High speed 'wobble'

[Coops]

Hi Jeff, boat is over at my mum's house (as a 51 year old it sound weird saying that!) so I can't take proper look til the weekend. From memory it has a single chine that follows through to the stern finishing with a shallow V about 10 inches wide. I find that with the motor trimmed in it is more stable but the tubes start to drag, with a very small amount of trim the boat planes much more efficiently but kind of rocks from side to side pivoting on the centre line rather than squirming form side to side, though it feels like it could start to snake if upset by a semi beam on wave.........thanks for your help

[jeffstevens763@g]

i have had two boats with the planing pad [10 inches wide] the worst one was a quicksilver fast fisher with a 60hp on, any movement in the boat of weight [someone moving] would throw it on one side or side on waves would make it want to turn into the wave bit scary when it first happens, best way i can explain it is its like walking on ice with just your heel the boat is pivoting on that pad on the plane mine was arrow shaped with the point toward the bow about 600mm long i had my engine set up for me so no issues there, by the sounds of it its just little things prop damage possibly pitch,tube pressure,engine position. in my opinion i would take loads of pictures of the engine & prop checking if its bent by spinning it by hand in neutral,its position on the transom, the hull & tubes also check as others have said mountings/steering stick the pics on here with prop size and the guys will sort you out & give best advice.

cheers

[Coops]

I'll get onto it Jeff - the rib purchase was an excuse to keep my two teenage daughters interested in family time on the water (we also have a laser 16 and a Chapparal 240 plus various kayaks!) so I'm even more sensitive to making sure we have a predictable piece of kit.
Gotta say as a newbie here - amazing community, great to see.

[matt h]

Also if you were to get to its top speed and let go of the steering wheel, does it want to turn either slowly or more aggressively?

if so alter your trim tab anode, (above the prop)

[Last Tango]

Originally Posted by Coops

Hi Last Tango, that's a good question - the prop on appearance is a little chewed but I'm not getting any significant vibes through the rev range. Keen to understand how the prop could create this kind of instability? Thanks for your help.

It's just something that has to be right. If it's a bit looks chewed, it's hit something and could be well off "true". I'm thinking more of it causing trim/cavitation issues rather than vibration and if the prop isn't "threading" properly it could be creating a much higher than normal rotational effect.

[Coops]

Originally Posted by matt h

Also if you were to get to its top speed and let go of the steering wheel, does it want to turn either slowly or more aggressively?

if so alter your trim tab anode, (above the prop)

It did pull hard to the right and the tab was central so I moved it to counteract as far as I could (not quite 45 degrees) which counteracted the torque at high speed but it still pulls at low speed