Three numbers, not one
- Maximum horsepower — the number everyone quotes.
- Maximum engine weight — the number that actually governs most small tenders.
- Shaft length — short shaft is the design assumption on much of the inflatable-catamaran market. Get this wrong and the boat is unusable.
Practical guidance
On a packable tender, every kilogram on the transom is a kilogram you lift over the pushpit twice a day. A 3.5 hp two-stroke-era engine weighed very little; a modern 6 hp four-stroke does not. Be honest about what you will lift at 60.
Electric outboards have become genuinely viable at the small end. The Takacat T220UL, for example, is designed around propulsion of roughly 2 hp equivalent and around 10 kg — and for many owners that is the whole boat solved.
Buying boat and engine together
There is a real argument for buying the tender and outboard from the same brand ecosystem. Mercury is the clearest Australian example: inflatable, outboard and national engine dealer support in one transaction, which matters enormously when something fails in a regional port.