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  #11  
Old 07-18-2012
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Re: Pad eyes for tethers and jacklines

What ever you do, don't buy Chinese!

Heard stories of Chinese shackles, and swivels, failing.
Why?
Because they're cast, not forged, and the grade of SS has more shine and polish rather than strength.

Dick
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Old 07-18-2012
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Re: Pad eyes for tethers and jacklines

I missed that you were considering Starboard. I don't know anyone that has used it for backing plates, and I would absolutely not recommend it. It is barely self supporting, let alone capable of taking this type of load. What I believe you are thinking of is called G10. Which is a FRP board that is very strong, and absolutely suitable for this type of thing. Theoretically it is strong enough to be tapped, but I would go with big washers. Of course titanium plate is always an option

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Originally Posted by Flybyknight View Post
What ever you do, don't buy Chinese!

Heard stories of Chinese shackles, and swivels, failing.
Why?
Because they're cast, not forged, and the grade of SS has more shine and polish rather than strength.

Dick
There's nothing wrong with cast parts if they are cast properly. The issue is when the casting is done poorly you can get gas bubbles inside the molten metal that massively reduces the strength of the part. This is one reason our castings are done in a vaccum. To ensure there is no trapped gas that can weaken the part.
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  #13  
Old 07-18-2012
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Re: Pad eyes for tethers and jacklines

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Originally Posted by Stumble View Post
I missed that you were considering Starboard. I don't know anyone that has used it for backing plates, and I would absolutely not recommend it. It is barely self supporting, let alone capable of taking this type of load. What I believe you are thinking of is called G10. Which is a FRP board that is very strong, and absolutely suitable for this type of thing. Theoretically it is strong enough to be tapped, but I would go with big washers. Of course titanium plate is always an option
Hmm.. ok, maybe I'll replace those plastic backing plates... just when I was getting ready to do some racing!

I wouldn't consider aluminum, either. If for no other reason, the problem with galvanic corrosion from the stainless bolts.. and I have Tefgel to prevent it- it's just not worth the hassle when I have perfectly good stainless sheets sitting in the garage to use.

Last edited by Irunbird; 07-18-2012 at 09:29 PM.
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Old 07-19-2012
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Re: Pad eyes for tethers and jacklines

I absolutely agree that jacklines, tethers, and attachments should be up to the correct standard. However, it is ironic that with all the intense talk, and research involved in this, the most likely failure mode is simply not clipping in.

Back to the attachment point question: Would it be a better idea to have a short jackline on the cockpit floor? That would provide a little shock absorption, and distribute the load to two attachements.
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Old 07-19-2012
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Re: Pad eyes for tethers and jacklines

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Originally Posted by Barquito View Post
I absolutely agree that jacklines, tethers, and attachments should be up to the correct standard. However, it is ironic that with all the intense talk, and research involved in this, the most likely failure mode is simply not clipping in.

Back to the attachment point question: Would it be a better idea to have a short jackline on the cockpit floor? That would provide a little shock absorption, and distribute the load to two attachements.
That's the best idea I've had to date. What I'm currently planning is to install one folding pad eye (Wichard, probably) in the cockpit floor up close to the companionway bulkhead and a non-folding pad eye (eye strap) on the floor at the back of the cockpit under the tiller- both with big backing plates, and put a twist or two in the 1" tubular webbing so it's easy to grab. This way, it's easy to clip in before coming up out of the cabin before you hop out. I still don't see how using Starboard as a backing plate is a bad idea. One opinion suggests that it could crack, but I don't see how. Where I've used it so far is under both pairs of winches (primary and cabin top), and there is negligible flex in the mounting surfaces where they are. The cockpit floor might flex a bit more, so I intend to use stainless plates for those pieces of hardware.
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Old 07-19-2012
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Re: Pad eyes for tethers and jacklines

I do about the same thing – I have a large folding pad-eye in the cockpit below the companionway and one each in the aft corners. I run two jacklines in the cockpit mainly for the convenience of getting around the pedestal when swapping out helmsmen. I highly recommend using some quarter inch Garolite as a backing plate (G-10 is their general purpose grade). It is very dense and strong (Known in some circles as “the poor man’s carbon fiber”). Starboard is relatively soft and I’d be concerned about using it in applications where it can compress, thus loosening the screws. G-10 can be worked and shaped with simple hand tools (I use carbide blades and drills). You can also bed G-10 with epoxy, eliminating point loading on an uneven surface. Stainless is a PITA to work with (cobalt drills, cutting oil, work tempering and polishing) and the only time I use it as a backing plate is when it would show in the cabin.
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Old 07-19-2012
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Re: Pad eyes for tethers and jacklines

That's one of the most attractive features about HDPE- you can drill through it in an instant. I always use very big fender washers (at least 1" in diameter, depending on the anticipated load, but the ones supporting the primary winches are 1-1/2" dia.). There's no way I can see those things pulling through the Starboard, and I didn't just trim the Starboard to the same diameter as the winch base- they extend out at least 1-2" beyond.
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Old 07-19-2012
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Re: Pad eyes for tethers and jacklines

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Originally Posted by Irunbird View Post
That's one of the most attractive features about HDPE- you can drill through it in an instant. I always use very big fender washers (at least 1" in diameter, depending on the anticipated load, but the ones supporting the primary winches are 1-1/2" dia.). There's no way I can see those things pulling through the Starboard, and I didn't just trim the Starboard to the same diameter as the winch base- they extend out at least 1-2" beyond.
And yet you will never see a builder use it for this. Certainly it can work, but it has shortcomings:
* It creaps under load (bolt loads). Take a piece and really load it up for a few weeks, and notice that the bend becomes perm and that it creaps.
* Fender washers, unless they are thick, distort under extream load. They don't destribute the load as far as you think. Combined with creap, not so good.
* No sealant will stick well.

HDPE is good stuff for certain things--I use it--but not for this. I wouldn't rip out what you've done; it sounds good. It can work, sure, but there are better choises. That's all we're trying to say.
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Re: Pad eyes for tethers and jacklines

Thanks for the explanation, Drew- that makes sense. These bolts are in direct view nearly every time I'm on the boat, so I'll keep an eye on them. If they start working loose, I'll know it. I suspect that happened a bit on my J24, but I attributed that to my not tightening them down completely on the one side that it happened. I'll replace them at the first sign of wiggling loose.

Ray
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Re: Pad eyes for tethers and jacklines

Iron,

The very thing that makes it easy to drill through is the same thing that makes is completely unsutable for use as a backing plate. Pretty much any metal would be better, even assuming galvanic problems than HDPE.

I didn't want to get into a technical issue since its so clearly a bad idea, but here goes...

HDPE is an extremely week material, and is terrible at absorbing impacts. It was never intended to be used as a backing plate particularly in a critical application, you littlerly are risking your life on a material that simply isn't up to the task. HDPE is for cutting boards not backing plates.

So just a quick chart to give you an idea of what you are using...

............yield str......tensile
316.......34,800psi....79,800psi
6061 al..21,000psi....35,000psi
HPDE....2,100psi.......3,400psi

Yup HDPE is roughly 1/10 the strength of Aluminium, which is generally not considered a particularly strong metal. And 1/20the the strength of 316, which is a pretty weak steel.

But since you aren't going to put it under tension, but compression so let's see how it hold up there...

HDPE ......3,000psi
316.........36,000psi
6064 Al....34,000psi

Again 1/10 the strength of the other options.

HDPE also has a habit of deforming under load, so if you tighten the nuts down, you are going to push the material out of the way. This is called plastic deformation, and HDPE is highly susceptible to it. Again because it's yield strength is so low. Over time the backing plate will literly move away from the compressive force of the nuts and thin out over the area you most need it to be.

Your concerns about galvanic corrosion, while warranted, are causing you to use a completely unsutable material. If you want to use a plastic, then use G10 which was designed to be used as backing plates. Or switch to a matching bolt/backing plate metal. If you don't want metal or G10, at least use some plywood. It is a much better material for this than HDPE board.
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