Understanding Boat Bilge Pumps: How Do They Work?

A bilge pump is an essential piece of safety equipment found on most boats. Its function is to remove water that collects in the bilge – the bottom of the inside of the hull. This water could be rainwater, water from cleaning, leaks, or built-in coolers that drain into the bilge.

The bilge pump is a crucial safety feature as it prevents the boat from flooding or sinking. There are two main types of bilge pumps: manual and automatic. Manual bilge pumps are a good option for small recreational boats such as kayaks and canoes, while automatic bilge pumps are activated by water levels in the bilge and are perfect for boats of any size.

Manual vs automatic bilge pumps

Manual bilge pumps are commonly used on small recreational boats, such as dinghies, kayaks, and canoes. These pumps are hand-operated and allow water to be pumped out at the user's discretion. They are perfect for non-motorized marine applications and do not require electricity. However, they have extremely limited applications and require manual pumping.

Automatic bilge pumps, on the other hand, are more commonly used on larger boats and modern vessels. They operate with a float switch, which activates the pump when water reaches a preset level. This ensures that water does not fill up past a certain point and protects the pump from running dry. Automatic bilge pumps can be further categorised into centrifugal, diaphragm, and reciprocating pumps.

Centrifugal bilge pumps are the most popular type due to their low cost and ability to pump large volumes of water. They are submersible and use an impeller to increase the speed and pressure of incoming water. However, they are ineffective at pumping water uphill and cannot remove all water from the bilge.

Diaphragm bilge pumps, on the other hand, are self-priming and can be mounted away from the bilge, making them less prone to damage. They are better at pumping water uphill than centrifugal pumps and can remove all water from the bilge. However, they cannot handle much debris and are only suitable for small to medium-sized boats.

Reciprocating bilge pumps, also known as piston bilge pumps, are similar to diaphragm pumps in their ability to pump water uphill. They are self-priming and can handle fluids more viscous than water. However, they have limited applications due to their low water displacement and intolerance to debris.

In conclusion, the choice between a manual and an automatic bilge pump depends on the size and type of boat, as well as the user's preference for convenience and control. While manual bilge pumps are limited to small vessels and require manual operation, automatic bilge pumps offer more flexibility and can be found on a variety of boat types.

The function of a bilge pump

Bilge pumps are essential safety equipment for any boat, as they prevent the boat from flooding or sinking due to excess water in the bilge. They are rated by the volume of water they can remove in one hour, expressed in gallons per hour (GPH).

There are different types of bilge pumps, including manual and automatic pumps. Manual pumps are typically used on small recreational boats, such as dinghies, kayaks, and canoes, and require someone to operate them. Automatic bilge pumps use a float switch to activate the pump once the water level in the bilge reaches a predetermined level.

Most boats have a primary pump located at the lowest point of the bilge, and some may also have a secondary pump located higher up to provide redundancy in case the primary pump fails or is overwhelmed.

Bilge pumps come in three main types: centrifugal, electric diaphragm, and reciprocating. Centrifugal pumps are the most common type, using a rotating impeller to push water up into the discharge hose. Electric diaphragm pumps use a diaphragm to create suction and draw water in, and they can be mounted away from the bilge. Reciprocating pumps, also known as piston pumps, use a piston to draw water in and discharge it, and they are often used in conjunction with centrifugal pumps to handle thicker fluids.

Types of bilge pumps

There are several types of bilge pumps available, including electric, manual, and engine-driven solutions. The type of bilge pump that is best for your boat depends on several factors, including the size of your boat, your boating habits, and your preference for convenience or reliability. Here is a list of some of the most common types of bilge pumps:

Centrifugal Bilge Pumps

Centrifugal bilge pumps are submersible pumps that use an impeller to increase the kinetic energy of the water, allowing it to be pumped out. They are typically less expensive than other pump types and can handle large volumes of water. However, they are ineffective at pumping water uphill and do not remove all water from the bilge.

Electric Diaphragm Bilge Pumps

Electric diaphragm bilge pumps are self-priming and use a diaphragm to draw in and displace water. They are better at pumping water uphill than centrifugal pumps and can remove all water from a boat's bilge. They can be mounted away from the bilge, making them less prone to damage. However, they cannot handle much debris, and their flow rate is typically lower than that of centrifugal pumps.

Reciprocating Bilge Pumps

Reciprocating bilge pumps, also known as piston bilge pumps, are self-priming and effective at pumping water uphill. They can handle fluids that are more viscous than water. However, they are even less tolerant of debris than diaphragm pumps and cannot displace as much water as other pump types.

Manual Bilge Pumps

Manual bilge pumps are hand water pumps used for non-motorized boats, such as kayaks, canoes, and dinghies. They do not require electricity but have limited applications and require manual pumping.

Submersible Electric Pumps

Submersible electric pumps are placed in the lowest part of the bilge and are the most popular type of electric bilge pump. They are cost-effective, have high outputs, low amp draw, and are easy to install. However, flow rates decrease as the discharge head increases.

Flexible Impeller Pumps

Flexible impeller pumps are excellent for handling bilge debris without damage and offer good flow, low cost, small size, and easy maintenance. However, most flexible impeller pumps must not be run dry as this will damage the impeller.

Diaphragm Pumps

Diaphragm pumps are ideal for shallow bilge boats, as they can remove all but the last drops of water. They can be run dry and can be mounted in a high and dry location, simplifying installation and improving serviceability.

Bilge pump maintenance

The bilge pump is a crucial piece of equipment on a boat, designed to remove water from the bottom of the hull, or bilge. Given its importance, regular maintenance is essential to ensure the pump functions when needed. Here are some key maintenance tips to keep your bilge pump in top condition:

Cleaning and Debris Removal

Over time, debris such as leaves, grass, twigs, and sediment can accumulate in the pump, leading to clogs and reduced performance. Therefore, it is important to periodically inspect and clean the bilge pump and the surrounding bilge area. Remove any visible debris by hand and use a wet/dry vacuum to clean hard-to-reach areas.

Testing the Internal Sensor

Modern bilge pumps often have internal sensors or float switches that detect water levels and automatically activate the pump. It is crucial to test these sensors regularly to ensure they are functioning correctly. This can be done by manually triggering the sensor or simulating water ingress to observe the pump's response.

Check Wiring and Float Switch

If your bilge pump is running constantly, there may be an issue with the wiring or float switch. Inspect the wiring for any signs of corrosion or damage. Ensure the float switch is free of debris and functioning properly.

Outlet Hose Inspection

Although outlet hoses are durable, they should be regularly checked for any signs of damage or clogging. If the hose is clogged, it could affect the flow rate of water being discharged.

Check the Impeller

For centrifugal pumps, a faulty impeller can render the pump inoperable. To test the impeller, disconnect the pump and attempt to turn the impeller by hand. If it does not turn freely, the pump may need to be replaced.

Regular Visual Inspections

It is recommended to perform regular visual inspections of the bilge pump and its surrounding area. Check for any signs of damage, corrosion, or debris buildup. This proactive approach can help identify potential issues before they become bigger problems.

Manual Activation Familiarity

Familiarize yourself with the manual activation mechanism of your bilge pump. In an emergency, you may need to override any automatic systems by using a touch-button located on the pump itself.

Use Bilge Cleaners

Bilge cleaners are designed to break down sludge and grime that can build up inside the pump over time. They help keep the pump running smoothly and can be used while the boat is in the water, eliminating the need for pre-rinse before heading out.

Inspect and Clean Filters

Regularly clean the filters in your bilge pump to prevent debris buildup. Before heading out on the water, ensure that all debris is removed from the filters to maintain optimal pump performance.

Test the Pump Before Departure

Before departing on a voyage, it is crucial to test the bilge pump to ensure it is functioning properly. Pour a few gallons of water into the bilge and observe if the pump activates and removes the water. If the pump fails to activate or remove the water, perform maintenance or seek professional assistance before venturing out.

How to choose the right bilge pump

Choosing the right bilge pump is crucial for the safety and maintenance of your boat. Here are some factors to consider when selecting a bilge pump:

Type of Bilge Pump

The three main types of bilge pumps are centrifugal, electric diaphragm, and reciprocating. Centrifugal bilge pumps are the most common type and use an impeller to force water out of the boat. They can handle large volumes of water and small debris but struggle with uphill pumping. Diaphragm bilge pumps use a valve to remove water and are self-priming, making them great for uphill performance. However, they have poor flow capacities and cannot handle debris. Reciprocating bilge pumps, or piston pumps, are similar to diaphragm pumps but can handle more viscous liquids. They are also self-priming but struggle with debris and have lower flow rates.

Size of the Boat

The size of your boat will determine the required capacity and number of bilge pumps. Larger boats will need a higher-capacity pump and may require multiple pumps in different compartments. Small boats can usually get away with a single pump but may benefit from a secondary pump as a backup.

Manual vs. Automatic

Manual bilge pumps are hand-operated and typically found on small watercraft like kayaks and canoes. Automatic bilge pumps, on the other hand, are powered by an electrical current and are more common on larger watercraft with onboard batteries. They use a float switch to activate when the water reaches a certain level.

Gallons Per Hour (GPH)

Bilge pumps are rated by their capacity in gallons per hour (GPH). However, the actual performance may be lower due to factors such as the distance between the bilge and outlet, hose type, and hose length. As a rule of thumb, you can expect the pump to operate at around 60% of its rated capacity.

Installation and Accessibility

Ensure that the bilge pump is installed at the lowest point of the bilge. It should be mounted level or with the outlet facing up to prevent air locks. The pump should also be easily accessible for maintenance, cleaning, and debris removal.

Check Valves

Consider installing a check valve in the discharge line to prevent water from running back into the bilge when the pump shuts off. However, keep in mind that check valves can get clogged with salt and debris, so they must be regularly inspected and accessible.

Frequently asked questions