How tight should my forestay by on a Prindle 16?
the entire rig, forestay and sidestays, should be tight enough that if your cat was upside down, the mast base would not disconnect from the mast step, but not overly tight that your mast cannot rotate.
Turbo
I say, as thight as you can get it
as turbo said - but not overly tight that your mast cannot rotate.
My Prindle 18 is pretty tight but here is a quick tip you may or may not know. Once you get tightened. Tape off the turnbuckle and leave it at that tension don't loosen the turnbuckle when ready to trailer instead have someone hang on the trap lines of one side. While they have the tension on that side remove the side stay clevis pin and move that stay up 4 or five holes then re-pin it. Make sure the person holding tension can be relied upon to hold on till the pin is in because it is possible to drop the mast. This will de-tension your rig and you can up-pin the forestay to lower the mast for trailering. Next time you setup you forestay is all ready where it needs to be. Just pin It then have someone hang on the traps again and move the side stay pin back to its original spot. If not sure check the other side first or make a mark on the hole you usually sail in. This will help decrease your setup time but does require help. You only have to loosen one side stay the other can stay as is.