We had a 2004 Capri 16.5 for about 18 months and the boom can definitely be a head knocker! Fun boat though - we could overtake a lot of larger boats on the lake. The only problems we had were that my wife always came home wet after a really "good" sail and there was no way to overnight, so when the Capri 22 came along, well, what the Admiral wants, the Admiral gets.
Ours came with a topping lift that was a piece of line that ran from the masthead. If I recall, there was a loop tied in the end that I just slipped over the end of the boom just before we dropped the sail. The topping lift had to be removed when we sailed or it would foul the top batten. When not in use I cleated the topping lift off to spare cleat on the mast. I don't know exactly what was used but it felt like spectra or one of the other kevlar type lines - not much thicker than parachute cord but very strong.
Prior owner had the halyard rigged wrong -- just through one sheave instead of over both sheaves - that made it really hard to raise the sail the last foot as it was run through the small hole between the mast and masthead fitting. He had the topping lift rigged through the front hole the forward side of the masthead fitting and held in place with a big washer. I took that out, rigged the main halyard correctly, and then put a pad eye at the top for the toppiing lift. I used one of the screws for the masthead fitting so I only had to drill/tap one hole.
Another option would be to go with a boomkicker. That will cost more than a 20' piece of line but then there's no line to mess with. We've got one on our Capri 22 and love it - unless you're close hauled it lifts the boom as you tack so there are fewer knocked heads.
If you're going to leave the boat in the water I *strongly* recommend that you get a main sail cover and jib sleeve. We had the red/white/blue sails and the prior owner had obviously left them on with no protection - there was obvious fading. Also, it's worth the money to ship the main off to Ullman in Sain Diego and have them put in a set of reef points. Makes it much easier to sail in heavier winds. I built my own jiffy reefing system and it worked great.
Finally, there's a great group of Capri 16.5 owners on groups.yahoo.com They had plenty of good advice when we had ours and will be happy to do the same for you.
The Capri 16.5 is a great little boat - have fun!
