A couple of years ago, my family and I decided that we were going to cross the gulf stream in our little 21, bowrider. Aside from all the excitement and the hours we spend looking for stuff to do in the Bahamas. I had the job to make sure Our boat was in optimal condition and take all necessary safety precautions. That’s when I decided to install a second (backup) bilge pump. I want to share with you all I found on my research, as well as my experience installing it in my boat.
Adding a second bilge pump is an excellent idea for any boater spending prolonged periods of time on the water. I usually trailer my boat, but for this adventure, the boat was going to sit on the water for 11 days.
Keep in mind that most bilge pumps are electric and susceptible to failure. Your boat can take water in many ways like waves, rain, wake from a bigger boat, and forgetting to put the drain plug on. Your boat should be able to pump this water out, especially if spending the night on the water. Adding a second bilge pump to your boat will give your boat a better chance to stay afloat in the event of a failure from the main pump.
Here are some considerations to take when installing a second pump on your boat.
Use Automatic Or Manually Activated?
Your back up bilge pump should be automatically activated with a built-in or external float- or electronic-water-sensing bilge pump switch. This way, if water gets on your boat and reaches a certain level, the switch will automatically activate the pump to start pumping water out. In my opinion, it is necessary to have a system that will enable itself if needed. If an emergency occurs, the last thing you need is to have to remember to activate the bilge pump. Also, if you leave your boat in a dock overnight and it rains, the bilge pump should be able to kick in by itself.
There are many great pumps in the market with a built-in float switch and super easy to install. This is why I see no reason to use a manually activated pump on a small boat. Keep in mind that with a manually activated bilge pump, you have to be there and finally turn the pump on. This would be very inconvenient in case of an accident or just simply living your boat overnight in the marina.
Where Would Be The Best Place to Put It?
The pump should be installed as low in the bilge as you can and as close to the transom as possible. The logic behind it is that when the boat is on the water, the weight of the engine will make the bilge area near the transom, the lowest place of the boat. Also, keep in mind that when the boat gets on plane, the bow will rise, and water will run to the stern.
Also, try to install it in an accessible location. This is recommended, so you have easy access to it if, for some reason, it stops pumping. Keep in mind that it is an electric pump and can fail for many reasons, and you have access to it fast if needed. Some people install them underneath the engine, and it becomes a nightmare to get to when they need to service it.
What Is The Best Way To Connect It?
The best way to wire a bilge pump is to go directly to the battery with the proper fuse and a switch (float or electronic water sensing), or to a bus bar that is always on. It is also recommended to use the appropriate marine-grade wire with heat shrink on all connections.
The common mistake a lot of people make when wiring pumps, is to wire them after the shutoff switch or the main circuit breaker on the panel. A lot of times, people accidentally turn off the bilge pump when they turn off the main power, and unfortunately, their boats sink. This is why it is vital to wire the bilge pump directly to the battery.
To test if the existing bilge pump on your boat is wired correctly, turn off all the power by turning off the shutoff switch. Then try to run the bilge pump by lifting the float switch. If the pump is wired correctly, it should turn on. If it doesn’t turn on, my recommendation is that you rewire it directly to the battery as soon as possible.
Should It Be Higher Than The First Pump?
This topic is often on debate, although most experts on the subject recommend that the second (backup) bilge pump should be mounted higher than the main one. It should be installed about 6 to 10 inches higher.
What we are looking for by installing the second pump higher is redundancy. Some people like to install the second bilge pump at the same level as the principal pump and just install the float switch higher. The problem is that debris tends to accumulate at the bottom of the bilge and can damage the pump’s propeller with time.
Installing the second pump up higher will solve this problem. Mounting the second pump higher, you will also avoid running both pumps together all the time. Remember, the second pump is a backup to be used only when the primary pump can’t keep up or not working at all.
“T” Pumps Or Second Thru-Hull Install?
It is always better to put in a second thru-hull. In my opinion, the use of “T,” “Y,” or check valves is a problem waiting to occur. With a “T,” you run the chance of pumping water back into the boat. Check valves can clog up, preventing both bilge pumps from pumping water out.
There’s also the fact that any hose of a given diameter can only handle so much water. You will be lowering the pumping capacity of both pumps since they will be fighting each other.
I know that Installing a thru-hull can be intimidating (you have to drill a hole on the side of your boat literally), but believe me, it is pretty easy even for beginners.
Save yourself some problems down the lime and install tour second bilge pump the right way. That is, each pump should be totally independent of the other.
Related Questions
How big of a bilge pump do I need? It is hard to figure out a specific number that would work for all boats. Keep in mind that there are hundreds of boat manufacturers and thousands of models and shapes of boats. So the capacity of the bilge pump you need will be determined by the size and shape of your boat.
It’s also important to keep in mind that in most cases, your bilge pump won’t perform to its pump rating. Usually, those ratings are accurate on a perfect scenario, it is safe to say that your boat is probably not an ideal scenario. Some of the stuff that. Help diminish a bilge’s pump capacity are voltage drop from the battery, the height of the thru-hull vs. the height of the pump, and the size of the hose.
To be on the safe side, I would count on the actual capacity of 60 percent the advertised rating.
With that been said, below is a chart of the minimum bilge pump needed based o boat size, according to David Pascoe, a renowned Marine Surveyor with whom I agree.
| Boat Length | No. Pumps | Total Capacity GPH |
| 16’-20’ | 2 | 2500 |
| 21’-26’ | 2 | 3000-3500 |
| 27’-35’ | 3 | 3500-4500 |
| 36’-42’ | 3 | 6000 |
| 43’-49’ | 3-4 | 8000 |
| 50’-59’ | 4-5 | 9000-10,000 |
| 60+ | 4-5 | 10,000+ |
How does water get in the bilge of a boat? There are a significant number of ways for water to get in the bilge pump. Here is a list of some of the most common ways.
- Rainwater
- Splash from waves
- Vent hole in anchor compartment
- Fishing rod holders draining into the bilge
- Melted ice on built-in cooler
- Fish box drain into the bilge
- Drain plug
- Drain plug seal
How do you test a bilge pump? On most boats, you should be able to put the drain plug on and pore enough water on the bilge to activate the float switch. Just make sure to remove the drain plug when done testing to get read of any exes water.