Rig Tension
Printed From: Yachts and Yachting Online
Category: Dinghy classes
Forum Name: Dinghy development
Forum Discription: The latest moves in the dinghy market
URL: http://www.yachtsandyachting.com/forum/forum_posts.asp?TID=11881
Printed Date: 09 Jul 25 at 8:13am
Software Version: Web Wiz Forums 9.665y - http://www.webwizforums.com
Topic: Rig Tension
Posted By: about a boat
Subject: Rig Tension
Date 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?
Thanks
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Replies:
Posted By: JimC
Date Posted: 09 Feb 15 at 2:35pm
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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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Posted By: Rupert
Date 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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Firefly 2324, Puffin 229, Minisail 3446 Mirror 70686
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Posted By: Time Lord
Date 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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Merlin Rocket 3609
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Posted By: zippyRN
Date 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.
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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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Posted By: NHRC
Date Posted: 09 Feb 15 at 11:25pm
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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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Posted By: Daniel Holman
Date 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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Posted By: NHRC
Date Posted: 09 Feb 15 at 11:59pm
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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.
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Posted By: NHRC
Date Posted: 10 Feb 15 at 12:05am
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The 3.5 mm Dyneema SK99 we have been tested averages at just under 1700kgs.
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Posted By: Daniel Holman
Date 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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Posted By: NHRC
Date Posted: 10 Feb 15 at 12:16am
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Higher modulus
You won't see creep without a micrometer if you can splice correctly.
The ultra modulus SK 99 is even more impressive. You can drop down to 2mm braided and be stronger than Dyform wire and with no creep, IF YOU SPLICE CORRECTLY.
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Posted By: Daniel Holman
Date Posted: 10 Feb 15 at 12:40am
What about the constructional creep? I.e. bedding in of the braiding? Even the pre stretched 78 max bedded in loads the first time it was used and even with massive bury - don't think they were bad splices.
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Posted By: Woodbotherer
Date Posted: 10 Feb 15 at 9:18am
So, as an aside and I came into this game being instructed to put massive rig tension on at all times (Musto Skiff) I now hold the opposite view and have my own theories, but can someone explain to me how it was the Blaze rig is so much faster being sloppy shrouded?
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http://www.edgeactionsports.co.uk/collections/soundcast-portable-weatherproof" rel="nofollow - Soundcast Weatherproof Speakers
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Posted By: Chris 249
Date Posted: 10 Feb 15 at 9:40am
Originally posted by NHRC
The 3.5 mm Dyneema SK99 we have been tested averages at just under 1700kgs. |
Where's the emoticon for slack-jawed amazement? I've been out of the loop for such things and that seems to be amazing.
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Posted By: JimC
Date Posted: 10 Feb 15 at 9:59am
Originally posted by Woodbotherer
So, as an aside |
A trapeze boat with conventional spreaders needs massive rig tension because the trapeze unloads the windward shrouds and reduces effectiveness of the spreaders. Indeed in extreme cases the windward shroud unloads completely and instead of the windward spreader pushing the mid mast to leeward the lee spreader is pushing the mid mast to windward. So crew gets on wire and the mast dumps all the power. A non trapeze boat doesn't have that problem, nor does a trapeze boat with diamonds rather than spreaders.
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Posted By: iiitick
Date Posted: 10 Feb 15 at 10:03am
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Going back to the beginning of this thread, why would a mirror which is presumably gunter rigged need any rig tension other than to keep the mast up?
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Posted By: JimC
Date Posted: 10 Feb 15 at 10:16am
Posted By: Jon711
Date Posted: 10 Feb 15 at 10:35am
Originally posted by iiitick
Going back to the beginning of this thread, why would a mirror which is presumably gunter rigged need any rig tension other than to keep the mast up? |
The OP quoted the figures for a bermudan mast... So that figure sound about right to me, but as Rupert says will not be as important as the correct rake..
Jon
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Blaze 711
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Posted By: MerlinMags
Date Posted: 10 Feb 15 at 11:42am
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Another aside - when I add rig tension to my ancient Merlin, all that happens is the hull's beam reduces slightly!
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Posted By: jeffers
Date Posted: 10 Feb 15 at 12:01pm
Originally posted by MerlinMags
Another aside - when I add rig tension to my ancient Merlin, all that happens is the hull's beam reduces slightly! |
And the centreboard gets harder to move?
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Paul
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D-Zero GBR 74
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Posted By: jeffers
Date Posted: 10 Feb 15 at 12:05pm
Originally posted by Woodbotherer
So, as an aside and I came into this game being instructed to put massive rig tension on at all times (Musto Skiff) I now hold the opposite view and have my own theories, but can someone explain to me how it was the Blaze rig is so much faster being sloppy shrouded? |
I am sure other can explain far better than I but it means you can have different tensions on the rig. Upwind, sheeted in the rig is tighter and you ben the mast using the mainsheet.
Offwind the mast is straighter giving you a fuller sail.
Downwind having sloppy shrouds allows the rig to be a little more upright.
When I had my Blaze you didn't really use the kicker aside from to stop the boom lifting on a reach. This may have changed now with a more refined sail and a carbon mast.....
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Paul
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D-Zero GBR 74
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Posted By: jeffers
Date Posted: 10 Feb 15 at 12:06pm
Oh and as an aside I sailed a brand new Supernova on Sunday. His rig was 'Blaze floppy' but seemed to work fine aside from a complete lack of feel from the mainsheet.
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Paul
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D-Zero GBR 74
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Posted By: Woodbotherer
Date Posted: 10 Feb 15 at 12:44pm
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So I guessed as much, but I wonder if a new carbon rigged Blaze would show the same improvement, making the rig floppy help the tin rig, but a more 'flexi' carbon, would that benefit from loose rigging or would that need tightening up a bit, my view would be the latter.
Although the floppy rig without kicker would help that running by the lee effect offwind.
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http://www.edgeactionsports.co.uk/collections/soundcast-portable-weatherproof" rel="nofollow - Soundcast Weatherproof Speakers
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Posted By: Rupert
Date Posted: 10 Feb 15 at 12:44pm
Floppy rigged boats are a compromisein order to get things working upwind as well as down. Firefly - floppy rigged, no shroud adjustment allowed on the water. The sails are cut to suit this style of sailing. Albacore - loads of rig tension, but you can let it off to bring the mast upright going offwind. I imagine that Applecore sailmakers have a different brief to Hydes with the Firefly.
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Firefly 2324, Puffin 229, Minisail 3446 Mirror 70686
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Posted By: patj
Date Posted: 11 Feb 15 at 6:28am
Playing the rig tension on a modern Albacore is a major learning curve! Shrouds can be eased singly or evenly as a pair, mast ram can be adjusted up and down and jib tension adjusted, all whilst still handling main, kicker, outhaul, cunningham, jib sheets and flyaway jib pole and still keeping head out of boat enough to sail a serious race!
For a modern Merlin, add in to all that the complications of a symmetric spinnaker and twin fly-away poles and you can see how these classes remain challenging to their sailors.
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Posted By: Time Lord
Date Posted: 11 Feb 15 at 9:12am
On many modern Merlins you have the shrouds, jib tension, kickers and lowers linked so that only one string needs to be adjusted when you want to rake the rig.
Flying the spinnaker does not increase the workload except as it is launched when the puller and pole downhaul are pulled on before/after - no adjustment needed. I suppose you may want to adjust the pole height but most would set this before a race and leave it.
Rig tension is normally set so that the leeward shroud does not pant on a beat - no idea what loading as have never bothered to measure it.
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Merlin Rocket 3609
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Posted By: craiggo
Date Posted: 11 Feb 15 at 7:52pm
Most classes I'm aware of that have tensioned rigs are running more than 270lbs of rig tension on 3mm 1x19 stainless wire. On the Grad I run around 360lbs and know of others using 400.
You have to remember that safe working loads are given for safety critical applications and last time I looked the roof on my boat want safety critical. For dinghies a safety factor of 2 is ample so I'd be comfortable going up to 50% of breaking strength. After all most failures are at the swage and not in the middle of the wire.
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Posted By: NHRC
Date Posted: 12 Feb 15 at 8:49am
Originally posted by Daniel Holman
What about the constructional creep? I.e. bedding in of the braiding? Even the pre stretched 78 max bedded in loads the first time it was used and even with massive bury - don't think they were bad splices.
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Pre-stretch after splicing.
78 did have a large amount of creep, 90 was a great deal better.
For example I did some testing with Lasers race kits. On the first part of the vang I spliced two strops same length (1200mm, I think) one in 2.5mm SK78 the other in 2.5mm SK90. I think both ropes were made by FSE.
After 20-25 minutes sail testing in 20 knots wind the SK78 strop had stretched 70mm the SK90 just 7mm.
When I made the same component in SK90 and hung a 20kg weight on it over night after sail testing there was no stretch/creep.
I am making up a new set of rigging for my Merlin including getting Stu West (west engineering- http://www.westengineeringltd.co.uk ) to make me some T5 end fittings that slot into standard spreaders.
I am going to go with a two part shroud, like on a yacht. One part deck to spreader, next part spreader to Hounds at the mast.
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Posted By: gordon1277
Date Posted: 12 Feb 15 at 8:56am
Hi NHRC
I just took the dyneema shrouds of my Phantom based on the comment from a rigger that although most of the reference to UV issues was incorrect he was more worried about abrasion from grit, as my boat is in the compound at Lee with SW salt water and sand in the breeze I thought it best to swap to wire.
What are your thoughts on this?
Also dyneema shrouds hum under load in a breeze and it can be distracting but you can tell the tension by the note.
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Gordon
Lossc
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Posted By: NHRC
Date Posted: 13 Feb 15 at 12:57am
Originally posted by gordon1277
Hi NHRC
I just took the dyneema shrouds of my Phantom based on the comment from a rigger that although most of the reference to UV issues was incorrect he was more worried about abrasion from grit, as my boat is in the compound at Lee with SW salt water and sand in the breeze I thought it best to swap to wire.
What are your thoughts on this?
Also dyneema shrouds hum under load in a breeze and it can be distracting but you can tell the tension by the note.
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You can use a dyneema cover on even very thin diameters which will stop the resonance and protect against UV.
I have not seen dyneema degrade through the particles in the air like salt and sand. Vectran does definitely suffer from this but dyneema is pretty durable. I don't think your informant is correct from experience.
It is a lot easier to examin dyneema than it is wire, you must constantly check your rigging up above and on the boat for breakages and other issues. I trust dyneema more than wire.
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Posted By: ohFFsake
Date Posted: 19 Feb 15 at 12:10am
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Back to the topic of Mirror rig tension...
Worth remembering that the Mirror doesn't have spreaders - even the Bermudan rig. So rig tension serves pretty much one purpose, ie to control jib luff sag. It doesn't really affect mast bend or mainsail shape at all.
So in light airs let it off to put the curve back in the jib luff and in strong winds wind it on to correct for any sag. But if you are wary of stressing the hull it's not that critical as you can achieve much the same with a decent kicker or via mainsheet tension.
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