Caution, the following discussion is 'mostly' for CUTTER RIGS, not for 'sloops', although the 'link' described at the end is applicable to 'both'.
I too have a T-37 and have used the selden folding rule method on the backstay to supposely set tension on the furling headstay. I'm still not certain if that tension gets transmitted to the headstay if the mast is beefy. For example undo the headstay and then look up the mast. I can detect no bending what so ever with the headstay undone and with 20% on that backstay. Not sure what spars you have, but mine are keel steped New Zealand spars. Best Regards.
Cutter rigs with TWO stays in front of the mast are an ENTIRELY different 'animal' from a simple rigged sloop with one stay in front of the mast. The problem is with a cutter you have TWO stays reacting to a SINGLE backstay, Intermediate stays to react with the forestay (that stay thats immediately in front of the mast) .... and worse the sails in the foretriangle are of different areas and differing aerodynamic functions and reactions TO the stays on which they are mounted.
The FUNCTIONAL problem with a cutter is: if the larger headsail becomes windloaded it reacts by 'transferring' part of it load to the smaller forestay (in proportion to the aerodynamic forces generated by each sail ... and the staysail 'under' a 'topsail' isnt going to have the same aerodynamic forces being generated as if it were flying 'alone') .... and the headstay becomes 'more slack' as a result. With a slack headstay a cutter rig will not 'point', will heel over aggressively and will be slow as hell and start 'slipping off to leeward' when going upwind. The net result is an extremely complicated rig tension problem ... and with MANY 'variables' acting at the same time.
Soooo ... I first set up the rig like it were a sloop 15% in caps, 4 lowers and backstay/headstay ..... intermediates and forestay at 0%. then readjust forward and aft lowers to get at least 1/2" mast prebend.
THEN 'work-up' in increments the forestay and intermediates to ~10-12%. You DO NOT want more than 10-12% on an intermediate or you risk pulling the chainplate off of its knee attachment. Final 'tune' of my 'basic' setting is to put the backstay at ~20% and 'leave it' (If I were circumnavigating, that backstay would be at ~15%).
With the 'basic' cutter rig tune as above ........
When needing to "point"/beat, I watch how the headstay sag to leeward is matching the luff hollow curve (where the luff hollow curve 'should' be . see 'article' listed below) and either slack off the forestay and/or when in 'normal' ≤15kts. apply running-backstay tension!!!!! .... alternatively its easier just to run forward and slack the forestay down to 3-5% (a good guess) !!!!!!! with such 'adjustments' the boat will 'stand up' with less heel, take off like a rocket, and point like a banshee.
With the 'normally unloading' slack headstay you will be tacking through 95-105°, with a tight headstay / loose forestay you can easily sail to well over 35-40° apparent ... (and sheet the yankee 'inside' the cap shrouds if you want and without 'pinching' or 'barberhaul' the headsail/yankee !!!!!). Slacking off the forestay will 'transfer' most of the backstay (15-20%) to the headstay.
When going downwind, I keep a taught forestay ... as downwind it makes NO difference (relatively) how much the headstay goes slack.
When sailing in BLAMMO conditions ... with no headsail, a staysail + deep reefed main ... I bring the forestay full TIGHT, upwind or down.
Cutters really need to be able to continuously adjust FORESTAY tension ... according to the present wind and seastate condition .... but of course while watching the 'rest of the rig' so that nothing goes much over 30% tension for accelerating 'fatigue' considerations.
Bob Perry, I think, has addressed all the 'tension', etc. complexity issues on cutters with: "Simply sail them like a sloop" .... which means to me get rid of the forestay/staysail/intermediates when sailing in normal conditions (slacking/removing) ... and only use the 'excess' when in Blammo or survival conditions.
I still occasionally race my Ty37, am a 'fanatic' even when 'cruising' and therefore dont mind doing all the on-the-fly rigging and sail changes.
Here's the link that refers to 'matching the 'cut' of the luff to the sag of the headstay .... applies to ALL sails that are attached to 'stays' ... cutter or sloop, make no difference. If anyone cant read this 'article' give me a PM and Ill reply with an email copy. http://i1086.photobucket.com/albums/...LuffHollow.gif
If you want to get a cutter rig to 'point' that headstay HAS TO BE taught .... and I think that the forestay has to be SLACK as the 'easiest' way to auto-tighten the headstay. Headstay + forestay does NOT equal one backstay (in tension-speak) but enough load for TWO bacskstays. 15% + 15% = 30% ..... and thats at or near the 'fatigue endurance limit' for 300 series stainless.
MOST times you dont 'need' 15% in a forestay so why do it as it only automatically slacks off the headstay?
hope this helps. ;-)