The forecast was perfect. A high-pressure system was going to remain stationary just north of the Greater Antilles for the next 48 hours, giving us ample time to make the 500-mile run from St. Thomas in the U.S. Virgin Islands to Providenciales in the Turks and Caicos Islands. My friends Josh and Caitlin had looked forward to this trip for months. After purchasing their 45-foot Symbol trawler in St. Thomas, they were finally ready to bring it back to their home in North Carolina.
As a stoutly built, semi-displacement boat, the trawler carried 750 gallons of fuel in two outboard tanks, monitored with easy-to-read and accurate sight gauges. The boat burned precisely 9 gallons per hour at 9 knots—1 nautical mile per gallon. Josh figured the math was simple; on the planned 56-hour run, they would consume 500 gallons of fuel, leaving a 33 percent margin of safety.
Since this was a new boat to them, Josh and Caitlin had no way of knowing that its fuel pickups were so high in the tanks that the last 250 gallons were effectively unusable. When Caitlin woke Josh at 5 a.m., the fuel pressure alarms were screaming, and she had slowed the boat to an idle. By using the fuel-polishing pump to transfer fuel from one tank to the other, they managed to keep the fuel high enough in one tank to feed the engine. They limped slowly into the only fuel dock for a hundred miles, paying $3,500 for precious diesel.
Mismanagement of the fuel system is one of the most frequent causes of trouble for long-distance power cruisers. Whether the problem is caused by inattention to tank levels, debris in the tank, water contamination, incorrect filters or a lack of regular maintenance, the result is the same: a fuel-starved engine. In the open ocean, where propulsion is critical to keeping your bow or stern safely into the seas, fuel-related issues can escalate quickly into serious stability problems.
Boats utilizing a day tank that needs to be replenished to feed the engines are susceptible to human error in monitoring and moving fuel as needed. Even when fuel use is watched correctly, there are numerous other fuel-related problems that can contribute to a stopped engine. Fuel system reliability starts long before you leave the dock.
One of the most common sources of fuel contamination is bad fuel from unreliable suppliers. Diesel fuel can contain water, sediment or microbial growth that can clog filters and disrupt engine performance. When purchasing fuel, especially in remote areas, prioritize marinas with a reputation for clean, high-quality fuel.
If you’re unsure about the supplier’s reputation, take a proactive approach: Use a fuel sample jar to inspect the fuel visually before filling your tanks. Look for signs of cloudiness, water or debris. Consider adding a biocide or fuel stabilizer after refueling, particularly if the fuel will sit unused for a while.
On your own boat, the best way to avoid fuel degradation problems is to use your boat. Allowing fuel to sit unused in tanks is asking for trouble. If you can’t use your boat, the next best alternative is to polish the fuel on a regular basis. Maintaining the fuel system is a vital part of maintenance, especially for boats with large tanks or those used intermittently. Even high-quality diesel can degrade over time, leading to the accumulation of sludge, microbial growth or water at the bottom of the tank.
A good fuel-polishing system draws fuel from the lowest point of one tank and typically recirculates the filtered fuel to another tank, removing contaminants before they can clog your engine’s filters. Josh and Caitlin’s trawler was equipped with such a system, but many boats are not. Adding a dedicated fuel-polishing system is a worthwhile investment for any long-distance cruiser.
Polish your fuel regularly—more often if your boat sits idle for extended periods or if you suspect contaminated fuel. When our trawler, Liberdade, is in port for extended times, we fully circulate all of the fuel through our onboard polishing system with a large-surface 1-micron filter.
When buying a used boat, fuel tanks are often overlooked during pre-purchase inspections. Tanks can accumulate years of sludge, sediment or microbial growth, which can clog filters and reduce usable fuel capacity—just like in Josh and Caitlin’s case.
When taking ownership of a used boat, have the fuel tanks professionally cleaned and inspected. Check for signs of corrosion, leaks or residue. Ensure that the fuel pickups are positioned low enough in the tank to access the full fuel supply. Even for new boats, regular tank inspections and cleaning are essential to prevent long-term issues.
Fuel filters are your last line of defense against contaminants reaching your engine. But not all filters are created equal, and improper selection or installation can lead to problems. Filters are rated by their micron size, which determines the size of particles they can trap. For most diesel engines, use a coarse filter (30-micron) as the primary filter to catch larger debris. Use a finer filter (10-micron or smaller) as the secondary filter to catch finer particles. Some boats even have a third filter.
On Liberdade, we use a 30-micron primary in a twin-filter arrangement. One of the filters is in standby mode, immediately ready to be placed into service at the switch of a valve. The fuel then goes through two filters on the John Deere engine, a 10 micron followed by a 2 micron. Filters that are not in sequence in a descending order can lead to reduced fuel flow or premature clogging. Regularly inspect and replace filters according to the manufacturer’s recommendations, or more often if operating in areas with poor-quality fuel.
Accurate fuel monitoring is critical for long-distance cruising. Beyond sight gauges, consider upgrading to a digital fuel flow meter for real-time data on fuel consumption and remaining capacity. Knowing the exact fuel available, and ensuring it’s accessible, can prevent unpleasant surprises offshore.
Always carry a fuel reserve beyond your calculated needs. Weather, currents or unexpected detours can increase fuel consumption, and a conservative safety margin can make all the difference. I recommend at least a 25 percent to 30 percent fuel reserve.
Fuel system reliability is critical to safe, enjoyable power cruising. By choosing reputable fuel suppliers, polishing fuel regularly, maintaining clean tanks, using proper filters and planning with conservative margins, you can significantly reduce the risk of fuel-related issues.
Josh and Caitlin learned an expensive lesson the hard way, but their story is a reminder that thorough preparation and proactive maintenance are the keys to trouble-free cruising. After all, when you’re hundreds of miles from shore, the last thing you want is to hear the alarms of a fuel-starved engine.
