Poor mans way to lock down the tiller - I screwed a cleat into the bottom of the tiller. I then run a line athwwartship to both docking cleats on the back corners of the boat. The line loops a few wraps around the cleat on the tiller. Then when I need to lock it down, I just pull the line tight. It still slips a little and can be forced when necessary, but it allows me to move around the boat to take care of stuff.
Of course the most recent problem I had, was a boat full of first timers. Thinking I could have them hold the tiller, I didn't bother with the line. Problem was, they had no idea which way to push the tiller to turn. I gave the tiller to someone and said hold us into the wind - turned my back and went to the front of the boat. The boat turned and I had to run back and take over the tiller. This happened more than once, but it never dawned on me that they didn't understand which way the tiller turned to turn the boat. This was in 20 mph winds in a 17 foot boat. Eventually I reefed the main - things were much more tame after that. My kids who were also first timers said this first experience sailing was either terrified or board, nothing in between. They are willing to go again, so I've not lost the battle.
RL 24 NEW to me April 25th 2014
AFC 17' 2+2 (sold in 2012)
Sunfish project boat
Sailing a large boat on a small lake is very tacky.