This reply from Pat Porter(if you ever have the chance to meet this man,tap into his wealth of knowledge on racing the 16)
"Mike, I read the forum this morning. Yes I have some definate feelings on how the tiller is best held. After many years of holding the tiller underhand I changed to the overhand position about five years ago. I wish I had always held the tiller overhand because it would have prevented many tacking problems and flips that had ocurred during my 25 years of holding the tiller underhand.
Let me explain when I sail overhand and when I still sail underhand and why. Overhand, it allows you to rock and twist your body forward bringing your tiller hand in front of your body. Thris provides more steering control, better boat balance more flexable body possition inrelation to the crews possition. You can see what I mean by looking at photographs of teams while they are double trapping. It is especially evendent on the Tiger. Overhand greatly simplifies tacking. I do not cleat the main during the tack. Prior to the tack I transfer the mainsheet to the tiller hand, two fingers and thumb hold the tiller two fingers hold the mainsheet. As I come in off the wire, I rock the tiller up as I press it forward turning the boat through the tack. Rocking the tiller up maintains the the same sheet lenght between my hand and the blocks which holds the sail tight untill I pass head to wind at which time I release the sheet change hands and spin the tiller and call the jib crossing.
Underhand; I use the underhand position when I round the weather mark. As I approach the mark I change from overhand to underhand. (I have frequently dropped the tiller doing this because I just throw it up and regrab it) I then transfer the uncleated mainsheet to my tiller hand. This time I hold the mainsheet and tiller together griping with my hand. This allows me to let the mainsheet slide through my hand to let the main out as I round the mark. While I'm doing this I pull my left arm back to steer the boat around the mark and use my right hand to grab the trap handle to come off the wire.
Now Gavin has a different approach to the weather mark rounding. He holds the tiller overhand and usually does not transfer the mainsheet. He stays on the wire untill the rounding is almost complete. As the boat comes around, from the wire he steps on the REAR crossbar and walks onto the tramp from the back of the boat. He then colapses and moves foreward on the boat for the downhill run. I sat on a press boat at the weather mark in Mexico and watched him make this move over and over. He is the only person that I know that rounds quit like this. Also one day on the beach he tryed to teach me how to do it. I never could.
A couple of things that I should also mention. My boat has NO weather helm but I don't think that should make any difference in how you hold the tiller. When I go out on the wire I hold the tiller in one hand and the mainsheet in the otherand I don't use the trap handle. When I come in off the wire I hold the tiller and mainsheet in one hand and I use the trap handle with the other.
So there you go. Hopefully this will stimulate some thought."
These photo's illustrates what Pat was talking about when he mentioned a more flexable body posistion.All the top sailors sail with this torqued upper body.As you can see they are taught at a young age.