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Marine Bilge Pumps  

Captain Sheriff’s Marine Tech Tips

Marine Bilge Pumps  

With spring boating season around the corner and mariners anxiously waiting to unveil their vessels out of cold storage, a very common overlooked safety item may need your attention this season.

Bilge pumps are an important safety item that may save your life. Unfortunately, many boaters are unaware of the potentially detrimental issues that may be lurking from the switch panel to the bilge pump keeping it from effectively pumping water overboard when needed.

While articles about bilge pumps would seem less than exciting to read, A TRUE but dangerous    experience of a client trying to sell his gasoline powered inboard vessel comes to mind while composing this article. Thankfully, it ends without personal injury and a little humor.

In my clients effort to sell his vessel, his fishing partner, a service salesman from the auto dealership, was instructed to perform a sea trial for a potential buyer. While the potential buyers were getting briefed on the features and benefits of this vessel, a family member turned on the sink for a drink of water. Something fishy was going on when 87 Octane unleaded fuel came from the sink faucet since someone had apparently put a small amount fuel instead of water in the fresh water holding tank. The salesman decided to drain the fuel contaminated fresh water holding tank into the bilge and then drain the fuel from the bilge by utilizing the bilge pump dumping it into the seawater at the marina. Besides this being a bad idea and illegal, when he turned on the bilge pump a faulty wire connection created a spark. The spark ignited the gas fumes in the bilge and every hatch on the boat blew open and or off the hinges with the explosion created in the bilge. Fortunately, the vessel was at the dock and the small fire was extinguished with the help of the dock master. Once the smoke settled, the salesman maintaining his cool composure informed the potential buyers that the firm asking price was now negotiable due to the minor fire and smoke damage. The potential buyers told him that they were literally blown away by the demonstration but the whole buying experience left a bad taste in their mouth.

While this story may seem over the top, it is true. Raw fuel, fuel vapors in the bilge and wiring issues are prevalent in the marine environment.  

Determining how many bilge pumps

The first issue is how many pumps should you have and what pumping capacity is needed. The chart below indicates the minimum standard number of pumps based on vessel size and capacities rated in gallons per hour or GPH. This is where the variables begin. If a boat has compartments that are blocked off prohibiting free flow to another compartment, a bilge pump should be installed in that area as well.  Keep in mind that most pumps fail due to poor wiring, float switch and or a battery failure.  The best solution for safety is redundancy. In addition, a high capacity pump that can be readily attached to a battery with a length of hose as a final backup is a good idea to carry on board.

 

 

The chart is a general recommendation for the number of bilge pumps and capacities.

Boat Length 16' - 20' No. Pumps: 2 GPH: 2500
Boat Length 21' - 26' No. Pumps: 2 GPH: 3000 - 3500
Boat Length 27' - 35' No. Pumps: 3 GPH: 3500 - 4500
Boat Length 36' - 42' No. Pumps: 3 GPH: 6000
Boat Length 43' - 49' No. Pumps: 3 - 4 GPH: 8000
Boat Length 50' - 59' No. Pumps: 4 - 5 GPH: 9000 - 10,000
Boat Length 60' - 60' No. Pumps:4 - 5 GPH: 10,000+

Marine grade batteries

Redundancy starts with two batteries or more and multiple bilge pumps in the event a failure takes place when you need it most. The right type of marine grade battery is as important because, more than likely, if you need the bilge pumps operating due to potential sinking, you probably will not have engine power during this dilemma to charge the batteries. Marine grade batteries are much heavier than conventional batteries because they contain a lot more lead. The additional lead provides deeper cycling needed for marine applications.

Bilge pump capacity. GPH

Based on my experience and research, the pump ratings on bilge pumps are very inaccurate. Bilge pump ratings do not allow for pumping vertical and the different types of bilge hoses that vary in resistance. An example of this is corrugated bilge hose versus smooth bore. Smooth bore is more efficient and is the preferred hose of choice. Keep in mind that the outlet is usually smaller in diameter and resistance is increased there as well.  For these reasons, it is a good idea to think about installing a larger pumping capacity pump because you may not be getting the GPH pump rating you paid for.

Bilge pump selection

Bilge pumps are tested and ranked on several criteria areas. The ability of the bilge pump to pump vertically a few feet since that is real world situation. The type of wire the pump utilizes, copper versus tinned and the float switch and design in addition to several other key areas. I have attached a link to an article from powerboat reports that reveals the performance of several bilge pumps for additional review.

http://www.powerboat-reports.com/sample/bilge.html

Bilge pump installation

A couple important tips include making a safety loop above the outlet when piping overboard. This keeps water from coming back in through the outlet if the water gets above the thru hull fitting. Bilge pumps should be wired so that if you have a main shut off switch, the bilge pump is still powered live to the float switch should the vessel take on water at the dock or while unattended.  The pump should be wired so that the bilge can be turned on manually by a switch and automatically with the float switch. Another critical point is to make the connections above the bilge area so that the wiring connection is not subject to water. In addition, utilize marine grade wiring and heat shrink type connections. Marine grade wire is tinned and is much more resistant to corrosion.

Summary

Our sea conditions in Rhode Island can change quickly. If you take a wave over the stern or side, you want bilge pumps and electrical systems that can get the job done effectively. Inspect your hoses, connections, batteries and determine the existing pump capacities you have currently. Keep in mind that even newer production boats may be rigged without marine grade wiring and or marginal capacity bilge pumps as well.

Good luck and safe boating!

Captain John Sheriff has a BS degree in Industrial/Automotive Technology.

Former technical service representative for General Motors

President, Sheriff 5 Star Automotive Service Consulting        www.sheriff5star.com

Owner, Captain Sheriff’s Ocean State Synthetics                   www.oceanstatesynthetics.com        

Owner, Captain Sheriff’s Fishing Charters                             www.fishingchartersri.com  

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