Boom preventer: Antal low-friction ring vs turning block opinions?

[benz]

The small radius won't be a problem for Sta-set, especially since I doubt you're loading to anything near it's working load.
It's neat how many uses there are for very simple things on boats. I think for many years (and still as well), manufacturers have duped consumers into thinking that something more complex must be better. It has been the source of much profit for them, and much unnecessary clutter for sailors.

[Stumble]

Actually modern high tech stuff is less prone to bending issues than older lines. Dyneema has been shown to retain full breaking strength at 1:1 bend:size.

[allene]

Originally Posted by Stumble

Actually modern high tech stuff is less prone to bending issues than older lines. Dyneema has been shown to retain full breaking strength at 1:1 bend:size.

That is not actually true. Dyneema loses half its strength at 1:1 bend radius. You are probably thinking that 1:1 is OK for an eye splice, which it is but an eye has 2x strength of the line so 2 x .5 = 1.

I did some tests with a 90 degree bend and some Amsteel and some StaSet. I lost 20% with the Amsteel and 40% with the StaSet. It is my opinion that low friction rings are really only good with Dyneema or other slippery line. Use a block with double braid.

You might find this interesting.
http://L-36.com/more_low_friction_rings.php

[Stumble]

Allene,

Wow what a dumb mistake. I was looking at the sizing chart for minimum diameter bails for eye splice load not the D/d chart. Thanks for the correction.

[benz]

John,

For your purposes the Antal rings are perfect. The bend radius on one is far grater than say, a carabiner, which strength-wise, would still be strong enough. Unless you're suing ridiculously thin Sta-set (like 1/4"), your preventer is not going to feel itself strained.

It's easy to get tied up in knots worrying about ultimate loads and percentages of breaking strength and bend radiuses, but all that applies more to folk who are trying to shave as much weight and windage as possible, such as the ever-obsessive racers. On a nice, heavy, low-tech cruising boat such as yours, I suspect all the lines are comfortably fat, for ease of handling, and you're not pushing any material to the extreme where a bend radius would be life or death.

Use a ring. Enjoy your life. Cruise.
Ben

[allene]

I just read the original post again. You want to make a boom preventer by going from the boom end to the foredeck and back to a winch. I have tried this using StaSet and it didn't work for me. The problem was the stretch of the line. Work out the geometry yourself calculating the total length when prevented and the total length it would have to stretch to to flip to the other side. Part of the problem is that this geometry has a lot of "gain" or leverage on the load so your line is going to be heavily loaded and thus stretch a lot. I would suggest you use dyneema for most of the preventer and splice some staSet just for the last bit. Use interlocking eye splices. That is what I ended up doing.

That said, the ring is fine. I use my foredeck cleat as the turning block.

[JohnV]

Thanks to you all for your thoughts.
Re: the stretch that allene mentioned, I'm using sta-set x in order to reduce stretch, and the portion of the line from the boom to the foredeck is Amsteel blue.
I will research more the effect of such a sharp, low-radius turn in the line before I make up my mind. The times this system will be put to hardest use will be to withstand a sudden and significant load from a back-winded 353 sq ft mainsail, so I guess the numbers will have to determine my course forward.
I've also seen that Colligo sells a similar part to Antal's that has a larger radius.
Thanks again for the help with this.
John V.