See full version: How to Determine the Outboard Motor Size for Your Boat
Work the equation the other way if you boat by yourself. Divide by 1.10: 120 / 1.1 = 109. Boating by yourself, you could get about the same performance from a 100 or 110 horsepower motor as you do from a 120 horsepower motor and save fuel.
Your boat will tell you how much outboard it needs. Every boat has a maximum number of people it can carry, a maximum load of equipment it can carry and a maximum horsepower rating. The horsepower rating is based on the boat's "hull design speed." Even if your boating needs and circumstances may be different than those the designers used when doing their calculations, you can use their work as a beginning and, with a bit of math and a look at your boating habits, determine the right outboard motor size for your boat.
Ask yourself how many people are usually with you when you go boating. Use a calculator, if there are several passengers, to multiply the top horsepower rating by 1.10. If the plate says a 120 horsepower engine is the largest you should use, then: 120 x 1.1 = 132, or a 130 horse motor, since the horsepower of outboard motors is rated in multiples of 10. This adds ten percent to the horsepower and will make it easier for your boat to carry the load of several people more efficiently.
Locate the National Marine Manufacturers Association Certification Plate on the inside of the stern of the boat. The NMMA plate contains important information which you should know, including the number of people the boat can carry and the horsepower rating of largest motor you should use.
Will Charpentier is a writer who specializes in boating and maritime subjects. A retired ship captain, Charpentier holds a doctorate in applied ocean science and engineering. He is also a certified marine technician and the author of a popular text on writing local history. here
Go with the max you can. Best for fighting currents and some reserve power. The difference in fuel is hardly noticeable. more
The old blue and white Honda's are great motors, require little added maintenance and are not that much heavier. If you are choosing between a 6hp and the Honda 7.5, I'd go with the Honda.
Just to add a small note: The 6 hp I use is fine for me, since I'm almost always on small lakes. I use it on the river, but only when I'm by myself. [links]
Not knowing the size of the river and what the current is, I can't say for sure, but most 12' boats do fine with a 6-or-so.
I had a 12' Alumacraft semiV. Ran a 9.9 McCullough on it and it ran out really well.
I think the easiest way to tell is to weigh the boat. a 170# 12 footer today is rated at 10hp a
200# is rated at 15. Older boats from say the 60s a 90# is rated at 6 hp a 140 at 30hp.
I think weighing is easier than trying to match up size.
I have a friend with a 14 footer that you would swear was a 12 even on a trailer
where boats seem bigger.I think a couple of guys could weigh a 12 or 14 ft bare utility on a bathroom scale.
We used to car top a 15 ft Lone Star on top of a van.
A 10 hp could make over 20 on a 12 footer The bigger the a bare bones boat the easier to get on plane with a load. [links]
Re: 12 Foot aluminum, max horsepower?
I second Bob, a 10 is about the biggest you can safely run on that and it is really all you need, a 15 would be downright scary and unsafe, what brand and year of boat would help too. more
The easiest way is to look at similar size boats being sold with similar beam (width) and hull design and look at their specs.
Re: 12 Foot aluminum, max horsepower? more
As we mentioned earlier, you need to match the size of your outboard to the size of your boat to ensure that you have sufficient power for speed, maneuverability and safety. However, the advantage of going with a smaller outboard is that it's easier to lift and carry. Most 2HP-10HP outboard motors weigh in the neighborhood of 35 to 90 pounds. When you move up to 20HP-30 HP, you can expect you motor to weigh roughly 100 to 160 pounds.
Measure from the top of the transom to the bottom of the hull – this measurement should be taken in the center of the transom for a single engine application. For a short shaft, your transom height should measure 15 to 17.5 inches. If your transom measures 19 to 22.5 inches, you'll need a long shaft. And there are extra/ultra-long shafts for transoms measuring taller than 22.5 inches. The ultra/extra long shaft models are commonly used in kicker and auxiliary applications where the outboard is mounted to the port side of a main motor, or on a bracket (as is the case with sailboats). [links]
Already have an outboard but want to retrofit it with an electric start? Beware. It may be more cost efficient to buy a new motor with electric start.
If there's one point of discussion in the world of outboard boat motors, it's the debate between 2-stroke and 4-stroke motors. In reality, both are good choices. Which is best for you depends on what features are most important to you. more
Boaters – and prospective boaters – invest considerable time in evaluating different types, makes and models of watercraft before purchasing a boat. But, when buying outboard boat motors, do they take enough time to ensure they're getting the outboard that's best for their boat and leisure activities? Not always.
Do you want 2-stroke electronic fuel injection (EFI)? 4-stroke EFI? 2-Stroke direct fuel injection (DFI)? Or an old-school 2-stroke carbureted model (Effective July 1, 2019, U.S. retailers can no longer sell these due to environmental laws and regulations limiting carbon emissions)? more
Jake . a 3 hp will move a small 12' jon OK. I rather have a 3 HP than a paddle . you are not going to be "flying" by no means . [links]
Jake . a 3 hp will move a small 12' jon OK. I rather have a 3 HP than a paddle . you are not going to be "flying" by no means .
I would look for a good used larger motor over a new lower HP motor . just be careful and check a used one out good before hand . more
If that is what you can afford . get it . but a 9.9 or so would be better . so would a 5 hp or a 7 hp . [links]
I fished the Satilla for many years with a Elgin 7.5 on a 14' jon boat . it was slow . but I caught fish .