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  #31  
Old 07-24-2012
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Re: Pad eyes for tethers and jacklines

If you are still thinking of using a short jack line on the cockpit floor, one thing to consider is how many people you will have on the boat. With multiple pad eyes the loads would be spread around. A taut jack line on the other hand concentrates all the load. The force does not even get spread to the two anchor points. In fact if the jack line gets deflected by about 30 degrees, the tension on the jack line is twice the force on the tether. At a deflection of 10 degrees, the tension is almost 6 times the force.

If you have 4 people each weighing 200lb, you are approaching the 5000lb force specified for the components. Since the effect is like sweating a line, where the force gets magnified most when the jack line is almost straight, you would at least want something that stretches for the jack line.
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Old 07-24-2012
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Re: Pad eyes for tethers and jacklines

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Originally Posted by Stumble View Post
For the OP on an Olson 30, the laminate where he is talking about is either 1 or 2 layers thick, and that's it. I actually own an Olson 30 and know exacally where he is talking about. So for this installation I think the risk is much higher, than if you were talking about a high strength area where there is a lot of deck thickness to help absorb these loads.
I was on the boat just yesterday afternoon, and will be again today. I'm fairly sure the cockpit floor on my Olson has more than two layers of fiberglass laminate. I'll take a closer look today, but it's going to be another few days before I go at it with a drill to see for sure. I've ordered 5 Selden folding pad eyes, so I have enough to put two on the cabin top (for the jacklines running forward to the bow cleat) and three in the cockpit floor (two back at the tiller end and one just below the companionway). Obviously, I won't do this if I don't think I can reinforce them with stainless backing plates to hold well enough, and there are plenty of people around here who's opionions I trust, both offshore racers and experienced cruisers.
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Old 07-24-2012
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Re: Pad eyes for tethers and jacklines

Re the U-bolt resposes:
A marine u-bolt comes with 2 plates and 4 nuts/washers.
One pair goes under the substrate, one pair above it, and the bolts are tightened against each other. The 2 plates sandwich the substrate/deck/whatever. Properly bedded, they would be no less watertight than a conventional padeye.
They also resist sideways movement or bending because the 4 nuts and 2 plates, plus the backing plate, form a rigid unit. Perhaps incrementally less rigid than a forged 1-piece padeye, but I guess that's the crux of my question. How much less rigid is it, and how rigid does that union have to be (given that the bolt itself is strong enough) in order to reliably stop a fall overboard?
This is not something that will be subject to stress in normal use, remember. It sits there with a tether dangling from it, stressed no more than are the deck cleats many people tie off their jacklines to. So I don't see where repeated loading will gradually degrade the integrity of the boat surface that it's mounted on.
Again, I think it's a matter of whether the bolted joint can be made as safe as a one-piece joint. Because if it can, you can mount several of them for the cost of a Wichard.
(And perhaps thereby make yourself more apt to clip on to one!)
John V.
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Old 07-25-2012
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Re: U bolts as padeyes

I couldn't picture what you were describing so I did a little research.
Wichard Stainless Steel U-Bolts
I assume this is the kind of u-bolt you are talking about.
I am also wondering what the answer to your question is regarding this.
We are currently working on setting up our tether system and these have a very high load rating for the money!
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Re: Pad eyes for tethers and jacklines

My original question, was where to locate the pad eyes for attaching tethers (which will greatly depend on your boat and it's design) and what kind of attachment hardware is most suitable. When the question about using a simple u-bolt came up, I think the most important feature to consider is the sheer strength at the location where it is bolted. If you have a very thick portion of deck where those are located, and you provide adequate backing (and perhaps deck plates), then you are probably safer than just attaching them to a thinner surface (some cockpits, for example, are very thin in the floor, and are not well-suited for placing something that will likely "wiggle" itself loose and/or potentially rip free). I'm going the safer route, since some of my crew approach 200 lbs and I've bought enough folding pad eyes and stainless backing plates. They will be mounted to a horizontal surface with enough strength to absorb the shock of someone that large falling from across the deck in the event of a wipeout.
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Old 07-25-2012
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Re: Pad eyes for tethers and jacklines

Quote:
Originally Posted by meteuz View Post
If you are still thinking of using a short jack line on the cockpit floor, one thing to consider is how many people you will have on the boat. With multiple pad eyes the loads would be spread around. A taut jack line on the other hand concentrates all the load. The force does not even get spread to the two anchor points. In fact if the jack line gets deflected by about 30 degrees, the tension on the jack line is twice the force on the tether. At a deflection of 10 degrees, the tension is almost 6 times the force.

If you have 4 people each weighing 200lb, you are approaching the 5000lb force specified for the components. Since the effect is like sweating a line, where the force gets magnified most when the jack line is almost straight, you would at least want something that stretches for the jack line.

Actually, with 4 people on the jackline, you are WAY past the rating. The underlying engineering calculations are based upon a maximum of 2 people per jackline.

Interestingly though, all of the the tether breakage stories I have found were sailors hooked to a pad eye, not a jackline. That is because with no stretch, a sailor moving at 8-10 knots (not unrealistic in a knock down or wave strike) will generate forces over 5000 pounds, because tethers don't stretch. Either the hardware or the sailor breaks (sometimes both). Making the tether softer--in a controled manner--solves the problem.

Yates is starting to pilot test tethers with energy absorption sections. I'm testing a pair. They look something like the helo lanyards, but with 2 legs.
Helo-Ops
Actually, the 43-inch lanyard would work very well for many.

A LOT more fall testing has gone into the helo tethers than marine equivalent.
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Re: Pad eyes for tethers and jacklines

Irunbird, I think you're right to consider the strength of the boat surface--no point in losing a crewmember and an expensive pad eye to a weak deck. And if you are responsible for a crew's safety, you're safest to go with something proven and not experiment. It's just too bad they can put such a dent in the budget.

TJVanginkel, the Wichard u-bolt pictured is slightly different from what I'd thought to use. I've seen others without that annular bulge, and instead with 2 nuts on each leg of the bolt. My thiniking is that the paired nuts tightened together with those oval plates and appropriate washers between them, plus a wider backing plate, would spread the side-ways strain on the deck in the same way that the plate on a pad-eye does. The Wichard bolts don't look like they would accomplish that.
John
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Re: Pad eyes for tethers and jacklines

woops- just realized after reading my post that I mentioned attaching tethers directly to the pad eyes- that won't happen. There will be 1" tubular webbing run to attach tethers to, and the tethers should be the shock absorbing type. I'm of the frame of mind that my crew need to provide their own tethers/harnesses/pfd's, and I'll provide the boat and solid jacklines. Most of them have good shock-absorbing tethers, but I haven't seen the tethers for all the crew yet.
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