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Sail & Rigging - Swan 41 lower shrouds upgrade
09 March 2022 - 11:12
#1
Join Date: 02 March 2007
Posts: 83

Swan 41 lower shrouds upgrade

Following on from my previous post, Allspars have suggested increasing the lower shroud diameter from 8mm to 10mm. As I had serious problems with failure of the lowers during an Atlantic crossing ( my post of 10th Dec 2011), I was interested in the possibility.

  There seems to be confusion about the clevis pin diameters. The old lowers fitted in Grenada had an eye diameter of 14.4mm. The captive pins on the mast have a diameter of 14mm, and were a good fit in the eyes.

Looking at various eye terminals in the rigging shop, even 8mm terminals have a larger hole and are quite a loose fit on the pin. The 10mm terminals have an eye diameter of 16.5mm.

How important is it that the clevis pin should be a good fit in the eye?

The 10mm terminals will fit in the space available for two adjacent 8mm terminals as they have a slimline design.

If I go for 10mm rigging, will I actually achieve anything if the limiting strength factor is the 14mm pin?

 

Trinket, Cosmo Little

 

 

13 March 2022 - 09:33
#2
Join Date: 02 January 2008
Posts: 1547

Dear Cosmolittle
Originally there were Norseman terminals, but 14 mm pins do not appear in their newer catalogues for 8 mm wire, Maybe the Norseman standards were different back then
What size holes are there in the chainplates? 
You could make stronger pins from rod rigging. Non-swaged terminals are recommended, for example Petersen Hi-Mod
Usually the aft lowers are more loaded than the fwd ones.
It is important for long life that the pins fit the holes closely, and that the eyes fill the gap in the tangs
Kind regards
Lars

16 March 2022 - 09:54
#3
Join Date: 02 March 2007
Posts: 83

Dear Lars,

Thank you for your advice. Based on the mast pin sizes, and the fact that the 41 rig was designed for 8mm lowers, and 56 boats have been sailing around for 40 years without much trouble, we are going to re rig with 8mm lowers!. However we are going to use terminals throughout.

We considered replacing the all bronze rigging screws with new bronze/stainless types, however the rigging screws ( possibly original?) are in perfect condition with no apparent wear on the threads or pins, so we will use the originals.

The mast repair is slowly progressing, with the internal sleeve being made. I would like your further recommendations as to the size , and distribution of the screws used to secure the sleeve. The welded aluminium pole track on the front of the mast limits the position of the upper screws to some extent. I have removed two reaching pole fittings which are secured with 8off  M6 screws each tapped into the mast. Allspars suggested replacing these with longer screws tapped into the sleeve, however M6 screws seem small to me to secure the sleeve.

  The joiner in the mast uses larger screws which might be M8 or even M10.

  It seems to me that unless the sleeve is very tightly secured to the mast, it will not have any effect. Allspars say they will use sme fiorm of adhesive as well as screws, but due to the difficulty of cleaning the inside of the mast, I am not convinced that the adhesive can be relied upon to provide any strrength.

best regards  Cosmo Little

 

 

 

16 March 2022 - 10:21
#4
Join Date: 02 March 2007
Posts: 83

Dear Lars,

I have attached some pictures of the mast with the fittings removed

Cosmo Little

 

17 March 2022 - 09:54
#5
Join Date: 02 January 2008
Posts: 1547

Dear Cosmo Little
Thank you for the photos
The bronze rigging screws originally came from Lewmar. They are likely to be in order, but it is advisable to clean the threads thoroughly and inspect the thread bottoms carefully for cracks.
If the mast crack will be welded, the contribution of the inner sleeve is reduced, and you could use half the number of screws in the length direction.  Look at the mast joint
I would not rely much on an adhesiver for the reason you mention, and in this case also as you can hardly control the gap between the surface, i.e.the adhesive thickness.
Kind regards
Lars

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