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Old 20 May 2014, 14:21   #1
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9.8 hp tohatsu

Hi all I have the above engine (2 stroke) on a 3.2m sunsport v air hull,when there are two people in the boat with light fishing tackel I can get on the pane easey and at 5500rpm, if I add a small child I can only just get on the plane and can't get the engine to rev above 4100rpm I have a standered prop, what prop should I order to use when I have a heavier load that would take me to 5500-6000 rpm.
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Old 20 May 2014, 14:30   #2
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You need to reduce the pitch. Stick with the Tohatsu prop, just an inch or so less pitch.
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Old 20 May 2014, 15:30   #3
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Ok thank's I have just been out to look at the size of the prop I have it just say's F8.5 so do i just buy a 7.5 ??
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Old 20 May 2014, 15:45   #4
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I can plane at 3/4 throttle on my 3.3m with 2 adults, 2 x 25kg kids and some kit.
When fully loaded WOT then a passenger shifts back then forward whilst it hops on the plane easily. I use the standard 8.5 prop.

We shift weight to get it up on the plane. You can feel it and the acceleration. I have to back off as 20 knots in a small loaded boat is scary.

Make sure that your boat is up to pressure to.
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Old 20 May 2014, 15:52   #5
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yes the boat is up to pressure, the boat fly's with me and a freind around 30 stone (pair of us) and light tackel, but if I add a small child it won't rev over 4100rpm I'm looking to get the revs up, I will change props according to my passengers'
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Old 20 May 2014, 15:55   #6
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OE prop range for the 9.8 was 6.5" to 9.5".

I think the 6.5 may be a little too far, the 7.5 sounds good if you only need a little bit of extra help to plane.

Just to add, a 6.5 on say a Yamaha would be classed as a "High Thrust" prop for moving heavy displacement boats about, it may turn into an egg whisk on an inflatable.
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Old 20 May 2014, 19:14   #7
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7.5 will work I have both depending if I am using the engine on sib or as aux on the RC check out eBay reasonably priced new props on there
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Old 21 May 2014, 12:51   #8
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Thanks all for the replys I will get a 7.5 over the weekend and let you know the results
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Old 21 May 2014, 13:18   #9
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I'd be interested to hear how that goes - I'm thinking about the same move...
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Old 21 May 2014, 13:20   #10
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Quote:
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I'd be interested to hear how that goes - I'm thinking about the same move...

Haven't you been thinking about that for over a year now?!!!!!

Take a punt!
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