A look 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. Learn insdier 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.
SETTING THE PARAMETERS
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.
The miles per gallon (mpg) that your boat achieves is influenced by a number of variables like weight, engine size, prop size/type/pitch, accessories (like a T-top, hardtop or canvas) the size of the crew, bait/ice/chum and how much fuel you have in the tank. If you spend most of the time fishing in the bay or just off the beach, it probably doesn’t make sense to carry 150 gallons or more of fuel in the tank if you are not going to use it. You are just lugging along all of that extra weight, which will adversely impact your speed and range. A gallon of gasoline weighs approximately 6.3 pounds, so subtracting 50 gallons of fuel from your tank saves you 315 pounds of overall weight. If this is the plan, be sure to use an E-10 fuel treatment like those offered by ValvTect, Starbrite or MDR to neutralize any potential water condensation from the exposed walls dropping into your fuel tank, which is no bueno for E-10 gasoline.
KNOW YOUR BOAT
One of the first things that I do when I purchase another boat (I am currently on vessels #14 and #15 right now.) or when I help one of my charter clients run the numbers with their vessel, is to perform a detailed performance evaluation that is consistent with the theoretical parameters that we established earlier in this article. The one thing to remember about these comparisons when reading the details of a factory-sponsored test (versus your real-world experience) is that the manufacturers are always looking to show their boats in the most favorable light. Accordingly, their vessels are usually tested under ideal conditions, with less of a load and fuel state than most folks would typically employ in their everyday travels. Most test reports state as such if you read the fine print. The manufacturers’ reports are still very useful in giving you a benchmark of performance, top speed, relative fuel economy and range, but just be advised that your results will most likely vary from the norm and will probably be a tad lower in every category.
When conducting two season’s worth of evaluations on my current charter boat, a gently-used 2006 EdgeWater 228CC, I tested out a total of eight different stainless steel propellers of various blade configuration, diameter and pitch. The winner was the one that worked the best under the usual mix of conditions that I experience on an average 100-nautical-mile round trip in bay and ocean waters, and there were some significant differences among the candidates. Some props that appeared to be clear-cut winners in the bay had issues handling an agitated, choppy ocean. In contrast, some props that were slightly slower in the bay, were stalwart performers in big water. My goals were to enable the EdgeWater’s F225 Yamaha four-stroke outboard to achieve the upper middle (5600-5700 rpm) of its 5000 to 6000 rpm operating range at wide open throttle when fully loaded and to get the fastest usable speed in the typical engine cruising speeds of 3700 to 4700 rpm.
Even though the original EdgeWater/Yamaha 2005 factory test results for this boat and motor combo were spectacular, there was no way that I could replicate it with a full tank (125 gallons) of fuel, a T-top with canvas enclosure, three people and 800 pounds of fishing gear onboard using the same prop—welcome to the real world. I ran through a quartet of Mercury props and a quad of Yamahas before settling in on the Yamaha 15½D x 17P, 3-blade, SDS, Saltwater Series II wheel that seems to make this boat and 12-year-old motor strut its stuff with maximum usable speed and predictable fuel economy and range.
MAXIMIZING RANGE, SPEED AND FISHING TIME
To summarize the data I accumulated, the EdgeWater’s optimum cruising speed is achieved in the 4000- to 4500-rpm range, which is where you would expect it to be for a four-stroke outboard if propped correctly. To ascertain this vessel’s range under ideal cruising conditions, you would take 2.22 nautical miles per gallon (@ 4000 rpm) and multiply that by 90 percent of the fuel tank’s capacity (assuming that you started with a full tank of fuel). This EdgeWater is equipped with a 125-gallon fuel cell, so the formula is 125 x 0.9 = 113 gallons of usable fuel. Translated, this center console’s theoretical range is 113 x 2.2 = 249 nautical miles. It also offers me 11 cruising hours of range at an optimum speed of 22.6 knots/10.2 gph, determined by taking 113 gallons of usable fuel and dividing it by 10.2 to produce the magic number of 11.07 hours. So I can choose wherever I want to go to fish within reason, with the knowledge that I will have enough fuel to get there and back.
But be cautioned; these stats are in the bay, under ideal circumstances. To peg my vessel’s best real world range out on the briny, I dropped the optimum nautical miles per gallon number from 2.22 down to a flat 2.0 nmpg. Recalculating the max range numbers, the revised formula is 113 x 2.0 = 226 nautical miles. And this works; every offshore trip that I did last year with a full load of fuel, bait, chum, ice, fishing gear and three to four anglers onboard supported this 2.0 nmpg number like clockwork. For my furthest offshore excursion in 2016, I conducted a 168-nautical-mile round trip from Jamesport, through the Shinnecock locks, out Shinnecock inlet, to the 50-fathom line south of Montauk in Block Channel and back for a total of 84 gallons of fuel used, which is 2.0 nmpg right on the number. This trip included trolling at 2000 rpm/6.8 knots (@ 2.43 nmpg) drifting with the engine on while wreck-hopping and working the lobster pots for dorado (@ 0 nmpg) and running there and back at 4500 rpm/26.3 knots (@ 2.21 nmpg) to maximize fishing time.
The key ingredient of the performance analysis is that my boat has a sweet spot between 4000 to 5000 rpm, as clearly indicated by the science of its performance chart, where it gets essentially the same linear fuel economy (within 10 percent) a hallmark of Yamaha’s first-generation F200/F225 V-6 four-stroke outboards. This means that if the ocean or bay are relatively flat and calm, I can run more aggressively to the fishing grounds at 26 to 30 knots (4500 to 5000 rpm.) If the ocean is rough that day (like usual) I can slow it down to 4000 rpm/22.6 knots with no penalty for fuel economy; it will just take a bit longer to get to the destination, subtracting from the amount of time we have allotted to bend the rods.
If the fishing grounds are 30 nautical miles distant, a boat running there at 30 knots will arrive a half-hour before a boat running at 20 knots and be the first one to the sweet spot. When the fish are there and in a biting mood, this time advantage is huge! If throttling up to 30 knots or more is realistic given your vessel’s optimum fuel efficiency bandwidth, and it doesn’t adversely impact your overall range, this is definitely the way to go if sea conditions permit, and you want to get the maximum amount of fishing time. Just be advised, no matter the size of your boat and how it’s powered, the ocean only lets you go so fast and it might be considerably below your vessel’s top speed or optimum cruising speed. This go-fast concept is the core belief of the SKA circuit and big-money tournament fishing and has bred a series of speedy sportfishers that were covered in detail in last month’s Boat Sense; go there fast and get the maximum amount of fishing time.
Knowing your boat’s optimum fuel economy numbers and its realistic range based on current fuel capacity and optimum cruising speeds are the secrets to knowing how far you can travel and how much fishing time you will get when you arrive on station. It will also tell you when you will have to leave to get home before sunset, race around a storm front, or avoid a potentially unfavorable wind-against-tide scenario in your home inlet without running out of fuel.