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Rig Tension

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    Posted: 09 Feb 15 at 2:25pm
SO looking at the tuning guides for the Mirror. Using the P&B guide for the Bermudan mast it says use 160lbs of rig tension. I pulled on around 140lbs and did not want to go any further. As it was the shrouds would give off a high pitched ping when plucked and I had the mast rake correct. Given the boat is a 1986 Bell built boat I did not want to over do it on the fittings. So is 160lbs really what would be required?

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Post Options Post Options   Quote JimC Quote  Post ReplyReply Direct Link To This Post Posted: 09 Feb 15 at 2:35pm
If it makes you feel better that's really not a very big load compared to some boats. I used to use 600lbs down the shrouds on my Cherub, and much the same down the checkstays which terminated at the same point, but the boat was built and engineered to take those sorts of loads, and in any case they wouldn't be necessary on a Mirror. Trapeze boats need far greater tension.
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Post Options Post Options   Quote Rupert Quote  Post ReplyReply Direct Link To This Post Posted: 09 Feb 15 at 3:25pm
On an old Mirror, the most likely thing to break with too much rig tension is the shroud plate, which are often screwed into wood which is slowly rotting, and certainly wet. Once you have checked these are OK, 160lbs should be OK. Worth checking the sheerline isn't distorting.

Have to say, though, that I doubt it will make a huge amount of difference to the speed, putting the extra tension on. Mast rake much more important.
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Post Options Post Options   Quote Time Lord Quote  Post ReplyReply Direct Link To This Post Posted: 09 Feb 15 at 4:47pm
Once saw an old GP14 being brought up the slipway as it was taking on water. As it went onto the trolley, you could see the foot of the mast sticking 2-3 inches out of the bottom of the boat.

The owner had been told that he needed to put on more shroud tension so that he would go faster! Had the opposite effect!!
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Post Options Post Options   Quote zippyRN Quote  Post ReplyReply Direct Link To This Post Posted: 09 Feb 15 at 5:05pm
Originally posted by Rupert

On an old Mirror, the most likely thing to break with too much rig tension is the shroud plate, which are often screwed into wood which is slowly rotting, and certainly wet. Once you have checked these are OK, 160lbs should be OK. Worth checking the sheerline isn't distorting.

Have to say, though, that I doubt it will make a huge amount of difference to the speed, putting the extra tension on. Mast rake much more important.

indeed  so , i also wonder whatthe rated  working load of the  old style cast eyes is ... in gunter rig days  mirrors ran  minimal rig tension 

160 lbs is  small potatoes in rig tension terms  but if the boat structure or the fittings  aren't  sound .. 
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Post Options Post Options   Quote NHRC Quote  Post ReplyReply Direct Link To This Post Posted: 09 Feb 15 at 11:25pm
Safe working load on 3mm wire rigging is about 126kg which is 270lbs that is with a 4:1 factor from the average breakload.


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Daniel Holman View Drop Down
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Post Options Post Options   Quote Daniel Holman Quote  Post ReplyReply Direct Link To This Post Posted: 09 Feb 15 at 11:38pm
I thought 3mm wire broke at a tonne?!Or is dyform different?

Never ceases to amaze me how much load can be taken by light structure as long as the structural arrangement is adequate and the reinforcement is applied correctly
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Post Options Post Options   Quote NHRC Quote  Post ReplyReply Direct Link To This Post Posted: 09 Feb 15 at 11:59pm
Non Dyform breaks at about 720 kg as an average break test. To be safe i would say to you that Dyform is in the 850 kg mark, can go at over 1100kg but averages about 850-900kg from testing.

Edited by NHRC - 09 Feb 15 at 11:59pm
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Post Options Post Options   Quote NHRC Quote  Post ReplyReply Direct Link To This Post Posted: 10 Feb 15 at 12:05am
The 3.5 mm Dyneema SK99 we have been tested averages at just under 1700kgs.
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Post Options Post Options   Quote Daniel Holman Quote  Post ReplyReply Direct Link To This Post Posted: 10 Feb 15 at 12:11am
How is that different from SK78 or 90 then?
Playing creep off against modulus..

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