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Old 06 June 2010, 07:55   #1
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Country: UK - England
Town: Oldham
Boat name: Aqua Vitae
Make: Ribcraft 4.8
Length: 4m +
Engine: Yamaha 75hp
MMSI: 235115057
Join Date: Jul 2005
Posts: 331
Tune the engine or change the prop?

Once again, I am consulting the vast knowledge of the RIB.net gurus!

I have a 3.6m Tornado with a 25hp Mariner marathon 2-stroke on the back. It will give me about 23kn on a flat day, fully loaded with 3 on board. It sometimes takes a while to plane, and I have to move all the crew to the front to get it on the plane at times.
Most of the time, I am cruising but I sometimes pull an inflatable or wakeboarder.

I'm wondering whether to tune up the engine or change the prop. I guess I'd need one prop for cruising and one for towing, though I may be wrong!

Prop details:
Diameter - 10 3/8
Pitch - 11
Material - Alum
Blades - 3

Thanks guys and girls!

Tim
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Old 06 June 2010, 12:16   #2
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Country: UK - England
Town: Sussex
Make: Ceasar Surfcat
Length: 4m +
Engine: Tohatsu 50hp
Join Date: May 2006
Posts: 105
That engine is easy to tune to 30- Just remove the restrictor/gasket from between the carb/engine, refit gasket from a Tohatsu 30(or make one yourself to suit the larger opening), then advance the timing by 5degrees by altering the timing advance rod. It makes a notable difference.(It should do anyways being a 20% hike in power)
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