CC and James have given you some pretty good tips.
I think the real issue here is that somehow you are not moving back on the board,
you are not getting hooked in and in the straps (or at least not at a time that will cause your board to accelerate more) and since you are not placing your weight fully on your harness, you simply aren't getting the required Mast Foot Pressure (MFP) needed to drive your board steadily forward without any "wobbles".
You may think you are fully planing, and in control, but you really are pretty much at the mercy of your rig.
If you sheet in more, it wants to pitch you over the front of the board.....why?
Because you aren't back on the board and in the footstraps where the power in the rig will make you go faster, not go over the front.
I have not said this as much recently as I did a few years ago.
You have to "go through the gears" in the same fashion you would with a manual transmission in a car or motorbike.
First gear is where you get the rig powered up, but you do so carefully so it does not have the ability to throw you around. If you sheet in a little, the rig powers up a little. If that's too much, unsheet (sheet out) a bit and the power will be reduced.
OK, time for 2nd gear.
Now you need to begin to move back on your board slowly and progressively as the boards speed begins to build. You need to stay over the boards centerline so it does not round up or "wobble".
You need to move back at a rate that keeps the board accelerating. Do not try to "accelerate the process" but rather let the speed of the board set the rate at which you move back.
At this stage you are moving your feet back and slowly increasing the pressure on the rig.
OK time for 3rd gear....
Now you will be back far enough on the board, rear foot right over the centerline and behind the front footstraps (do not go too far back and cause the nose of the board to "pop up" andf kill your speed).
If you put all your weight on the rear foot, right over the centerline on the board, the board will continue to accelerate and there should be no wobbles.
Now slide your front foot into the front footstrap.
Once you are comfortable in this position, hook in to your harness.
OK, now it's time to go for 4th gear and get your back foot into the rear footstrap as you continue to rake your rig back and sheet it in progressively more.
The goal here is to continue to keep your board accelerating, and progressively get more and more "mast foot pressure" (MFP) to drive your board forward from the mast foot, not from your legs and down through your body.
In 4th gear your body starts to be "suspended" from your rig and you can begin to lean out and back to get better leverage on the rig.
Any required steering can be done with the legs both pushing/pulling, and "rolling" the rear of the board.
Roll the lee rail down a little and the board will heqad upwind "on the fin".
Roll the lee rail down a lot, and the board will head off pretty drastically like you where initiating a jibe.
Roll the upwind rail down a bit and the board will head upwind, but on the shape in the bottom vs the lift from the fin.
Could be your "speed wobble" is occurring as you roll the board slightly back and forth.
OK, once you get this far, it's time to go for 5th gear and really get the final acceleration.
You now are all the way back and outboard on your board, your rig is raked back until the foot angle is parallel with the top of your board or the surface of the water.
The rig is fully sheeted in. Your weight is suspended off the harness and you are keeping your weight as far from the boom as your arms will reach.
The board is totally being pushed along by MFP.
Do you have any video of you out sailing.
Send me a clip and I can provide much more "to the point" information on what you may be doing that you'd want to change.
My guess would be that you are in the "semi planing" mode (nearly all boards have a bit of a "speed wobble" when semi-planing) and you just need to "shift gears" a bit to get beyound this stage.
Hope this helps,
Last edited by Roger; 24th March 2008 at 04:44 AM.