Could you install double sets of stays and shrouds?

[GILow]

Originally Posted by UNCIVILIZED

PS: When it comes to doubling up on shrouds, it's not Too uncommon, to see 2 cap shrouds per side, & double lowers (fore & aft leading). As these are the 2 places, generally speaking, which get the highest side loadings on the rig. And which the rig will, without question, fail, if they do.
Look at boats designed for expeditioning, especially at the extreme ends of the spectrum, latitude wise.

Yes, this describes our rig. And the bit that slightly bothers me is that with all this reinforcing the ONLY bit that is not duplicated in any fashion is the rear stay. And when we run under MPS I am quite concerned with strain the rear stay must be under.


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[Adelie]

Provided all the connections to the mast and hull are also duplicated, then yes you could reasonably do so and expect better resistance to failure.

The exception is the forestay. In that case a sail sets on the stay and tension in the stay affects sail shape. The sail itself also imparts a load on the stay and changes the load in it. Getting enough tension into the forestay carrying the sail is a real problem and a big reason double headstays have not caught on with the possible exception of the solent stay which is set slightly behind the headstay rather than a pair of forestays set side by side. Tensioning issues are not quite as bad but you wind up with sail handling problems.

Safety concerns about increasing the mass of the rigging are overblown I think. The standing rigging is 10-20% of the total mass of the rig, so doubling that would be equivalent to using a thicker walled mast section. While the added weight aloft would mean that the vessel had less static stability and needed to reef earlier, it would also increase the roll moment of interia and the boat would be less suseptible to capsize in breaking waves.

The big impediment other than money that I see is to provide duplicate attachement points for all the shrouds and stays. At deck level it's not that hard:
-For the back stays bring one to center line and split the other so it lands on both quarters.
-For the shrouds land one set on deck with chain plates thru the deck to bulkheads and land the second set at the deck edge with chainplates attached to the hull.
-For the headstay land it at the stem like normal and for the solent stay it lands 12-18" aft and continues thru the deck to ultimately anchor to the hull lower on the centerline, like a bob-stay but with the loads going a different direction.

At the mast end you need to install a whole new hounds 1/16th or 1/8th mast height below the truck. Here you can attach the solent and the redundant shrouds. In order to install the second set of lowers you will again need to install a second hounds just below the lower spreaders (and uppers if it is a double spreader rig), but this starts to put loads out of position for supporting the spreader if the primary lowers fail. But that than nothing though. The big trick is the second backstay, its attachment point can't come down the mast because it will conflict with the main sail. That means both backstays are attaching to the mast at the same location. You could probably work out some way use different cotter pins and different tangs on the truck, but they would still both be anchoring to more or less the same chunk of metal at the masthead. There would still be redundancy but it would not be complete.

I wouldn't go down this path, but it is do able and not a complete waste of money.

What I would do is install a removable staysail stay with running back stays. This provides somewhat redundant mast support near the top end, provides functional advantages in the ability to set heavy weather fore-sails but allows you to clear the foredeck for easier short tacking. This assumes the boat came with double lowers, it not I would retrofit them.

[Stumble]

I have never liked this type of system. If you don't trust your standing rigging then replace it. Adding a second set doesn't make things any safer, it just adds more weight high up.

And I have real doubts that it doesn't make the rig weaker actually. To do this right you need to drill a lot of holes into an aluminium spar, each hole weakens that section of the mast appreciably. Add enough holes, and sure the rigging will still be there, holding up a stub of the mast where it sheared from the loss of strength due to rigging holes.

In my experience masts come down for one of three reasons...

1) corrosion on the rigging - solvable by replacing old rigging with new
2) the boat rolled - nothing is saving the rig from this
3) a defect in the extrusion of the mast - extra rigging isn't going to help here either

In no case that I am aware of (except AC boats and the like) was the cause of a rig failure lack of strength in the rigging.

[Orion Jim]

There are rigs which have the redundancy you seek. I have a cutter. It has two head stays, one for the yankee and one for the staysail (don't everyone take a cheap shot, I know technically it's not "two head stays" but should one part the remaining one would most likely keep the rig intact until a jury rig was in place). I also have two intermediates which keep tension on the staysail stay in addition to the normal two lower shrouds on either side plus two uppers and a backstay. I have eleven shrouds and stays, the loss of any one would not necessarily be a catastrophic loss and might very well provide the safety factor you seek in a conventional rig.

[GILow]

In reference to the points made above, particularly re twin forestays:


We have twin forestays that are not side by side but one in front of the other. Not solent-style, but parallel the whole way, separated by about 12 inches. Point taken about the difficulty in tensioning, but on ours the main tension is on the stay with the furling foil and maintains a reasonable sail shape. Probably not good enough for a racing sailor. Should the foil damage and break that forestay, the stay in front of it is full sized and could take the entire load, while also allow the attachment of hanked sails.


We also have a removable staysail with running backstays. I imagine that in the event of a failure of one or more of the upper stays, this could be used safely in conjunction with a reefed main to limp home.


The addition of the various other lower stays means that we have 14 stays on the mast, which is a lot of windage, but feels very secure. Our boat was originally rigged for long distance offshore work and the setup reflects the attention to safety and redundancy.


Matt

[Jman]

If you are so concerned the the designer failed at the load potential, then:
1. Don't buy that boat.
2. Way increase the size the size of the stays, you don't even need to double it is diameter to get twice the strength, now you have eliminated stay failure.

And where is the weak point? as many have said, drill more holes in the mast, not if the mast or spreaders were the weak point all along, or would become so with additional holes. Chain plate failure may even be more common than stay failure, was that the weak point?

If two sets are of stays are better than one, then why not 4? Or 8? Well if we were all sailing around with guitar string rigging maybe it would could get a good band going?


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[UNCIVILIZED]

Guys, I'll confess that this thread's gotten a bit silly. Somewhat due to a bit of misinformation, & or lacking information, possibly by folks not fully understanding rigging; practices, calculations, safety factors, etc. So I'll try to clarify a few things.

On "holes" in masts:
When you put in a hole for the bolt which connects a tang to the spar, you don't just drill a hole big enough for the appropriate sized bolt, & then simply bolt things together.
What's done, is to drill a hole of sufficient size to allow a compression tube big enough for the bolt to be put into the mast. Then, overtop of the ends of the compression tube, doubler plates are (or should be) welded onto the mast walls, overtop of the ends of the compression tube. And when done properly, the ends of the doubler plates are feathered down with a grinder so that there are no hard spots created on the tube.

That, & in areas of the mast which the designers are concerned with stupidly high point loadings, complete collars can be fabricated & attached in a similar manner. Witness the spreader root pads welded to the spars on some masts.

Also, in high load areas on rigging tubes & such, it's common practice to weld on additional reinforcing plates or material. Note the presence of "doublers" affixed to many booms for several feet forward & aft of a (rigid) vang's attachment point. As well as in other high load areas
Such can, & is also done on masts; on the outside, & inside.

For example, on particularly tall masts, if you look closely, sometimes you'll see rows of screw heads, or ground down spot welds, around the masts mid points. This is due to the mast having been assembled in 2 pieces, & the riggers inserting a tapered doubler on the inside of the tube, to strengthen things where the spar halves are connected. But in a way which spreads the loads from this strengthening so as not to create any excess stiffness, or hardpoints strength wise.

Or, on racing boats, it's common practice to sleeve the mast tube, with a slightly smaller section on it's inside, from the step, up to about the 1st set of spreaders.
This allows them to run a smaller diameter, lower windage tube, & still maintain sufficient strength in the more highly loaded areas of a spar.
Which, commonly, is up to the 1st set of spreaders, especially on a multi-spreader rig. Particularly so on a racer, where the lower panel of the spar can see huge thrust loads placed upon it by the spinnaker pole. Especially when they stuff the pole into the water while doing high speeds.

The only catch to all of this being, that most series of aluminum used in spar building, loses a significant amount of strength when welded. However, over time this strength returns.
But still, tube scantlings are calculated to deal with all of these sorts of attachments from the time the NA pulls out his slide rule, on calculation #1.

Backstays: There are a couple of KISS solutions -
Most (modern) racing, & RTW boats use "Running Backs" in lieu of conventional, fixed backstays. And unless the crew does something dumb, these hold up the mast quite well. And have for decades. So doing an approximation of the same on a cruising boat will work just fine.
Enough, so that, if you like, you can set one up on either side of the spar, & lead them to independent chainplates on the stern. Never needing to touch them for the length of the voyage, if such is how you chose to rig them.

NOTE: That with such a setup, or runners which go to, or near to the masthead, should a cap shroud fail, the runner can/will take up a significant portion of the missing support. But that due to lead angles & geormetry, won't be strong enough to take it all, unless... you grossly oversize it. Which, given the strength of say, Dux, or Compacted Strand wire, is possible.

Option #2;
Create a bridle type chainplate @ the masthead, just below the primary backstay. And from it, you run backstay #2 down to the transom in the conventional manner. With one backstay or the other, terminating in a bridled chainplate, dead ended to tangs just forward of & outboard of the transom. And the other going to a conventional, mid-line chainplate, on the transom.
If this 2nd backstay is of the synthetic variety, negligable weight is added, although it does add windage.

BTW: For anyone concerned about the strength of their rigging, especially their backstays. Unless you're rountinely pulling the kind of stunts which these guys are, I wouldn't fret too much. LUV This Vid!!!

https://www.youtube.com/watch?v=dXM_93TIMZE

[GrahamHO]

A normal multi strand rigging wire ( excepting rod rigging) is 1 /19. That is each single wire has 19 strands in one bundle. So your rig is already held up by 19 bits of wire on each "stay". What happens to cause that to break? Most commonly I understand is corrosion. At some point maybe at the bottom of a stay / shroud where the water drains and there are salt deposits corrosion affects each strand. In slow motion, one strand breaks then all the stress comes on each of 18 remaining strands which progressively fail one by one, more and more rapidly until it appears that one stay has broken suddenly.

If you double the number of stays surely each one will have a similar age and degree of corrosion so the progressive failure and associated shock load will continue in the next stay if there has already been enough force to break one stay.

If you are really worried, why not just use for example 8 mm 1/19 instead of 6 mm? The problem comes attaching it to the mast where you will need a bigger hole in the mast to take the fitting for heavier wire. Then you need a heavier mast to take the bigger hole. Your chainplates will also be weakened by a bigger hole. We all know a chain is as strong as its weakest link.

If you have 2 wires you will need 2 holes.

Now with either heavier wire or doubling up you have increased the weight aloft.

To prevent excessive heel you need to balance that with more ballast. But the center of gravity of the rig is say 20' high, and the COG of the keel is only 5' below the waterline. Therefore you need to add 4 X the additional rig weight to the keel to maintain balance. This puts more strain on the rig.

If the additional weight in the rig is say 40 lb, the keel will need 160 lb extra weight making the boat 200 lb heavier.

It's not only the wire that can break. A spreader can fold or a mast can fail in compression.

To a degree you can actually make a rig safer by making it lighter, requiring less ballast. That's why most of us use aluminum instead of wood for our masts, and now carbon fibre is starting to replace aluminum. Also fibre shrouds being lighter are starting to replace wire.

[Snowpetrel]

One small consideration is the extra pretension loads the extra rigging would put on the mast and hull. You'd need about 10-15% pretension on an inline rig to control stretch and sag, double the shrouds and you might be able to back off the pretension slightly, maybe to 10% in each shroud. Any Less is going to cause a lot of issues with loose stuff banging about. This makes the pretension load nearer 20% total. As we work down the rig with each shroud pair having a little more pretension this will start to add a lot of extra load to the mast and hull. Though a well built hull, and a decent sized mast should be able to cope with this without issues.
However if it's a highly strung swept spreader rig the shroud pretensions tend to be nearer 20-25% to control fore and aft bend and forestay tension. The extra pretension on the additional shrouds now start to add a lot of extra load to an already delicate setup.

But Jon Sanders rig on Parry Endeavour worked well for him, and I think from memory one shroud did fail, and the backup meant he could keep sailing.

Look at the crash test boat series on YouTube. Check out the dismasting video

http://m.youtube.com/watch?v=d-jqwkNXMIY

interesting how hard it was to pop the rig... Properly sized rigging doesn't break due to overloading. It's normally stress corrosion cracking or poor articulation putting uneven strains on the strands.

I guess that's a plus to the doubled up rigging concept.

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[GILow]

Originally Posted by Snowpetrel

But Jon Sanders rig on Parry Endeavour worked well for him, and I think from memory one shroud did fail, and the backup meant he could keep sailing.

From my memory of visiting the boat in Freemantle one of the forestays had also broken, but I think this occurred in some kind of collision. The pulpit was badly damaged and the forestay had been lashed back to the stem fitting with some kind of line and clamp arrangement.


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[Snowpetrel]

Certainly an epic voyage. Probably one not to be repeated in a long, long time. I loved the way he ran out of methane to preheat his keep stove halfway through the first lap, So he just primed it with Keri. Apparently the deckhead was black from smoke. In this day of everything having to be perfect it's refreshing to see someone that just gets on with it.

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[GILow]

I confess, I have never felt the slightest urge to be an adventurer, that is, until the moment I stood in front of that boat. Then I had the most overwhelming desire to drop everything and just go.


Mind you, a certain CF members writings on their Antarctica journey gave me a similar feeling. :^)

[Blue Stocking]

Saw a large cutter with dual fore'n'aft headstays, 3" apart. Bell-cranked at stem, with 1 turnbuckled, self-equalising tensioner.

[GrahamHO]

Adelie, you are absolutely correct about the advantages of using running backstays even if the rig does not necessarily need them. They greatly decrease the compression in the mast and if rigged out to the stern quarters they decrease the rigging load. I have them and use one of them if I am a long reach and expect the wind to increase. On my fractional swept back spreader rig, they attach to the mast just above the hounds. My second reef is designed to be just below the hounds. That gives me in effect a compact masthead rig (when using the second reef) that I can tack with both runners fully on. There is of course an unused length of mast sticking up above the hounds.

[Jman]

Originally Posted by GrahamHO

Adelie, you are absolutely correct about the advantages of using running backstays even if the rig does not necessarily need them. They greatly decrease the compression in the mast and if rigged out to the stern quarters they decrease the rigging load. I have them and use one of them if I am a long reach and expect the wind to increase. On my fractional swept back spreader rig, they attach to the mast just above the hounds. My second reef is designed to be just below the hounds. That gives me in effect a compact masthead rig (when using the second reef) that I can tack with both runners fully on. There is of course an unused length of mast sticking up above the hounds.

Agree with everything you say, except compression. A loaded running back straightens the mast, increasing compression. You could say it it greatly reduces mast bend. They are there on your fractional rig specifically to put more tension on the head stay.


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