Is Your Bilge Pump Equipped to Keep Your Boat Afloat?

Before you sink money into a new boat, make sure your vessel will float as well as your Rheos sunglasses for boating.


Bilge pumps are the often-forgotten but crucial equipment that acts as your last line of defense against sinking. And simply having one installed isn’t always enough. In theory, a bilge pump should be able to protect against modest breaches in the hull without worry. But in practice, most pumps are only designed to remove the occasional rainwater — not manage a leak.


Water can flood a small hole in mere minutes, and because most pumps are designed to work best when hooked up to an on-shore electrical system, it’s imperative you understand how yours properly functions.

There are three common types of bilge pumps: 


  • Centrifugal  These pumps rotate a solid impeller like a turbine. Water enters, picks up speed as it rotates, and then is pushed out by its own force. These types of pumps must be sitting in water to work, but are highly recommended because they’re low-maintenance and less likely to clog.
  • Diaphragm  While these pumps can’t move as much water as a centrifugal pump, they can be run out of the water without fear of damage, and can push water uphill much easier. However, unlike a centrifugal pump, small debris can cause pump failure.
  • Manual  Keeping a manual bilge pump onboard your boat is crucial. If your electrical system is flooded, you’ll need a manual pump to help with the damage. But this in no way should be your only bilge, since you’re unlikely to physically keep up with the force needed to push out water.
A boater gives the thumbs up sign to a fellow water-lover.
Boaters slow their motorboat down to an easy wake.


Capacity and Voltage

Your pump may be rated for 500gph (gallon-per-hour) or similar, which is the rate at which the pump can push water out. However, there are outside factors which can impact the pump’s performance. Figuring out what your boat bilge is realistically going to pump out means understanding what’s impacting its effectiveness.


  • Consider your battery and electrical power. Keep in mind that in perfect conditions, you’d be using shore power with the engine running to pump out water. It’s best to assume that without your bilge battery being actively charged, you can see a 20 percent drop in pumping capacity. 
  •  Be mindful of bilge pump placement. While pumps are typically designed to pump water horizontally, pretty much all of them will first pump water vertically, because they’re below the waterline. How high your pump pushes water vertically is called “head,” which can greatly decrease your capacity. Consider where your bilge is located compared to the water line and adjust as needed to increase capacity. 
  • Test it out. To determine your real-life pumping output, do a trial run by measuring the volume of water the pump moves over the course of one minute, then multiple by 60 for rate per hour. This will help you decide if you need more pumps or a higher-rated pump.


Three fishermen wearing Rheos protective sunglasses speed through the open seas.

There are a few tips we recommend to ensure your bilge pump is safely secured.


  • Install it in an easy-to-reach location.  Underneath your engine is not a good spot — you need access to your pump to clean the strainer/remove debris, and ensure it’s working correctly. 
  • Keep everything above water level.  Avoid corrosion issues by moving all electrical equipment well above your normal water level. And have a professional take a look — your trusty roll of electrical tape is not ideal for something this important. 
  • Carefully follow the installation directions.  A number of problems can occur with your bilge pump if you don’t read the user manual carefully. For example, don’t change your fuse sizes just because you thought something bigger would be better.



Your bilge pump just needs a little love. It works hard to keep you safe, so routinely check your pump for any damage or clogs due to debris. Keep it free of oil and sludge so nothing slows it down. And lastly, always make sure your valves, fuses, hoses and wires are intact and protected from corrosion. With the basics of the bilge in mind, you’re ready to hit the open seas on a boat trip!


4-engine offshore boat night boating at dusk.