How Much Horsepower Do You Need? The UK Outboard Motor Guide

Outboard horsepower ranges from 2.5HP for tenders to 300HP+ for offshore boats — the right size depends on your hull weight and intended use, not just boat length. Buying too little HP leaves a boat sluggish and struggling to plane; buying too much adds unnecessary weight, cost, and strain on a transom that isn't rated for it.

Portable: 2.5HP–6HP

Suits dinghies, yacht tenders, small inflatables and auxiliary power on a sailing yacht. These engines weigh 13–30kg, are easy to lift on and off a transom, and often have an integrated fuel tank. Browse our Portable Outboards.

Mid-range: 8HP–40HP

The workhorse band for RIBs, day boats and small fishing craft. This is where electronic fuel injection starts to appear, improving cold starts and fuel economy. Browse our Mid-Range Outboards.

High-power: 50HP+

Offshore boats, larger RIBs, and commercial or twin-engine setups. At this range, drive-by-wire throttle control and multi-valve engines become common. Browse our High-Power Outboards.

Electric HP-equivalents

Electric motors are rated by an HP-equivalent figure for comparison — our range spans roughly 0.5HP-equivalent trolling motors up to 40HP-equivalent pod drives. See our electric outboards explainer for how the rating works.

Shaft length — the other half of the equation

Measure your transom height from the top edge to the bottom of the keel: roughly 15in (38cm) needs a Short shaft, 20in (51cm) a Long shaft, and 25in (63cm) an Extra Long shaft. Getting this wrong causes cavitation and poor performance regardless of HP.

Worked examples

A 12ft RIB for weekend use: typically 15HP–30HP mid-range, Long shaft. A yacht tender under 3m: 2.5HP–6HP portable, Short shaft. Sailing yacht auxiliary power: either a 4-stroke portable or an electric equivalent for silent manoeuvring in marinas.