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Old 01-12-2019, 13:48   #1
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Staysail stay tension - brain fart

A couple of months ago I was reading up on cutter rigs and came across this dissertation on the staysail and it’s stay tension. The article argued strongly for the stay to have little tension, something like 15% of what was carried in the foresail stay.

Now I can’t find that damn article. I THOUGHT I read it on Attainable Adventures/Morgan’s Cloud web site. But damned if I can find it there.

So I could use some help locating that article if anyone else can recall it.

But also to revisit the topic of staysail tension in general seeing as how it’s probably unavoidable not that I’ve broached the topic.

FWIW, our boat is 44’ LOD, 37’ LWL, 49’ LOL (including the 5’ boom.). The staysail stay is set back perhaps 6’ from the foresail stay.

I’m recalling reading the article with the argument for little tension and now that I’m on the boat again I want to revisit the reasoning before messing with the tension.

Many thanks.
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Old 01-12-2019, 13:52   #2
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Re: Staysail stay tension - brain fart

Unless you have something to oppose the pull of the inner stay, it will pull your mast out of shape if too tight. It's purpose isn't to hold up the mast, like the forestay's is. Even with aft-led intermediates or runners, you simply don't need the kind of tension on it that the forestay requires.
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Old 01-12-2019, 16:00   #3
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Re: Staysail stay tension - brain fart

Quote:
Originally Posted by hpeer View Post
A couple of months ago I was reading up on cutter rigs and came across this dissertation on the staysail and it’s stay tension. The article argued strongly for the stay to have little tension, something like 15% of what was carried in the foresail stay.

...

I’m recalling reading the article with the argument for little tension and now that I’m on the boat again I want to revisit the reasoning before messing with the tension.
As I understand it, the argument is that:

(1) research into rig tension and sail trim has for the past century been focused on sloops, the foresail of which is cut so the luff mates with the stay sag that is a consequence of a stay pretensioned to about 12% (10 - 15%) of wire rope working load;


(2) the forestay (aka staysail stay) of a cutter does not need to be pre-tensioned to that degree. A cutter sails well with its headstay pretensioned to about 12% of wire rope working load and with its forestay pretensioned to a moderate level of about 5% of working load. Then higher tension is applied to the halyard of the staysail to shape the sail correctly (judged by the relative position of maximum draft or camber).
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Old 01-12-2019, 16:07   #4
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Re: Staysail stay tension - brain fart

Thanks for these answers guys. This aligns well with my murky recall and makes perfect sense.

What interesting is that in seeking the article I read I read through a bunch of stuff about stay sail shroud tension here on CF and it was, to my ear, not nearly as well reasoned as what you have explained in this two succinct posts.

Many thanks.
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Old 02-12-2019, 03:49   #5
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Re: Staysail stay tension - brain fart

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What interesting is that in seeking the article I read I read through a bunch of stuff about stay sail shroud tension here on CF and it was, to my ear, not nearly as well reasoned as what you have explained in this two succinct posts.
In defense of CF, I note that I put forward much the same argument as in post #3 of this thread in an earlier thread: http://www.cruisersforum.com/forums/...ml#post2914150
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Old 02-12-2019, 03:55   #6
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Re: Staysail stay tension - brain fart

Yes you did, and here it is. I must have missed it.

Quote:
I dinnae have a furler on my forestay, because Led Myne is a traditional cutter with a headstay and forestay (on which she carries a hanked on staysail).

Having said that, I'll take a stab at the problem:

1. The problem exists because sailmakers, riggers, and those working on the physics and performance of triangular sails flown afore the mast have concentrated almost entirely on sloops, not cutters, for the past century or so.

2. The theory is that a sailmaker cuts a triangular sail (to be flown afore the mast) with a luff curve that suits the sag in the stay on which the sail is flown. The rule of thumb varies a little from sailmaker to sailmaker partly because of differences in what rigging experts say. But the common ground is that the sailmaker assumes that the stay is made of wire rope tensioned to somewhere in the 10 - 14% of working strength (within the elastic range). That tension is necessary for satisfactory performance going to weather.

3. Not many cutters are designed or built to have a tension of 10-14% of working strength in their forestay. But they are designed and built to have a tension of 10-14% of working strength in their headstay (which carries a jib, a jib topsail, a genoa, a yankee ... etc, whether hanked on to the headstay or set to groove in a foil). The cutter is usually built to have a tension in the forestay (the stay carrying the staysail) of about 5% of the working strength of the wire.

To carry more than 5% tension in the forestay needs:

(a) more displacement (more material) built into the foredeck so it can bear the higher wire tension; and

(b) more displacement (more material) in the mast and in running or fixed backstay(s) and/or in aft intermediate stays to balance the forestay tension and maintain the desired mast curve.

Since more displacement costs money and a time penalty, few boats were built that way historically. Particularly with a plastic bucket of a boat (i.e. a GRP hull and deck as on Led Myne), it's clear that increasing the wire tension in the forestay from 5% to 12% is reversible - it's within the elastic range of the steel wire, so releasing the tension from 12% to 5% has not changed the length of the wire. But it's less clear what happens to the GRP deck: the elastic limits of a GRP deck are not well known and cranking on tension may change permanently the camber of a GRP deck.

4. A staysail cut to suit the sag of a 5% tensioned forestay works well in cutter mode. (and so the owner of a traditional cutter need to discuss with a sailmaker to ensure the sailmaker understands a cutter rig and does not misunderstand that the sail will be used on a stay with 10-14% tension).

5. When a cutter rig is reefed down (i.e. the headsail dowsed and the staysail becoming the source of drive and balancing a reefed mainsail), the traditional cutter sailor has two or three options:

(a) ignore the issue, because it's in the context of high winds and no sensible person is aiming to sail harder than a close reach in those conditions;

(b) temporarily increase the tension in the forestay to something in the 10 - 14% range (and care less about what that does to the shape of the mast, which is anyway carrying a reefed mainsail); or

(c) solve the problem by increasing halyard tension in the staysail halyard (and leaving the forestay tension at 5% of its elastic working strength).

That solution, namely 5c, is what I and all cutter sailors I know, do. As far as I can see, managing the location of the maximum draft of the sail can be done with adjusting halyard tension whether the sail is run in a groove of a roller-furler foil or hanked onto a stay.
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Old 02-12-2019, 03:57   #7
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Re: Staysail stay tension - brain fart

It’s an interesting topic because it seems to argue away from a curling staysail and for the hanked on variety.

Compromises.

But then I guess we could discuss the merit of self taking stay sail booms. LOL

Once again - many thanks
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Old 02-12-2019, 04:33   #8
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Re: Staysail stay tension - brain fart

"Even with aft-led intermediates or runners, you simply don't need the kind of tension on it that the forestay requires."


However when reefing down the foresail will usually be struck , and the stay sail will be the work horse going to weather.
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Old 02-12-2019, 05:35   #9
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Re: Staysail stay tension - brain fart

Perhaps you were reading Morgan’s Cloud’s:
“Cutter Rig—Optimizing and/or Converting”https://www.morganscloud.com/2015/10...or-converting/

More from “The Offshore Voyaging Reference Site” ➥ https://www.morganscloud.com/tear-sheets/

A couple of years ago we discussed “Forestay Tension for Cutters“
http://www.cruisersforum.com/forums/...rs-187459.html

And “Adding a cutter rig / sloop to cutter conversion”
http://www.cruisersforum.com/forums/...ml#post2423133

Although she doesn’t discuss tension, Carol Hasse (sailmaker extraordinaire) offers advice on staysails:
https://www.porttownsendsails.com/pdf/staysail.pdf
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Old 02-12-2019, 12:47   #10
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Re: Staysail stay tension - brain fart

Interesting thread. I sail a ketch but have a detachable forestay to be set up close behind the (roller) forestay so as to take a hanked on storm jib when needed. The detachable forestay has a Highfield lever plus a screw thread to increase tension by hand & possibly also by spanner (wrench in U.S.?).
Understand the issues about foredeck strength (reinforced for purpose) but leaving that aside, have always wondered how much tension to put in that detachable forestay.
Less than main forestay sounds good, taking up max tension on storm jib halliard. Thanks to all for information.
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Old 02-12-2019, 15:32   #11
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Re: Staysail stay tension - brain fart

Quote:
Originally Posted by FAST FRED View Post
"Even with aft-led intermediates or runners, you simply don't need the kind of tension on it that the forestay requires."


However when reefing down the foresail will usually be struck , and the stay sail will be the work horse going to weather.
That is immaterial. If the stay'sl gets carried away, stay and all, the mast will still stay up. If the forestay goes, so will the mast. Therefore, proper forestay tension is the more important consideration.
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Old 02-12-2019, 15:40   #12
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Re: Staysail stay tension - brain fart

Sailnet has some discussion here:
https://www.sailnet.com/forums/gear-...ter-print.html
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Old 06-12-2019, 18:03   #13
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Re: Staysail stay tension - brain fart

My cutter rig has fixed intermediate back stays and so staysail stay and the intermediates work together and have the same tension. They hold the mast very straight but also help create a very stiff rig.

Yes, fixed intermediate back stays reduce the ability to go downwind but I have decided that is a small cost to get a stiff rig. No problems in 40 years, including ocean passages (new stays, of course, over the time).

I've had a furler on the headsail since 1992 but only recently put one on the staysail. Wish I had done so earlier as I'm making much better use of the various combinations now. Was often too lazy or too dry to go on the foredeck (and get wet) to hoist or drop the staysail.

Cheers, Jim
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Old 07-12-2019, 05:53   #14
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Re: Staysail stay tension - brain fart

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Originally Posted by oceanshoretiga View Post
My cutter rig has fixed intermediate back stays and so staysail stay and the intermediates work together and have the same tension. They hold the mast very straight but also help create a very stiff rig.

Yes, fixed intermediate back stays reduce the ability to go downwind but I have decided that is a small cost to get a stiff rig. No problems in 40 years, including ocean passages (new stays, of course, over the time).

I've had a furler on the headsail since 1992 but only recently put one on the staysail. Wish I had done so earlier as I'm making much better use of the various combinations now. Was often too lazy or too dry to go on the foredeck (and get wet) to hoist or drop the staysail.

Cheers, Jim
Our smaller boat, a 33’ steel cutter also has permanent runners.

Your comments make a lot of sense.
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