MAtt, I use a Loos metric gauge for tensioning my shrouds, my Mark I eyeball, and model 3a seat of the pants.
When I adjust shrouds, step 1, I want around 1000kg (2000lb) force on the shrouds, (the stay is furling so not accounted here, but around 20% of cable breaking load), to start with when setting the mast in “neutral”. This is calculated in function of shroud breaking strength. Which in my case is almost 10 000Kg (20000lb). So I use 10% for shrouds and 20% for stay.
Setting the tension is a dynamic thing, normally I like the maximal tension possible (except downwind) the limit is breaking point of attachments, etc. when the wind is high (above 18 to 20kts), and loose rigging when bellow 15 kts.
Tension depends on the sailing you will be doing, we want loose rigging in low winds and tight in higher winds.
Since the stay is fractional, and I don’t have a diamond mast top, and if I see the bend is too much, I reduce stay tension, but this is also affected by backstay, so be carefull
Normally I like a tension that keeps the leeward shrouds slightly tensioned, not too loose, I don’t like them flapping when not tensioned due to wind power on sails, so I adjust jack accordingly.
The intermediate shrouds are more complicated to tune, because you need to climb the mast, so normally I use 20% breaking point as a start. And that is done as the wind changes, only adjusted when racing, we send a monkey up the mast to adjust.
So when sailing, the more rake makes the boat weather helm more when upwind, and because I need all help at low winds, to power the boat, I want maximal rake, of course now the boat has more weather helm, but steers better.
Please note this, my mast has 2 levels of spreaders, so the low shrouds I can control tension in middle of mast, and some lower mast bend, not too much because my mast is keel stepped and more ridgid bellow, the high shrouds control stay tension and how much the top of the mast falls to leeward, and the middle shrouds, control the middle of the mast
The back stay controls the bend on top and the tension of the stay.
Generaly if the wind is lower than 15kts, I let the mast down to make less tension, this causes more bend to the mast and more bag to the sail, but also reduces the space between the genoa and the main sail!!! Ehehehe
Then as the wind picks up I tension the mast, the number exactly I don’t know..I use my ears and my eyes to feel the boat…and go to the shrouds and feel them, tense with high winds, not so tense in lower winds....its ahrd to tell, but next time, I will measure and let you know, OK?? Promise.
I do mast tension play even when crusing…its fun…Fred already knows how to jack mast!!
But generally its done in function of the wind...
Did I help?