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Old 30 May 2014, 09:49   #1
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Full throttle?????

Hi

I have a small 3.6 m Ali hull rib with centre console and a new Yamaha 20hp four stroke

Problem is that although boat and engine Set up is fairly light ( about 130 kgs) with me (13 stone) wife 10 ish! Stone and kids 11 and 7 it just doesn't seem to quite get on the plane . Even at full throttle the yam engine doesn't seem to be revving that much - could it have been set up wrong meaning that full throttle on the remote lever is not translating to full on the engine. How can I check this?? Is there a simple way ??

I would have thought 20 hp would've this set up along at a reasonable pace but I think I am only getting about 13 knots?

Thoughts????
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Old 30 May 2014, 10:08   #2
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you should easily plane with that. remove airbox cover and check the butterflies (round plates) are opening fully when control is fully forward
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Old 30 May 2014, 10:15   #3
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Thats a lot of weight for 20hp to get on the plane.....

seriously - with 40hp it may still take some time to get going ....

You need a very low pitch prop to spin the engine to full revs - at present its like trying to pull away in third gear in a car full of people......
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Old 30 May 2014, 10:52   #4
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Easy way of checking, leave the wife and kids on the pontoon and go out for a test run on your own. Full throttle and record what revs and speed if you have a guage.
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Old 30 May 2014, 11:28   #5
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Cheers guys

The problem is i dont have a rev gauge so difficult to tell - i am just going by ear and pace!

The rib goes better ( obvious i suppose) with just me on it but i still thought it would have had more go loaded up - some guys in the same bay have a3.4 m with 20 hp tiller steer and it flies with 4 , 16 year old boys on it?!

If i need to reprop are there any recommendations on pitch or is it a bit trial and error?

Festinghouse-thanks i will certainly check the butterflies
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Old 30 May 2014, 11:32   #6
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and see how long you can leave them on the side for....
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Old 30 May 2014, 13:17   #7
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Full throttle?????

Hi,
Would be surprised if standard prop as supplied on a new 20hp engine with your set up is unsuitable, but something probably not quite right. Plenty of cheap induction tach's available on e-bay to check revs at wot.
Before considering changing prop I would check remote throttle adjustment, engine height / trim, and weight distribution (some up front to get bow down while getting onto plane).
Not wishing to rub salt in but our 3.5m sib with 20hp 4 stroke planes effortlessly with three adults aboard so can understand your disappointment. With two aboard we can pull a ringo and on a good day a knee board - just!
Hope you get it sorted.
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Old 01 June 2014, 03:31   #8
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Thanks all for comments -some stuff for me to try out and see where i get to

Cheers
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Old 01 June 2014, 05:27   #9
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Originally Posted by PeterM View Post
seriously - with 40hp it may still take some time to get going ....
No way. That package sounds very similar in weight and power to mine. 2 Adults, 2 kids probably similar total load to mine gets on the plane fine. 4 adults gets there without two much difficulty. All with 20HP. The only way a 40 could struggle is if you massively over-propped it in the hope of achieving ridiculous speeds on a flat calm day: speeds that you'd probably never attain because a wee boat at silly speed is terrifying.

Northsearibber - you need to give us more info -->
- engine make/model (and recommended rev range)
- current prop size
- speed (take a smartphone in a waterproof bag) with you and with you and the family
- picture of the engine height
- details of the engine trim
- an idea how much experience you have
- ideally a picture of it "not quite on the plane"

People will then be able to give you a better idea. In terms of prop selection without a tacho you'll be stabbing in the dark.
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Old 02 June 2014, 08:06   #10
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Cheers for that

Engine is a Yamaha f20 2013. Prop size is 9.25 x12.

Speed - would have to let you know exactly but about 12/13 mph.

Engine height is fine I think- cav plate is level with hull bottom

Trim - is a difficult one - I have played about but one hole out seems to be best - I think according to the manual each hole is 4 degrees?

The pictures I will need to get next time - but not sure if the answers above spark anything obvious?

I have ordered a cheap induction tach but cant really believe that the standard prop is not within its range on this size boat/load, although at least now I can check
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