Boat Buyer's Guide: How Much Horsepower Do You Need?
When spec'ing out a new powerboat, the first question most buyers ask is, "How much power do I need?" We understand that. Most people want more of everything, and we like cracking open the throttles and feeling the wind in our rapidly thinning hair, too. If money's no object, why not? The cost of adding horses isn't much compared to the bottom-line price of a new, nicely rigged boat. But sometimes pure muscle should take second place to finesse. Matching the drive system to the boat's intended use, or picking the right number of engines, can be as important as total horsepower. Here's a quick guide to help make those decisions.
How Much Power?
First thing’s first: how much power does any boat need? Today, no reputable builder will sell an underpowered sea dog and suffer slings and arrows from unhappy buyers who trade up to another builder's boat in a couple of years. Unless a builder is offering true "granny power" to keep base cost low, the "standard," i.e., least expensive, option should be satisfactory. Upgrading horsepower often adds to the bottom-line cost faster than it adds performance to the boat, and this is more common as power and speed increase.
Outboard Engines
Choosing 350-hp engines rather than 300s might be worth the price of 3-4 knots of extra speed to some buyers, but jumping from 350 to 400, maybe not so much. If we found a boat that suited us in most ways, but whose price was within budget only with standard power, we'd go for it. How much time does anyone actually spend with the throttles wide-open, anyway? Cruise speed, comfort in choppy water (which means throttling back), and fuel economy is far more important.
Depending on the size and weight of the boat, again, the builder knows how the boat will perform, so you should ask the dealer his recommendations for the cruising speeds you wish to achieve. Use BoatTEST’s data for the boat you want to purchase, or for similar boats, as a good guide to what you can expect.
Stern Drive Boats
The days when entry-level boats were powered with the 3.0 L 135-hp GM block are pretty much over. Virtually all builders have upgraded to the 4.3 L or 4.5 L 200-hp to 250-hp stern drive engines, as the 3.0 L engine is no longer available.
The expected load is very important for sterndrive boats when selecting horsepower. If you are going to have lots of people on board and want to do towing sports, we recommend going for the big engines offered. If your boating will be just mom and dad and two small kids, the standard engine should be fine.
Inboard Diesels
On larger, diesel-powered boats, load is not such a critical factor. Here, you want to find at what speed the boat will go at 80% load, or a few hundred RPM below WOT. This speed depends on the size and type of boat. A 42-footer (12.8 m) might be comfortable cruising at 27 knots, a 55-footer (16.8 m) might best be operated at 17 to 20 knots, and so forth.
Some motoryachts have optional engines that will drive them at speeds in excess of 30 or even 40 knots, but buyers need to ask themselves if they really need to go that fast. Except in near-calm conditions, these top speeds are inadvisable. Most guests will be uncomfortable banging around at high speeds in a rough chop. And, of course, these engines process fuel at a prodigious rate.
High Performance Boats
Shopping for a high-performance boat? Then forget the foregoing; there's nothing worse than show without go. Who wants to ride around on a boat with sexy graphics, plush upholstery, and race-bred controls and rigging, but with puny engines under the hood?
Folks shopping for a high-performance boat should buy the biggest engines they can afford, even if it means not adding other, less important, options. Otherwise, they'll face the scorn of the go-fast crowd. (They must also learn how to drive the boat, or they'll wind up upside-down.)