standing rig alignment and cyclic loads

[Alby1714]

Hi all,
I would like to benefit from the knowledge of this forum by asking a few questions.
Please bear with me if the topic has already been discussed.
In most modern boats the shrouds connect to the chainplate by means of a swaged terminal screwing directly into a turnbuckle that has a toggle below connecting it to the chainplate.
In some older boats the turnbuckle has a toggle on top as well.
In a perfect world the perfect alignment of the shroud wire with turnbuckle and chainplate in both static and dynamic conditions would make both toggles unnecessary.
In our world, particularly under dynamic loads while sailing, perfect alignment will not be maintained (assuming it was there under static conditions which is not to be taken for granted), because the whole rig bends and twists and therefore the connection swaged terminal-chainplate experiences both linear forces and torques causing cyclic loads which in the long run induce fatigue and possibly failure (usually of the swaged terminal).
Current practice has done away with the top toggle. Why ?
Is the top toggle simply considered unnecessary or perhaps also detrimental ?
Can you please comment on the relative pros and cons of the two configurations ?
Thanks.

 

[gonzo]

A crimped threaded connection is cheaper and easier to install. It is a development that made the older method obsolete. They have been proven to last for decades of sailing.

 

[Alby1714]

Thanks Gonzo for your reply. I agree it is cheaper because one saves the top toggle (material) and also on time to install (labour).
Swages last a long time but the opinion of various riggers that I see in the press is that the rigging should be replaced (depending on a number of factors) every 10 to 15 years; these figures vary, but nobody recommends to keep the rigging for decades.
They also say that most failures occur at the wire-swage connection which seems to be the weak link in the system and which is present in both configurations (with or without the top toggle).
In this respect one opinion I collected outside this forum is that the additional freedom of movement allowed by the toggle in turn allows cyclic loads to cause fatigue over time exactly at the wire-swage interface eventually leading to failure. We are talking here about minute movements. This would happen in particular when the stay is the leeward shroud which, being unloaded, is freer to move. If this were true then the toggle would not only be more costly but also detrimental.
I do not know whether this is correct. What do you think ?

 

[gonzo]

The short life expectancy is for race boats that put a lot of tension on the rig. If you keep it loose, the rigging will last for decades.