A few ideas...
Seadog: There are a few things I can add on this issue. The first is to repeat what Shane said. There are 2 types of lines. Some that stretch, and some that don't. If you didn't purchase the jib halyard on your boat, you don't know that the previous owner didn't put on a "stretchy" line, and this could be causing your problem. Do you still have the "wire rope" halyard, or is your jib halyard all line? If it's all line, it absolutely must be lower stretch type of line. When I had the wire rope jib halyard, I found that it didn't stretch much, but I still had to work at getting it tight enough.The next thing is do you have a jib halyard winch? I added one a few years ago after doing without one for 20 years. It's easy to tighten up the jib halyard with a winch on the mast. We don't even need a handle to tighten it, if it isn't too windy. If you don't have a winch for your jib halyard, do you have "jam" type cleats on your mast? If you do, you can put some of the free end of the halyard around the non-jam side of the cleat, then put the halyard over that piece of line and then pull on the halyard. The free part acts as kind of a bushing or roller to reduce the friction, and alloy you to pull the line much tighter. Once you have pulled it tight, then you can jam the halyard into the jam cleat. The above suggestion isn't a good as a winch. The little Anderson stainless steel winch is pretty inexpensive, and looks and holds up to the weather great. One more thing, if you have a little piece of line at the bottom of the jib to get it off the deck and above the bow pulpit, that line, (and I just can't remember what it is called), must also be low stretch line. I'm sure you will figure out a solution. I hate to see my jib scalloped. It does seem to destroy the performance of the boat when going to winward. Plus you are always looking at the jib when you are going to winward, which makes it even worse. Aldo