New outboard technology plus an uncertain economy equals a trend toward repowering. That's a simple formula. But choosing the right power doesn't follow easy equations.
Historically, boating anglers have opted for maximum horsepower on their transoms. Getting to the fish fast and getting home quickly spells customer satisfaction. But with fuel prices fluctuating and savings more important these days, anglers are throttling back - checking out minimum versus maximum power. And in fact, throughout 2009, outboard manufacturers generated a host of new lower-horsepower outboards.
The question is: How low can you go?
Highs and Lows
Boat manufacturers determine max horsepower based on U.S. Coast Guard regulations and formulas. Federal authorities do not regulate minimum horsepower, but builders do offer various power packages.
Max horsepower is all about safety; minimum horsepower is all about expectations. "We usually opt to go with higher horsepower," from a marketing standpoint, says Jeff Hudson, engineering manager for Century Boats. "We've learned today that expectations are high. When people get into boats, they expect them to perform."
So the first step toward repowering is to consider how you use your boat. Do you run offshore most frequently in rough seas where you can't run at wide-open throttle? Do you troll? How fast do you need to cruise? How often are you on and off plane?
If the performance numbers that really matter to you all start with a dollar sign, you need to know and remember that top-end speed and time to plane may bleed off as you drop horsepower and fuel-efficiency could vary.
Physics and Power
"Boats have a tremendous amount of drag, so you don't want to under-power them," says David Meeler, product-marketing-information manager for Yamaha Marine Group Company. "People don't really understand how much drag there is. If everyone stands up on a boat and you chop the throttle, everyone's going over the bow.
"But when it comes to actually determining the cutoff level for what's too low, there's no scientific formula."
That's because so many factors come into play. A deep-V hull, for instance, needs more horsepower to get up out of the water than a flat-bottom skiff, which practically starts out on plane.
Also, while bigger engines cost more, they often prove more fuel-efficient at speed because they don't have to work as hard as smaller engines. But that's dependent on the overall weight of the boat, including its contents.
You might be able to pay a naval architect several hundred dollars to run a power-curve analysis on a given hull and outboard, or you may convince your dealer to test a particular hull with smaller and smaller engines. But the best option for choosing ultimate horsepower is to research performance bulletins for your vessel and outboard.
Performance bulletins can be found on the websites of all major outboard and boat manufacturers, or you can request one through your dealer. Know, however, that manufacturers test boats based on what they consider to be the optimal packages for performance. Still, these bulletins offer a way to compare two, three or more outboards side by side.
For instance, at a midsummer Yamaha product rollout last year for the new F25 and T25 outboards, the company hung an F25 on the new Sundance FX 17 Flicker flats boat. Sundance and Yamaha have tested that same vessel with F50, T60, and 70 four-stroke and two-stroke engines. Max power is rated at 70 hp.
Here are some of the numbers; all packages were tested in light winds and warm temperatures with two people aboard, a full fuel tank, one battery and safety equipment:
|Engine||Time to Plane||Optimal Cruise||Top Speed||Package Price|
|F25 (four-stroke)||6.43 seconds||10.5 mph @ 3,500, 11.67 mpg||25.9 mph @ 5,800 rpm, 8.09 mpg||$13,690|
|F50 (four-stroke)||4.68 seconds||23.7 mph @ 4,500 rpm, 8.78 mpg||32 mph @ 5,800 rpm, 6.67 mpg||$16,290|
|T60 (four-stroke, high-thrust)||3.68 seconds||17.8 mph @ 3,500 rpm, 9.37 mpg||35.5 mph @ 6,050 rpm, 6.12 mpg||$16,980|
|70 (two-stroke)||4.59 seconds||23.8 mph @ 3,500 rpm, 6.26 mpg||39.1 mph @ 5,500 rpm, 4.95 mpg||$15,680|
The least expensive package is the Flicker with the F25 four-stroke. The best hole shot goes to the T60, and the best top-end goes to the 70 two-stroke. Comparing gas mileage gets tougher.
If a 10.5-mile-per-hour cruising speed suits your style, you'll get 11.67 mpg with the F25. But if you want to cruise at about 20, you're looking at 8.78 mpg (at 4,500 rpm) with the F50 and 6.26 mpg with the 70.
Of course, these bulletins are just guidelines. You may carry more people and gear aboard on any given fishing trip; more weight affects speed and fuel economy. Pricing, generally not found on bulletins, can vary from dealer to dealer, especially these days.
Larger vessels with sharper V-hulls and more weight may not be suited for a wide variety of power options. Often, manufacturers run tests with only one or two outboard packages, sometimes three.
Century specs out its 3200 center-console for twin 225-, 250- and 350 hp four-strokes. For instance, a pair of 250s allows the 32 to cruise at 24 mph, turning 3,500 rpm and getting 1.69 mpg. The 350s push it to 32 mph at 3,500 rpm, but fuel-efficiency remains a very viable 1.44 mpg.
Top-end speed with the 250s hits 47.8 mph at 6,000 rpm, getting 1.12 mpg. With the 350s, the boat moves 55.4 mph at 5,800 rpm, with 0.84 mpg.
"A general rule of thumb from a technical standpoint is that 10 percent, or a little less, of your stated horsepower is going to be your gallons per hour at top speed (note: not miles per gallon)," Meeler says. "A 250 at wide-open throttle will burn a little less than 25 gallons per hour. A 350 is going to be about 33 or 34 gph."
Again, the choice usually boils down to what you do with your boat, he adds: "I've got a boat with a 175, but I really could do what I do with just a 10. I never run over about 1,000 rpm. I'm just puttering around, doing a little fishing. If that's the way people use their boats, they don't need the top of everything."