A better design on Rope Clutches - Survey

Discussion in 'Boat Design' started by JeroenM, Mar 18, 2013.

  1. michael pierzga
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    michael pierzga Senior Member

    Would be nice is you figured out how to reduce the price. 2,500 dollars for a 4000kg rated spinlock is a but pricey.
     
  2. pdwiley
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    pdwiley Senior Member

    Probably not because an adjustable clutch only addresses half the problem.

    Human hands simply cannot grasp and haul on thin cables effectively. Therefore if you reduce line size to what is needed for the expected breaking strain using modern synthetics, you *have* to go to captive drum winches or some analog. This leads to line speed handling issues as I have said.

    I'm more used to dealing with big wires on drums - trawl winches etc. You don't have or need rapid retrieval which is completely different to a sheet winch on a small boat. Same basic issue writ large though - humans are incapable of handling the lines without massive power assist.

    With that caveat, yes, an adjustable clutch is a good idea in theory provided it doesn't increase complexity, weight and cost to any great degree. The fact is that some bonehead is bound to screw the adjustment down if there is one but as you can't make anything idiot-proof, as long as the consequences fall on their head, fine.

    PDW
     
  3. michael pierzga
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    michael pierzga Senior Member

    Half the reason you put a cover on modern low stretch ropes is to increase rope diameter to benefit human hands, winch self tailers, jammers....and keep chafe and UV off the load bearing core.

    You should investigate whether your proposed customer uses standard double braid or low stretch ropes.

    I only use modern low stretch on the main and genoa halyards. These are half halyards .
     
  4. Moggy
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    Moggy Senior Member

    No but then maybe they work them harder than me?! Mine are also mounted on the mast in a slightly unusual setup, maybe that keeps them cleaner?!? I can say that I know or have an opinion on it.
     
  5. Joakim
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    Joakim Senior Member

    What do you mean by cleaning? I have never taken one to peaces. Just some rinsing with water after winter storage. I also think Lewmar works the best. Have you seen the clutch test in Yacht 19/2008 (http://www.yacht.de/service/downloa...ction/ASC/rubrik/123/Ausr├╝stungs-Tests.html)? It's in German, but at least you can see the measurements, if you don't understand German. Lewmar D1 won the small clutch class and D2 the bigger one.

    E.g. D2 was able to hold 10560 or 8160 N (polyester vs. dyneema) while Spinlock XTS only got 7000 or 5870 N despite having indentical working load (800 vs. 790 kg). They also tested the XTS with dyneema + extra Vecran cover and got about 10000 N. D2 was not tested in that setup.

    At 5000 N D2 had slipped just under 20 mm with both ropes while XTS had already slipped ~35 mm.

    Even D1 (with only 500 kg working load) was better than XTS. It held 8430 or 6160 N and slipped about 30 mm at 5000 N.

    Lewmar is far from horrible to the cover. I raced a 28 footer with 8 D1 quite a lot for a four seasons and I could not tell from ropes (8 mm dyneema) where the clutch has been. I quite often used the controlled release possibility of Lewmar slipping a few cm of a rope without using a winch.

    Now I have raced two seasons a 35 footer with 6 XTS and can easily see where clutch has been on the ropes (10 mm dyneema). Of course the loads are bigger, but so are the clutches and ropes.
     
  6. Stumble
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    Stumble Senior Member

  7. Joakim
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    Joakim Senior Member

    Yes they finally made it to production. How well do these work? How long they last and do they need service? How difficult is it to put the rope in place (this is the only drawback of Lewmar).

    They seem quite price at least for smaller boats, which do not require more than Lewmar D1/D2 or Spinlock XAS/XTS. The smallest model costs $179. For the same price you can buy a tripple D1/XAS or double D2/XTS.
     
  8. Stumble
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    Stumble Senior Member

    No clue yet. I haven't seen one yet, just the add. But I thought it was interesting that these are designed to address the exact problems we have been discussing.

    Note that their rated strength is significantly higher than a standard clutch of the same size range. But their prices are also double...
     
  9. Joakim
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    Joakim Senior Member

    No they don't. E.g. the 8 mm rope model specifies 1800 kg BREAKING load while Lewmar D2 (8-10 mm model) specifies 1200 kg SAFE WORKING load and Spinlock XTS (8-14 mm model) 1000 kg SAFE WORKING load.

    You can't compare BL, which has no safety margin, to SWL, which is totally safe to reach.
     

  10. Skyak
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    Skyak Senior Member

    I am pleased to see this new concept make it to market, but I am surprised by the price and the length.

    My performance fears would be backlash and wear. I don't see how this could not have significant backlash due to the angle of the braid which would make it a problem on halyards. The way it releases from one end makes me think that there is a critical friction the line pulls through causing wear, vs well designed clutch which snaps clear.

    When I look at this I can't help thinking I could make a better one with piano wire.
     
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