Broken lower shrouds Dear Forum, <>
It has been a while since I have been on... went sailing. We have travelled from Denmark to Antigua where at the moment we have the pleasure of seeing S&S classics such as Bolero in action. It has been a weird year lots of storms when there should not have been and no wind where there should have. Anyway we spent three days in a Beaufort 10 between Portugal and Las Palmas. During my standard rig check I found some hairline cracks in the fittings at the base of the spreaders and broken strand in the baby stay (fixed). Our next stop I found a broken strand in at the base of starboard inner shroud (replaced). Sailed from Puerto Morgan the Canaries to Mindelo in the Cape Verdes 6 days ... 850 miles trying to keep her around 8 kts and below but occasionally surfing to 12 (rig check) all was well. Crossed from Mindelo to Martinique...during this leg we broke six strands at the top of the shroud in the port side lower..2150 miles.. 19 days VERY slow. Seven days under 80 NM per day. We were chased by 2 40 foot cats who could not catch us so can't complain but it was a slow trip so no real strain on the rig. Anyway fixed. Now sitting in Antigua... just for fun up the rig and... 2 strands broken in the starboard side lower (at the top next to the spreader). Note this one was replaced in the Canaries so was new.. This original rig has done a crossing with me before without problem and the rigging was replaced 5 years ago. The only change has been that I have moved the mast forward on the foot circa 2cm. SO thoughts??? <>
By the way we meet Plankton on Martinique and shared some S&S Swab 40 stories. Pictures to follow.<><>
All the best from <>
Storm Svale<>
See my post of 7Feb 2012, and replies. We really need an answer to this problem. One rigging company commented to me that 8mm shrouds for the lowers was a bit light considering the weight and section of the mast. However the failures are always at the swage terminals. I cannot believe that the wire is not strong enough. When our lowers failed during an Atlantic crossing, the center 7 strands of each wire was intact, and we did not break any of the shrouds. Presumably the remaining strength was 7/19 of the original wire strength, and was adequate. I am sure that the problem is fatigue failure of the wire caused by the swages.
Dear Mike and Cosmolittle
There are several possible reasons for this, all of them may contribute with their part.
The first two are related to fatigue.
-The wire terminal attachments are out of alignment causing the wire to bend at the end of the terminals.
-The leeward shrouds go slack, and can slop around in a seaway, this creates bending and jerking at the end of the terminals.
The third one is related to the swaging. Overswaging can damage the outer strands, flattening them at the end of the swage, and causing weak points in the strands here.
Cosmolittle's experience with all outer strands breaking at the terminal would suggest this problem.
Proper swaging terminals have their ends tapered off for reducing the compression locally. It appears there are also terminals without tapering, and they should be avoided.
The suggestion is to use Norseman terminals even if they cost more.
Kind regards
Lars
Dear Lars and Cosmo,
Thanks for the quick replies.
First it is 10 mm wire with swages at the top and Staylock fittings on the bottom.The terminal of the fitting (male end) is smaller than the gap between the female fitting on the mast so could be that it is slightly twisted here? I will try to put in some spacers to avoid motion.
Re: leeward shroud flopping. They are tightened so there is no slop in 20 kts.
Re: Swages. All swages were done by the same guy and I have no problems with the outer shrouds or the forestay...
Mike
Can you determine if the broken strands are deformed at their breaking point? Probably they have flattened. A magnifying glass is needed, strand diameter is 2 mm.
If the male end (eye) is smaller than the gap in the fitting this allows some movement, and is not detrimental.
Is the swage body curved or straight?
Norseman and Sta-Lok are both swageless fittings, and use the same principle for holding the wire.
Kind regards
Lars
Dear Mike,
not being such a high sea navigator I might be wrong, but here is the result of my own experience.
First you'll fing below a little drawing showing that filing one or two millimetres from the angles of the steel straps of the mast might help a lot to obtain a good alignement of the cables without noticeably reducing the overall resistance.
Second: I really do not understand how the lowers on the leeward side when sailing close hauled with a 15 to 20 kts on the deck, can still be tight. Are you sure they are not too tight?? On our 41 with a tall rig, single pair of spreaders, they are really very slack on the leeward side in these conditions, and my intention is to put some bungees in between the two (forward and backward lowers) to avoid them moving around, as recommended by Lars in a previous link I was unable to find. After more than 20 years in these conditions we never had any broken strand.
Of course the head shrouds should be very tight.
Kind regards.
Philippe 41/022
Could it be that trade wind passages result in greater stress on the lowers? The Swan 41 is quite a stiff boat, and has a sharper roll than I have been used to with previous boats. We at times rolled 15 degrees one way, 20 degrees the other. The mast is undeniably much heavier than modern masts, and each roll will stress the shrouds to maximum tension, and then completely slack.
What is the recommended static tension for the lowers? The cap shrouds should be tensioned to 20% of the wire breaking load (according to several rig tuning handbooks that I have consulted), however it is not clear as to the correct tension for the lowers. Normally when sailing hard to windward, I would say they were slack, but certainly not flopping around.
Dear Philippe and Cosmo Little
Would like to comment on the subject of pre-tension, as I have been interested in these things for a long time.
The recommended method of pre-tensioning is described in the Owner's Manual text in the Forum maintenance section.
With this method extreme tensions are avoided, instead the slack on the leeward side is just removed when heeled, but no more, and the loads in the windward shrouds are not increased, in fact are the same as without pre-tension.
The main difference is when the yacht is upright, then there is about 10% pre-tension in the shrouds, varies somewhat depending on rigging sizes and geometry.
Rig tuning handbooks apparently recommend more, but once the slack is removed on the leeward side there is no benefit going to higher loads except for racers, this means they are ready to shorten the life of their standing rigging for a very small reduction in the fall-off of the masthead.
If you take a look on the Forum under Sail & Rigging, "44 New Rod Rig" two diagrams are presented, showing the rig geometry without pre-tension, and with the recommended amount. It can be seen that the rig will be much straighter on the wind with pre-tension while the loads in the shrouds still are the same, as explained above. Just the slack is removed.
Happy First of May to all!
Lars
Just back online we were anchored off Barbuda with no internet. Anyway, I installed a new port side inner which due the size of the swage caused a bend in the shroud. It looked like the pre picture in Philippes message. I have moved the staylock to mast and the swage to the deck and that is working... Lars unfortunately the old wire and fittings are gone so I can't look at them.. This is a problem when traveling!!
