Aero benefits of a straight forestay

. . . nice, but I couldn't find the forestay control.

 

Ha Ha, Isn't that a work of "Art Deco". But have you ever ridden in one, I think better than a Caddie. Engaging a pothole is like a heavy hull sliding down into a trough and it's enertia pushing you thru that next big sea. Better get back on deck i'm getting weasy

 

True, but potholes seemed less er, fashionable back then . . . besides, I would have been comparing it to a pushbike!

 

My thoughts on tensioning forestay.
a boomed jib, where the gooseneck is positioned aft of the sails tack, allowing a fuller sail with slacked sheets, and a flatter sail close hauled.
Maybe an enterprising rig designer could incorporate a forestay tensioner in the jib boom, so, the harder you hauled in the sheet, the tighter/straighter the stay became, at the same time as the increasing foot tension flattened the sail. I have no mechanical idea how it could be or IF it SHOULD be attempted!

 

Reminds me of my old model sail boat, lovely hand-carved hull and keel with cast lead ballast. My best buddy had a clunky-looking boat with flat transom, vertical stem and sheet-steel keel that sailed rings around my more elegant craft. Still stewing over that after 65 years!

Back then I thought all jobs had to be club-footed. I can maybe see how it would improve working upwind but not very compatible with a genoa I'm thinking

 

Genoa goes on the forestay on a cutter. Inner staysail boomed.

 

Vas jokin, yah?

 

Racing Vagabundo when we're reaching or running the forestay is slackened, when we’re climbing say 50 degrees apparent and above is where we start tightening.

I often depends on that foresail were running. If it’s our no.1, 150% jib it’s much easier to see the effects and we play with tension much more than say with the no.3 or the blade up. And again to coincide with your sail choice it makes the biggest or most noticeable visual sail shape difference in lighter winds.

The rule of thumb we follow is the same as main halyard tension. We sag the forestay to give the sail power and tighten to de power. Tightening the fore stay moves the draft point further back flattening the sail, it also gives a finer entry angle. Loosening has the opposite effect. That Finer entry angle is what helps you climb, and reduces that knuckle along the leading edge, it you find your pointing really high better than others in a regatta for example but you aren’t going quite as fast you could actually slacken the forestay a bit to balance the height and speed.

It takes quite a bit of feel and practice to notice the performance difference for each sail, (Heavy 1,2,3 light 1,2,blade, large Yankee, small Yankee) but this is all set up time. Once set up mark of on the backstay your settings for the sails and you’re away! After the 3rd or 4th year on vagabundo our setting marks are falling off and we adjust buy looking the sail shape and feel easier with the sails that we have raced with for a while.

Remember though, when you adjust you backstay it also effects the bend in the mast, again more bend in the mast pulls the luff forwards flattening the belly of the main. But you can tweak that using other methods depending on your set up, Halyard tension first, cunning ham, then outhaul, kicker, backstay and finally check stays.

I hope this helpes

 

Three pages, no answer, and we still don't have word from one professional sail maker.

My prediction of the answer is that there is no answer because sag is a tool for optimizing sail shape. A straight jib luff is the flattest jib shape for upwind, righting moment limited sailing. In this one condition straighter is better. How many AC monohulls were broken in half cranking up fore stay tension?

But, if you had a carbon nanotube head stay that never sagged I don't think any racers would want it because it would take away some of their adjustments.

 

More likely that sailmakers are too busy this time of the year to read these forums. And not many sailmakers are interested in the theory side of sailing, concentrating on practical matters and making ends meet .

In theory, the effect of sag would be minimal, like Remmlinger suggests in post #13, if sag would mean a simple geometrical translation (without rotation) of the mid-profiles with the sagging of the stay. But sagging hardly ever happens like that, normally the luff moves while the leech stays put, and that modifies sail shape in many ways detrimental to performance. By the cut of the luff curve the sail can be targeted for a certain wind range, but it will only be optimal in certain conditions. Hence you need to adjust the sag & trim the sail when conditions vary.

Anyone who sailed in the IOR times fractional rigs, with adjustable running backstays, knows how important the correct sag is for performance, while sag per se is nearly irrelevant. With the running backstay and in-line spreaders you had perfect control on the forestay sag, and the runner was nearly as important a control line on the boat as the main sheet. With the "modern", back swept spreaders, nearly-masthead rig, controlling sag has become very difficult and you have lost a lot of the ability to cope with different conditions.

One important aspect about sagging is pitching in waves and the associated, unavoidable pumping of the forestay. Here, the stiffness of the hull and forestay itself becomes paramount, since you cannot adjust the tension/sag of the forestay in every wave. There, even the weight of the luff profile (like a genoa furler) makes a big difference, and also a lighter sail will be better than a heavy one.

 

Excellent clear educational response, Mikko. Even this old sailer (never too old to learn) picked up a few points. Tnx. Geo.