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Boat Sense


The Fisherman's "Boat Sense" column for July looks at your boat’s optimum fuel economy and realistic range, the secrets to knowing how far you can travel and how much fishing time you will get.

By Capt. John N. Raguso
Knowing your boat's optimum fuel efficiency and range are key considerations when maximizing fishing opportunities, particularly when pressing your way offshore.

I have been a professional boat tester for four decades and have authored over a thousand published evaluations of boats and motors for their overall performance, handling, fuel efficiency, etc.

In this month’s Boat Sense (July, 2017 edition), I detail my insider tricks on how to tweak maximum range and usable cruising speeds out of your old or new boat, with the net result being to extend your fishing time out on the water.

Every boat test starts the same way, with a spreadsheet that sets up the parameters of capturing critical data to determine if a vessel is achieving its maximum potential for speed, range and fuel efficiency. Just about every boat manufacturer employs a similar methodology, either by themselves with their in-house engineering staff, or in collaboration with one of the outboard (or inboard) engine manufacturers. Yamaha, Mercury, Evinrude and Suzuki all feature dedicated websites with many hundreds of current and historical boat tests for the reader’s perusal.

As a general rule, when determining if a vessel is equipped with sufficient range for canyon running, I have always employed the rule of 10 and 12. An ideal bluewater boat should have a minimum of 10 hours cruising range at optimum fuel efficiency throttle settings, but 12 hours is really the “magic number” as it eliminates a lot of unnecessary math calculations when underway and most causes for concern about potentially running out of fuel in the dark ocean or a raging inlet.

To see how this works in real life, let’s assume that your favorite 28-footer equipped with twin 250-horsepower outboards burns 22 gallons of fuel at an optimum cruising speed of 27 knots when fully loaded with fuel, ice, bait, fishing gear and crew. How large should your fuel capacity be to accommodate the minimum guideline of 10? Take your hourly fuel consumption of 22 gallons and multiply it by 10 to get a baseline of 220 gallons. But it’s inadvisable to use the stated capacity of the existing fuel tank, since your fuel pickups can’t access every bit of fuel sloshing around in the tank’s bottom. Most engineers use 90 percent of the tank capacity as a realistic usable fuel measure, so we add another 25 gallons of capacity to the tank to get to a total of 245 gallons. A 245-gallon fuel cell will offer a net 220 gallons of usable fuel at the 90 percent capacity benchmark. If your boat doesn’t have a tank that size, you are not going to be running to the canyons safely.

How does that translate to a real day out on the blue water? Let’s say that it will take half an hour to get to the inlet from your dock and three hours to run to the 100-fathom line. Double that for the return trip and seven of the 10 hours of your vessel’s stated running range is already spoken for without even bending a rod! If trolling is on the menu, you will typically burn a third of the running fuel consumption number (7 gph) when tooling along at 7 knots or so (at 1 mpg), so you can safely drag the baits through the water for nine hours—and there’s your day planned out scientifically.

It works out to seven hours of running, plus nine hours of trolling, for a sun-up to sun-down experience. But you are right on the edge with only 10 hours of fuel capacity when running, hence the concept that 12 (or 11) hours of travelling at optimum cruising speed affords you a more favorable comfort zone. If your boat burns less fuel than stated in this analogy, or is faster or slower, then the numbers change and everything needs to be recalculated. Hostile sea conditions also skew the numbers, with the result being to cut down on your range. If our theoretical test boat were to spend 10 hours running at an optimum speed of 27 knots, its max realistic cruising range would be 10 x 27 = 270 nautical miles.

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