Adding a skeg can correct a kayak that tends to turn in one direction. It will also increase tracking (reduce maneuverability), and reduce weatercocking (or increase leecocking) and reduce broaching in following seas.

Test the kayak on a flat still day. Get the kayak up to speed and holding the paddle back like a rudder coast until the kayak is going straight at a distant object. Then lift the paddle out of the water and continue coasting see if the kayak continues straight. Turn around 180 degrees and do it again to be sure there is no wind, current or chop affecting the kayak. Try it several times with the paddle on each side of the kayak. If the kayak turns the same direction every time you have a trim problem. First check that your buns are on the centerline of the keel. Then wait for a windy day and paddle crosswise to the wind to see if your kayak leecocks or weathercocks move the seat back or forward (respectively). Once the seat is positioned for and aft be sure it is centered over the keel laterally. Then do the still day test again. Then go paddle with a following sea or next to the powerboat marina to catch several following wakes to see how much your kayak tries to broach when shoved from behind by a wave. Then start to think about adding a skeg or a trim tab. After any modification you will have to do the testing all over again. If you add a skeg you will also have to move the seat forward to avoid leecocking.

My Yare broached with any hint of a following wave, tended to turn slightly right and weathercocked. So I added a long skeg, more like extending the aft keel down. I then built up epoxy on the back edge of the skeg on one side and sanded on the opposite side creating a 1-1/2 inch wide trim tab or fixed mini rudder. Straightened the kayak right out, really reduced the broaching and eliminated the weathercocking. Then it tracked like it was on rails. I have been trimming the skeg off a little at a time to make it turn easier but still not broach excessively. I cut about half of it back off and it is about where I want it for my broaching tolerance and turning is reasonable. But now it has starting to weathercock too much again. Since it tracks better (harder to turn) weathercocking is more of an issue because it takes a harder stroke to correct. I have now just finished enlarging the cockpit aft 2-1/2" to deal with the weathercocking. I expect when I move the seat back the skeg will be a little deeper in the water and I'll want to trim off a little more of the skeg.

It has been a lot of work to modify the kayak. The fixed skeg wasn't too bad but shaving off the coaming and rebuilding it larger was an effort. I wanted to do it also to make laying back easier for rolling and to allow me get my long legs in and out while sitting. I used the standard CLC coaming dimensions but with the low fore deck on the Yare and with my long legs (I'm 6'-2") the opening just wasn't long enough. As my paddling skills improve the skeg seems to be getting smaller and smaller, kind of like training wheels. I think I'm getting close to having the kayak trimmed to my liking.

My suggestion is to paddle a lot before modifying your kayak. You will get some paddling in that way and you will be more certain the modification is needed for all paddling conditions. Trimming is a compromise between several handling characteristics of your kayak; explore them all before getting the saw out.