There has been a lot of chatter on the John Welsford Yahoo group about a anchoring system fro tidal areas, Here is a system short description of a system we used when I was younger.
We used to camp next to a tidal river and we used a system similar to this to change the position of our boat (reel in to board at high tide or move the boat further out at low tide. It worked pretty well and you could almost get in without your feet getting wet.
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The System - drop your anchor in deeper water with enough anchor chain and a small length of rope. At the end of the rope secure a good quality marine pulley. Then you create a loop of rope with two hook clips on (boat length apart on that loop - to clip you boat on to)
Then there is another anchor on the beach with a line that is connected with a pulley to the loop. This way you can reel your boat in and out from the boat or from the beach. You use the free side of the loop (the side where no hook clips are) to cleat it off at the correct position you want your boat.
It sounds complicated, but once you set it up once it is a piece of cake.