Rod to Wire Conversion (on a Mast) Help needed Please

Discussion in 'Sailboats' started by UNCIVILIZED, Nov 12, 2014.

  1. UNCIVILIZED
    Joined: Jun 2014
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    UNCIVILIZED DIY Junkyard MadScientist

    Guys,
    It's likely getting to be time to replace the rigging on the boat, & I'm looking for ways to save a bit of coin. Particularly as it's rigged with Rod, & the Pro work which needs doing on such, let alone just the materiel costs for new rod + accessories, are EXPENSIVE.
    So... I'm thinking on switching to wire, & could use thoughts & tips on any key points in doing it.
    - Any wizards out there, or tips/links to guys who are geniuses with this new compacted wire stuff? I ask, partially because, as of last check there weren't but a few shops in the US who even worked with, or carried it. That, & I'm also curious as to folks experiences with & thoughts about it.
    - Also, tips & links to rigging geniuses who are up for a challenge, and or websites on rigging & wire wizardry would be very much welcomed also.

    Anyway, I know that of course, the wire needs to be rated on par with the rod it replaces strength wise (stretch too if I can manage it). And that I'll have to do some "recalibrating" when it comes to fittings like spreader ends. If not just outrignt build some new spreaders (no biggie there).
    Plus, of course the most important point is that I'll likely have to fabricate/have made, some new tangs & compression tubes for'em. And of course, make sure that everything's properly toggled, & in alignment etc.

    So, bonus points for anyone who can spell out any great solutions to such a (hypothetical) swap, & or put together a KISS plan for such. And like I said, I'm definitely open to any good POC's for folks to help me with, or school me on this project. Be it for a fee, or otherwise. That & links/addy's to good rigging sites.

    Ah, & details wise. The rig's a tall, skinny, bendy thing (with LOTS of pre-bend), 3 sets of spreaders, a detachable baby stay, light weight runners & checks, plus of course a hydraulic backstay.

    Thanks in advance,
    UNCIVILIZED
     
  2. gonzo
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    gonzo Senior Member

    I think the rig will have to be completely re-calculated. Kiss methods work fine for low tech things, but this may be too sophisticated for just a simple swap. Cable will stretch more, which will change the stress to different parts of the structure.
     
  3. Joakim
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    Joakim Senior Member

    Wire has about the same stretch as rod, if they have the same breaking strenght. Wire is just 20-40% bigger diameter, weighs more and has much more windage (bigger diameter + uneven surface).

    Often wire has even higher breaking strenght and thus less stretch. E.g. for my boat Selden has specified V1/D1 7.1 mm as rod and 10 mm as wire, V2/D3 6.4 vs 8 mm, D2 5 mm vs 6 mm and FS 6.4 mm vs 7 mm.

    So wire V1/D1 have 29% higher breaking strenght, stretch 20% less, but weigh 55% more and have at least 100% more windage. 9 mm wire would have been more reasonable, but maybe Selden uses only 8 or 10 and 8 was too weak.

    The other ones have about equal breaking strenght, except the forestay, which has lower and thus stretches much (24%) more.
     
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  4. gonzo
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    gonzo Senior Member

    Breaking strength is proportional to section area. What difference does it make if it is one or several strands. Actually, imperfections in the surface have twice the effect in failure than internal ones. That means that the more surface area, the less tensile strength. As for stretch, cable strands are formed in a spiral and they tend to get straight under tension. That produces more stretch than in a rod. There is rolled wire that approximates the behavior of rod, but it has work hardening which may be a problem. A substitute for rod may be one of the new synthetic fibers.
     
  5. Joakim
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    Joakim Senior Member

    Navtec 1x19 8 mm: Breaking Strenght 4640 kg, weight 0.312 kg/m, stretch 0.001883 at 1000 kg load: http://www.navtecriggingsolutions.com/rigging.html

    Navtec Nitronic 50 rod 6.4 mm: Breaking Strenght 4670 kg, weight 0.249 kg/m, stretch 0.00183 at 1000 kg load: http://www.navtecriggingsolutions.com/rigging.html

    Navtec Dyform 7 mm: Breaking Strenght 4910 kg, weight 0.26 kg/m, stretch 0.001902 at 1000 kg load: http://www.navtecriggingsolutions.com/rigging.html

    So from Navtec at the same breaking load dyform stretches most (4% more despite 5 % higher breaking streght) and 1x19 is quite equal to rod (3% more stretch at 1% lower breaking strenght).

    Some other brands have may have a bit different numbers.
     
  6. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Rod rigging is decidedly stiffer and has less stretch than wire, but usually costs about 3 - 4 times as much. Going to wire, from rod will require a complete overhaul of the terminations, which will be very costly, though with this, still may be cheaper than a new whole rod setup. If terminations inspect good, then just replacing rod is pretty easy. Rod lasts a lot longer then wire, though if actively raced, you'll likely need the ends reformed every half a dozen years or so. Simply replacing rod is a lot easier than wire and the usual recommendation is a full disassembled, die inspection twice a decade. Cruising yachts don't place very high demands on rod generally, with loading in the 15% - 20% range, while racer will usually push 50%, so you can get a lot out of rod, compared to wire.
     
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  7. Joakim
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    Joakim Senior Member

    The data Navtec have on their website doesn't support that, if you keep the breaking strenght constant.

    For the same diameter 1x19 has about 22% and dyforn about 15% less material. Also there is other movement as pure elongation, thus they stretch more. For Navtec dyform breaking strenght is about the same 15% lower, but for Navtec 1x19 it is considerably more lower (up to 40%). Some other brands have 1x19 only 22% lower than Navtec rod. I guess that dependens on the cold working and detailed material used.

    For some reason the stretch reported by Navtec for rods equals to elastic modulus of about 170 GPa, while Nitronic 50 (and 316L) should have 193 GPa. 1x19 has apparent (area calculated from diameter) elastic modulus of 108 GPa and dyform 134 GPa.

    Many sources state, that 1/2000 stretch equals to 5% of breaking strenght for 1x19 and 7-7.5% for rod, which would not be true for Navtec specs. For them 1x19 would be 5.7% and rod 5.8%. Using Selden value for 8 mm 1x19 breaking strenght (56 kN) it would be 4.7%.
     
  8. gonzo
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    gonzo Senior Member

    The elastic modulus is a ratio(in %) of how much a material stretches before reaching plastic deformation. It has nothing to do with how much it stretches for a given tension. Percentage of stretch and breaking strength can be calculated for a material, but are not necessary relevant on this application. Other considerations, like fatigue, are more important.
     
  9. Joakim
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    Joakim Senior Member

    If wire/rod is chosen for a given load + safety factor, stretch vs. %breaking load has very much to do with how it will stretch for a given tension.

    Fatique will depend on how large % of breaking strenght the cyclic load is and on material used. The base material in rod and 1x19 is about the same, so fatique will depend on the safety factor used. Is a different safety factor used for rod and 1x19? For a racing boat shorter life span could be accepted in order to reduce weight and windage, but then stretch would increase.
     
  10. gonzo
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    gonzo Senior Member

    Stretch vs breaking load has nothing to do with how much it will stretch for a given tension. For example, aluminum has a Young's modulus of 69 and a yield strength of 95. Copper has a Young's modulus of 117 and a yield strength of 70. Nylon has a Young's modulus of 3 and a yield strength of 45.
     

  11. Joakim
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    Joakim Senior Member

    If you have 1/2000 stretch at 5% of breaking load (not yield load), then you can calculate stretch at any load from known breaking load or vice versa.

    Of course different materials have different modulus and breaking load. Even the same material (same chemical composition) have very diffrent values depending on heat treatment, cold working and construction (eg. 1x19, 7x19, dyform, rod).

    Iron has modulus of 210 GPa. Stainless steels are typically 190-200 GPa. Nitronic 50 is 193 GPa. Then 1x19 has only 108 GPa and dyform 134 GPa due to construction.

    Nitronic 50 can have breaking strenght anywhere from 650 to 1700 MPa depending on annealing and cold working: http://www.specialtysteelsupply.com/brochure/nitronic-50-technical-data.pdf

    At the higher lewels of cold working used for stays yield strenght will be very close (90-95%) to breaking strenght.

    Modulus doesn't depend on cold working nor from heat treatment. Thus higher breaking strenght steel (or aluminium etc) will stretch more at given load, IF breaking load is used to choose the correct diameter.

    According to data given by Navtec they seem to use lower breaking strenth steel for 1x19 compared to dyform and rod. For that reason 1x19 doesn't stretch more at given load compared to dyform and rod at the same breaking load.
     
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