A better design on Rope Clutches - Survey

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

  1. JeroenM
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    JeroenM Junior Member

    Hello, my name is Jeroen.

    I'm doing a survey that is regarding the completion of my master project at the Hague University, studying Industrial Product Design at the Composail project in the Netherlands.

    A problem that is common is the wear that occurs to both the lines as the rope clutch itself. My job is to take a fresh look at the problem and to come up with a solution.

    For this I need information from people with sailing experience and would like to ask you to help me. It will take around 5 minutes.
    Your opinion is very much appreciated!

    Also you could win a day trip for 2 persons with the GP42-Composail match sailing yacht.

    Link to the survey --> https://docs.google.com/forms/d/1s0p5NAskU09vVQIxaMfCMqreRMcjc-ZNdzRbeQwOdhA/viewform

    Thank you very much!
     
  2. Stumble
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    Stumble Senior Member

    As I mentioned in the survey, my biggest complaint is clutches that were sized originally for Dacron line don't fit modern high strength stuff. Requiring people to add bulking splices to dyneema lines to fit minimum clutch requirements.

    In addition clutches that are designed to grab modern, highly slipper line, so covers aren't required just for the grip.
     
  3. JeroenM
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    JeroenM Junior Member

    This is actually a really good point!
    The market of lines is changing more and more towards thinner and stronger lines. This brings a whole new perspective on stopping these type of lines.

    Thanks for the comment!
    I will take this into account.
     
  4. Stumble
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    Stumble Senior Member

    It was actually on my mind. I spent today splicing up new halyards, and had to add covers at the clutches to meet their minimum size requirements. And I can't replace the clutches since the ones rated for smaller line aren't strong enough.
     
  5. Skyak
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    Skyak Senior Member

    I spend more time thinking about what should be than what is and I have been thinking that these high strength lines should be handled completely different -wound on captive drums with one variable gear drive and clutches to the various drums. The force/size is such that there is no good reason to put your hand on a line and many good reasons not to.
     
  6. pdwiley
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    pdwiley Senior Member

    You're hitting limits of human structure here as well.

    It's all very well having say a 3mm line that has the same tensile strength as say 12mm 3 strand silver rope but if you can't haul on it, what good does it do you?

    So - you either put a non-structural sheath over the line to get to an easily handled diameter to suit human beings, or you treat it more like wire and wind onto a captive drum of some sort - keeping in mind the downsides of the old wire drum winches and their bad habit of breaking bones when the brake was released improperly.....

    PDW
     
  7. Stumble
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    Stumble Senior Member

    PD,

    At some point the line is too strong for the clutches. And frankly many control lines are already at loads so far beyond the capability of hand manipulation that I don't see retaining that as being of much value.

    As an example however, the Spinlock XX clutches, which are some of the highest holding power i know of, have a breaking strength of just shy of 4,000lbs. With a minimum line size of 8mm. The strongest line available at 8mm is D12-90 with a breaking strength of 6,200lbs. This difference is what I am concerned about.

    Further the line closest to the breaking strength of the clutch would be 6mm. So people are being forced to use larger line than necessary to fit the clutches, or covers for no reason other than as bulk.
     
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  8. Robjl
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    Robjl Senior Member

    Cover strength

    I have just read these comments and remembered how my spectra 8mm halyard in a clutch that was supposed to handle it functioned....the cover broke when the spectra core inside obviously slipped and transferred the whole load to the cover. I replaced the 8mm with 10mm to solve the problem. the core strength is now way over what I need, but if the core slips the cover still holds...so far.
     
  9. Moggy
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    Moggy Senior Member

  10. JeroenM
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    JeroenM Junior Member

  11. pdwiley
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    pdwiley Senior Member

    I can see arguments against. For example you want to recover a lightly loaded line fast, if it's on a captive drum self-locking winch sized for the line's working load (or worse, breaking load), you're screwed. What now? 2 or 3 speed geared electric or hydraulic winches with rapid speeds as per some machine tools I use?

    Perhaps there's a market for titanium clutches to handle the extra strength of the synthetic lines? Of course this leads directly to how good your bolts are, and then what those bolts attach to. Frankly I'd rather a line broke than it held while pulling a big hole out of my deck or cabintop where the winch or clutch *used* to be.

    I think, now I consider it, that I can't see the point of using running rigging with tensile strengths vastly in excess of the anticipated load and then increasing the strength of every other component to cater for the line, at the expense of easy handling. I'm sizing my running rigging for ease of handling and even if 3mm Spectra or similar was adequate in terms of strength, I'd still use 10mm or 12mm braided or 3 strand. If a clutch slips at less than the breaking strain, that's actually a good thing IMO, as long as it holds for its rated load.

    PDW
     
  12. JeroenM
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    JeroenM Junior Member

    But what if you could adjust the slipping strength of the clutch? So the clutch would slip, on your call, when the load becomes to much that it is critical for the rest of the gear on board. So you won't pull a big hole in your deck, where the clutch *used* to be.

    Would you then consider thin, no cover, dyneema for instance?
     
  13. Fanie
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    Fanie Fanie

    I suggested an adjustable clutch long ago as it makes sense - it will prevent capsizing in the event of an unexpected squall. Thin lines tangle easier than thicker lines and is a lot better on especially cold hands.

    This in many cases is called a deck port
    Comes from experimenting where the deck is sturdy enough to hold...:rolleyes:

    What goes ZZZZ ! click click ?

    ZZZZis the wind pulling the line through the clutch and the click click is your heels and head going through the clutch if you stood with the foot in a loop ;)
     
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  14. Moggy
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    Moggy Senior Member

    Not in my experience, the load is distributed over a greater area and the action of the clutch creates multiple friction points between the cover and the core. It is the only clutch that I have owned that you can release under load without worry.

    I can't say that my experience is exhaustive, maybe others can criticize but I think it is the best design going.
     

  15. JeroenM
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    JeroenM Junior Member

    Ooof!! That's something to thing about! Must be horrible....

    Now that the reactions of my survey come in, I see a trend coming on that the most used rope clutches are Spinlock on top and Lewmar second. The rest is far behind. I have to wait a bit more to get a good conclusion out of it, but in other fora I hear a lot of positive reactions about the Lewmar rope clutch.
    I guess it also depends on the type of material that the lines are made of and the forces that come with it.

    Also I saw someone mentioning about cleaning the Lewmar often to be reliable. Is that also your experience?
     
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