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

[JohnV]

I'm considering using an Antal low-friction ring in place of turning blocks on my boom preventer. The current design is, the (Sta-set X) preventer line runs from boom-end through a large snatchblock on the foredeck back to a turning block aft of the primary winch, thence through a rope clutch to the winch. The boat is a heavy 33' cruiser (Alajuela).
The load on it, as I see it and when in use downwind, is normally static and minimal with occasional minor bumping from the boom in light air. The real load would be a shock in the event of an accidental gybe, and then during the process of easing pressure off the line. So I question the need for a (more complex & costly) block, given all of that. Seems to me that actual drag or friction in its intended use would be an advantage, rather than an obstacle.
By the same logic I could use another ring in place of the block at the foredeck, from where the preventer line returns to the boom end.
Thanks for any thoughts or opinions on this.
John V.

[benz]

Hi John,

Antal rings are great for any application where you're not heaving lots of line though under load: I'd not use one for a mainhalyard, for instance. But for your purposes, they're perfect. I run my Stay'sl and jib sheets through Antal rings rather than blocks, and it works perfect (high load/short run).
Ben

[Ian McColgin]

I can see the rings for fairleads and lizards but what's the effect of turning modern cordage through ninety or more degrees over such a small radius?

[JohnV]

Thanks for the replies--
Ben, those gizmos are such a break with tradition that I think most of us--at least true of myself--are hard-wired to overlook them.
Ian, that question was one of the reasons for my post. A bigger radius would be preferable, but in this application, is such a small radius still a problem even though the actual load is static, momentary and infrequent? I don't know the answer to that.
John

[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.