What Size Bilge Pump Do I Need On My Boat? | BoatUS

Ever wonder what size bilge pump you need on your boat? The answer isn't always simple. BoatUS Magazine associate editor Mark Corke walks you through some realities that affect bilge pump capacity to help you calculate the size bilge pump you need to keep your boat dry and safe. Learn how to make proper waterproof marine electrical connections at • How To Make Waterproof... . Read more about bilge pump capacity calculations to determine which size you need on your boat at www.boatus.com/expert-advice/...
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[@Captdal]

Thanks always for the info !

[@boatus]

Thanks, as always, for watching, Dal!

[@catherineharris4746]

Outstanding!👍👍👍

[@boatus]

Thanks for watching, Catherine. Glad you found it helpful.

[@geraldvarner4311]

If you don't think the Coast Guard mandates a bilge pump on a charter boat, try telling that to a Coast Guardsman the next annual safety inspection. In fact, he will tell you that a vessel over 26' requires TWO bilge pumps and of a CERTAIN size hose!

[@boatus]

You're correct about requirements for commercial boats, gerald. No requirements for recreational boats, however. Always seemed odd.

[@markmaugle4599]

My bilge pump hose has a vacuum break in the line. Which is better a check valve or vacuum break?

[@boatus]

Hi Mark. Thanks for the question. A vacuum break is perhaps better known as a siphon break and does not impede flow in the way that a check valve does. So the quick answer is, stick with the siphon break. Hope this helps! Let us know if you can.

[@scottdowney4318]

On my 37 foot sedan cruiser, I have 2 aft bilge pumps, 2000 and 500. In forward bilge I have 3 pumps. Two 3700, and one 2000. They are all Rule pumps. I figure redundancy is a good idea. I have a somewhat watertight aft bilge, it comes up all the way to the floor, sealed. Which isolates one bilge from the other. I once tested how it works by opening up the aft bilge to the sea. The water came in fast at first, the rear of the boat dropped about 6 inches, and at that point the water inflow had slowed a lot, very much so that a bilge pump could keep up with the water rising. Useful say if a hose came loose from a thruhull.

[@boatus]

Thanks for watching, Scott. Redundancy is a good idea for sure. Glad you were able to safety test out your system. Sounds like it could be a life-saver if you ever need it. Here's hoping you never do!

[@miralemnermina142]

@@boatus as an boat eletrician I've already seen setup like that save lifes a few times. People don't care about pumps or float switches so they just fail and no one knows until it's too late. Also make sure to have an alarm hooked up to the float switch as well. It makes my head hurt when I remember how many boats lack these basics features. PS: Great channel BoatUS!

[@boatus]

@@miralemnermina142 Thanks so much for your comment and for watching!

[@miralemnermina142]

@everyday tenor I found sponge works very well in blocking holes as well 👍

[@boatus]

@everyday tenor You are absolutely right! Bilge pumps aren't meant to pump out water in an emergency like that. Best to call the Coast Guard in that situation. They are there to remove nuisance water so it doesn't accumulate and become an issue. Good tip on the carrot! Or keep a TruPlug on board if you don't regularly keep a carrot around.

[@paoloaccad1561]

hi. we are building a 13meter sports cruiser with 3 watertight bulkheads (4 compartments). Throughout my research, I kept on seeing 2000-4000GPH capacity requirement for our boat size. My concern is do I have to distribute the capacity equally among the 4 compartments? I'm thinking of using around one 800GPH pump per compartment. Is it enough? I cannot find a sizing calculation from ABYC. Thank you in advance.

[@boatus]

Thanks for the question, Paolo. Long answer coming. Disclaimer: Without seeing your boat, we can't really give you specifics, but we can answer your general questions based on the information you've given us. Anything mentioned here should be taken in that context and not as advice. The American Boat and Yacht Council (ABYC) has not set requirements concerning bilge pump capacity, although the American Bureau of Shipping recommends one 24 gallons per minute (gpm) pump (that’s about 1,440 gallons per hour, or gph) and one 12-gpm pump for boats under 65 feet. The Lloyds’ standards relate to vessel length and volume, recommending a 50-gpm pump for a boat of about 50 feet. In our opinion, bigger is better (within reason of course), and no boat ever sank due to having too much pumping capacity. Based on boat size alone, we'd recommend a minimum of 5,500 gph electrical pumping capacity for a 40-foot vessel-divided among a 1,500-gph primary pump and two 2,000-gph backup pumps. This is a minimum and can be bumped up, especially where extenuating circumstances apply (such as increased vertical lift due to a deeper bilge, etc). Keep in mind, though, that this is for a boat with no separate watertight compartments (i.e., one primary bilge that the entire vessel drains into). For the boat you describe, you're correct that each of the four watertight compartments should ideally have its own dedicated bilge pump. If it were our boat (this is purely personal opinion), we would install the following: 1. One 1,500 gph pump in each separate compartment. 2. For the primary or main bilge compartment (i.e., the one containing engine shaft penetrations, etc) we'd also add a 2,000 gph backup bilge pump. 3. If any of the other separate compartments contain any penetrations below the waterline (thru-hull for example) we'd suggest bumping the 1,500 gph pump to a 2,000 gph unit. 4. VERY IMPORTANT: Regardless of what you decide to do, we'd strongly recommend installing a high-water bilge alarm with a sensor located in each separate bilge compartment, as well as a visual “bilge pump on” light at each helm station for each of the electric pumps. The alarm will let you know about high water in the compartment, while the bilge pump on light will notify you before the alarm goes off that something is going on (i.e., a pump that rarely comes on is on, or is staying on longer than usual). Finally, remember that bilge pumps are not emergency pumps, which is another topic altogether. Hope you find this helpful. Good luck with the rest of your build!

[@paoloaccad1561]

@@boatus Thank you very much for the informative response! Much appreciated. We will just use a portable pump as a backup so it can be used in whichever compartment needs extra pumping.

[@boatus]

You're very welcome, Paolo.

[@cornelisvanderbent8569]

Why should the pump be able to pump out thousands of gallons per hour?

[@boatus]

Thanks for the question, Cornelis. As we mention in the video, stated bilge pump ratings are only under ideal conditions, which are definitely not the case on a boat. Because of efficiency losses due to voltage drop, static head/vertical lift, and hose resistance, the pump must be sized larger than you might need in order to pump out that water. So, for example, a 1,000 gph pump might only pump about 300 gallons per hour (which is only 5 gallons per minute) calculating 30% loss for the hose, 20% loss for vertical lift, and 20% loss for voltage drop. Obviously the bigger the boat, the larger the bilge pump you need. Hope this helps!

[@tomm1968]

At 1:34 he states "we need to do some calculations" and then he continues to talk for another 3 minutes without ever explaining what those calculations are. Sure, lots of important considerations are mentioned, but not the "calculations" he mentions to properly size the pump (for both head and flow). I came here looking for a rule of thumb for that, and didn't find it. I own a sailboat, and my bilge is on top of the keel, in a very narrow space between the keel bolts. Granted, the bilge capacity is quite small. So how small is large enough? It seems to me that my bilge pump sizing will be driven more by what will physically fit than with how quickly it can empty the bilge.

[@boatus]

Thanks for the comment, Tom. Fast forward to 2:20 and he goes over all the calculations that will help you determine how much water your bilge pump ACTUALLY removes. I think you'll find what you're looking for, however, in this article: www.boatus.com/expert-advice/expert-advice-archive/2014/december/bilge-pump-capacity-do-the-math Hope this helps.

[@tomm1968]

@@boatus My problem is that all these calculations tell me how much my pump actually moves, not how much capacity my boat needs. That answer is provided in the table from West Marine that you cite in your article. However, that table makes no allowances for the type of boat and the nature of the bilge you're pumping out of. For example, a low-deadrise deep vee powerboat hull will carry a lot more water for a given depth than my 25 ft sailboat with the bilge draining into the narrow keel stub. 6 inches in my bilge is a lot less water than that 20 ft powerboat. So my question is not how much does my pump move, but how big of a pump does my boat need?

[@Case-qy4xy]

Is this English???

[@boatus]

It's in English. Video produced in the USA. Our expert happens to have a British accent.