One of the most asked questions of boat owners is: “How much horsepower do I need for my boat?” Whether you are tired of your old engine or it simply doesn’t work as well as it used to, the amount of horsepower you put on your boat is crucial.

The answer to this question is not simple because there are some criteria that you need to consider before getting to the right conclusion. You also need to understand what is horsepower and how it is calculated to be able to make an educated decision before getting a new engine for your boat. 

What is Horsepower?

A horsepower is a measuring unit that is used to measure how powerful an engine is. It’s used for all types of engines including boat engines. It was named horsepower because at the time an engine was invented, people were still using horses to do their work and go from one place to another. For marketing reasons, the scientist that invented the steam engine calculated how much work one horse can do in one minute and discovered that a horse could move 33,000 pounds for one foot in a minute. To make people understand that the engine he created can also do mechanical work, he explained to the people how many horses one of his engines can replace. That’s why the measuring unit is called horsepower and why it’s defined as a unit of power that is equal to 550 foot-pounds per second. 

How is Horsepower Calculated?

To understand how the amount of horsepower of a boat engine is calculated, we must talk about torque first. Torque is a force that is able to rotate the body of the item it is applied to. In our case, the propeller is used to move the boat. In the boat engine, the torque is critical and it is related to horsepower. To relate the two, you need a dynamometer. This dynamometer is able to put on a load on the outboard motor engine and measure the power it can produce. Once the amount of power is known to us we can determine the torque force. To calculate the horsepower all we need to do is to multiply the torque by RPM (revolutions per minute) and divide the result by 5252. The final number you get is the horsepower of the gas engine.

How Much Horsepower Do I Need For My Boat?

The safest way to determine how much horsepower you need for your boat is to know the total weight of your boat. The rule of thumb is to have 25-40 pounds of weight per 1 horsepower. If your boat weight is 800 pounds you would need a 32-20 horsepower engine. 

Although this method works and it’s generally safe, you can go with a different approach but you will have to take into consideration some other factors such as manufacturer limits, primary use of boat, how many people you plan on taking on the boat and so on.

Manufacturer limit

To check the manufacturer limit, locate the capacity plate or grab the manual. There should be a few lists with limits that you should not exceed to stay safe on the water. Among these lists, you will also find the maximum horsepower your boat can handle. Based on that you will know if you need a smaller motor or a larger one. 

What will you use your boat for

Another important factor is boat use. You won’t need a lot of horsepower if you are planning on cruising with friends and family but if you plan on pulling wakeboarders, tubers, and water skiers, you will definitely need higher horsepower. The more equipment and boat weight you add the more horsepower you need to be able to pull all that weight efficiently. 

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Number of people on the boat

The number of passengers you plan on having on the boat is also going to have an impact on the horsepower you are going to need because more people means more weight. If you are going fishing alone or with one other person, you won’t need several outboard engines to pull your weight because the boat won’t be that heavy. On the other hand, if you often enjoy going out on the water with your entire family, you may need the extra horsepower.

Fuel efficiency

If you are one of those that want a fuel-efficient engine, the amount of horsepower of your engine will directly impact the fuel consumption so you should select the engine carefully. If you pick a higher horsepower engine for your boat it doesn’t mean that it will be less fuel-efficient. You need horsepower that would work between 3,000 and 3,500 RPM to be as efficient as possible. Depending on the feet in length and the weight of your boat, you may need more horsepower to make sure it’s working in the sweet spot. You don’t want to get a lower horsepower engine and have it work on full throttle all the time because full-throttle consumes more fuel. 

Federal Regulations

Determining the maximum horsepower of your boat is important because of the law as well. Overpowering your boat is illegal as it is unsafe and may endanger your life and those in the vicinity. Usually, the capacity plate should have this listed because these regulations require them to put it on the plate. If you follow the recommended amount you shouldn’t have any trouble with the law.