Right Boat – Right Motor Size?
Here is a guide to the correct outboard motor size for your boat.
|Motor HP||Boat length (feet)||Boat length (metres)|
|2hp – 10hp||8’ – 12’||up to 3.5m|
|5hp – 15hp||8’ – 14’||up to 4.2m|
|9hp – 20hp||11’ – 16’||up to 4.5m|
|20hp – 40hp||13’ – 18’||up to 5.0m|
|40hp – 75hp||14’ – 20’||up to 5.5m|
|90hp – 140hp||16’ – 25’||up to 6m +|
Small Outboard Motors
2hp – 4hp Outboard Motors (Usually weigh under 19 kg)
Small outboards are common for portable boats such as canoes, folding boats, inflatable boats, dinghy’s, small sailboats, small pontoon boats and other small light weight boats. These outboards are often two strokes but four stroke engines do start from 1.5 and up. They usually do not have gears although some might have ‘Drive’ and ‘Neutral’. Often the whole outboard motor rotates 360º which is OK for short maneuvers in reverse. Small outboards are usually relatively light weight and have a carrying handle. Four stroke engines are usually a little heavier than two stroke engines.
Small outboards will push small boats up to 8 to 15 kph depending on power, boat weight and design, wind and current.
As auxiliary motors on hulls weighing a bit over 300 kg and around 4.5 m long – small outboards should often get up to a suitable speed for trolling, once again depending on several factors. These small outboard motors are small, light and easy to transport. Stow 4 strokes the correct way (Usually with the fuel tank down and the carburetor to one side.) or the engine oil may flood the cylinder and carburetor.
5hp – 6hp Outboard Motors (Around 18-25 kg)
This hp range of outboards is ideal for a variety of applications including small inflatable boats up to 3.5m in length, portable folding boats, larger canoes with caution, 2.5-3.5m dinghies and inflatable’s. Hulls such as these typically weigh up to about 115kg and require a short shaft (15” shaft length) outboard motor. All outboards in this hp range should also be available in 20” long shaft configurations which is ideal for trailer yachts and auxiliary/trolling motor applications for hulls less than 6m length.
Engines in this hp range are typically 1-cylinder, although some 2-cylinders do exist. Heavily laden boats will not perform well with these small motors.
Engines in this hp range feature heavier duty construction and enhanced manoeuvrability features such as forward-neutral-reverse gears. These engines may have integral fuel tanks and/or separate fuel tanks.
Engines in this range will propel most hulls at approx. 16-28kmh with one person and light load. A good size motor trolling motors on run abouts, yachts to 20ft, and emergency motors on runabouts.
Engines in this range are lightweight, compact and easily transported and many have foward-neutral-reverse gears.
8hp – 9.8 hp ( Weight 25-45 kg)
Small and powerful this hp range is popular for use with inflatable boats of 3m – 4.5m, aluminium boats 3m – 4.5m in length, larger portable folding boats, and lighter fibreglass boats up to 4.5m. These hulls typically weigh to 136kg and require a 15” short shaft length outboard. Engines in this hp range are also available in 20” long shaft and 25” extra-long shaft length making them ideal choices for trailer yachts to 7 or even 8 metres. Also used as emergency auxiliary motors and for trolling. Newer four-stroke outboards in this range are equipped with advanced features such as audible and visual warning indicators for low oil pressure and overheating and electric start and 12v charging capabilities are usually offered as options in this hp range. Most engines in this range feature 2-cylinders and run more smoothly than single cylinder outboards. Outboards will usually come with a 24L separate fuel tanks but four strokes may have an 11 litre tank.
Engines in this range will propel most hulls at about 15-28kmh with one to two persons and/or a light to moderate load
They are a good choice for trolling motors, yacht motors and auxiliary outboards.
15hp – 25 hp (Weight abround 36 kg-52 kg)
These motors can be heavy to handle but are still considered to be a ‘small’ outboard motor.
This hp range is quite popular for use with inflatable boats 10-14ft, aluminium fishing boats 12-16ft, flat bottom boats 12-16ft in length, fibreglass boats 12-16ft in length. These hulls typically require a 15” short shaft length but may require a 20” shaft length as you approach 16ft in length. These hulls weight to 250 kg.
Engines in this hp range are available in both 15” short shaft and 20” long shaft. These hp outboards are ideal for river trolling, as auxiliary motors and in heavier trailer yachts.
Newer four-stroke outboards in this range are equipped with advanced features such as audible and visual warning indicators for low oil pressure and overheating. Electric start and 12v charging capabilities are usually offered on optional models in this hp range. They are usually smooth running and come with auxiliary fuel tanks.
Engines in this range will propel most hulls to around 40 kph with one or more people and moderate to heavy load.