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-   -   Help w/ proper name ... (http://www.sailnet.com/forums/gear-maintenance/55546-help-w-proper-name.html)

wind_magic 06-21-2009 04:32 PM

Help w/ proper name ...
 
I'm trying to figure out what this is called besides just "metal ring". :)

http://www.birdalog.com/productimages/tw5159s.jpg

What I am looking for is something like that, but big, like four or five inches in diameter, that is cast and not welded (for strength) and can hold like 1000lbs of weight when secured with line. What would you call something like that, does it have a proper name ?

scottyt 06-21-2009 04:35 PM

a properly welded ring will be stronger than a cast one

wind_magic 06-21-2009 04:39 PM

Quote:

Originally Posted by scottyt (Post 498661)
a properly welded ring will be stronger than a cast one

Good to know, thanks. :)

So is it just called "welded metal ring" ?

sailingdog 06-21-2009 05:36 PM

Just curious, what are you planning on using it for. One that can support 1000 lbs. of weight safely is going to be relatively thick and heavy. If it is going to be supporting something overhead, you'd want a fairly significant safety factor in calculating the SWL.

wind_magic 06-21-2009 08:22 PM

Quote:

Originally Posted by sailingdog (Post 498682)
Just curious, what are you planning on using it for. One that can support 1000 lbs. of weight safely is going to be relatively thick and heavy. If it is going to be supporting something overhead, you'd want a fairly significant safety factor in calculating the SWL.

Dog, what I want to do in the abstract is to have a load that has two rings on it, one on either side, and to lift that load with ropes on either end pulling horizontally so that the load is suspended in the air and is between two ropes as if it was suspended over a river with the ropes tied at either shore.

I'm starting to think that screw links like the ones that climbers use might be better able to hold a load instead of something round like a metal ring.

http://www.rocknrescue.com/acatalog/OvalscrewLink.jpg

capttb 06-21-2009 08:55 PM

Not sure but maybe what you describe is a "figure 8" they are available made from a variety of materials and sizes.
Figure 8's

jgeissinger 06-21-2009 10:37 PM

It's just a stainless O ring. WM has them up to about 2 1/2 in. They are used regularly for rope bridles on hoist launched boats such as Lido 14s, CFJs, etc. Sorry but I don't know where you would get a bigger one. Also, as scottyt said, cast is not really stronger. Forged and welded would be my choice.

sailaway21 06-21-2009 10:41 PM

Windy,
You'll find more strength in a shackle of some sort versus a ring, or steel grommet, if you will.

You should though be aware of some basic cargo gear factors before you attempt the suspension of such a heavy load.

If I understand your goal, it is to suspend a thousand pound weight by way of two lines, one to either side of the weight, and have the lines as nearly horizontal as possible. My first, and facetious, question is; have you ever seen a twelve inch mooring line (circ.)? (g) The non-facetious point is that, when suspending a load between two lines in such a manner one must be conversant with the stresses involved in the geometry of the two lines.

On board ship we'd call each of your lines a "fall". If we were suspending a load of 1000 lb between two falls where the angle between the falls was zero, both vertical, the strain on each fall would be 500 lbs. This is the lowest stress possible on each fall. As we separate the hauling part of each fall, and we'll assume that the fall angle for each is an equal distance off the vertical, the strain on the falls increases. At a fall angle of 90 degrees, each fall 45 degrees off from the vertical, the strain on each fall is 750 lbs. At a fall angle of 120 degrees, each fall 60 degrees off the vertical, the strain on each individual fall would be equal to the load suspended, 1000lbs. That 120 degree fall angle is regarded as the maximum safe working fall angle for cargo operations, btw. Anything after that is regarded as "tightlining", your objective, I believe. The danger in that is that at, say, a 150 degree fall angle, each fall 75 degrees off the vertical, the strain on each fall would be 1900lbs. Note though that the combined forces that you are subjecting the falls to, wherever to which the falls are attached is 3800lbs. As you approach a fall angle of 180 degrees, both falls at 90 degrees from the vertical, you reach a strain on each fall approaching infinity.

These problems can be solve either geometrically or trigonometrically but I lack the equipment to diagram it for you here. You might google the parallelogram method of strain analysis for more detailed information.

I think you'll now appreciate my facetious example. Btw, a 12" mooring line is a 4" diameter line and when constructed of nylon has a breaking strain of around 324,000lbs, and using a safety factor of 5, would give a working load of 64,800lbs. If it was to be contemplated that there might be shock loading, one would use a safety factor of 9, giving it a working load of 36,000lbs. At that fall angle of 150 degrees we'd be able to only support a load of 18,950lbs safely!

(by my quick calculations, to support a load of 1000lbs, you're going to need line with a breaking strength of 14,343lbs to suspend that load with a fall angle of 176 degrees, allowing no safety factor for working load. With a safety factor of 5, that's a line capable of 71,715lbs. 2" diameter nylon should do you.) I'd be looking for some 50 ton shackles and leave the climbing gear out! (g)

sailingdog 06-21-2009 11:06 PM

Solid welded links are probably stronger than screw links, if less convenient. I'd agree with Sway that holding a load up by two essentially horizontal lines is not a wise thing and quite dangerous. The forces involved are quite significant and unless you're really aware of them, you're going to get someone killed. His point about the loads being enormously magnified by the lines being so close to horizontal is one you have to pay attention to.

This is kind of why I was wondering what your purpose for the rings was.

Just for yucks and giggles, take some small stuff, say 1/8" rope and try lifting a 50 lb. weight so that the two cords are horizontal as you've indicated you want to do. I know a 1/8" rope will hold 50 lbs. pretty easily, since the stuff I use has a breaking load of almost 450 lbs. I bet the rope breaks before you can support the 50 lb. weight with the lines almost horizontal.

Quote:

Originally Posted by wind_magic (Post 498705)
Dog, what I want to do in the abstract is to have a load that has two rings on it, one on either side, and to lift that load with ropes on either end pulling horizontally so that the load is suspended in the air and is between two ropes as if it was suspended over a river with the ropes tied at either shore.

I'm starting to think that screw links like the ones that climbers use might be better able to hold a load instead of something round like a metal ring.

http://www.rocknrescue.com/acatalog/OvalscrewLink.jpg


patrickrea 06-21-2009 11:31 PM

Back in my days of theatre rigging and flying large PA stacks, fabric or wire rope slings were good and quick links were never allowed because of they way they can loosen when vibrating. A shackle is the proper device as you can safety wire them.


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