A few toggle design choices

[Joe Henderson]

Dear Paramita,

Listen to Brion, you are getting free advice worth it's weight in gold...or non-broken masts.

If you wanted to create and examine a stress raiser in the laboratory, you could do no better than obtain a Gibb/Navtec Tee terminal.

They were marginal in the seventies, have not been improved by the manufacturing facility being shuttled from pillar to post in the last ten years or so as large machine shops bought and sold the rights to the design with not much regard to the end user.

The last lot I received looked like they had been made in some back street hovel in Karachi. I am always suspicious of bent or "Forged" stainless fittings that have been linished all over, they had obviously been worked to within an inch of thier lives.

Gibb managed, through a triumph of development over design, to make the things fairly reliable.

They paid attention to material specs, carefully controlled the pre-heating of the area of the upset forging of the head and flattened the head, gripped the tip and bent the radius of the neck all in one motion on a fairly complex jig.

All this was done by the same couple of chaps for the duration of the production in Warsah. When M.S.Gibb got sold, I asked if the tooling and expertise went with the sale, " Dunno" was the answer!

The manufacturers are aware of the shortcomings of the design, Vis the missive about the terminals not being reccomended for Dyform wire.

This is why the spade type shroud terminal from the same makers was instigated

The last word about the things is best from Johnny Green, late of Sparcraft UK.

They would only use them for checkstays....or stirring their tea... or, at a pinch, as fishing weights.

Then again, Sparcraft would not allow a concentrated loadpath to pass through a weld either.

Solid engineering expertise and experience, you see, just like Brions advice.

Good luck,

Joe.

[paramita]

Ok. So lets open the retro fit with tangs can of worms! A few questions (please feel free to answer any questions I'm not smart enough to ask)

1. what's the best method for attaching the tang?
   
   • Im imagining (hoping this isn't a terrible idea) that I could through bolt from one side of the mast to the other using the existing holes for the T-balls. My concern here is weather or not a bolt through the center of the mast would interfere with internal halyards or electrical wiring.
   • If a through bolt is the way to go could some one point me in the direction of what type of nut and bolt is recommended for this application.
2. do I need to have the tang fabricated to match the angle I measure for the current shroud? or are there standard aftermarket tangs I should look at?

[Douglas]

Gulp ! that's a heap of information you are after ,,, but all of it, is important information .

Both Brion and Joe's answers on this forum have helped me heaps , in the past .

Maybe you would like to search the forum for , mast bushings .

Of course Brion uses Skeen's (sp-?) book for scantlings sizes , but I found similar info in that Ferro Cement Construction book , by Bingham .

Without this forum , I wouldn't have been able to fabricate a complete new mast in SE Asia , on a pontoon , next to the boat !

[paramita]

So I'm looking at the size of my existing t-ball backing plates, the clevis pins at the bottom of my shrouds, and compression tubes available from rigrite (http://www.rigrite.com/Spars/SparPar...sion_Tubes.htm).

Currently all the pins for my shrouds at the deck are 1/2" or less. All my shrouds have the GIB 740-7 sized backing plate which has a 5/8" wide slot. Rigrite sells a compression tube (K-9632) with 1/2" I.D. and 5/8" O.D.

I'm wondering if there would be any issues simply using a 1/2" through bolt with that compression tube leaving the backing plates? I assumed it would be ideal to leave the backing plates in as it couldn't hurt to have the mast wall reinforced.

Removing the plate would would leave a 7/8" wide cutout which (from looking at Rigrites site) would allow me to use through bolts as large as 3/4".

I've attached a sketch of my proposed plan. Any input would be greatly appreciated.