Yam F115 underpowered

[kalokeri]

I have a Yamaha F115 on my Ribtec 655 ex camel trophy. Now I’ve only just put it together as it was sunk so I acquired a second hand engine.
I’ve 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 there’s 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?

[Pikey Dave]

Engine is overpropped & underpowered for size of the boat.

[kalokeri]

I have an option to get a year old F150, will that be enough?

[Pikey Dave]

Originally Posted by kalokeri

I have an option to get a year old F150, will that be enough?

It’ll be a big improvement. What is the boat rated to?

[kalokeri]

The capacity plate is missing, I have one on order from ribeye but I think originally they were launched with a Honda 150

[Pikey Dave]

Originally Posted by kalokeri

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??

[kalokeri]

Ribtec, ribeye bought them out so they are providing a new plate

[Last Tango]

Originally Posted by Pikey Dave

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

[kalokeri]

Originally Posted by Last Tango

But.... reving to 5000 I'd have expected it to do better than 15kn

Yeah that’s what I thought. At 5000rpm the engine sounds sweet but just no power. The prop on it is 13 1/4 x 17 k

[kalokeri]

That’s on flat water too

[Pikey Dave]

Originally Posted by Last Tango

But.... reving to 5000 it should be producing around 100hp ?
I'd have expected it to do better than 15kn

It’s barely planing at that, the engine might not have enough oomph to get the boat over the hump.

[Xk59D]

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.

[kalokeri]

The rib has sat in the water for about 2 months with no anti foul. Is that likely a reason?

[Pikey Dave]

Originally Posted by kalokeri

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 ?

[kalokeri]

Originally Posted by Pikey Dave

Err yes. Anything else you want to tell us[emoji849]?

Would that stop it going above 15kts?

[Pikey Dave]

Originally Posted by kalokeri

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?

[kalokeri]

No, I haven’t

[Xk59D]

Oh dear

[69cmw]

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 [emoji90][emoji90], no speed and struggling, they took it out the water, jet washed the hull and that sorted it [emoji848]

[Iron Dials]

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.