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S&S Swan Maintenance - Rig Failure warning
30 August 2014 - 12:45
#1
Join Date: 01 February 2007
Posts: 234

Rig Failure warning
I recently had a failure of my D1. The split pin which locks the clevis pin in place snapped, causing the clevis pin to shoot out and the rig detach from the shroud plates. The initial cause appeared to be the bottle crew straps not being parallel. On investigation it can be seen that the straps are not sitting correctly on the shroud plates forcing them open, so putting pressure on the split pins. Further investigation showed that the shroud plates seem to have bent over time under load causing the lead from the rig to not align as designed. A temporary solution has been to pack the clevis pin with washers until later this year when the shroud plates can be removed and straightened. All 4 shrouds have the same problem. CHECK YOUR RIGS.

Mis alignment of bottle screw

Clevis pin sprung open

Temporary fix

31 August 2014 - 03:46
#2
Join Date: 08 May 2009
Posts: 7

Interesting.

31 August 2014 - 09:33
#3
Join Date: 02 January 2008
Posts: 1547

Dear John
Thank you for the pictures.
The standing rigging has been replaced, and the toggle geometry is now different.
Under high load these toggles tend to straighten out, and this opens their bent legs and loads the split pins.
With these toggles it would be advisable to use clevis pins with nuts on their ends.
The recommendation is to avoid these toggles on ocean-going yachts. Another thing to avoid are T-terminals at the upper end of shrouds.
Kind regards
Lars

31 August 2014 - 12:30
#4
Join Date: 01 February 2007
Posts: 234

Lars, I agree that a bolted clevis pin is a stronger option. That will be one of this winters jobs.
1.Should I attempt to straighten the shroud plates? Their removal is pretty easy.
2.If removed the shroud plates, how would you recommend that I straighten them?
3.How was the original geometry / position of the shroud plates relative to the rig worked out and is any tolerance in alignment acceptable?
John B
Swan 411 010

31 August 2014 - 17:12
#5
Join Date: 02 January 2008
Posts: 1547

Dear John
Thank you for the information.
1, 2. If the chainplates are out of alignment more than 1 degree (17 mm/meter) it is recommended that they are bent into proper alignment. This can be done without removal, they are of stainless steel and this is a soft material. A big wrench with an extension should cope with it.
3. Single lowers chainplates were installed in close to vertical position. Allowed tolerance see item 1 above.

The gap between chainplate and toggle should be as small as possible. The big gap in the first picture doubles the bending load in the pin, and forces the toggle to take up a misaligned position under load.
The geometry is better in the third picture, but the recommendation is to use stronger pins because the bending loads are still much higher than for a close-fitting toggle without spacers. Stronger pins can be made for example out of rod rigging. Nuts required also with this geometry.
Kind regards
Lars

31 August 2014 - 19:41
#6
Join Date: 01 February 2007
Posts: 234

Dear Lars, would you know the likely operating loads on the clevis pins so I can specify to riggers.
I guess the loads would be different for the shrouds and the inner stays (D1s).
John B

01 September 2014 - 12:54
#7
Join Date: 02 January 2008
Posts: 1547

Dear John
The recommendation is to size the pins so they are 25% stronger than the shrouds considering the additional bending loads with these toggles.
Kind regards
Lars

03 September 2014 - 01:57
#8
Join Date: 16 May 2009
Posts: 252

I recently had a failure of my D1. The split pin which locks the clevis pin in place snapped, causing the clevis pin to shoot out and the rig detach from the shroud plates. The initial cause appeared to be the bottle crew straps not being parallel. On investigation it can be seen that the straps are not sitting correctly on the shroud plates forcing them open, so putting pressure on the split pins. Further investigation showed that the shroud plates seem to have bent over time under load causing the lead from the rig to not align as designed. A temporary solution has been to pack the clevis pin with washers until later this year when the shroud plates can be removed and straightened. All 4 shrouds have the same problem. CHECK YOUR RIGS.

John:

I appreciate the post and will check. While on the topic, your pictures remind me of another concern I have (having the 411 also) that being the screws that hold the fittings to the deck just look small to me. I expect they're sized correctly, but by eye they just seem small. Mine were replaced in 2000, so at least they're not original. I would advise anyone with original screws here to change them and take care to do that correctly. Any comments on this point would be appreciated as always Lars -

Thanks,

Geoff, Corazon, 411 #41

03 September 2014 - 08:44
#9
Join Date: 02 January 2008
Posts: 1547

Dear Geoff
If you mean the triangular deck plates around the chainplates, they are cosmetic, and not attached to the vertical lugs. Small screws suffice.
Kind regards
Lars

03 September 2014 - 09:16
#10
Join Date: 16 May 2009
Posts: 252

Dear Geoff If you mean the triangular deck plates around the chainplates, they are cosmetic, and not attached to the vertical lugs. Small screws suffice. Kind regards Lars

Thanks Lars - then what ties the lug down structurally? Is it bolted into the knee with transverse bolting?

03 September 2014 - 09:50
#11
Join Date: 01 February 2007
Posts: 234

Yes, tied with bolts. Its worth taking them out during a maintenance period and checking / re fitting etc. Take care to properly refit and use the correct Sika products to stop leaks.
I will this winter straighten the shroud plates as recommended by Lars and get them checked for cracks etc. They are made from a single piece of stainless so no welds.

John B

03 September 2014 - 16:43
#12
Join Date: 16 May 2009
Posts: 252

Yes, tied with bolts. Its worth taking them out during a maintenance period and checking / re fitting etc. Take care to properly refit and use the correct Sika products to stop leaks. I will this winter straighten the shroud plates as recommended by Lars and get them checked for cracks etc. They are made from a single piece of stainless so no welds. John B

Of course.  I think I have seen posts with the bolting shown - I don't know how I could have thought those tiny screws held anything, but I am sure glad to know they don't.  I know the previous owner stiffened the knees on my boat, I don't know if he changed out the bolts, but I am going to make sure.  I have all good new standing rigging and want to know the foundation is solid.  I appreciate this post in that regard very much - thanks again.

03 September 2014 - 16:43
#13
Join Date: 16 May 2009
Posts: 252

Yes, tied with bolts. Its worth taking them out during a maintenance period and checking / re fitting etc. Take care to properly refit and use the correct Sika products to stop leaks. I will this winter straighten the shroud plates as recommended by Lars and get them checked for cracks etc. They are made from a single piece of stainless so no welds. John B

Of course.  I think I have seen posts with the bolting shown - I don't know how I could have thought those tiny screws held anything, but I am sure glad to know they don't.  I know the previous owner stiffened the knees on my boat, I don't know if he changed out the bolts, but I am going to make sure.  I have all good new standing rigging and want to know the foundation is solid.  I appreciate this post in that regard very much - thanks again.

17 September 2014 - 18:44
#14
Join Date: 01 February 2007
Posts: 234

I have just returned from the Southampton boat show and spent quiet a lot of time talking to riggers and mast manufactures. The situation is not unknown. Most of the better built yachts have welded SS washers onto the shroud plates. When questioned they say this distributes the load better on the clevis pins, so reducing the potential deformation on the clevis pin. The split pin is not meant to take any significant load. Only Reckman use bolts to secure the straps on rigging screws. Checking a few S/S Swans yachts in my marina others have the same problem of misalignment of the straps and the consequential opening.

25 October 2014 - 13:56
#15
Join Date: 01 February 2007
Posts: 234

Photos of the repairs to the chain plates. The chain plates were straightened in a hydraulic press, then washers weld on both sides. Due to elongation of the original holes a tube was also inserted. With the washer attached, the bearing surface of the chain plate to the clevis pin increased by a third.I increased the size of the gap through the deck around the chain plates to allow more mastic to be pumped in. I rubbed the chain plates with a plastic scourer to roughen up the surface, then applied a Sika primer and mastic on the stainless. I have fitted thin plastic washers in remaining gaps and fitted external washers on the outside of the straps to restrict all possible movement.

Amount of bend in chain plate

Refurbished chainplate fitted

S/S washer welded to chainplates

25 October 2014 - 15:25
#16
Join Date: 02 March 2007
Posts: 83

Dear John,

Your ground bonding wire looks very thin. This has to carry very high currents in case of lightening strike. Nautor originally used quite thick cable for bonding_ perhaps the professor could comment

best regards

Cosmo Little

26 October 2014 - 08:39
#17
Join Date: 02 January 2008
Posts: 1547

Dear Cosmo Little
Nautor used cable with the cross section 10 sq.mm, this corresponds to 19735 Circular Mil area, and this falls between AWG 8 and 6, choose AWG 6.
Kind regards
Lars

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