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Thread: Tether Hooks

  1. #61
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    Default Re: Tether Hooks

    Quote Originally Posted by grumpy_o_g View Post
    I'd rather get the not going overboard in the first place bit as right as possible and find I've wasted all that money...
    A deep centre cockpit boat with the boom above head height is a good start
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  2. #62
    Join Date
    Dec 2013
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    Default Re: Tether Hooks

    Quote Originally Posted by Roberto View Post
    Apart from hooks, there is this standard requiring 2k kgf breaking load on tethers: where does it come from?
    A load of 2 tons halfway the spine of a human being -where most LJ harness attachment are- would most surely break it in two: given lifejackets, plb and all sort of locating beacons, from the regulatory point of view wouldn t a lower breaking strength tether be better, leaving the person alive in the water instead of hanging paralysed on the side of the boat? (Referring to the 1.9ton load on the spine, *not* the never fall overboard story)
    That would require a chapter to explain. I have published a number of articles on the dynamics. Much of it is safety factors (WLL is 5-10x below the BS) and allowances for wear. Sufficient to say that the requirements are proven in theory and practice, and that a few worn tethers and harnesses have broken, suggesting the number is not too great.

  3. #63
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    Nov 2011
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    Default Re: Tether Hooks

    2 completely separate issues developing

    Helmets

    There appear to be 2 applications

    One is to protect the head when doing mast work, and from personal experience head protection would be, is, invaluable. I use a helmet if I need to do mast work at sea

    Secondly related to the tether thread - there is a considerable danger with any sea running for an individual put over the side to allow recover of an unconscious MOB for the recovery individual to have their head hitting the hull.

    Head hitting the boom - more of an issue, but not to be ignored, on smaller yachts. I don't see yachtsmen wearing helmets for this situation - as it could occur at any time and yachtsmen are unlikely to put a helmet on as soon as they raise sails - and keep it on until they drop sails.


    The second issue is standards, testing and sailing.

    Sailing seems to adopt standard from other industries, some of which are inappropriate. Some standards, from other industries, that are appropriate are not adopted. Some equipment is unique to sailing - and has no standards.

    Thinwater has mentioned standards adopted for climbing and these standards are more stringent than that for sailing - yet it is the same kit. (Slight drift) - we have a fixation with chain strength (that is commonly what chain size is about) yet people use undersized shackles. People use swivels - and there is no side loading specification - and guess how swivels often fail. Manufacturers test inappropriately for sailing - and use that data as part of a marketing tool. Some sailing equipment is not tested, or if it is none of the data is published.


    But returning to the thread

    If you go overboard in 'blue water' particularly, but not exclusively, at night your chances of recovery and survival are very low.

    Stay on the boat!

    and having a reliable tether, jackstays, hard points etc - and using it, them - is fundamental.

    The cost of the kit - tether, hook, harness, LJ, PLB are expensive - when I crew offshore, I take my own (in the same way I take my own foul weather gear). Its not that I don't expect the owner to supply the kit - I know that in most cases mine will be better.

    On the Clipper yachts all the safety gear is supplied. I did wonder if you were a crew member what the position would be if you refused to use their kit (specifically tether) and demanded to use your own.

    Jonathan

  4. #64
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    Default Re: Tether Hooks

    The helmet thing was more of a tickler. I would not have looked into it unless I had been asked to.

    On my cruising cat, my uses might be as Neeves suggested, but in truth I never had one available anyway. The boom was above the hard top.

    Racing boats and small boats are different. They turn quickly. The boom is nearly always low enough to swat you. Boats speed in double digits are commonplace.

    Finally, there is the subject of children and college kids. A dinghy boom is generally not lethal, but it can be bad, and the sailors are both inexperienced and distracted.

    No single answer. That said, I still think the US Sailing statement is political.

  5. #65
    Join Date
    Sep 2016
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    273

    Default Re: Tether Hooks

    Quote Originally Posted by thinwater View Post
    In some ways, the requirements of a sailing helmet might be more like that of a bike helmet (one hard hit), but with better coverage.
    What you have described here is almost precisely what is offered by climbing polystyrene helmets. They work on the same principle as a bike helmet (energy absorption through destruction of the foam) but are especially good for withstanding side impacts (which is a risk in climbing if you fall and swing into the rock).

    To address Neeve's point about low participation in this thread, we did have an extensive thread about this very topic not so long ago:
    https://www.ybw.com/forums/showthrea...harness-report

  6. #66
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    Default Re: Tether Hooks

    Quote Originally Posted by TLouth7 View Post
    What you have described here is almost precisely what is offered by climbing polystyrene helmets. They work on the same principle as a bike helmet (energy absorption through destruction of the foam) but are especially good for withstanding side impacts (which is a risk in climbing if you fall and swing into the rock).

    To address Neeve's point about low participation in this thread, we did have an extensive thread about this very topic not so long ago:
    https://www.ybw.com/forums/showthrea...harness-report
    Thank you for the link; I somehow missed the earlier discussion, which I have now read through. Having been a "customer" of the MAIB in my day job a couple of times, I have a great deal of respect for them, and if they are taking their time there will be a good reason for it.
    Last edited by Minn; 12-02-19 at 14:04.

  7. #67
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    Nov 2016
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    Default Re: Tether Hooks

    I'll raise a point which seems to have been missed along the way, regarding the microcrystalline structure of alloy carabiners.

    It was discovered many decades ago, during research into climbing 'crabs', that microscopic nicks and scratches on the surface of alloy 'crabs' have a serious effect on the Ultimate Load they can carry without failure. This is due, as I recall, to the surface treatment of the products being significant in the overall performance of the designs, and that microscopic as well as visible nicks and scratches have deleterious effects. I also seem to recall that exposure to salt.... i.e. salt water.... enhances this degradation.

    Climbers of a certain vintage were very wary of getting their expensive 'crabs' wet on seacliff climbs.

    This is a topic for engineers, but the research has previously been done. Perhaps it will re-emerge.

  8. #68
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    Default Re: Tether Hooks

    No aluminium hooks for me, then. On the subject of barely visible degradation, I looked carefully at my webbing jack stays and saw one spot where I strongly suspect that someone had trodden on the webbing whilst wearing shore shoes, perhaps with a bit of grit on the heel, and slight damage had started. Perhaps a point to bear in mind.

  9. #69
    Join Date
    Sep 2016
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    273

    Default Re: Tether Hooks

    I have found this paper on aluminium in marine environments:

    http://www.almet-marine.com/images/c...vironments.pdf

    I would summarise its conclusions as being that it is perfectly possible to design aluminium parts for use in marine environments (see: all our masts, aluminium hulls) but that items which have not been specifically designed for this use may be at risk. NB it is perfectly safe to use aluminium climbing equipment in a marine environment (assuming you are using it correctly) so long as you perform visual inspections of your kit. Massive deposits of white crystalline alumina or seized carabiners would be cause for concern, but can easily be avoided by washing in fresh water after use. I am not sure how salty the environment inside cabins is and whether this would affect long-term storage onboard.

  10. #70
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    Default Re: Tether Hooks

    For anyone reading the above article:

    Most, many components used in the marine industry and manufactured from aluminium alloy use the 5083 alloy. From memory Fortress anchors use the 6061 alloy (its certainly a 6000 series), I suspect because it is more amenable to extrusion. The Guardian anchor is not anodised (but the Fortress is - people who use the Guardian do not complain of corrosion). Most items of climbing equipment are made from the 7075 alloy - as it is, or was, one of the strongest aluminium alloys. 7075 is now a bit 'old hat' (I think it originated in Japan and was used to manufacture Mitsubishi fighter planes in WWII). Stronger aluminium alloys based on lithium as one of the alloying elements are now available and used extensively in civilian aircraft (and I assume military aircraft) Boeing and Airbus. 7075 (and many of the Lithium aluminium alloys) cannot be welded nor bent.

    I have not seen any corrosion data for the newer lithium aluminium alloy but 7075 is not as corrosion resistant as the series 5000 alloys - Our aluminium Excel anchor has a 7075 shank and has been sitting on our bow roller for over 5 years and the anchor itself is around 10 years old - the shank has not dissolved into a pile of aluminium hydrate. Our shank is not anodised and anodising would improve corrosion resistance. In terms of a tether hook (which if aluminium will be made from the 7075 alloy)- good housekeeping should ensure longevity, grease 'hinges', wash in fresh water, store dry (in the same way you care for your LJ . I can see some potential for accelerated corrosion, for example carabiner gates, where the spring might initiate corrosion (but only if left to fester in the damp) - TLouth7's point about good design. We have taken that point to heart and replaced our stainless bolts that secure the 7075 shank to the fluke and replaced with 7075 bolts (the bolts are not load bearing). Presumably climbing equipment manufacturers are careful over this issue - as most climbing at some stage involves rain or snow.

    I cannot comment on scratches on the strength of 7075 - has anyone any reliable data on the failure of aluminium (which will be the 7075 alloy) climbing equipment? It is very difficult to see how any item of climbing equipment will not be scratched and scored at some point so if scratching is an issue I would have thought reputable manufacturers would issue warnings. and the users (climbers) would have regular forums about maintenance, dangers and failures.

    As an aside - 7075 does not bend, yield, it snaps like glass - failure would be an actual break. I k.now - I've tested it (and the fracture surface looks like broken glass).

    7075, and especially the lithium aluminium alloys are expensive.

    Jonathan

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