Lower Shroud Tension

Discussions relating to rigging
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Terry
Cruising
Posts: 229
Joined: Thu May 18, 2006 8:56 am
Location: Gwynedd, North Wales

Lower Shroud Tension

Post by Terry » Mon Sep 10, 2007 9:18 am

Out sailing the other day I noticed that the lee shrouds had gone horribly loose when close hauled so I anchored at the first opportunity and tightened them up. It took three and a half turns on each cap shroud to get them reasonably tight but I will have to use a more scientific approach the first chance I get.
Can anyone tell me just how tight the lower shrouds should be in order to maintain mast pre bend? As soon as I put more than a little load on them the mast ends up ramrod straight and a little more and it may well invert. Things are a bit better when the back stay's tensioned though.

Terry
Cruising
Posts: 229
Joined: Thu May 18, 2006 8:56 am
Location: Gwynedd, North Wales

Post by Terry » Mon Sep 10, 2007 11:58 am

Hi Dave
I have to say that anyone who manages 7+ knt on a reach in a swift has got to be listened to! (Respect man)
Although my grasp on foil dynamics is somewhat limited, I have always thought that the reason why swifts have aft swept spreaders was to bow the mast forward at that point (or have I got pre-bend all wrong?)

Phil De Troy
Making way
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Location: Seneffe (Belgium)
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*** PROBABLY SPAM *** Lower Shroud Tension

Post by Phil De Troy » Mon Sep 10, 2007 1:08 pm

Depends also on the shape of the luff.
Almost straight, tension on the lower shrouds.
Round luff (up to 2 times mast section), shrouds loose, juste tension minus two or three turns.

Then with little wind, the mainsail has power, when there is more wind and the boat heels, the mast has to be bended to flatten the sail, and the lower shrouds have tension ONLY in this configuration.
When there is a backstay, hoist the mainasil in little wind, lower shrouds loose, you bend the mast with the backstay until the sail is just flat, than give tension to the lower shrouds.

Phil
----- Original Message -----
From: Terry (forum-rigging@swift18.org)
To: forum-rigging@swift18.org (forum-rigging@swift18.org)
Sent: Monday, September 10, 2007 11:18 AM
Subject: *** PROBABLY SPAM *** [Swift 18] Lower Shroud Tension


Out sailing the other day I noticed that the lee shrouds had gone horribly loose when close hauled so I anchored at the first opportunity and tightened them up. It took three and a half turns on each cap shroud to get them reasonably tight but I will have to use a more scientific approach the first chance I get.
Can anyone tell me just how tight the lower shrouds should be in order to maintain mast pre bend? As soon as I put more than a little load on them the mast ends up ramrod straight and a little more and it may well invert. Things are a bit better when the back stays tensioned though.



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Phil De Troy www.MicroClass.org

noodle
Site Admin
Posts: 83
Joined: Sat May 06, 2006 10:43 am
Location: Eastleigh, Hants

Post by noodle » Tue Sep 11, 2007 7:56 pm

Hello, SNIPE here, No 53, so quite an early bird. SNIPE was found languishing on its trailer, having been immobile for many years. Happily, on investigation, it proved to be capable of being returned to service with everything in excellent order.

I had given up sailing, or so I thought, after moving down from the Scottish Borders 5 years ago. I had sailed a Hunter F1 in the Windermere Winter Series and on the Scottish West Coast. Although a very different performer, the Swift shares the F1s fractional rig and I rig SNIPE without much tension in upper or lower shrouds, to the extent that the leeward shrouds sag off when on the wind. On the F1 we rarely ever used backstay except in strong winds to flatten the top of the sail and tighten the jib luff. We used some backstay when flying the kite. I certainly don't put in any pre-bend.

I have used the same technique to sail SNIPE and find it to be impressively close-winded and fast upwind, with a far smoother motion in a seaway than the Hunter, although the Hunter could be made to plane on a reach.

Robin Rew, Banbury

johnsti
Under way
Posts: 23
Joined: Sun Dec 03, 2006 9:56 pm
Location: Nottingham / Derby Border

rigging

Post by johnsti » Tue Jul 01, 2008 1:40 am


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