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How to Polish Your Fuel to Keep Your Boat Running Smoothly

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Polished fuel

Polished to Perfection

Fuel polishing and air-separation systems are great ways to improve fuel efficiency and keep your cruising hassle-free.

Fuel treatments and additives can go a long way towards keeping your boating season trouble-free. But when you get into diesel-powered vessels that are 40 feet or more, the best way to remove water—and the nasty stuff that comes with it—from your fuel tank (or tanks) is to add a fuel-polishing system to your engine room. While initially developed for large yachts and commercial vessels, fuel-polishing technology has caught on with owners of smaller, medium-sized boats these days as well.

What is a fuel-polishing system? Companies like Reverso Pumps, Algae-X, ESI Total Fuel Management , Gulf Coast Filters, and others offer their individual versions, but essentially, most any system pumps fuel out of a tank through a fuel-water separator and then returns it to the tank clean and ready to burn. 

Think of it as an insurance policy for your boat’s fuel system. When a secondary filter on a vessel without a polishing system gets clogged with algae or some other contaminant, the fuel pump may starve. What follows may entail a burnt-up pump, an air-locked engine, or worse. But hey, when a filter clogs in a polishing system, you simply replace the element in the device and you’re good to go.

Breathe Easy

At the 2013 Miami International Boat Show, Northern Lights introduced the Diesel Exhaust Cleaning System (DECS) for its generators. This technology removes soot and particulate matter as it’s emitted from a diesel engine. In DECS, exhaust gas is routed through a catalytically coated ceramic filter that traps these contaminants. DECS is unique because it uses a passive regeneration process that doesn’t require additional equipment, controls, or regeneration time. It also monitors engine information, reduces carbon monoxide by up to 98 percent and diesel hydrocarbons by up to 95 percent, and is CARB Level 3 certified.

The size of a fuel polisher has more to do with a boat’s fuel capacity than her LOA. Many trawlers have uncommonly large fuel tanks because they are intended for extended cruising, so you’d use a higher-capacity polisher than you might on a boat set up more for overnight or weekend cruising. Trawler companies like Selene, Grand Banks, and Kady-Krogen are installing polishing systems on the majority of their boats today. Most companies that build polishing systems use a well-known separator from a company such as Racor or Separ. Polishing systems are based on a gallons-per-hour rating. If a 65-foot trawler carries 2,000 gallons of fuel, a 600-gph polishing system is recommended.

To get an idea of what a variety of systems will cost: the Reverso 150-gph Fuel Polishing System retails for $2,883. Step up in size to the Gulf Coast Filters FPS-Deluxe-Magnum 360, which is rated for 360 gph, and you’ll spend $6,697. And finally, the Algae-X Smart FPS LX-F is rated for 600 gph and sells for $11,699.

A key to an effective polishing system is its ability to pick up fuel as low as possible in a given tank. The best time to polish fuel is right after a fill-up. Sediment or growth from microbiological organisms resting on the bottom of the tank gets stirred up during fueling. While suspended, these bits of debris and water get pulled into the filters and extracted. You might need to change the unit’s filter element afterwards, but you’ll be ready to cruise with confidence.

The AirDog Fuel-Air Separation system ( takes cleaning your fuel even further. In addition to polishing, it removes air and vapor, a grim combo that can retard injection timing, increase fuel consumption, lower power output, and increase emissions.

When you’re cruising in big seas, the fuel in your tanks sloshes around and traps air in the resulting foam, which the fuel pump then inhales. As the pump’s inner components rotate, the aerated fuel is carried from its inlet side to its pressure side in the gear-tooth cavities. Without adequate pressure to fill these cavities, vapor forms in the voids. Fuel containing entrained air from sloshing and vapor from pump cavitation now flows into the injection system, thereby causing higher fuel temperatures, lower engine rpm, and all the other issues already mentioned.

Because the AirDog replaces your engine’s factory-installed lift pump and filter system, it is able to remove air and vapor from the fuel before it gets to the injectors. Denser fuel combusts more efficiently, producing more power, higher engine rpm, better efficiency, and lower fuel temperatures. Air Dog claims fuel savings of 7.9 percent in a 60-foot cruiser powered by twin 660-horsepower Caterpillar diesels. The company also says that in a Sea Ray 460 powered by twin 450-horsepower Cummins diesels, the owner reports a 20-percent savings in fuel costs at cruising speed, while a 2003 Tiara 3500 Open powered by twin 370-horsepower Cummins diesels, reportedly uses 25 percent less fuel at 2500 rpm with an Air Dog system.

There are three available types of AirDog systems. The Basic AirDog FPII-250 is for engines with a fuel-flow rating of 160 gph or less. It retails for $1,595. The Standard AirDog FPII-250 Marine system for twin-engine vessels flowing 160 gph or less sells for $3,649. And finally, the Deluxe AirDog for twin-engine installations flowing 160 gph or less comes with everything that you get with the standard version plus two high-efficiency fuel-polisher systems with filter heads. The Deluxe AirDog for systems that flow 160 gph or less has a price of $3,995.

In any case, with either the latest in fuel polishers or an AirDog Fuel-Air Separation system onboard, you’ll know for certain that your boat’s fuel is as clean as possible. Which, one way or another, may help you enjoy polishing off something else much more pleasurable when you reliably and efficiently arrive at your destination.

This article originally appeared in the August 2013 issue of Power & Motoryacht magazine.