Outboard Motors for Small Boats: The Fit Guide Nobody Gave You
Horsepower gets all the attention, but most motor regrets come from the wrong shaft, the wrong weight or the wrong mounting. Get the fit right and everything else is easy.
Outboard motors for small boats are compact engines sized to a small hull’s transom height, weight limit and maximum horsepower, so the propeller sits at the right depth and the boat stays balanced.
Rhys and the propeller that kept breathing air
Rhys bought a tidy little 6 m (20 ft) trailer sailer and, on a mate’s advice, a second-hand short-shaft 5 HP. On flat water it was fine. The moment a swell rolled through the harbour mouth, the stern lifted, the prop sucked air and the motor screamed like a kettle.
He tried trimming it lower. He tried moving the crew aft. He tried shouting at it. Nothing worked, because the problem was a few centimetres of aluminium. His transom bracket sat at long-shaft height, so the prop was barely underwater even at rest.
He swapped to a long-shaft 6 HP. Same power, extra 13 cm (5 in) of leg, and suddenly the prop stayed buried through the swell. Docking went from nervous to boring, which is exactly what docking should be.
His advice to anyone asking: measure before you buy, because no amount of horsepower fixes a propeller that is out of the water.
What shaft length does my small boat need?
Measure from the top of the transom (or bracket) straight down to the bottom of the hull. The anti-ventilation plate should sit roughly level with, or just below, the hull bottom.
| Transom height | Shaft to buy | Typical boats |
|---|---|---|
| About 38 cm (15 in) | Short shaft | Inflatables, dinghies, most small RIBs and skiffs |
| About 51 cm (20 in) | Long shaft | Sailing yachts, some dayboats, higher transoms |
| Bracket on a yacht or catamaran | Long shaft (sometimes extra long) | Auxiliary power where the stern rises and falls |
| Square-stern canoe or kayak mount | Short shaft or electric tiller | Light craft, shallow water |
How heavy a motor can a small boat carry?
As heavy as the builder’s plate allows, but lighter is usually better on a small hull.
A 2.5 HP motor weighs around 13 to 17 kg (29 to 37 lb), while a 25 HP can be 68 kg (150 lb) or more. On a 3 m (10 ft) inflatable, that extra weight at the stern lifts the bow and makes the boat slow to plane. Keep within both the maximum HP and the maximum load, and remember the motor, fuel, people and kit all count.
- Tiller steering suits almost every boat under about 4.5 m (15 ft).
- Fit a kill cord and wear it.
- Choose an electric Torqeedo to cut stern weight on the smallest craft.
Well-fitting outboards for small boats
Picked for common small-boat setups. Prices are starting prices in USD.
How do I check the fit before ordering?
- Find the maximum HP and load. Check the builder’s plate or manual.
- Measure transom height. Top of transom to bottom of hull, in a straight line.
- Check transom thickness. Most small motor clamps take a transom up to about 5–6 cm (2–2.4 in); check the spec.
- Plan the tiller swing. Make sure the tiller can turn fully without hitting seats or tubes.
- Consider fuel. Built-in tank for tiny motors; a separate tank needs a safe place to sit.
Outboard motors for small boats: FAQ
What happens if my outboard shaft is too short?
The propeller draws in air (ventilation), losing grip and speed, and the water intake may not pick up enough cooling water, risking overheating.
What happens if the shaft is too long?
Extra drag, spray and reduced speed, plus a higher chance of grounding the skeg in shallow water. It is less harmful than too short but still inefficient.
Can I put a bigger outboard on a small boat?
Never exceed the maximum HP on the builder’s plate. Overpowering can make the boat unstable and may affect insurance cover.
Is tiller or remote steering better for a small boat?
Tiller steering is lighter, cheaper and simpler, and it suits nearly all boats under about 4.5 m (15 ft). Remote steering makes sense on larger consoles.
Send us one measurement.
Your transom height is all we need to steer you to the right shaft and motor.