There are a number of changes and/or additions we made to our first I-20 (Excalibur) after we bought it in the Fall of 2000. All of the changes I will describe are designed to eliminate mistakes that could cost valuable time, and, perhaps, places in a race.
Starting at the bow, I recommend having adequate purchase on the adjustable forestay. Our boat came with a 2-1 purchase, which isn't enough to tension the rig enough when hoisting the jib. This lack of purchase caused us to have to have Jim lean heavily on the tightened forestay as I raised the jib, in order to get it tight enough. So, we increased the purchase to 5-1, which is enough to do the job. Both the forestay and the jib luff controls are led to the cockpit roll at the front of the cockpit.
Looking at the spinnaker next, the spinnaker halyard has historically been a problem. The halyard, of course, is led back to the skipper, who does the hoisting. The problem is, what to do with the halyard tail when the spinnaker is up. What invariably happens is that you go to drop the chute and the halyard is tangled around the skipper's feet. This can create some very exciting moments. Or, as happened to me in one M-20 National Championship race in 1976, you can lose a regatta because of this one problem. I was in second place approaching the leeward mark in the last race. If I finished second in that race, I would win the regatta. Sure enough, the spinnaker halyard tangled and I was unable to lower the chute. By the time we got things squared away, we had lost eight boats and the regatta. I decided I would find a solution. What I did then, and what we have done to our I-20, is to install a spinnaker halyard take-up reel, attaching it with hose clamps to the starboard rudder post. We bought a spring-loaded take-up reel at Menards, one which came with a electrical cord attached. We removed the electrical cord and substituted a light line. Whenever we step the mast, we pull out the light line and tie the end of the spinnaker halyard there instead. Now, whenever I hoist the spinnaker, the halyard tail retracts into the take-up reel instantly. In addition, when it comes time to drop the chute, I just pop the halyard out of its cleat, and Jim can pull the chute down. The tension in the take-up reel is enough to keep tension on the halyard as Jim pulls it down, thus freeing me from having to feed the halyard to him. Also, we attached a strong clothespin, wrapped with tape so it wouldn't fall apart, to the outboard end of the port jib sheet track. The spinnaker halyard is clipped in this clothespin all the time the chute is down. When the chute is hoisted the halyard just pops out of the clothespin. This clothespin keeps the spinnaker halyard taut and away from the jib sheets.
On both the spinnaker and the jib, we replaced the Harken Ratchet Cheek Blocks that came with our boat with Harken Ratchamatics. This change has made all the difference in the world in tacking and jibing. Now, when we tack, when Jim lets go the leeward sheet, it actually goes out! And, when we jibe, the leeward spinnaker sheet flies out so fast that our jibing improved dramatically the first time we used the new blocks!
Our outhaul didn't have enough purchase, and had one of the very bad jam cleats. We replaced the outhaul with an all internal system with a cam cleat on the underside of the boom. The new purchase is 6-1.
The cunningham also didn't have enough purchase, so we replaced that with an all new system under the deck giving us 8-1 purchase.
The vang had the same problem, not enough purchase, so we replaced that, too, with a system with a lot more purchase, 24-1. I now feel, though, that probably this is overkill, 12-1 being enough.
I suggest 6-1 purchase on the backstay and 3-1 on the main traveler. The backstay and cunningham absolutely must be led to the skipper on both sides. Apart from the mainsheet, these are the two most important controls. They must have enough purchase that you can adjust them easily, and they must be located so that you can adjust them often.
We have experimented with several different arrangements of hiking straps. We have concluded that the best arrangement is for the forward ends of the crew straps to be fastened on the centerline and the aft ends fastened outboard. This allows Jim the maximum amount of room up forward, and assists in preventing tangles among the rats nest of lines he has to deal with. For the skipper, the forward ends should be outboard and the aft ends on the centerline of the boat. Both sets should be supported with shock cord to hold them in the perfect position so your foot can snag them without you having to look.
There are lots of preferences regarding compasses. My preference is to have one on each side deck, such that when I am sitting out, the lubber lines are perfectly aligned with the center of the compass and my line of sight. This way, only the briefest glance is necessary in order for me to know my angle at any moment. And, if you don't have compasses at all, get them. There are numerous cases where I would round a leeward mark, glance at the compass, and know instantly whether I was on the lifted tack or not. This knowledge has often made the difference in winning a race or regatta.
I prefer tillers with the ends cut off. I used to find whenever I tried to steer with my foot in the tiller bar, that the end of the tiller would hit my thigh. Cutting off the tiller ends has made all the difference, and has solved this problem completely. Be sure that your tiller extensions are long enough and flexible enough to enable you to sit out far enough, and yet still steer easily. I like to use a length of fiberglass batten.