Roll & yaw under power

[vintraq]

I am looking at a 36 foot, 470hp single diesel powered planing hull shaft drive that has issues at speed and under fast acceleration. She is stable to about 13knots, but will roll to starboard, and yaw to port accordingly, above that speed or if placed under heavy power from still. Any thoughts? Trim tabs fitted (made a slight difference).
Cheers.
Vintraq.

[hmattos]

What is the hull form - any concave surfaces? Which way does the prop rotate?

What happens once she is fully on the plane - what speed can she attain?

With our boats we deliberately put mass on the starboard side to counter the prop torque of large single outboards.

[Frosty]

Sounds like too much weight forward to me, far too much.

Or the hull is hooked?

[vintraq]

Thanks hmattos. I've not been underneath her yet, but given she is based on a crayfishing boat, imagine there aren't concave surfaces beneath. It's getting her to the plane that is the issue, and once there she gets the wobblies, forcing powerdown and off the plane. Clockwise prop rotation, can get to around 22 knots (scary once there though). Like the idea of counterweghting the load.

[vintraq]

Thanks Frosty. Do you mean actually hooked as in bent? Any ideas where I can get info on how to calculate appropriate weight distributions?

[Frosty]

Yes --the same as what Vintraq is suggesting I think. The boat will suck onto the surface and sometimes pop up at a hight speed but basically handles terrible.

Look down the length of the boat from the front or rear ,--it should be flat.

This is usually from sitting on a badly adjusted trailer.

[hmattos]

Vintraq,

Sounds like you have a prop line which is pussing way above the centre of drag, so as others have said, try moving the centre of gravity back.

You can get some idea of where your L Cof G is by puting the boat on a single axle trailer - or equivalent - or for your size of boat lifting the boat with a sling arrangement. If the boat is in the water, you can get some ideas by photographing the boat with a known moveable load at the bow, stern and centre. If you have plenty of friends who are prepared to be weighed, take a scales to the boat, weigh the ten people and get them to walk from bow to stern as a group. Take some photos and you mey get some idea what you have to do to move mass back.
Good luck