Another option is to move your trailer axle back. Check your trailer for bolt holes to move it back one hole (mine has holes to do this) or if its clamped to the frame. Back increases the tongue weight and visa versa.
If your rig is heavy just bring the proper wrenches, your board and scale and go down early to a launch site and tie up your boat, launch and tie up the boat then go to the parking lot to move the axle (don't do it on the ramp).
If U-bolt clamped, move it back like 2-4 inches. Then put a small board on a bathroom scale to check the tongue weight it each time its moved to get the proper %. Then you might have to move your winch again.
I think I set mine at 10%, so the boat does not rattle around while Im towing it. Google "trailer tongue weight".
This article says 9-15% of your gross weight of your rig including gas and gear etc
http://auto.howstuffworks.com/auto-p...gue-weight.htm