Originally Posted by Kestrahl
Actually tides have very specific instructions for sail designers as to slide spacing. I presume this is due to the track being plastic as opposed to alloy. There is no way around the large stack height with tides track system unless you ignore what tides tell you.
As to the cunningham, maybe you should go take so photos of sail shape on a stiff masthead rig cruising yacht with cunningham on and off upwind. Then computer analyze them, it'll be a learning
On Cunninghams, it's a bit silly to debate the point, as, put simply. The math don't lie. And besides, they work... in the real world anyway.
Let's say, for instance, that the distance from your gooseneck, up over the halyard sheave, & down to the winch is 100' total. If things stretch 0.1% as the breeze changes, not at all outside of the norm with even less than 10kts of wind
Then even using a super hi-tech halyard & sailcloth, you're going to see 1.2" of difference in luff/halyard length (or more, fairly easily). Which is definitely enough, in an astute sailor's book, to warrant re-tuning one's (halyard, or rather, to make things FAR easier - Cunningham) trim.
For as the breeze pipes up, I've yet to be on a boat (of any size bigger than a bathtub) where such a change in luff length isn't noticeable. Ergo, my firm suggestion for incorporating a Cunningham.
Put a few small witness marks on the sail & spar if you don't believe the math. They will shift as the AWS changes.
Why one would intentionally leave off this control feature, especially on a style of boat which has less of them to begin with, leaves me scratching my head.
The length (stretch) changes under varying loads, of the involved materials, are easy enough to look up & calculate. And a 0.1% change in length due to stretch is well within reason (if you do). Actually it's a fair bit less than the norm on a lot of boats. Assuming, that is, that you do the math on stretch due to wind
changes. Even if you're running the lowest stretch materials which $ can buy.
Regarding stack height, & sail attachment spacing, yes, I've been known to "color outside of the lines" - with, & within reason.
Pretty much due to the Fact that some areas of sails (& the attachment points in said locales) are much more highly loaded than in others. And it rarely hurts to "tune" a main's attachment to match.
Such is pretty easy to visibly see. Just look at the wrinkles & load lines in the cloth in any properly hoisted & trmmed sail. Or for those with Ray Charles's sail load analysis ability, look at the density of load carrying fibers in the various areas in laminated, load mapped, sails. And how a main's primary loads in the middle portion of it have little (relatively) to do with resisting transverse, & or angular loads.
If such information is in doubt, then witness the "stunt" during a certain America's Cup ('92, or '05), where the French team actually REMOVED a good portion of the luff section of their main, & re-used said (measured) area, on the sail's leech. Where it is actually loaded, & generates much more drive.
Or that on a properly trimmed mainsail
, a large percentage of the luff is simply lightly fluttering when going upwind (assuming no full battens in that area).
The simple answer is that in some areas, with exception for where the reefs
& full battens lay, is that the load on a mainsail's luff is almost entirely generated by halyard tension, period. There's not a lot in terms of wind/trim created stresses being generated in terms of holding it onto the spar (relative to other locations on/in the sail).
Or again, go back to the pre-sail track days, & witness the Fact that slug spacing on highly loaded/performance mains was (and is) FAR higher on the upper & lower thirds of the sail. Even on boats using full on, stainless steel
, or aluminum