Let's Talk About Boat Engines: How Much Horsepower Does my Boat Need?
Match horsepower to your boat's size, weight, and intended use. A small aluminum fishing boat typically needs 25 to 50 hp. A 20-foot runabout handles 150 to 200 hp well. Always check your boat's maximum horsepower rating, printed on the capacity plate, and never exceed it. For casual cruising, stay near the lower end of the rated range to save fuel. For watersports or faster travel, aim closer to the maximum. Factor in total load, including passengers and gear, when choosing your engine size.
Whether you're buying a new boat or simply a new engine, you'll probably end up asking yourself one very frank question: "How much boat engine horsepower does my boat need?"
The answer to that question can vary widely depending on what your vessel is being used for and how much you actually have to spend on an engine. More money means a bigger engine but you do run into diminishing returns after a certain point.
While some answers might be nebulous, the goal here is to provide you with the full picture so that you can make an informed decision about which boat engine to choose and how much horsepower your boat requires.
If you're buying for someone else, you might want to check out the holiday boating gift guide.
How Much Horsepower Does My Boat Need?
Caring For Your Engine
Whatever boat engine you decide on, no matter the horsepower, you'll need to care for it properly to ensure that it lasts. Better Boat de-salt concentrate can help remove salt deposits that might otherwise destroy your engine. You can keep your engine operational for a very long time with proper care.
What Is One Horsepower?
The scientific formula is Horsepower = Torque x RPM / 5,252. If you're like most boaters, that kind of formula doesn't mean a whole lot when it comes to purchasing a boat engine.
A simpler way to think of it is: One mechanical horsepower can lift 550 pounds (or 250 kilograms) 1 foot in 1 second.
With that in mind, all you really need to calculate is the weight of your fully loaded watercraft and how fast you'd like it to go.
If you're putting around in a 14-foot boat that weighs roughly 1,500 pounds, how much horsepower do you need to get it moving 1 foot per second? If you said 3 then you'd be completely correct based on the simplest math.
Of course, a foot per second isn't very fast at all. It comes out to roughly 0.68 miles per hour, which is probably not going to be sufficient for anyone who is looking to actually get somewhere.
Horsepower Per Pound For Boats
When calculating boat engine horsepower, a good rule of thumb is one horsepower for every 25-40 pounds of weight. So, that 1,500-pound boat from the earlier example would have 37.5 horsepower on the low end and 60 on the high end.
Still, it's not a very big engine, but it's leagues better than the 3-HP engine that the amateur calculation came up with.
There are many variables involved in cruising around on the water. Wind and currents will always push you to go their way, and you need the engine power to maneuver your boat quickly. But how quick is too quick?
There are a variety of factors that need to be considered when you're looking to buy a boat engine with just the right horsepower.
5 Factors To Consider
Manufacturer Limits: The biggest thing to be aware of is the recommended manufacturer limits. You definitely don't want to overpower your boat unless you're absolutely sure of what you're doing. Doing so can quickly lead to losing the boat engine or crashing the boat. Trust the manufacturer; they usually know best.
Boat Horsepower-to-Weight Ratio: One horsepower for every 25-40 pounds of weight is usually sufficient, but you'll need to compare these numbers with the other factors in this list to see if you should go with the higher or lower end.
Boat Use: Is this engine going to be your primary movement option? Sailboats generally don't need a massive engine. Speedsters love a big engine, but if you're just a fisherman who enjoys trolling the waters and cruising around at your leisure, you definitely don't need to overdo it on the engine.
Number of People Aboard: When calculating the weight for your horsepower-to-weight ratio, you'll need to ensure that your number is the weight of your vessel when it is fully loaded. So if a heavier passenger wants to go boating, tack on an extra 10-HP to account for the added weight.
Fuel Efficiency: Obviously, the bigger the engine, the thirstier it will be. When you're boating on a budget, it might be wise to go a little slower with the smaller engine option. You'll save money on the engine itself, as well as the gas for it in the long run.
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