Dyneema truckers hitch shroud

[Anton B]

So I made a trucker's hitch-like assembly that I am thinking of using for adjustable shrouds. I couldn't get any pics that made sense, so I made a video.

What do you think? I haven't tested it yet but will try breaking it next week.

Anton

https://www.youtube.com/watch?v=_iOZ...ature=youtu.be

[Anton B]

Come to think of it, this is an ideal way to rig up trapeze lines on a catamaran!

[Brion Toss]

I have watched and re-watched that, but still don't get it. Could you make a drawing? Something clearer? It looks fascinating.
Fair leads,
Brion Toss

[Ian McColgin]

I think the round thimbles let things move. Other than that, it appears to be a trucker's hitch - a demo with thicker line would help - arranged such that the bitter end is pointed back down and secured with a taughtline hitch, perhaps, doubled around for that funny finger loop and inexplicably leading to a bungee cord.

It seems like rather more adjustment than needed, much more readily changed adjustment than one sees in shrouds, and probably less mechanical advantage unless it's a very small rig.

A fun variation might be a compound trucker's hitch on the model of a Spanish burton.

I'm still getting used to the idea of modern synthetics that work as shrouds. Way cool but anti-intuitive to my mind.

[MarkG]

The out of box thinking here, at least for me, is splicing a dumb sheave onto a shroud to gain mechanical advantage. So let's invent some shroud fittings to take advantage of this.

The upper fitting (upper deadeye) has two dumb sheaves, sized correctly for the shroud. An eye splice in a short piece of shroud goes around the dead eye. The tail of this line is then spliced into the shroud an appropriate distance above the deck.

The lower fitting (lower deadeye) also has two dumb sheaves. A simple winch, with a ratchet that allows the drum to turn only in one direction, is on one side of the deadeye, A cleat is on the other side. The deadeye is attached to the chainplate. The winch should go where it is most protected, even if this makes winching inconvenient.

The shroud goes through the lower deadeye and upper deadeye twice, giving a 5 to 1 mechanical advantage.

The shroud then goes to the winch located on the lower deadeye. As many turns as possible are taken on the winch. Then, with someone tailing the shroud, the tension on the shroud is adjusted. Loosening the shroud is done by manually lifting the ratchet.

The end of the shroud is then secured to the cleat. The tension should be low because of the winch turns. If possible, the cleat should be designed to store the tale of the shroud securely.

The lower fitting could also be modeled after a come-along with a removable handle. One end attaches to the chainplate and the other end to the deadeye. The shroud end is attached to the come-along drum which also provides secure storage.

A third option for the lower fitting would use a worm gear turning a drum. This has the fewest parts, has a really large mechanical advantage, stores the shroud tail, and locks the drum in place with no pawls. The initial take up of of slack would be slower, but that is not much of a penalty. If the winch is strong enough, deadeyes would only be needed for really high tensions.

The intent is to provide high, easily controlled, shroud tension. It might even replace turnbuckles on larger boats.

Thoughts? Did I miss something that makes this impractical? If it is practical, what are the disadvantages?

Mark Gardiner

[Anton B]

Mark G, that is basically what I was getting at, but hadn't gotten as far as to incorporate the deadeyes.
I have read that Amsteel shrouds move too much and need to be adjusted frequently, at least on boats that get rigged and de-rigged, probably having to do with constructional stretch, so I was thinking about ways to do that easily.
Now that I have made it, and thought about it, I am convinced that this is a really good way to do the adjustment on the trapeze lines, since they need a large adjustment, and it needs to be able to be done on the fly easily. They don't need much advantage, since you can lift your body weight a bit while adjusting.One common way to do it is to use about $100 worth of pulleys per trapeze, 4 per boat. I can get this done for nothing if I make my own low friction rings.
It definitely does not have enough advantage for shrouds on a large monohull, but I am doing this on a Prindle 19 catamaran, which weighs 380Lbs, has a 31' mast, and the technique for adjusting the shrouds as they are now is to use the boom and main sheet to pull down the boom on one side and then the other to relieve pressure on the shrouds to move a pin in a hole in the shroud adjuster, so really I won't need any advantage at all.
I may still just use a soft halyard with multiple knots, as described in another thread.

[Anton B]

I hope this photo of a drawing will elucidate a bit. For clarity, a splice is shown as two lines adjacent. Stitching is shown where the long splice is meant to be stationary, and the whoopee sling style splice (hereafter referred to as WS splice) is shown as two lines adjacent without stitching, and I hope the fact that there is a tail sticking out shows. The tail is used to attach a bungee that will hold tension on the whoopee sling splice so that it can be slid up and down to adjust the length of the whole assembly. It is a combination of Essington's idea to use a WS splice for a boom topping lift, though I don't think it will work without the bungee to keep tension on it.
That was on this thread:
http://www.briontoss.com/spartalk/sh...?t=2178&page=2
Also, it was partly an idea that came from the Constrictor jam cleat, which uses a line running through another one to grab it just like I am doing. Here is the Ronstan product page:
http://www.ronstan.us/marine5/constrictor.asp
Here is what I hope is a link to the drawing I made of my idea for what I am calling a trucker's hitch trapeze line assembly:

[IMG][/IMG]

[Essington]

The deal with a whoopie sling is that the tail is fed back through the standing part to create the adjustable eye. What this does is guarantees that the sling stays locked while it is under tension.

What you are using here is what I call a Textile brake. where the standing part is fed through the tail Or even a completely separate line. The difference from a whoopie is that the brake can be adjusted while the main line is under tension. This might be convenient in some situations ...

1) It doesn't create a stress riser (weak spot) where the brake enters / exits the loaded line.
2) Sometimes it is handy to adjust something along a loaded line.

However the nature of a brake like this is that ... well ... it can be adjusted while things are under load due to the tail of the chinese finger trap being free (unloaded). Even with bungee to tension the tail to prevent unwanted movement, an errant sheet or simply rubbing against it while walking past could adjust your length (in the case of a shroud, that could have catastrophic results).

So, I'd be really hesitant to use such a construction on a mission critical load.

A regular style whoopie sling could probably work fine for a trap adjuster on a cat (albeit more fiddly than a normal jam cleat), but a textile brake like this would dump you in the water the first time the tail of one of your lines went over the top of the trap wire.