My current boat has a navtec hydraulic backstay on a mast head rig, along with with a baby stay that goes about 2/3 up the mast. This is a new thing to me as all my previous experience has been on boats with either split backs or no adjustable backstay at all. That said I've found it to be essential upwind on the race course to pull the baby stay on tight and crank in the back stay, and it's been a lot of fun to play with a new sail control.
However, I had a situation the other day that got me wondering what was too little and what was too much tension on the back stay; while heading downwind on a leisure sail, no spin or anything, I asked a non-sailor friend to ease off the back stay. It didn't occur me to mention that when you turn the knob to ease it, it continues easing until the knob is turned back. About five minutes later the rig was so lose that the forestay turn buckle was bouncing back and forth off the deck on either side of the chainplate. it was so lose that the five shims placed in the mast when it was stepped all fell to the floor inside. I cranked the stay back on until most the sag was gone and everything has been fine, although I can't get the shims back in the mast, I don't imagine that matters much. Basically, I was surprised to see that it can ever get this loose, IMHO, it was dangerously loose. If it's possible to ease to this degree, is it also possible to crank it on way too tight, even to breaking load (for example if I had been as undetailed in my instructions and asked a inexperienced crew member to put crank on the back stay and he just went all the way to the end of the rod.) There is a gauge on the pump that lists tells the load between 1 - 6 kpsi. I've found that half way between one and two the rig is pretty tight with minimal bend in mast, but how much can I go? Can I find some recommended min and max tensions somewhere on the web? Boat is C&C 35-3.