rigging question

[dolphin]

good day to all here !
recently, i am planning to change some rigging wire and would like to ask, how you decide, what size of rigging screw and shackles to use with 8 & 10 mm wires
present situation on the boat is the same size rigging screw and shackles with 8 & 10 mm wire ! (the boat "survived" with present set up more than 30 years /forums/images/graemlins/smile.gif and i just ask for clarification)
when research for the SWL, realised that the strongest part is the wire , followed by rigging screw and shackles !!!
what is actual / max load i can estimate ?
the boat is 37' sloop with weight of about 9 mts and sail area of about 60 sqm
thanks

 

[Salty John]

According to the information I have the recommended wire size for a 10 ton displacement cruising boat is 8mm for shrouds and backstay but the forestay is right on the border between 8mm and 10mm. So, 10mm would be the right choice.
If the rigging screws are M16 thread which are normally recommended for 8mm wire they will also take 10mm wire. In your case this selection would be OK because 8mm wire has a WL of 5400 kg and 10mm is 8400 kg and an M16 rigging screw would have a WL of 8000kg. An M20 thread rigging screw has a WL of 13000kg.
I'm not a boat designer, just passing on what information I have from various reference books.

 

[oldharry]

Shackles? Should not be any... The fastening points on both hull and mast should allow for either an eye or a fork fitting on the corresponding screw or wire terminal, which is secured by a large clevis pin held in place by a split pin.

Shackles generally have a SWL way below any other component in the rig, creating a serious weak point, and can come undone anyway.

 

[VicS]

[ QUOTE ]
Shackles? Should not be any

[/ QUOTE ] Agreed!
If necessary toggles can be used to articulate the connection (or to extend the rigging)

 

[ean_p]

Hi John
could you list the ref book titles please , sound interesting

regards

Ian P

 

[dolphin]

thanks to all replies !

i understand, what you all are saying but something is very confusing as the boat had many miles under the keel with this set up ! i do not believe that the disigner have made the things wrong !

the boat is equiped with tweens forward 8mm (side by side),
all others wires are 10 mm ; atf - are also two backstays , shroud - each side one and low shrouds (below spreader) are 2 each side !
total rigging wires are 10 pcs!

is this change something or make sence ?

thanks again

 

[Salty John]

Hi Ian,
In this particular case the ref books are:
The Boat Data Book; Ian Nicholson
Spurr's Boat Book; Dan Spurr
Plastimo Catalogue
Johnson Catalogue

 

[ean_p]

Thanks for that John, I've got a copy of IN book somewhere but will have a look out for 'Spurr's'.

thanks again

Ian P.