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Old 09-07-2017, 03:30   #1
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Forestay Tension for Cutters

I was always taught to leave the inner forestay slightly loose, so that the backstay and forestay can balance each other without the inner forestay stealing backstay tension from the forestay.

This would seem to be especially important on a boat with in-mast furling, as the mast section is massive and rigid. So it would be easy for backstay tension to get diverted to the inner forestay, if that's too tight.

OK, so here is my problem -- when you need some tension on the inner forestay, it's supposed to be runner to the rescue. But my mast is too rigid! The runners don't bend the mast at all, and very little influence inner forestay tension.

I'm just about to add a little tension to it, because I use the staysail a lot, and I need for it to have good shape.

But I'm afraid that will spoil the forestay tension

It's rather awkward to adjust forestay and inner forestay tension on my boat because of the 400S Furlex furlers, which require a lot of fiddling to get at the turnbuckles. So it's hard to just experiment with it.


Anyone else encounter this problem?
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Old 09-07-2017, 04:39   #2
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Re: Forestay Tension for Cutters

I find that I too have to carefully balance forestay and jibstay tension--can't have both bar-tight at the same time. I haven't decided which I'd rather have tighter....
The only solutions I can think of are 1) Aft-led intermediates to tighten the inner stay against. Or 2) really, really strong hydraulic ram running backstay tensioners.
Both options are inconvenient and expensive, so I hope someone can come up with something better for you.
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Old 09-07-2017, 04:43   #3
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Re: Forestay Tension for Cutters

We've got a cutter rig on Athene and furlers on yankee and staysail, which seems to be a similar arrangement to yours.

However, our Selden mast has a certain amount of built-in pre-bend (our main is fully battened rather than furling).

Holman and Pye, the designers, advised me when I bought the boat that the inner forestay should be kept reasonably tight; the runners on the Oyster 435 were designed simply to stop the mast pumping in a head sea rather than to apply tension to the staysail luff.

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Old 09-07-2017, 05:44   #4
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Re: Forestay Tension for Cutters

Quote:
Originally Posted by athene View Post
We've got a cutter rig on Athene and furlers on yankee and staysail, which seems to be a similar arrangement to yours.

However, our Selden mast has a certain amount of built-in pre-bend (our main is fully battened rather than furling).

Holman and Pye, the designers, advised me when I bought the boat that the inner forestay should be kept reasonably tight; the runners on the Oyster 435 were designed simply to stop the mast pumping in a head sea rather than to apply tension to the staysail luff.

GORDON KNIGHT
Howdy, Solent neighbor.

My boat's manual doesn't give any advice like you've gotten, but it sounds reasonable. My runners do almost nothing to the staysail luff tension. Nor do they do anything with regard to mast pumping, since my mast seems immune to pumping under any circumstances -- never a tremble in tens of thousands of miles of sailing in all conditions. Query what the heck the runners are even for -- other than making me feel better when using the staysail in a big blow.

It's frustrating.

I guess despite the hassle of lifting the Furlex furlers to play with stay tension, I'm just going to have to see how far I can go with the inner forestay before it starts to steal tension from the forestay. The possible combinations with different levels of backstay tension are extremely numerous -- bleh.
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Old 09-07-2017, 10:17   #5
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Re: Forestay Tension for Cutters

Sounds like a couple of hours of rig tuning are in your future... but I have seen it before. The upside is on a very stiff mast tensioning the inner stay probably won't steal much tension from your forstay. If it does just a touch more backstay will probably fix it for you.
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Old 09-07-2017, 10:18   #6
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Re: Forestay Tension for Cutters

Wouldn't the answer depend on the rest of the rig layout? The mast is a complex column structure subject to dynamic loading. Attachment points of the inner forestay relative to spreaders and shrouds, and use of running backstays may counter or increase the inner forestay load etc
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Old 09-07-2017, 12:41   #7
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Re: Forestay Tension for Cutters

I don't have any answers myself, but I have often found good answers in the technical documents of the Seldén home page. They could contain some useful information.
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Old 09-07-2017, 14:33   #8
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Re: Forestay Tension for Cutters

they need to be even / if sailing with reefed main and staysail only / running stays take some of the load / they never seem to be perfect but it's best if all tensions are even / when the pressure is on from the wind there will be a slight slackness on the lee side / if you try and correct you can damage hull fittings and sometimes the hull
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Old 09-07-2017, 15:28   #9
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Re: Forestay Tension for Cutters

Running backstays and staysail/forestay match to each other, and so are meant to be.
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Old 12-07-2017, 02:42   #10
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Re: Forestay Tension for Cutters

Both my boats since 1984 have been cutter-rigged.

Set the tension for the inner forestay. Then set the tension for the forestay. Then take up the slack on the inner forestay, which will have slackened as the top of the mast is pulled forward as you tightened the forestay.

If you want further fine adjustment, decide which is your most important foresail, and adjust accordingly.

If you depend on the staysail in heavy weather, using the runners is wise even if you can't visually detect the effect.

If in the longer run you start to obsess about it, get your sailmaker on board and ask him whether to cut the staysail flatter, which could improve the slot effect, but also give you upwind advantage when using the staysail without jib in heavy weather.

All the best!
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Old 12-07-2017, 02:58   #11
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Re: Forestay Tension for Cutters

Just to add a bit to my previous post: I also used to muck around with an inch here or an inch there, until I accepted that the main function of the staysail is to accelerate the apparent wind between the jib (yankee) and the mainsail, which it does by splitting the slot.

After you have tuned tension to your satisfaction, see under sail which of the foresail luffs lifts first. If the the jib, all good, if the staysail then either more tension if possible, or go ahead with the idea of cutting the Staysail flatter (because if it lifts first, it's ruining the slot).
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Old 12-07-2017, 04:11   #12
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Re: Forestay Tension for Cutters

A few hours of tinkering with things under sail will sort things out. Just go hard on the wind on a breezy day, & check the curve of the luff of each sail when going upwind, with & without a lot of backstay on.

Knowing that:
-The backstay will have more effect on the headstay than it will on the inner forestay on a masthead rig.
- Ultimately proper inner forestay tension trumps ideal headstay tension. Since if you're beating upwind in a stiff breeze, you'll have rolled up the jib on the headstay, & shifted down to the staysail anyway. Which, the importance of good sail trim goes up geometrically with wind speed. Part of this consisting of proper stay tension.
- And that on a boat with a conventional main, tightening up the backstay depowers the main at the same time that it tightens up the headstay. Thus improving pointing, while depowering the jib a bit due to a tighter headstay flattening it's shape, via the increased backstay tension.

Tuning things is really fairly simple. Sail for a bit with each jib. Check the luff curves of each (sag in their respective stays). Decide which needs some tension (or loosening). Roll up the jib(s) & adjust the stay(s). Unfurl the jibs, & repeat the process.
And while you're doing this, take notes on how much you tighten or loosen each stay (# of turns on the turnbuckle/rigging screw), as well as how much luff curve (sag in the stay) you have in each sail at said settings, in inches or cm (sight up the stay when the sail’s trimmed in). And also denote how much (measured) backstay you have dialed on at each turnbuckle setting, along with the amount of headstay sag in each sail with said rigging settings.

BTW, you do have a witness mark on the backstay, & a batten with index marks on it attached to the adjuster, so that you know what the backstay setting is, right?

Also record headstay & inner forestay sag vs. backstay settings. Along with wind speeds (true & apparent), pointing angle(s) each time something is adjusted. And sea state/wave conditions, since this will somewhat dictate how tight you want the stays, via both backstay, & turnbuckle stay tension. Given that it's tougher to point in lumpy seas vs. flat conditions. So different sea states will call for different settings on the sail. Specifically; the backstay, runners, jib lead position, & sheet settings.

Oh, & it doesn't hurt to also denote; VMG, CMG, & SMG at the various sail control settings, & sea/wind conditions as well. So that in the future you'll know what your targets are in terms of speed, & pointing angle.
It's a real world Polars check. And it pays to compare the real numbers to your theoretical Polars. So that if the 2 are grossly different, you know that it's worth playing with your rig & sail trim settings to see if you can match or exceed your Polars.

Also, once all of this testing & measuring has been done, it's smart to compile this data into a trim card. Which denotes the setting of each sail control for various combinations of wind & waves. As such a tool is invaluable for those who don't know the boat well, or are new to sail trim. Or just for when you're tired enough that it's good to have the data to refer to, to confirm your current trim settings.

BTW, for anyone interested, there's a bit of discussion on some of the various ways to adjust stay tension (including backstay) in this thread --> Adding a cutter rig / sloop to cutter conversion

Hope this makes sense, I ain't caffeinated up for the day as yet, & it's still a little while till sunrise

Basically, record everything you can, & turn the data into a useable sail trim & tuning guide (for your boat), for various conditions.
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Old 12-07-2017, 06:35   #13
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Re: Forestay Tension for Cutters

Thanks to everyone for all of the really helpful comments, especially from Christian and from Uncivilized. Lots of food for thought here.

There's a lot of talk in here about backstay tension -- but my boat doesn't respond to backstay tension like a normal yacht does -- that's because I have in-mast furling and great monster telephone pole Selden furling mast, 23 meters high. I do not play with the backstay for sail tuning -- you lose this control with in-mast furling, because you can't bend the foil without really screwing things up, and with my fat mast you can't do it anyway. So I set the backstay to balance the headstay tension and keep the foil straight (which requires the mast to be bent aft at the top a bit -- God knows why).

Playing around with inner forestay and headstay tension is more laborious than these comments contemplate -- because I have 400S Furlex furlers with internal rigging screws, so I have to slack the halyard, unscrew different bits, and lift the heavy furler up the stay to get at the rigging screw -- bleh. Every time I change anything in the stay tension. Especially not fun in a seaway.

But I see there's no other way to do it, so I will get to it. At the moment, both headsail luffs are saggy so I need to crank up the tension on both of them anyway.
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