Forestay vs Jib Halyard Tension

Jim 5757 · Oct 26, 2014

FWIW, I would think that if you bend the mast aft, you'll automatically tighten the jib halyard as well. On the other hand, you could adjust the jib halyard itself and not affect the mast bend significantly. ...but I could be wrong, too!
By the way, is your jib hanked to the forestay or is it loose footed?

shemandr · Oct 26, 2014

I wrote a response and didn't post it because I didn't think my first version addressed your question enough. So I hope this one does.
Jib halyard tension will indeed move the draft forward on the jib. Forestay tension will affect the overall shape of the jib profoundly, including flattening it. I don't know if it's correct to say tension on the forestay will move the draft forward, but it will allow the jib to fly in it's designed shape, if the sag of the forestay matches the curve of the luff which was built into the sail. A correctly shaped sail would never have the maximum draft aft of 50% the cord length. So, yes, the correct forestay tension would move the draft forward - from the misshapen draft aft position which too loose a forestay would create. But after you get the forestay tension correct for your sail and the wind conditions you move the draft with halyard tension. RichH has posted regarding at least several times and it would be well worth your time to search the threads for his posts. Read them and then read them again. Repeat until it feels comfortable to you.
The powerful, easy on the helmsman position is draft forward. The pointy but twitchy position is draft aft. You can remember this by thinking of the draft aft shape, or draw it on paper, as having a flatter entry. This is like a knife cutting the wind. Very clean but very prone to be off in either direction. I hope this helps.
If you have a tensioned halyard on a loose forestay you have made your halyard the de facto forestay.
I really hope there will be more posts on this. It's of more interest to me than some of the recent threads.

centerline · Oct 26, 2014

hejumper said:
Can someone help me understand the relationship of forestay vs halyard tension on the draft of the jib/genoa? In reading and discussions with sailors I understand that typically tightening the halyard moves the draft forward, towards the luff. Loosening the halyard moves it back, providing more power but less ability to point higher.

Then someone told me that tightening the forestay (by tightening the backstay) moves the draft back and loosening it moves it forward - that if you loosen the forestay, a slack rig, (moving the draft forward) you must compensate by loosening the halyard to bring move it back.

I guess you could have tight halyard on a loose forestay?

Even trying to capture this in text is confusing to me.

I've ordered Don's material so I hope that clears up my confusion…

Thanks! Larry

The forestay needs to be tensioned according to the rigging... it will affect the performance of the whole boat under sail... tight in a positive way and loose in a negative way..

If the sail.was cut for that boat by a quality sailmaker, The sail will be cut to compensate for the deflect of a properly tensioned forstay on that boat.
the halyard will still come into play even when the forestay is tight, in the same way the halyard comes into play on the mainsail with its rigidly tight and straight "mast"..

And depending on the rigging plan of the boat, if the backstay will ever come in to play for sail shape.

Tension the rigging to the recommended specs and then use the proper controls for sail shape as needed.

shemandr · Oct 26, 2014

hejumper said:
Here is a comment on rig tension from the book Jib Trimming by Felix Marks: "A slack rig results in a loose forestay, which intern results in the belly (draft) moving forward. This results in a wider groove. To compensate, you will need to move the belly back again by further loosening the halyard. A tight rig results in a tight forestay, which in turn results in the belly moving back. This produces a narrower groove and so you will need to further tighten the halyard in order to bring the belly forward again."

OK, I'll try to parse it part by part: "A slack rig results in a loose forestay" Agreed. "...which intern results in the belly (Draft) moving forward." Not agreed. "This (Belly moving forward) result in a wider groove." Agreed. "To compensate, you will need to move the belly back again by further loosening the halyard." Agreed if you want a more narrow groove. "A tight rig results in a tight forestay, which in turn further results in the belly moving back." Not agreed. "This (Belly moving back) produces a narrower groove ..." Agreed "..and so you will need to further tighten the halyard in order to bring the belly forward again." Agreed, again, if you want a wider steering groove.
Phew! It can make your head hurt. The problem with this narrative is that while I agree with some of the described rigging adjustments effect on sails, I disagree with the the starting points. Specifically, in the first part I don't think a loose rig moves the draft forward. And, in the second part I don't think a tight rig moves the draft aft. I'd be happy to listen to differing opinions but that' s the way I see it.

Joe · Oct 26, 2014

Jim 5757 said:
By the way, is your jib hanked to the forestay or is it loose footed?

say what? I hope you're asking if the head sail is hanked on or attached to a roller furling device.

Anyway rather than pretend to be an expert, I will provide this link. The essence is that halyard tension(luff tension) affects draft position.... whereas headstay sag (controlled by the backstay on a masthead rig, and running backstays on a fractional rig.) affects draft Depth..

That explains why increasing headstay sag is a common trim adjustment for downwind sailing.

http://www.quantumsails.com/Sails/Cruising-Support-HeadSailTrimGuide.aspx

Joe · Oct 26, 2014

centerline said:
The forestay needs to be tensioned according to the rigging... it will affect the performance of the whole boat under sail... tight in a positive way and loose in a negative way..

Sorry, but that is incorrect. A backstay adjuster, controls the headstay tension on a masthead rig... which affects headstay "sag".... on a fractional rig the backstay adjuster will be more important for bending the mast... which is a mainsail trim function. Once the mast rake is set with the backstay and headstay length adjustment.... controlling headstay sag on a masthead rig, or bending the mast on a fractional, becomes an integral part of sail adjustment.

centerline · Oct 27, 2014

Joe said:
A backstay adjuster, controls the headstay tension on a masthead rig

This is not true for all boats... some boats dont need a back stay, and still others dont have back stays...

it absolutely makes a difference where and how the shrouds are located as to what you can and cant do with the backstay....

i will stand by my previous statement..

RichH · Oct 27, 2014

Headstay tension defines the (catenary) curve that the sailmaker CUTS into the leading edge of the luff. Wire forestays stretch under sail loading, because the stainless steel used is elastic. A sailmaker usually cuts this smooth curved leading edge shape (called 'luff hollow') for 12-15kts of windstrength, and EXPECTS that the tension of the forestay will at about 12-15% of wire tension. So therefore, if the windstrength is much less than that 12kts. or well above that 15kts. the shape of the leading edge (luff hollow) wont match the sag in the wire.

There are two way to 'match' this sag ... and each method will produce slightly different results for slightly different reasons.
1. backstay tension increase - (and/or running backstay tension)
- which remedies the draft-aft / hooked up leech configuration of a too loose forestay (or a too tight jib sheet tension) and 'opens' the leech (leech becomes 'flatter') .... but doesnt change the shape of the 'luff entry shape' .... the apparent curvature that occurs 'right behind the leading edge of the sail'. The result is the 'mid sections' of the sail from luff to point of maximum draft are now closer to the boats centerline ... and the boat will point better than with a sagged forestay because the boat will no longer be 'skidding' off to leeewards.

2. Halyard Tension (increase) does all the exact same, with the exception that it ALSO causes the leading edge shape to become 'more rounded' up forward near the luff.

A more rounded 'luff entry' is more forgiving vs. luffing and separation stalls and will be more stable through a 'wider' range of sailing angles but not as fast as a 'fine' or flattish luff entry shape desirable for those who sail 'displacement' hulls as fast as possible.
A more rounded luff shape is desirable for VERY fast boats such as planing hulls and high speed catamarans .... and an inattentive and imprecise helmsman .... OR for sailing in unstable winds that constantly 'veer and back' through a wide angle.
A flattish entry luff is more desirable in constant speed winds and constant direction winds'; BUT, still needs a helmsman that is constantly 'on' to steer the boat correctly though the small range of saiiing angles that you get from a flat luff entry.
'Cruising cut' sails usually have a more 'rounded' luff entry - more forgiving for the inattentive helmsman.

For 'light' winds .... all the exact opposite as above - loosen the backstay but do keep that flattish 'luff entry' shape (or 'enjoy' lots of 'separation stalls')

Rx for jib luff sag:
Tighten the backstay 'to the exact amount' that 'matches' that 'luff hollow curved shape' that was CUT into the sail .... then, if more adjustment is needed, add halyard tension ... then if still too much 'sag' reduce jib sheet pressure and use a barber-hauler. If you add too much halyard tension, you will probably JAM (break ???) your furler in doing so.

IMO - this is the best first steps in 'matching' forestay sag and luff hollow curve: http://www.ftp.tognews.com/GoogleFiles/Matching Luff Hollow.pdf ...

B&R & other 'backstay-less' rigs: a good compromise, more stable for luff wire sag .... BUT once you go beyond those windstrength limits that 'really stretch out that elastic forestay', you MUST reef/reduce the jib or your just not going to 'point' as well as a boat with a full adjustable backstay. FWIW, I helped set of a Hunter with a B&R for racing, the only way we could make that boat 'point' well in the higher wind ranges was to install running backstays !!!!!!

shemandr · Oct 28, 2014

hejumper said:
Basically - It would seem then that you would adjust tension of the forestay to match the luff-hollow created by the sailmaker for the wind condition you are in and then use halyard tension to adjust the draft position and the "roundness" of the leading edge.

Yes! Not theoretical at all. It's the way your sail actually works. I'm sorry my explanation was weak. If I spent more time on it maybe it would have been better.

RichH · Oct 28, 2014

I learned about sewing a thin row of straight stitches behind the luff to visualize forestay sag/luff shape from the bowman on Ted Turner's 1977 America's Cup Boat - Courageous. He and several other members of that crew were workplace colleagues of mine some years later. I can remember those conversations as if it were 'this morning', and also conversations with other AC crew, etc. members over the years, as Im not bashful about my passion for sailing and racing and always tried to pursue to learn from those at the 'top of the curve'.
Some of this data/experimentation can be found in most Engineering College Libraries in a 'compendium' produced by NACA, the predecessor of NASA, entitled: Ancient Interface.

A lot of one designs do use and used to use cunninghams to 'round up' the jib luffs; but, those jibs are made with wire luffs inside a sleeve ... the jib (with integral wire luff) replaces (totally slackened) the standing rig forestay ... these boats usually have 'dynamic' forestay length adjustment so that they can rake the mast while on-the-fly.
For high end racing, to alter the luff shape, you change (peel) jibs.

Joe · Oct 28, 2014

centerline said:
This is not true for all boats... some boats dont need a back stay, and still others dont have back stays...

it absolutely makes a difference where and how the shrouds are located as to what you can and cant do with the backstay....

i will stand by my previous statement..

Didn't see any particular boat mentioned in your original statement... how would your premise apply to an Ericson 32 (subject boat).

Scott T-Bird · Oct 30, 2014

My Hobie had a wire luff and the luff tension was adjusted by the halyard. The forestay went slack when the halyard was tensioned. The rake of the mast was determined by the adjustable forestay length. If you weren't careful, you could over-tension the halyard and eliminate the desired rake as indicated by an overly loose forestay. Essentially, the wire luff takes the place of the forestay.

On my masthead rig, I adjust the backstay tensioner to optimize the sag of the forestay. With my hank-on sail, the luff is sail cloth that I don't particularly want to overstress. If I were to raise the sail to full height without using the winch, I normally find scallops between the hanks. If I over-tighten with the winch, I can find vertical creases running behind the luff. What I try to do is tighten just enough with the winch to remove the scallops and no more. So, if I'm adjusting sag with the backstay to realize a more-or-less constant sag regardless of wind strength (for upwind sailing), I shouldn't have to adjust halyard tension, no?

In other words, if my halyard is set to eliminate the scallops, it's a set-it and forget-it type of situation for me. Essentially, adjusting halyard tension for either jib or mainsail is something I rarely ever even think about when sailing.