One of the most important factors when buying an outboard motor is to match the correct horsepower with the boat you want to power.  It is very easy to under power as well as overpower your craft.  Under power your boat and you will be putting unnecessary drag on the motor and performance will be sacrificed.  Too much power can cause damage to your boat or even cause personal injury.  The most important factor in deciding on the amount of power to use on your boat is to always stay within the recommendations of the manufacturer’s horsepower maximum limit.  As a general rule of thumb, you should go with around 75% of your boat’s maximum horsepower rating.  If you plan to be fully loaded when you use your boat, try to get as close as you can to the upper horsepower limit.

Outboard Engines – Small:

2 hp – 4 hp (Less than 35lbs)

Most engines with this horsepower rating are two stroke motors with a few exceptions being four stroke. These motors are perfect for nearly any small boat. Some of the normal applications would be to use them on canoes, other portable boats, small sailboats, 8-12 foot aluminum jon boats, and even on inflatable boats.  If the boat you are using will draft in 4 inches of water when loaded – which usually means the capacity is one person with gear this size motor would be a good choice.  In many cases the gas tank is built into the cowling, where there is no need for a separate gas tank and fuel line.  When deciding on a motor in this class, you will need to consider its weight.  Motors of the same horsepower can vary greatly in weight, so depending on the boat you are planning to use it on; it may make a difference in performance.

Pros

-          Boats can reach speeds of about 5 – 10 mph depending on the weight of the boat and the power of the motor.

 

-          These engines will push a boat faster than trolling motors will.

 

-          You can use the motor as a ‘kicker’ motor and push a much heavier boat at respectable trolling speeds.

Cons

-          With a heavier boat power is dimished and you will be disappointed

-          Small gas tank limits range without extra fuel being brought along

 

5 hp – 8 hp (From around 40lbs- 60lbs)

These are portable mid-range light-weight outboard motors. These motors will plane out canoes, jon boats, portable boats, and small inflatables. These engines are nice because they are powerful and still light enough to transport with ease.  A perfect uses for these motors are on just about any small to midsize sailboats and to use as kickers on boats less than 20ft. These outboard motors are great for boats that weigh 50-250lbs, range from 8 to 14ft, and can be carried with two people or less.

Pros

-          You can expect to have a top speed of around 18 mph with one person on a light boat – the general range would be 10 – 18 mph

 

-          Will work great for trolling, sailboats, and emergency back-ups

 

-          Sometimes motors of this class will perform differently with several people on a boat or if the boat is fully loaded with gear.

Cons

-          Performance is great unless craft is fully loaded.  You tend to not be able to plane out.

 

9.9hp-18hp(From around 65-100 lbs)

Also called the powerhouse of small outboard engines, these engines are very versatile and are used in almost every small boating application. These motors are very popular for those needing the power to get to distant locations. They are also popular among fisherman who have at least 2 occupants aboard or have heavy gear to transport. They can be used on large sailboats ranging from 16-25ft with no problem and are an excellent choice for jon boats, large canoes, 9-12ft inflatables, and small fiberglass boats ranging from 11-16ft. Boats in this class usually weight from 120-600lbs+. These engines are still very portable and transported and moved around fairly easy.

Performance

-          You can expect to go about 15-25mph on light boats

 

-          If a 6-8 hp is not powerful enough usually a 9.9hp-18hp will be enough of an upgrade.  

 

-          Motors this size sometimes have an electric start option and battery charging capabilities

 

20-35hp (From 100lbs-150lbs)

These outboard motors are very popular outboards.  They bridge the gap between small and medium size fishing boats. These engines will move your light fiberglass skiffs and large jon boats at decent speeds.  For those who need to travel 5-30 miles, the best way to go is with no less than a 20 hp outboard motor. These motors are great for light boats ranging from 13-18ft as well as sailboats and pontoons. You can also use these engines on large inflatables, large canoes, 14-18ft aluminum jons, and large sailboats. If you carry 3 or more people and wish to get up on plane you should go with no less than a 20 hp outboard.

Performance

-          You can expect to go about 20-30mph on most light boats

 

-          If a 9.9hp-18hp barely planes your boat a 20-35hp will be a sufficient upgrade.

 

Large Outboard Motors

40hp -75hp

These engines are perfect for your 14-18ft fiberglass fishing and cruising skiffs. They work well on 16-22ft pontoon boats and 20ft+ aluminum heavy-duty jons.  These motors can get you to your destination at 30+ mph, which could easily pull a skier or inner tube.

90hp-140hp (V-4 or less)

These are your powerhouse midrange outboards.  They are used on just about any boat ranging from 16-25ft and will push bass boats and flats boats 55mph with ease.  They will work on 20ft-25ft offshore boats, and are ideal for your pontoon boat as long as it is rated for the hp.

150hp-300hp (V-6 and V-8)

These outboards are your big guns and will push your 22-28ft fishing craft and can also be used as twin outboards. They will run bass and flat boats at speeds of 60mph +. These motors are more common in the 25″ shaft length since they are found on the largest outboard personal watercrafts.

 

Shaft Length:

The length of the shaft should be considered when purchasing an outboard motor.  Shaft lengths are standardized to fit 15-inch, 20-inch and 25-inch transoms. If you choose a shaft that is too long it will extend farther into the water than necessary creating drag.  This will greatly impair performance and decrease fuel economy. If the shaft is too short, the motor will be prone to ventilation or cavitation. What is worse, if the water intake ports on the lower unit do not fully extend into the water, engine overheating is likely, which can result in engine and shaft damage beyond economic repair.

 

Final thoughts:

Overall, when buying a ‘small’ outboard, I would recommend that you get the upper end of horsepower recommended for your boat.  If you don’t you will be setting yourself up for disappointment.  As an example, I have a 10ft aluminum jon boat and put a 5.0hp Briggs and Stratten 4-stroke on it.  While the motor runs great, I took it out on a slough of the Mississippi river.  There was very little current and even less traffic.  My GPS told me that my average speed was about 8 mph, even with the boat overloaded with gear and myself (pushing the upper limits of the boat’s weight limit).   You would be surprised how slow 8 mph feels, even in a very small boat.  The recommended max hp for that boat is 9.9hp, which I will get if I decide to keep that boat. I guess my point is that you should get close to the upper end of the hp max rating or you will be disappointed.