Two- vs Four-stroke outboards

By: Andrew Norton

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  • Trade-A-Boat

Are four-stroke outboards worth the extra cost over two-strokes?

Two- vs Four-stroke outboards
Testing Tohatsu outboard motor

With the banning of the sale of new carbie two-stroke outboards in Oz next year, is it worth investing in a new four-stroke outboard or buying a two-stroke while you can? After all, outboard manufacturers must guarantee spares availability for 10 years after the sale of every engine.

So even if you buy a new two-stroke this year, spares will be available until 2028.

For sheer reliability two-strokes are very hard to pass up. For example, my 2005 Tohatsu M8B is the most reliable outboard I've ever had, simply because there's so little to go wrong compared to a four-stroke outboard. And its light weight of only 26kg means I can lift it from trolley to transom without breaking my back, whereas a four-stroke 8 weighs upwards of 37kg. Not only is this over safe lifting limits for one person but on my early seventies 3.35m Savage Gull tinny the weight on the transom would severely damage it, not to mention the old trailer on which it sits. This is a common problem with older hulls that were just not designed to take the additional weight of a four-stroke outboard.

In comparison, my 2003 Sea Jay 3.4 Punt is rated to 42kg on the transom, fine for the hull but not my back. So if I were to run a four-stroke 8 it would have to be a bolt-on unit meaning that when the engine needs a service the entire boat would have to be towed to a dealer, way more complex than just taking the outboard itself.

Another example is the 1988 3.6m Sea Al Super Skua I owned for 25 years. Though it was rated to 20hp this meant two-stroke and not four. The most powerful engine I tested on this hull was a Tohatsu M18, which weighed 41kg and drove the hull with two adults aboard out to a positively scary 27kts. Yet when I tested a four-stroke Yamaha F9.9 20 years later this engine weighed 40kg and drove the hull to just over 19kts. No way in the world could the hull take the 50kg-plus weight of a four-stroke 20. With both the Tohatsu and Yamaha engines freeboard at the short-shaft, transom was very limited and overall the hull felt unbalanced because of all the weight aft.

Having said that, engines like the recently released four-stroke Tohatsu MFS 20E have closed the weight gap. And having battery-less EFI it starts and runs so nicely in comparison to the two-stroke. Of course, being a four-stroke maintenance is higher but so is resale value because most new boaters are thinking four-stroke, judging by the total of 69 per cent of all outboards sold in Oz last year being low-emission units.

Smaller four-stroke outboards, those under 10hp, outperform their two-stroke counterparts because of the torque generated and the inherently better engineering. And on the right hull the four-stroke Aqualine F2.5 and Mercury F2.5 leave my lighter 1993 two-stroke Johnson 4 for dead while using less than half the fuel.

Check out the full feature in issue #502 of Trade-a-Boat magazine. Subscribe today for all the latest camper trailer news, reviews and travel inspiration.


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