Highfield

[crayiii]

We have a Highfield 340 with a Yamaha 20hp 4 stroke. With just two of us, we fly but with 4 people we can't get up on step, the motor bogs down, and the stern just rides low.

The prop is a 9.25x12.

I've ridden in other RIBs with MUCH smaller outboards that easily got 5 of us on step.

Is this an outboard issue (it's new), prop issue, or expectation issue?

[Hesti]

Weight distribution, engine trim and outboard shaft length can all be a factor.

Weight distribution - more weight forward? Anyway, play around with it.

Engine trim - trimming the shaft as close to the stern as possible may help to get on the plane.

Shaft length - the anti cavitation plates of the shaft should be pretty much on the same level as the underside of the hull in that area. If anything, the anti cavitation plates might even be a bit higher, say an inch, than the underside of the hull in that area.


If the above does not help, looking into the prop might.

[motion30]

12" seems like to much pitch. I have good results with a 4 blade with low pitch. 8 or 9 inches. I am more concerned about getting on plane with the load that I am top speed. You 11' boat should plane with 4

[JPA Cate]

The first thing I'd look at would be pitch. Changing it made the difference for us between planing with 4 and not. If the angle at the stern of the drive leg is correct, then moving weight forward a bit may help.

Go to the Yamaha folks and discuss an alternate prop that will meet your needs better, and keep the spare for when the new one fails or is damaged.

Ann

[motion30]

A hydrofoil device on the cavation plate works wonders as well

[lancelot9898]

I can tell you what worked for me in getting the dinghy to plane, although I was dealing with a much smaller outboard and dinghy than you and the my approach may not scale. I had a 10 foot wooden floor Achiilles with a 5 hp two stroke Nissan. There were two of us aboard and we could not get the thing to plane regardless of what we did. I called up Nissan and asked for a higher pitch prop and put it on. And while it took longer to get up to speed, the top in speed was enough to plane the thing and once on plane we could back off the throttle and shift our weight back astern.