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Buyers and Owners > All About Bilge Pumps

All About Bilge Pumps

Those Essential Devices for Keeping Your Boat Off the Bottom

byDavid H. Pascoe, Marine surveyor 

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Oh, what a boring subject, right? Yeah, I agree, reading about bilge pumps is not too thrilling. But this is a subject which I've been harping on for a long time, apparently without a lot of success based on the continuing and overwhelmingly casual attitude that boat owners have for their bilge pumping systems.

Just to give you a little background, I come from a family where marine surveying is something of the family tradition. Years ago, a large part of our family business was handling marine insurance claims. The hundreds of boats that sunk every year helped contribute to a very brisk business. Having spent many years investigating why they sank, I think I have a pretty good idea why. It's the casual attitude of both boat builders and boat owners toward bilge pumps.

Sail boaters are the absolute worst in this regard. For some strange reason, many of them just don't think that bilge pumps are important. Somehow they rationalize the idea that nothing is ever going to cause their hulls to suddenly flood, so a minimal pumping system is all that is really needed. As in just one pump. I never ceased to be amazed at the number of sailors who argue with me that one pump is enough. After all, the builder built it that way, and they have that nifty manual pump back there in the cockpit and that can really pump a lot of water. More about that later. FYI: Proportionately more sailboats flounder at sea even though powerboats outnumber them 8:1.

Of course, sailors are not alone in this attitude. For every sailor who thinks little about bilge pumps, there are probably three power boaters with the same attitude. So why the widespread lack of concern? Well, it's the same old problem of lack of experience; it's not until they have a problem that they become convinced of the seriousness of it. It's mainly the people who've had their hulls flooded or even sunk that take the matter of bilge pumps seriously. It's called learning the hard way. I can understand that. As a kid, I owned numerous small boats, and I can't begin to count the number of times they sunk because it rained hard, or the boat was leaky, and I had no bilge pump at all. Or if I did, I wasn't paying attention to whether it worked, the batteries stayed charged or whatever.

Unfortunately, sinking at the dock can be the least of your worries. The situation that can really get your attention is when you are at sea and something really big goes wrong, and now you are faced with the prospect of the boat going out from under you. Like having an exhaust hose fail and the engine pumps your hull full of water without noticing that until it's too late. That one happens a lot. Or a sea cock or other through hull fitting lets go because of some corrosion activity that went undetected because the sea cocks which are now 12 years old had never been taken apart and inspected. That happens a lot too. But when it happens at sea, and the boat has an inadequate pumping system,   you've got a disaster in the making. And if you've got your family aboard with you, well you may have to live with a guilty conscience for a while.

Let's start with the premise that next to the integrity of the hull, the integrity of the bilge pumping system comes next. Not the sails, the engines, the interior furnishings or the fancy electronic gizmos, just the plain old, lowly bilge pumping system. Bad things happen, that's why the government mandates that you carry life jackets aboard. But an even better approach is to have a good pumping system so that you have potentially less need   for those jackets.

What Makes for an Adequate System?

This is a question I've been struggling with for years. Unfortunately, there are no pat answers because the criteria for an adequate pumping system depends on the style of the boat, not merely its size. Some types of boats are more vulnerable than others, like sport fishermen and open boats. In any case, for every type there is a basic minimum. The table below lists what I think that minimum is based on boat length.

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 - 60 4 - 5 10,000+

There are two factors which must be considered, the capacity of pumps and the number of pumps. The number of pumps is important from the stand point that bilge pumps are not reliable because they are electrical devices submerged in water. Contrary to common belief, the pumps themselves rarely fail; it's the electrical system from which they operate that is usually the cause of the failure. Because of this, one way to improve reliability is with redundancy, or increasing the number of pumps to decrease the odds of complete loss of pumping ability.

Added to the equation is the fact that the pumps are only as good as the battery system supplying power to them. There's not much point in having a good pumping system if the battery system is not up to running them for the necessary period of time. We'll get into more about that in the Battery Power section later. Continued to page two.

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    Page 1
  • Introduction
  • What Makes for an Adequate System?
    Page 2
  • Evaluate the Number of Compartments
  • Determining the Number of Pumps
  • Outboards and Stern Drives
  • Capacity of Pumps
  • What Brand?
    Page 3
  • Pump Installation
  • Float Switches
  • Open Versus Covered Switches
  • Doing It the Right Way
  • The Discharge Outlet
    Page 4
  • Emergency Pumps - Who Should Have Them and Why
  • Battery Power
  • Wiring Pumps

Posted  November 10, 1998   (First posted   6/10/98 at www.yachtsurvey.com.  Page design changed for this site.)

About Author:
David H. Pascoe is a marine surveyor (1947-2018) with 40 years' experience.

He is author and publisher of power boat books:

"Mid Size Power Boats"
"Surveying Fiberglass Power Boats" 2E
"Buyers' Guide to Outboard Boats"
"Marine Investigations"

Visit  yachtsurvey.com  for more than 180 online articles.

David Pascoe's biography


David Pascoe's
Power Boat Books
Mid Size Power Boats Mid Size Power Boats
A Guide for Discriminating Buyers
Focuses exclusively cruiser class generally 30-55 feet
With discussions on the pros and cons of each type: Expresses, trawlers, motor yachts, multi purpose types, sportfishermen and sedan cruisers.

Buyers' Guide to Outboard Boats
Selecting and Evaluating New and Used Boats
Dedicated for offshore outboard boats
A hard and realistic look at the marine market place and delves into issues of boat quality and durability that most other marine writers are unwilling to touch.

Surveying Fiberglass Power Boats
2nd Edition
The Art of Pre-Purchase Survey The very first of its kind, this book provides the essentials that every novice needs to know, as well as a wealth of esoteric details.

Marine Investigations
Pleasure crafts investigations to court testimony The first and only book of its kind on the subject of investigating pleasure craft casualties and other issues.

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