With 12 mph winds you will need one off each side. I use a 7 foot piece of 3/8" and then have a 5 foot piece of 1/4" to attach to that when its real bad. 40 foot of rope on each side with a loop at 25 feet to use when in shallow water. This will stop my boat in 20 mph winds but a lot of this depends on the boat you are fishing, bigger heavier takes a little more to stop and a boat that sits high out of the water is harder to slow down.