Selecting the appropriate marine power is crucial for achieving optimal boat performance. US Coast Guard regulations guide this process on some boats, but among larger vessels over 20 feet in length overall, the calculation is guided both by regulations and by builder experience. Adhering to the manufacturer’s capacity plate is vital to avoid overpowering, which can lead to balance, buoyancy, and safety and handling issues. For monohull boats under 20 feet, Coast Guard regulations specify a formula based on boat length, transom width and transom height and factors such as manner of steering equipment to determine maximum horsepower.
What’s more, different types of boats require varying horsepower. For instance, easy-going pontoon boats run happily on 50 hp while performance-pontoon guys want 300 hp or more. Flats skiffs tend to go low on horsepower to save weight, but bass boats of a comparable size could carry up to 300 hp. Today’s offshore center-consoles and some cruising dayboats could carry as many as five 400 hp outboards. Ski and wakeboats often demand 300-plus hp to maintain towing speeds with ballast aboard.
The primary purpose of the boat significantly influences horsepower needs.
A general guideline once suggested 1 horsepower for every 25 to 40 pounds of boat weight. But, a 2,000-pound bass boat with only 90 hp on it would sit forever on the sales lot. However, that same vessel assumed to carry three passengers, tackle and 200 pounds of fuel would call for more like 150 hp. The weight of a boat properly loaded has to be considered.
The bulk of these considerations is addressed by the boatbuilder before the plan leaves the CAD phase. Once it does, a prototype is built and the power calculations are put to the test. In many cases, builders adjust the maximum horsepower up or down, based on performance factors experienced.
Rough waters demand additional power to maintain control at midrange rpm required by seas. Overpowering a boat poses risks, including reduced handling, failed transoms and voided warranties. Balance is essential.
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Larger engines can be more fuel-efficient than smaller ones struggling under heavy loads. They operate effectively at moderate rpm, conserving fuel.
Our test team usually encourages boat buyers to select the highest horsepower available on a given model. But we’ve found exceptions to that rule. Often, higher-horsepower models are built on a block that has been developed for lower horsepower. Horsepower is increased by raising the wide-open throttle instructions in a motor’s electronic control module. However, in many cases, “mapped up” motors don’t provide significant improvement over the engine one rung lower.
On my second Ranger 2510, I installed a 400 hp outboard. My previous one had the same block in a 350. Performance right up until WOT was comparable. Top speed was increased only 1 mph or so. But the extra 50 horsepower raised my insurance considerably, along with my purchase price. A single horsepower averages out at about $100, making the motor substantially more expensive.
When selecting between engines, choose the offering with the bigger displacement. That’s real horsepower that matters all the way through the power range. In multiengine vessels, that incremental mapped-up horsepower can make a noticeable difference through the power range.
Max power is always a powerful calling card.
When choosing horsepower—be it in a new boat or repowering an existing one—arm yourself with information. Study manufacturing performance reports on comparable boats. Follow published editorial reports such as those found on this site.
Remember, horsepower is king and more is almost always better.
