Synthetic shrouds on a 3 spreader rig?

[Gashmore]

Dynex Dux is looking more and more attractive to me but it looks like it has to be continuous rigged. I am not sure how I could rig a 3 spreader mast with it. I have chain plates for D1, V1 & V2 which would work for 2 spreaders but how do you handle the third?

Is it possible to splice D3 into the cap shroud at the second spreader? D3 would only be about 15' long so a turnbuckle at the tang end should be plenty to take up any creep.

[Joe Henderson]

Dear Gashmore,

Welcome to fibre standing rigging.

I have rigged numerous masts with Dux and as long as you pay particular attention to chafe prevention and shroud angles whilst being obsesively careful about lengths during splicing and after pre-loading, you should be able to use modified standard turnbuckles.

The D3 can be spliced into the V3/D4 but a better solution is to modify the spreader tip and terminate at an amply sized link plate or even a very stout ring.

The turnbuckle-at-the-mast-tang solution is an old trick and cleans up the spreader tips a treat at the expense of a slightly higher C of G. I do not know why more people do not use it!
I am at risk of teaching my grandmother to suck eggs now, but make sure you run some numbers on the loads involved and do not just take the sizes of the original wires and "go a bit bigger" otherwise you are floundering in the dark and may not get the result you need.

Regards,
Joe Henderson..

[Gashmore]

make sure you run some numbers on the loads involved and do not just take the sizes of the original wires

I have just spent the weekend with Mssrs. Larsson and Eliasson and it is easy to see how the original rod specs were calculated. For example the tension on V3/D4 comes out 4,100 lb. According to L&E for the top diagonal the design load is 2.8 times the tension or 11,480lb. D4 was spec'ed as -12 so I am pretty confident of that 4,100lb. The choices of all the other rod works out similarly. When it comes to selecting Dynex I think I just work with the tension and use a 5:1 factor to stay under 20% of breaking strength. In this case 9mm. Does that sound right? If so 11mm will handle everything below that.

Actually selecting Dynex is a lot simpler than optimizing rod. Rod would take 6 different sizes to minimize weight. With Dynex there are only two in the ranges I need. Makes for more windage but the weight up saving is amazing. Also I can make up a Brummel in a few minutes. I have to drive to Charleston to get a rod headed. :-)

[Joe Henderson]

Dear Gashmore,

You have a handle on the problem.

9 and 11 mm sound about right - as does the 5:1 safety factor.

You must pardon the pun, but you have hit the nail on the head when you talk about ease of modification etc. This I think will be the greatest boon and, paradoxically, the greatest threat, to the wider acceptance of fibre rigging.

With something so easy to access there will inevitably be the rash of bad and unsucessful projects until it becomes comonplace and accepted my the masses.

There will of course be the usual amount of litigation and argument when the first high profile rig comes down and hurts someone, but we will have to guard against that eventuality with competent workmanship and the education of our customers.

Regards,
Joe Henderson.