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Old 16 September 2018, 15:18   #1
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Yam F115 underpowered

I have a Yamaha F115 on my Ribtec 655 ex camel trophy. Now Iíve only just put it together as it was sunk so I acquired a second hand engine.
Iíve put recon injectors in, changed the VST filter, and cleaned the whole fuel system through. Now the engine will rev up to 5000rpm happily enough and stay there all day but it feels as if thereís not that much power. The boat will only just get on the plane and will only do 15 kts.
Is this engine just not powerful enough or am I missing something?
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Old 16 September 2018, 15:25   #2
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Engine is overpropped & underpowered for size of the boat.
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Old 16 September 2018, 15:26   #3
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I have an option to get a year old F150, will that be enough?
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Old 16 September 2018, 15:28   #4
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Originally Posted by kalokeri View Post
I have an option to get a year old F150, will that be enough?


Itíll be a big improvement. What is the boat rated to?
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Old 16 September 2018, 15:31   #5
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The capacity plate is missing, I have one on order from ribeye but I think originally they were launched with a Honda 150
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Old 16 September 2018, 15:32   #6
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The capacity plate is missing, I have one on order from ribeye but I think originally they were launched with a Honda 150


Ribeye or Ribtec??
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Old 16 September 2018, 15:35   #7
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Ribtec, ribeye bought them out so they are providing a new plate
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Old 16 September 2018, 15:36   #8
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Quote:
Originally Posted by Pikey Dave View Post
Engine is overpropped & underpowered for size of the boat.
But.... reving to 5000 it should be producing around 100hp ?
I'd have expected it to do better than 15kn
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Old 16 September 2018, 15:38   #9
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But.... reving to 5000 I'd have expected it to do better than 15kn
Yeah thatís what I thought. At 5000rpm the engine sounds sweet but just no power. The prop on it is 13 1/4 x 17 k
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Old 16 September 2018, 15:39   #10
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Thatís on flat water too
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Old 16 September 2018, 15:43   #11
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But.... reving to 5000 it should be producing around 100hp ?
I'd have expected it to do better than 15kn


Itís barely planing at that, the engine might not have enough oomph to get the boat over the hump.
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Old 16 September 2018, 15:57   #12
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Gut feeling is something isnt right here, either serious prop slip or revs wrong or something along those lines.

5k revs and 15 knots doesn't make sense.

Although the yam 115 isn't a powerful motor by any stretch and a 150 will be better ofcourse.
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Old 16 September 2018, 16:01   #13
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The rib has sat in the water for about 2 months with no anti foul. Is that likely a reason?
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Old 16 September 2018, 16:05   #14
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Yam F115 underpowered

Quote:
Originally Posted by kalokeri View Post
The rib has sat in the water for about 2 months with no anti foul. Is that likely a reason?


Possibly depending on any weed growth. Anything else relevant that we need to know ?
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Old 16 September 2018, 16:06   #15
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Err yes. Anything else you want to tell us?
Would that stop it going above 15kts?
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Old 16 September 2018, 16:07   #16
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Would that stop it going above 15kts?


Depends on how much growth is on the hull. Is the hull full of water, have you checked?
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Old 16 September 2018, 16:08   #17
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No, I haven’t
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Old 16 September 2018, 16:14   #18
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Oh dear
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Old 16 September 2018, 18:36   #19
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I remember reading an article in the powerboat and rib mag ages ago, the boat sat in the water for a few weeks without anti foul, when they went to use it it was a bag of , no speed and struggling, they took it out the water, jet washed the hull and that sorted it
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Old 17 September 2018, 04:27   #20
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How is the engine rigged? Is it the appropriate shaft length?
You mention you’ve put boat and engine together.

At 5000 rpm it’s not meeting much resistance from the hull (clean or dirty) so I would wonder if the prop is slipping by virtue of how is sits in the water flow.
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