rigging

[SailorW5]

Some rigging pointers needed. I have a 1990 26 s. Can I use shackle attatchements on my upper shrouds as attatchement points for my shroud cables. This is to facilitate removal and installation for off season and also to clean-up and make it the same on both stb / port sides. Right now i have to take out the bolt from the mast and remove the link plate that stays with the cable on one side and on the other is a clevis attatchement 1/4 inch pin. And, is changing to turnbuckles a good idea??

[Catigale]

You can shackle standing rigging, but you have to seize the shackle with either wire or a ziptie (the latter being formally blessed in Chapmans "Bible" recently)

This probably is as difficult as the removal you describe, though.

[SailorW5]

My big concern with putting a shackle at that point was, am I creating a sloppy point for the shrouds when tacking. I don't think so but I am fairly new to sailing, 6 sails under my belt. Another question on standing rigging is the use of turn buckles, I think I would like to convert but unsure of the proper working load and/or breaking strength rating to use for the shrouds. Again I want to clean up what’s there and standardize it all. Anyone with suggestions good or bad please feel free to give your 2 cents worth!!

Thanks Catigale for your response

[restless]

I like turnbuckles as it does make the setting alot simpler. The verniers are pretty good units though.. once set they are robust and reliable. Just keep an eye on ringdings remaining in good shape! turnbuckles with locknuts that aren't quite locked up can cause a few suprises... I would not use anything under minimum 1/4 inch on shrouds, though the forestay was (maybe it's 5/16??) . I know I went up a size when replacing my crappy forestay.
I think I put a few inexpensive 8mm ones on Restless, Part ractical, part coz they are prettier
Wired D shackles are cool. I tape over the wire as it can leave a nasty little razor spike...

[Catigale]

Ive written this before, but it has been ignored by many...

It isnt necessarily a good idea to change rigging on a Mac, and especially if you are following the 'bigger is safer' mantra.

Heres why.

All rigging needs to be tensioned in order to remove slack. If you dont do this, it fails under shock load or fatigue failure, from having been worked back and forth.

The tension required is about 10% of its breaking strength. The chainplates and hardware on the Mac are designed to take the load of the stock rigging under tension, but not much more than that.

If you go from 1/4 inch forestay to 5/16 your working tension has to go from something like 700 # tension to >1000# ...you had better be sure that the plates and attachment hardware are all up for this. I have no idea what their rating is.

..and to be completely anecdotal - I dont recall a single rigging failure on this board from strain, I can only recall fatigue failures almost certainly caused by lack of tension. Heavier rigging doesnt help you in the case of fatigue failure of course.

I remove impact with bridges from this discussion....

[heinzir]

I know that 10% is a rule of thumb but I wonder if it was actually calculated thru load testing or is an arbitrary figure that, through use, has been accepted as fact. Why not 9%, or 8%, or 5%?

At any rate, if you accept that shrouds should be tensioned to 10% of their breaking strength, going up one size will increase the amount of tension required to prevent shock loading. But this is much more pronounced in larger sizes. According to the WM catalog, the breaking strengths of 1/4" and 5/16" 1x19 ss wires in pounds are 8200 and 12500 respectively, a difference of 4300. That means that if you go from 1/4" shrouds to 5/16" you should increase the tension by 430 pounds.

But Macgregor/Venture boats (to the best of my knowledge) do not use rigging that big. I believe most come with 1/8". This is matched with 1/4" turnbuckles or stay adjusters. The most common rigging size upgrade on Venture/Macgregor boats is to go from the 1/8" wire to 5/32". (5/16 is the appropriate size turnbuckle of 5/32 wire.) The breaking strengths of 1/8" and 5/32" 1x19 ss cables are 2100 and 3300 pounds respectively, a difference of 1200. Using the 10% figure, this translates to a required static tension increase of 120 lbs. That really is not a great deal of additional strain for the chainplates.

Besides being stronger to begin with, the slightly thicker wire is also less likely to kink when raising or lowering the mast or securing for storage. A kink in the wire will greatly reduce its strength.

[restless]

Some interesting points. Reading my post I claim to have 1/4" rigging.. total lies! Just a crossed wire in the brain! My forestay was 3mm which I took up to 4mm. Or the nearest imperial equivalent.. don't remember now.
Anyhoo... I haven't heard of shrouds failing, though quite a few forestays have definately gone ping. As Cati says, probly through fatigue, due in this case to raising/lowering the mast and not being really careful with the top of the fstay.
This is one of my pet subjects... Rigging!!
Oh, and if you stick turnbuckles on... make sure they all face the right way up... they are directional and it can get really confusing if they are not all the same! Obviously being super bright I made sure mine went on correctly... (more lies!!)



In theory, there is no difference between theory and practice;
In practice, there is.
Restless web

[Catigale]

I know that 10% is a rule of thumb but I wonder if it was actually calculated thru load testing or is an arbitrary figure that, through use, has been accepted as fact. Why not 9%, or 8%, or 5%?

Good point, and worth researching. Certainly the sort of thing you a PE could comment on....

[magnetic]

My rigging is slightly loose; I can't quite tie a bow in the upper shrouds, but there's the making of a rabbit snare in there somewhere.

Today's tally was 3 small screwdrivers in the marina, 2 broken and a couple of very impressive blisters. The net result of this is that the furler/forestay now looks less like a crescent moon and more like a banana.

Tomorrow we move on to advanced rigging techniques, including "Replacing the stolen baby stays on the mast raising device" and "Trying to see if dropping the mast will make it easier to tighten the sliders". After that we will probably end the day with everybody's favourite - "Cursing the Cotter Pin" as we try to reconnect the forestay (which will for some reason have mysteriously become 5 inches shorter).

On the bright side, all of the lines are now attached to the in-line reef points, and what with the new lazyjacks and stuff, whipping the boom off should draw in the spectators. The mast rotates - for the time being at least - and for once even the masthead light is working. It won't last, I'm sure