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Old 03-05-2013, 05:07   #1
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Optimal length for Safety tether?

I follow F1 racing. Recently they've advanced safety with some drivers shortening the two tethers connecting the helmet to the neck brace (HANS device). Less rotation for the neck in a collision.

What's the best length for a safety tether afloat? I know there isn't a precise answer but I'm interested in design parameters and the thought process of the experienced members on this board.

Are higher jackline / shorter tether combos safer? Should the spot you end up being towed from be a design consideration for reboarding attempt?

Thanks - longtime reader of the forum.

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Old 03-05-2013, 05:10   #2
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Re: Optimal length for Safety tether?

Ideally, you don't want to have to re-board. You want the tether to keep you from going overboard in the first place. You want it to hold you in a place where you just have to untangle yourself and climb back onto your feet (or knees).

That's why the answer of what is optimal varies with each boat, boater, jackline arrangement, and so on.

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Old 03-05-2013, 05:38   #3
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Re: Optimal length for Safety tether?

The 'official' recommendation is all tethers be no more than 2m long, and it is preferred if each tether also has a 'short' 1m leg.

Here is a working draft of an article on tethers and jackline best practices

The very simple key point is that most boats today have jackline/tether systems which are a previous generation design and which do NOT meet the current ISAF recommendations nor these best practices.
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Old 03-05-2013, 05:52   #4
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Re: Optimal length for Safety tether?

ISO standard 12401 (EN 1095) specifies a maximum length of 2m (6.5') for safety lanyards, with a midpoint (1m) snaphhok.

“... 5.02.2 At least 30% of the crew shall each, in addition to the above be provided with either:
a) a safety line not more than 1m long, or
b) a mid-point snaphook on a 2m safety line ..."

Section 5 - Personal Equipment | special-regulations

An adjustable tether might be desirable, to allow the length to be set for the given situation. For safety, it is best to have little to no slack* in the safety tether when in use.

* Forces above 10kN begin to cause internal injuries. A fall of just 60cm (close to 2 feet) with an 80kg mass (about 176 pounds) can generate 16.7kN of force. Think about that for a minute, an average size man dropping only 2 feet can possibly generate enough force to seriously hurt you (if the gear doesn't fail first).

The Sailing Foundation Harness and Tether Study (1999) concluded, in part:

“... Our ideal tether would have a quick release snap shackle at the inboard end, and both a three foot and six foot leg. The six foot leg may have some shock cord built into it to help keep it from getting in the way while working the deck...”

And further reported (2011):

“... Warning: a safety line and safety harness are not designed to tow a person in the water and it is important that the shortest safety line length possible be used with a harness is used to minimise or eliminate the risk of a person's torso becoming immersed in water outside the boat, especially when working on the foredeck. 1m safety lines or the midpoint snaphook on a 2m line should be used for this purpose. The diligent use of a properly adjusted safety harness and the shortest safety line practicable is regarded as by far the most effective way of preventing man overboard incidents...”

Good article Evans!
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Old 19-05-2013, 05:03   #5
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Re: Optimal length for Safety tether?

For years I have been asking the people that make yachts WHY they fit safety lines that allow people to be thrown overboard and their answer is that's where we fit them. I will explain where and how the lines are fitted. I fit a strong "U" shaped fitting made of 15mm S/S to either side of the companion way then I fit a S/S wire 6mm thick with bottle screw to this and take the cable to the stem head fitting. This line is under tension to make sure it stays in position. The safety lines for the crew's harness is made of 15mm three strand polyester rope spliced at both ends and has a gibb attachment that can not come un done by accident on both ends this line is made to suit the yacht's size but is just long enough to be able to walk on deck with knees just bent a little. If the crew should be taken off his or her feet they can only fall ON the deck and therefor nobody needs to be recovered back on board. I have used this system on all my boats and when teaching and have never had a person fall overboard in 60 years. These are of course just my thoughts but it is something I have given great thought to over the years. Happy sailing to you all Pete
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