Some observations and thoughts...
Awhile ago I had started a thread on this topic because of some events I had experienced. I came away with the feeling that being tethered for one of those incidents might have led to injury.
I went off the back of our N-20 while driving downwind in the Annapolis-Oxford race. Alec was trapped and locked in with the chicken lines. Winds were around 20 and we were honkin'. Wave just popped me up and over the back I went. I had a grip on the mainsheet and held on for split second before that was ripped from my hand. Alec had issues getting back on the boat due to it starting to turn (throws your balance off). The boat ended up turning downwind, depowered, and with Alec still on the trap it capsized to windward. In the small amount of time it took for the capsize to happen a decent distance had been put between me and the boat. Once Alec had it together and started to right it, it was making pretty good time on its side. There was no way I could possibly swim to catch it.
I started to consider the idea of clipping in to the mainsheet hearing people mention the "it will sheet the boat and cause it to capsize" - but when you're going full tilt downwind the sheet and traveler are in anyway. And it then occured to me that if there is slack in the tether when you go over you could get hurt when the slack goes away and the force of a 400lb boat going 20 is transmitted to your body.
That having been said, the idea of being separated from the boat didn't sit too well either.
The other case was when a crew trap broke going upwind in biggish conditions. I'm not sure what would have happened if he was tethered, but the boat wasn't going as fast and I had control of the helm. As it was I was able to circle back and get him, but that also pointed out that safely getting to a COB in rough conditions can also be dangerous. Even parked the boat moved a speed that made it difficult to swim to, and getting close enough can set you up to hit the person in the water.
An additional one I know of is an A-Cat sailor that got separated from his boat during a regatta, the committee didn't know it, and he ended up swimming a decent distance to shore.
So, on the tethering side there are three cases:
1) Somebody falls off the boat upwind
2) Somebody falls off the boat downwind
3) Boat capsizes
You could probably add two additional factors - whether it is the crew or skipper that falls off.
I think on the whole, tethered or not, the likelyhood for a good outcome it increased if it is the crew that falls off, especially upwind, and that the danger of injury is much less.
I think the speed and power of the spin boats makes it potentially dangerous to be tethered if you fall overboard downwind. With somebody at the helm the danger is reduced. If the helm falls off, risk is higher.
In the case of capsizing, the normal slowish over she goes type being tethered would not be as much a safety issue and could keep you safe by not allowing separation. I think the regatta rules consider this case in specifying the length. The violent no warning capsize/pitchpole is a different story - by the time you come to your senses you might be in trouble. But with a longish tether you still may be better off with it. But I'm also not certain that with newer designs that happens as often, so there's a question as to whether that case happens enough to negate benefits in other cases.
I have started to think about using a short tether for helming downwind in the rough. Using the big boat idea of tethering to stay on the boat. You won't get dragged, but you better have conditioned thought to pop the thing off in a capsize. Again, this would only be used for the helm, and I have yet to actually try it (I'm not %100 percent convinced).
Once somebody is separated there are two things to consider:
1) Can you act quickly enough to stop the separation from increasing.
2) If you can't accomplish #1 can you safely stay in contact with the COB.
3) Can you safely retrieve the COB.
#2 speaks to people carrying radios, GPS, and signal kits (whistles, small flares, etc.) on their person.
We've started to carry COB throw bags for these cases. It may be possible after a capsize for a crew still with the boat to throw a line to the separated sailor. It can also be used for retrieval in that once the boat is righted the singlehanded sailor only needs to get close enough to throw the bag/line. It would seem that two would be preferrable, one stored under the tramp for a capsize, the other on top for a COB, but two may be a little overkill (certainly adds weight).
So, in the end as for the original question, should they be required? I don't know. It would be nice for a system to evolve that answers the concerns and optimizes benefits while mitigating the risks. Then having that required would be ok. Other than that it should be something recommended, and the sailors should think through the scenarios and plan for how to deal with each. The boats have changed, and the best answer may be several answers - one for each situation (upwind, downwind, skipper, crew, etc.).
Note that all of this is geared towards races where you need to fend for yourself. In a bouys race with a crash boat you can rely on for help, don't take the risk a tether may invoke. If you're on your own balance the risk of being separated with the risk of the tether.
