The slug at the clew end on my main sail has now pulled out of the boom track on two occasions in winds above 15. After the first occasion, I hammered down the edge of the boom track, but under pressure last weekend the slug once again pulled out.

Has anyone else had this problem ?

I am thinking of having sulgs sewn on to the entire foot of the sali to ease the pressure, and/or lashing the sail to the boom with either a line or a velcro strap through the clew, but am concerned what effect that would have on my ability to control the outhaul tension.

Use a sail tie or velcro through the clew loosely around the boom. I have an old Quantum main that doesn't have a clew slug and works just fine that way.

We've given up trying to keep the slug in the track on my 1980 hull. The velcro strap through the clew works for us.

This same topic came up a while back and I posted a photo of the stainless plates some boats have to prevent this. Although I do not do it, placing a nylon strap or sail tie is probably a good practice.

http://j30.us/ubbthreads/ubbthreads.php/topics/3051/Re_Repair_of_boom_slot.html#Post3051

(On an unrelated note, my boat now looks much, much better than it does in that pre-purchase photo in the linked thread)

If you are going to be making mods to your boom to re-inforce the end; while you are at it, here's another suggestion.
The last several main sails on Wildcat have been loose footed. As well, with few exceptions we take the main off the boat, roll it and store it below at the end of every day of sailing/racing. Dragging the car (slug) the entire length of the boom to remove the main is, at the very least, awkward. Our sailmaker took one look at what we were doing and suggested that about 3 feet back from the outboard end of the boom to cut a notch in the sail track that is large enough for the slug to be removed. 15 min with a Dremel, straigt edge, pencil and a little touch up paint was all it took.

Thanks for the advice, I'll think I'll try the velcro strap/Sail tie option and see how that works.

I had the same problem on (what looked like) the original 1979 boom. The track was badly worn from years of sail changing and adjustments.

The Velcro strap worked great. Mine is about 24" long and wraps through the clew and around the boom almost three times until...

I ended up replacing the boom with a boom tube from RigRite because the old boom had arrived from the previous owner with, er, a "slight bend" at the vang plate. (There's another, much longer story about me driving across the Canadian border at 11PM with an aluminum tube on the top of the car and no paperwork which I won't go in to....).

I moved all the hardware and rigging over from the old tube except for changing the Boom-Vang attachment point from the old surface-mounted style to the "thru-boom" style that Rigrite offers (Internal Boom Bail: K-11428 on their website here ) which requires a slot to be cut in your boom.

I also cut the new exit that Russ mentions and would HIGHLY recommend it if you have a loose-footed main that you roll off the boom each time, makes for very happy crew.