toggle strength

[benz]

I use toggles from time to time on my boat, and wanting to use them more (cheaper and lighter than shackles), I began to wonder how much force they're subjected to when loaded. Has anyone calculated this? What percentage of the load on the halyard, say, translates into a bending force on the (getting technical here!) sticky-out bits that the loop rests on? If anyone cares to do some destruction testing, I'll gladly spare a few toggles (I turn them myself out of hardwood on a lathe).
Ben

[Stumble]

Benz,

I have pretty much removed them, and shackles from my boat. For about $3 you can make dyneema soft shackles that have a working strength of 4,000lbs, and weigh nothing.

[benz]

Dyneema shackles are not always suitable. If you put a thin dyneema cord through a eye spliced in a fatter dacron cord, the thinner line can chafe and cut at the dacron, which is softer. But speaking of dyneema soft shackes, why not splice a toggle into the soft shackle and not lose the strength that the knot takes away?

[Ian McColgin]

Do you mean toggles like you use on standing rigging, usually eye and fork but sometimes fork and fork? Like with clevis and cotter? They are for a given pin size almost always stronger than shackles and given that they are drilled for pins are more suited for the high loads of rigging. But you'd not want to feed anything flexable - wire or fibre - through the eye. So I'm thinking you mean something other than what I know as a toggle.

[benz]

Hi Ian,

Not that sort of toggle. What I mean is a little hardwood rod which you splice a line around tightly (so it can't slip out). Then you can quickly work the toggle through a loop spliced in another line, and presto! The lines are joined without a knot or a shackle. Harken is making something similar out of aluminum that they call a "Dog bone", but those are expensive and (I think) ugly. if I can find a picture of one I have made up, I'll try and post it later.
Ben

[Ian McColgin]

Ah. Of course. I should have thought of that.

[benz]

Here's a pic--not mine, but a toggle in use. Sorry I couldn't get to load as a picture.
http://t1.gstatic.com/images?q=tbn:A...-3PCSo1_-o3x4w

[allene]

I have been working on this for several weeks after seeing an incorrect use of one an aluminum dog bone for a halyard on another rigging blog. There is a little trick that puts the pull force right above the head plate that one of my readers came up with. Here is how it looks on an old headboard.


I wanted the strength of aluminum but wanted it secure. I also wanted something I could make myself so that left out the doggie bone. The dog bone I saw (SOAK) was a little nicer than the Harken one but wasn't even available yet and not priced so clearly not an option. What I did was encase an aluminum rod in some tubular webbing and sew the splice to the toggle.

I wrote it all up HERE

Allen
L-36.com

[benz]

Hi Allen,

Pretty nifty--I wouldn't have thought of covering a piece of rod. I was going to have a little spliced loop that would accommodate the toggle every place that it was necessary. I don't have sails with headboards, but that's a nice way of getting the pull straight. I had considered drilling a small hole in the middle of a metal (bronze, of course) pin, spicing the line over the hole, and then carefully working a cotter pin through both legs of the loop and the hole, thus keeping the pin from slipping out of the splice. It could also be lockstitched that way...

[allene]

Originally Posted by benz

Hi Allen,

Pretty nifty--I wouldn't have thought of covering a piece of rod. I was going to have a little spliced loop that would accommodate the toggle every place that it was necessary. I don't have sails with headboards, but that's a nice way of getting the pull straight. I had considered drilling a small hole in the middle of a metal (bronze, of course) pin, spicing the line over the hole, and then carefully working a cotter pin through both legs of the loop and the hole, thus keeping the pin from slipping out of the splice. It could also be lockstitched that way...

I thought about a hole in the rod but it would be right where the stress was the highest and I didn't want to compromise the strength. I should have thought about it more as I just ran some numbers for this reply and it isn't that bad, especially if aligned correctly.

I noticed the toggles that SOAK are going to offer are 10mm in diameter and neck down to 7mm. My rod was about 8mm. The dogbone is then about 45% heavier and roughly 60% of the strength of the solid rod. On the other hand, drilling a 1/16 inch hole in a 5/16 rod would decrease its strength only about 3% if aligned perpendicular to the line and would be 68% stronger than the dogbone. It does seem to be very sensitive to the alignment of the hole as aligning it parallel to the line decreases the strength by 34%. In any event, keeping the hole or holes more or less perpendicular is how you would want it and it would still be stronger than a dogbone that necks down to 7mm.

I ran these numbers quickly so I hope I didn't get them wrong. The main point is that most of the strength of a beam comes from the top and bottom surfaces (think I-beam) so that a hole that runs perpendicular to the load doesn't change the strength much. On the other hand, the strength is diameter to the 4th power so a very small increase in diameter makes for a much stronger toggle.

One more point of interest. If aluminum is 2.7 times heavier than oak and 20 times stronger we can increase the diameter of the oak by 2.1x and get the same strength toggle and be only 16% heavier. Not bad.