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Old 08 February 2015, 10:31   #1
Country: UK - England
Town: Brighton
Boat name: Boat
Make: Avon
Length: 4m +
Engine: Outboard
Join Date: Feb 2015
Posts: 1
25hp 2-Stroke vs 20hp 4-Stroke for 4m RIB?

I am after some advice for my 4m Narwhal RIB. It had a 2001 25hp Mariner that was fantastic for purpose. It pulled a skier or wakeboarder just fine with a couple of adults on board. Although much of the time will just be fishing or playing. Engine is now dead and has to be replaced.
I am looking at either a new 20hp 4-stroke Tohatsu or possibly 30hp.

The 20hp weighs almost exactly the same 50kg as the old 2 stroke. Will the reduction in power make much difference. In particular is there more or less torque when pulling someone up out of the water? Or should I just go for the more powerful but much heavier engine 70kg+?

The other factor is the old combination could be recovered by hand on the local slipways so weight is quite important.

billybo8 is offline   Reply With Quote
Old 08 February 2015, 11:42   #2
Country: UK - England
Town: Bristol
Make: Ribcraft
Length: 5m +
Engine: Yamaha
Join Date: May 2006
Posts: 4,277
Ski with a 25 AND 2 adults???

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Old 14 February 2015, 16:23   #3
Country: New Zealand
Length: 3m +
Join Date: Nov 2014
Posts: 32
My 25hp commercial 2st evinrude smokes a 4st mariner 40hp in my mates rib
rusty McCaw is offline   Reply With Quote
Old 15 February 2015, 00:45   #4
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Country: UK - England
Town: Midlands
Boat name: ...
Make: Avon SR4/Zodiac Clas
Length: 4m +
Engine: Yam 40/Mariner 30
Join Date: Jul 2006
Posts: 977
25hp 2-Stroke vs 20hp 4-Stroke for 4m RIB?

20hp & 30hp fourstroke Tohatsus are very different engines.

20hp is a twin cylinder carbed, and the same as the 15hp, still classed as a portable engine. I would doubt very much you'd pull a skier with that. Certainly won't be as punchy 25 two stroke.

The 30hp, is a 3 cylinder efi, a proper engine, and should more than match your 25 2 stroke. For what you are after I wouldn't even consider the 20hp. If your using a trailer, i can't see an extra 20kg making much difference to launching/recovery.
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