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Sail & Rigging - A question for the Professor. SS vs Dyneema..
20 November 2020 - 17:19
#1
Join Date: 03 March 2007
Posts: 221

A question for the Professor. SS vs Dyneema..

Hi Lars,

As I mentioned earlier Iam switching from wire to Dyneema for the rigging. Just checked the fittings on the mast and this is a good move! I have what looks like stress marks on the mast fittings... ( look like little smiles where the SS plate is bent..). I don't think they are critical as there is no cracking  it do not want to try my luck! Removing and replacing them will be a major challenge. Stainless steel and aluminum welded together over50 years... I will see how it goes..

Anyway, to the question. What is the diameter of the large bolt bearing the brunt of the load on the fittings?  Plan B is to use an epoxy carbon powder mix to glue Colligo cheeky tangs to the mast supplemented with a SS bolt through the mast to the tang on the other side of the mast.  I would/ plan to use the same diameter bolt?!

For those of you interested I will photo document the switch if I do it.

Thanks in advance Lars

Mike

 

20 November 2020 - 19:48
#2
Join Date: 02 January 2008
Posts: 1470

Hi Mike

Unfortunately I do not have detailed drawings for your mast. 
I would suggest that the straps and screws are necessary also together with the tang bolt for carrying the loads properly.
Kind regards
Lars

21 November 2020 - 12:38
#3
Join Date: 02 January 2008
Posts: 1470

PS
 

Mike

Would suggest there is no need to remove the stainless straps from the mast if you do the following:
Cut off the straps some distance below the tang bolt - not too close - and make a new tang bolt similar to the present one, but with extensions each end fitting the cheeky tang holes, and threaded ends for its nuts. No threads on the new tang bolt except at the very end just for the nuts.
Not known if the spreader fittings are too close - to be checked
Kind regards
Lars

22 November 2020 - 04:16
#4
Join Date: 03 March 2007
Posts: 221

Thanks Lars!  Sometimes I Think you read my mind!!!! I fear that removing the bolts will weaken the mast so what you suggest is now plan A.  The only addition I can think of is bonding the cheeky tang to the mast with a graphite epoxy composite as well as the bolt. I need to figure out the optimum mix of graphite/graphine and epoxy to maximize bonding strength. I am going to look at the mast today and will send. A few pictures. 
THANKS PROFESSOR!!!

 

Mike 

04 December 2020 - 18:01
#5
Join Date: 03 March 2007
Posts: 221

Hi Lars,

 

It has been a bit crazy here!! Anyway,  I misinterpreted your earlier message.  You want me to put the Cheeky tang fitting on the existing SS tab after removing the 'arms' which hold the pin. Got it and it makes perfect sense!!  I think I will still have to make some spacers to support the Cheeky tang but this is a nice approach.. 

 

Here is a picture of one of the mast tangs and you can see the stress mark.  They all have a similar mark but this is the worst. 

 

Thanks again 

 

Mike 

Rig fitting with stress mark.

04 December 2020 - 18:08
#6
Join Date: 02 January 2008
Posts: 1470

Mike

Checking the marks on the tangs with Magnaflux Spotcheck would tell you if there are cracks or not.
Lars

07 December 2020 - 10:32
#7
Join Date: 03 March 2007
Posts: 221

Hi Lars,

 

Some cracks showed up with the magnaflux..  Glad I did this!!!  I guess all those miles and storms have weakened the fittings.  She and I have been through some good storms and I know she has, prior to me done a fair bit of racing.  She has done Cape Town to Rio in the 70s and I am sure a lot of other races given the verbal record I recieved when I bought her. Anyway, I will be ordering the fittings from Colligo today and am looking forward to quiet winter evenings in front of the fire splicing Dyneema. My wife knits, I splice (:-) 

 

Thanks and Be SAFE.

 

Mike

 

20 December 2020 - 14:19
#8
Join Date: 03 March 2007
Posts: 221

Hi Lars,

 

Another quick question.. The bolt holding the tangs on the mast below the spreader is 25mm thickness while the bolt at the mast head is 16,7 mm.  This does not make sense to me.  I would think the bolt at the masthead would be larger than the ones at the spreaders.. More load up there.  I find this odd.  At the moment i am going with a 5/8 titanium bolt at the spreaders and think I should do the same at the masthead. I will be removing the tangs as you suggested and mounting the Cheeky Blocks directly on the mast.  

 

Merry Chrismas 

 

Mike

 

21 December 2020 - 07:16
#9
Join Date: 02 January 2008
Posts: 1470

Mike

Pls look at the size of your D1 and D2 shrouds. D1 is bigger, and therefore the tang bolt is bigger.
The recommendation is to retain the upper part of the tang plates so they assist in supporting the new bolts
Wishing you a Merry Christmas
Lars

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