Problem getting on the plane - what's going on?

[Otter]

We've just got our first proper SRIB, a Seapro 340; the engine is a Mariner 15hp 2 stroke. With three up it gets nicely on the plane - but - as it does, a wave moves backwards in succession along the floor, you can feel it - I assume its the bow wave it's climbing? It's unsettling and makes it unstable, even on the plane it happens sometimes. It's hard to describe but it's something like a horizontal lump moving from bow to stern - am I making any sense?

Is the RIB overloaded? Is it pumped up enough? The sides seem very firm but I wonder if the floor is? It has an inflatable floor and beneath that an inflatable tube.

Advice very welcome!

 

[ontheplane]

These do this.

It's not a RIB - by definition it's not a "Rigid" inflatable boat if it's not got a solid hull - so it's an inflatable. You could try a bit more air in it - but to be honest, I think you need to get used to it a bit. Does it have any slats or similar? Can you fix them together?

 

[Otter]

It seems to have some aluminium slats, perhaps I need to deflate it and check how it's all put together!

 

[ontheplane]

Also try some of the little hydrofoils you fit to the outboard - many say they make a heck of a difference

 

[Otter]

Thanks - actually it's got them. I wonder if my engine angle is right? Should it be vertical when I'm on the plane? That means slanted when at normal speed

 

[Nick_H]

I don't know that particular boat, but the inflatable floor will need much higher inflation pressure than the tubes, so I suspect it's under inflated. You'll break the foot pump before you over-inflate the floor.

 

[Otter]

Thanks, really helpful - I think it's time to invest in a manometer!

 

[Tam Lin]

I thought this was a post about the fear of flying!

 

[Otter]

Hee hee.

Engine angle - should it be vertical or angled to the same angle as the stern?

 

[Nick_H]

Hee hee.

Engine angle - should it be vertical or angled to the same angle as the stern?

Generally you start with the cavitation plate (the flat section above the prop) parallel to the keel and broadly in line with it, or slightly above. You can then play around with slight adjustments to trim and engine height to see if you can improve performance.

 

[No Regrets]

Trim adjustments have a significant effect on these limited power things.

My Avon 280 with 6hp would only plane one up, until I adjusted the outboard trim, now it flies with two people and Dogs on board!

 

[Otter]

Thanks for both of those replies, I've definitely got the angle wrong then.

I spoke to the supplier yesterday and he said a big part of it is getting the weight back aft once we were on the plane, all of it behind the seat, there's a lot to learn here and all my guesses have been wrong so far! Apparently the symptom we're experiencing is called "wave hook".