge pumps needed depends on factors such as the boat’s size, design, intended use, and local regulations. Many boaters opt for at least one primary pump and a secondary backup pump for emergencies.