Fisho,
After many forms of trial and error I came up with a good formula for my heavy 16 fort haines 16C.
BIG diametre chain and LOTS of it.
I'm sorry I don't have the guage off hand but the links are probably 8cms long and I run nearly 4 metres of it. I used to drag all the time - outside and in the bay.
Shop proprieters told me I didn't need anything like that for my boat.
Now I don't drag!
Bugman