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.