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Current Replies for Mark V backstay tension
 
  Mark V backstay tension (copasetic)
Posted: 4:32:26 pm on 9/1/2011 Modified: Never
 
When Magique was acquired 4 years ago, it had no backstay tensioner. The boat was fast. I installed a tensioner on the split backstay.(a ring held by wire blocks to each split, pulled down by block and tackle shackled to the transom /rail corners) When sailing in light air, the main leach started "catching" on the backstay, and we often have to push it through by pulling the boom hard windward and then releasing. Sometimes we jerk the boom by hand and curse. Obviously, when the wind is up, the wind pressure pushes the leach past the backstay.
So, what is the solution? Remove the tensioner in light air? Is the tensioner on the split causing  a subtle change in the backstay angle?copasetic
  Re: Mark V backstay tension (bosco)
Posted: 6:28:06 pm on 9/1/2011 Modified: Never
 
Hi Copa,

 When you had no backstay tensioner it is likely that the single backstay was attaced midway across the transom and therefor it's attachment point was futher aft than the two corner points you are now using to attach your split backstay??????
  Also, sailmakers lately have beem adding more and more roach to their mainsails thus reducing the clearance between the leach and the backstay -- An acquaintance of mine, after getting a new mainsail, ended up having to add a 1/4 " plate extending backward 4" at the top of his mast for his backstay atttachment point just so he could tack his main winds under 12 knots !!!
  Re: Mark V backstay tension (ALAN FORD)
Posted: 11:20:43 am on 9/2/2011 Modified: Never
 
That 4 inch aft-reaching plate is a homemade masthead crane, which I suspect C&C would have used if they thought it was needed. However, they didn't! If the 4 inch one is OK, then why not 8 inches, allowing for a really large roach?
If you look at the "C&C Class Association Constitution and Rules", Part II, Article 1, General, it reads  "..........must sail with hull, deck and standing rigging substantially as built except as noted below". That includes the backstay I'm sure.
The PHRF-LO rating is based on the "Standard boat", and Article 3 gives no allowable variation for the mast.
Then if you go to the red section of Article 7, "Sail Specifications", "Mainsail", (2), and in particular to the last paragraph which is in italics, you will note the wording "Natural limit" which is referring to the Mk V's mainsail roach.
It even warns against having to use a flicker to force the sail to pass the backstay which is caused by too much roach.
All this is very close to my heart as my beautiful new laminated main (2010) suffered from the same problem in light airs, and finally I had to have the sailmaker cut a thin sliver from a part of the roach to make things go as planned.
Good luck!!!

Alan of SMOKE 1984 Mk V 002

  Re: Mark V backstay tension (copasetic)
Posted: 1:39:09 pm on 9/3/2011 Modified: Never
 
Thanks for the comments. 1. The backstay was split, even before I added the tensioner.
2. The main has not changed from before the tensioner.

When, I took the time to sit at the stern, on the mooring, and study the tensioner rig,I saw that the snap shackles for the tensioner are attached to the slots in the corner/transom rail in the holes which are forward of the attachment of the backstays. So the downward pull of the tensioner is not exactly in line with the backstay. So it pulls mostly down, but a scootch forward. Could this be the problem?

My thought:  
 attach the snap shackle to the "back" holes in the corner rail so the tensioner is exactly in line with the stay. This will take a little jury-rigging as the present snap shackles are too short-armed to fit in the "back" holes which are cut somewhat lower in the rail than the "forward" holes now being used.copasetic
  Re: Mark V backstay tension/followup question (copasetic)
Posted: 11:20:23 am on 9/4/2011 Modified: Never
 
What is the recommended backstay tension for the split rig on the Mark V without any load on the tension device? I assume you measure one value above the split and one half the value on each arm of the split?

Thanks for your advicecopasetic
  Re: Mark V backstay tension/followup question (Steve Reid)
Posted: 10:24:00 am on 9/6/2011 Modified: Never
 
The backstay tension affects two aspects of rig tension and boat performance. One it applies tension to the forestay by pulling the mast head aft. The more tension on the forestay the streighter it is and therefore the better you ability to point. It also has the effect of making your Genoa flatter and that also improves your ability to point. A soft head stay also helps power up the sail plan and so in lumpy seas or light wind you may want a softer head stay. You may also want a soft head stay when you tack and then slowly tension the back stay as your boat speed increases.
The other effect the back stay has on your rig is to bend the mast. A streight mast gives you a full main, great for power, not so great for pointig. So again going upwind as your boat speed increases you want to apply back stay tension. Downwind you want a slack back stay (full main).
On Still Knot Working we often let the back stay off as we entre a tack and then start putting tension on as we get the boat going coming out of a tack. At the same time we come out of a tack with the Genoa slightly eased and trim in as we build speed. Working the Genoa sheet, back stay and main sheet in unison to tension and flatten the sails.
There is no set tension, that I know of, for the back stay on any boat, it's not a static thing, like your uppers and lowers. I have a gauge, markings on the back stay, that we use as a referance. We use the gauge so we can get back to a setting, that we feel is right for the given day, each time we easy or let the back stay off.

Steve

Still Knot Working