I have done a lot of
single handing on my Caliber 40 during the last 20 years with a fair amount of it quite a ways
offshore. I have also done a lot of high angle rock and ice climbing so I have a fair understanding of tethers and falling.
As you say - the ONLY answer is don't fall off the boat. The tether needs to be short enough to keep at least half your body inside the life lines. When you fall - your center of gravity must remain over the
deck or you are dead.
The length of tether is one parameter of survival but the other, and maybe more important, is the location of the attachment point for the tether. A short tether attached to a jack line near the toe rail will allow you to go
overboard.
My only sailing experience going overboard was at 2 AM 85 miles west of
Vancouver Island at about 50 North in six foot seas and 25
knot winds. My brother was onboard in the
cockpit. I was on the foredeck trying to figure out why the staysail would not complete the tack. The clew of the staysail came loose and hit me in the
head - knocking me cold.
We were sailing hard upwind and heeled about 20 degrees. I slid down the foredeck and my feet and legs, to my upper thighs, went under the lower lifeline. At that point my 6' tether took up the slack as it was attached to a U-Bolt I had attached to the
mast about 3' above the
deck. I came to and crawled back onto the foredeck.
My brother did not know I had been knocked out and did not know I had slid overboard until I returned to the
cockpit.
IF I had been attached to the
jacklines we had running from the stern to the bow - I would have gone overboard and would certainly have drowned before my brother knew I was in trouble.
If I had not been wearing the tether and gone overboard my auto inflate
PFD would have kept me afloat and my ACR strobe would have flashed, but the boat was doing 6 knots in the
pitch black 52 degree ocean and there is absolutely no chance my brother would have been able to find me.
Do not fall overboard!
I use a 6' tether with a 2nd 3' tether sown to it so I can alway have at least one attachment to the boat when moving about. My boat has
jacklines on both side decks, from stern to bow. I have installed U-bolts in many strategic locations to which I attach myself when doing things like reefing, changing staysails, or
rigging the Code 0.
But, to be honest, when I single hand a lot, e.g. for two straight years covering 4,000 miles in Western
Mexico, I frequently do not use either a
PFD or a tether.
One hand for the boat, one hand for the crew. I've never had a single scary episode when I was not wearing the appropriate
gear.
But, I was a very serious rock climber for years and did some serious stuff without protection and was very used to making very careful and well calculated decisions and physical moves. I do not recommend my technique.