How to choose an outboard: four-stroke, two-stroke, or neither
Power is the last decision, not the first. Start with weight, usage and the cost of running the engine for ten years — then decide how many cylinders you need.
Buying an outboard is usually framed as a power question: how many horsepower. It is really a weight, usage and running-cost question, and horsepower falls out of the answer.
Start with the boat, not the engine
Every hull has a maximum power rating, and it is there for a structural reason, not a marketing one. Fitting the maximum is not automatically better: an engine at the top of the range adds weight on the transom, raises the centre of gravity and costs more to buy and service. A hull that planes comfortably at 60 percent of its maximum is usually the sweet spot for private use, and a working boat that spends its life loaded may genuinely need the top of the range.
Check three numbers before you compare brands: engine weight, the boat's rated maximum, and the weight of a full fuel load. A twin installation adds both power and weight, and it doubles the maintenance bill.
Four-stroke or two-stroke
Four-strokes burn straight petrol with a separate oil system, run quietly and idle cleanly. Traditional carburetted two-strokes burn an oil-and-fuel mix and lose up to 30 percent of their fuel out of the exhaust unburned. That is the comparison most people still have in their heads, and it is out of date.
Modern two-stroke direct fuel injection engines spray fuel into the cylinder at a moment when the exhaust port is closed. Nothing is lost, and they use roughly the same fuel as a four-stroke of the same power, with less weight and more torque low down. What they do not have is the four-stroke's quiet idle and its tolerance of being run for years at low load.
For a workboat that idles a lot, four-stroke. For a light, fast hull that will be run hard and can live with a little more noise, a DFI two-stroke is often the better engine and 30–40 kg lighter on the transom.
What we recommend for our hulls
On the 21 m centre console, a single 115–150 hp four-stroke is the right answer for most owners. On the 8.5 m landing craft, twin 150s give redundancy and the torque to push a loaded boat onto a beach. Above 10 m we usually quote inboard diesel on shafts, because at that size the fuel burn and the service access favour it.
Buying used, and re-powering
Re-powering an aluminium hull is genuinely practical — the transom does not rot and the hull does not care how old it is. Check the transom plate for corrosion around the mounting bolts, weigh the new engine against the old one, and budget for new controls and gauges. A 2009 hull with a 2024 engine is a better boat than a 2019 hull with a 2014 engine.
