Balancing forestay and jibstay tension ....

[RichH]

1. What is your recommended intial tension set up for forestay vs. jibstay on a cutter. I prefer a ~3/4" prebend in the (Selden) mast to lessen mast pumping; using more tension in the forward lower shrouds to accomplish the pre-bend. The *problem* is the 'balance' of tension between these two stays and to fit/match the 'luff hollow' of each sail at their maximum wind range. If I load up the jibstay tension obviously the forestay/genoa sags to leeward as a reaction .... and I lose pointing ability; but, if I fly just the staysail (without the genoa) I have go forward and tighten the jibstay to gain pointing ability in this shortened mode. Having two forward stays adds a great deal of complexity to rig tuning .... are there any 'rules of thumb'?The boat has intermediate stays; but, the shallow angle that the intermediates make with the 'hounds' is not very mathematically efficient. ..... or should I simply use running backstays to make such 'fine tuning' adjustments to control the differing amounts of forestay/jibstay sag?2. Early Island packets used a jibstay tensioning system that ran to a block at the hounds then to a winch at the base of the mast to control stay tension. The tack/deck connection was never disconnnected - leaving the doused staysail always connected to the wire. The obvious advantage of that system is that the staysail could be left hanked on to the jibstay and the jibstay could be totally slacked (dropped to the deck) to permit the tacking a genoa across the foredeck (and without fouling a genoa on the jibstay). The disadvantage was that the wire running over a block would soon fatigue and would soon fail. What would be your opinion to reapply such a system with a wire jibstay with a pendant of modern high tech line (able to make repeated turns over such a mast mounted block) and then run to a winch at the base of the mast? The question therefore is: are the modern high strength polymers up to the task of standing rigging --- no one wants rigging failures when on a long distance passage. My concern would be the constant movement of high tech rope constantly moving over a block as the rig/mast constantly deflects. The lever type of jibstay 'disconnects' dont appeal to me as the staysail has to be removed to 'store' the jibstay ..... when you NEED a staysail its a PITA to go forward and reattach everything. The old Island Packet system seems much safer 'on deck' if it could be made 'bombproof' using 'modern' materials. Opinion?"

 

[Brion Toss]

Wow

Hello,You've asked some deeply architectural questions, ones with numerous implications and variations, for forgive me if I ramble some here.First, let's call the inner stay the forestay, the inners sail the forestays'l, the outer stay the jibstay, and the outer sail the jibstays'l or Genoa, so we can be clear on which is which.The jibstay is opposed almost exclusively by the backstay, while the forestay is opposed to some extent by those aft-led intermediates, by the stiffness of the mast itself, a bit by the aft lower shrouds, and a bit, indirectly, by the backstay. The trouble is that none of these oppose the forestay very well, and that to the extent the backstay is involved it is losing some of its effectiveness in opposing the jibstay.Tuning the backstay sufficiently tightly (up to about 20% of rated break) can compensate for the extra load from the forestay, in part. But that locks you into keeping the forestay set up all the time, and really isn't optimal for either stay. Tightening the intermediates isn't much more help; as you noted the angle is so shallow that most of the work these wires accomplish is in adding compression to the mast. So the mast itself is called on to oppose the forward vector, which means you'll still have too much luff sag in a breeze, plus a mast shape that bulges forward at the height of the forestay, damaging mains'l shape.The root of the problem, I believe, is those damn aft-led intermediates. These have been promoted as labor-saving alternatives to running backstays, but they are just so much extra weight and windage, for all the work they do on most hulls. Unless the angles are as generous as possible, and the mast sufficiently stiff, and the forestays'l sufficiently small, they can't keep the forestay straight. And they prevent the main boom from swinging out as far as it might like, and they chafe the mains'l on a run. I do not like them.So, given a good mast section and appropriate wire sizes (your forestay is smaller in diameter than your jibstay, right?) running backs are your answer. To avoid making them so difficult to use that aft-led intermediates start looking attractive, make them out of high-modulus (HM) rope instead of wire. The rope is much lighter than wire, so it doesn't whip around, fouling sails and crew. It's also softer, so kinder to your mains'l. Most runners have block-and-tackle for tensioning, but over the years I've come to the conclusion that this is not optimal; there simply isn't enough mechanical advantage to take any slack out of the forestay, so at best you can only keep the mast from bulging forward. Extra prebend can help here, using the mast for a larger component of forestay tension, but it ain't optimal. In addition, the blocks are a hassle to overhaul and take up, and they bang around on the leeward side, and it's difficult to set them low enough that they don't want to smack crewmembers in the head. That's why I now prefer, whenever possible, to take the runners to heavy-duty deck blocks, and then lead them to winches. If you have secondary winches, great, just make sure of a good lead. If you only have Genoa winches, use the leeward one for the runners. It can take a bit of choreography, but not much. And in extreme conditions you won't be using the Genoa at all, so the runners will own the winches. I'll stress that proper line and block selection, as well as layout and installation is vital to this system, as with everything in rigging.As for the halyard/forestay question, this is indeed being used on many boats, particularly in Europe. Vectran would be the best material, running over a sheave at least 8 times the diameter of the rope. You won't see anything like the fatigue that you get with wire in this application. Having said that, I think it's a bad idea. Even if you can get sufficiently large rope onto a sufficiently large sheave, you are still asking this piece of gear to do double duty. You're also asking your winch and/or cleat and/or stopper to be responsible for standing rigging loads. And when you drop the forestays'l, you have just removed a backup means of keeping the mast out of the cockpit, should the jibstay fail. So I'm more for a forestay that is removable in light airs, but quick and easy to set up in a breeze. We usually use a Johnson adjuster with an Avibank pin.Hope this all helps. Lots of details left out, so feel free to follow up.Fair leads,Brion Toss

 

[RichH]

You confirmed my suspicion of intermediates

Thanks for the response to a complicated question.Indeed the intermediates make such a shallow intercept angle with the hounds of the forestay that by trigonometry I deem them to be worthless to support the mast while trying to tremendously overload their chainplates! My thoughts are to totally remove the (mathematically worthless) intermediates and simply replace with runners. Runners make better sense because I can attach them much farther aft from the mast for lower reaction loads (in comparison to the intermediate chainplates) to the deck attachments. I especially like your idea of leading the runners to a fixed deck block then to a winch .... saves head injury, etc. as I would rather be smacked by a rope than a block. Obviously this would not be a set-up for a genoa track attachment and would need some auxiliary support structure under the deck / hull to carry the load.OK!! an 8:1 block size would be a 'monstrosity' therefore not a good set-up. Im running 1/4" wire on my forestay. . I understand the mechanism of 'toggle';but, the Johnson adjuster looks 'light weight' in spite of its published rating. Thanks for your comments. I very much appreciate the time you take in reply of such messageboard discussions. I'll also pass this info to the Tayana Discussion group. thanks again, much appreciatedRich HampelAquila Ty37 #423