Mantus Chain Hook

[sabray]

My rubber snubber failed at the eye let broke/chafed on both ends.
Given its pricey value I chose not to replace. I went after the places of high failure. Chocks and attachment points. As as was said shock absorption can be done at better value. For low end stuff the rubber things are great but if it's honking I would go with dyneema at the chafe point and 3 strand at the wet area between.

[Cotemar]

Rubber Snubbers in the Bridle Snubber just remove the shock load.
The snubber elements themselves possess a nonlinear stress-strain curve.
The Snubber reduces the expected peak shock load loads 50%

[JonJo]

There is something fundamentally wrong with that plot?

Without the snubber, and ignoring the peaks, the loads without the rubber snubber are half those with the rubber snubber. Maybe I made a mistake as I would expect the results to be the opposite, lower troughs with the rubber snubbers?

On both plots peak loads are huge - much higher than anything I would dare test and much higher than anything anyone is likely to experience on a 36' cat.

The troughs are at 1t (with the rubber snubber) and at 1t all the stretch will have already, long ago - see below, been taken up in the rubber snubber - consequently anything beyond 1t is all about the nylon (in fact beyond 270kg its all about the nylon) - so why the 2 plots are so different is something of a mystery. I tested one of these rubber snubbers and the load at maximum stretch (64%), 3 turns of supporting rope, is around 270kg. I used a chain winch to develop load and measured using a 2t load cell. I was testing in the horizontal with each end supported by 36 inch diameter reinforced concrete pillars. I was not using nylon but an old double braid halyard (I was measuring stretch of the rubber). Beyond a 270kg load - manufacturers seem to imply they expect their rubber snubbers to fail (270kg is beyond their idea of a safe working load).

Hopefully someone will explain it as it looks to me as if the rubber snubbers are having a catalytic or synergistic effect - which merits detailed evaluation.

Jonathan

[sabray]

I guess that my experience with these is they work well at everyday stress. When heavily loaded at 45 to 55 and up they are not offering much. With all respect to cotemar we have a different experience. Like adding a weight like a killet the effect is best under low load.
I guess if it works for you that's good. Sure isn't hurting things like a killet wrapped around a line. This from a once killet fan.
I use the killet now for stapling the rhode of a second anchor down.

[Delfin]

Originally Posted by thinwater

3/16" Amsteel has a breaking strength of 5400 pounds. This is about 1/2 the strength of the chain. The working load is perhaps 4-7 times less than this. The size Amsteel loop that would fit through the G4 links is limitied.

Not sayin' this won't work, just sayin it might as well be matched with a lighter snubber.

5/16" G43 chain has a breaking strength of 11,600#, with an inside dimension of 1/2". You can easily fit a 7mm Dyneema Dux soft shackle through that, and it has a minimum breaking strength of 15,000#, which I believe would be a great deal stronger than a chain hook of any make I know of. With the 15% or so strength reduction from forming the shackle, this should match the final strength of the shackle pretty well to the chain. I use a 9mm Dyneema Dux soft shackle on 1/2" G4 and it is a good combination.

[Delfin]

Originally Posted by JonJo

There is something fundamentally wrong with that plot?

Without the snubber, and ignoring the peaks, the loads without the rubber snubber are half those with the rubber snubber. Maybe I made a mistake as I would expect the results to be the opposite, lower troughs with the rubber snubbers?

On both plots peak loads are huge - much higher than anything I would dare test and much higher than anything anyone is likely to experience on a 36' cat.

The troughs are at 1t (with the rubber snubber) and at 1t all the stretch will have already, long ago - see below, been taken up in the rubber snubber - consequently anything beyond 1t is all about the nylon (in fact beyond 270kg its all about the nylon) - so why the 2 plots are so different is something of a mystery. I tested one of these rubber snubbers and the load at maximum stretch (64%), 3 turns of supporting rope, is around 270kg. I used a chain winch to develop load and measured using a 2t load cell. I was testing in the horizontal with each end supported by 36 inch diameter reinforced concrete pillars. I was not using nylon but an old double braid halyard (I was measuring stretch of the rubber). Beyond a 270kg load - manufacturers seem to imply they expect their rubber snubbers to fail (270kg is beyond their idea of a safe working load).

Hopefully someone will explain it as it looks to me as if the rubber snubbers are having a catalytic or synergistic effect - which merits detailed evaluation.

Jonathan

It does seem to possess some miraculous properties - increasing tension at low loads and decreasing it at high loads. I wonder if you made rubber bullets out of this material whether their impact force would increase the slower the velocity?

[Delfin]

Originally Posted by JonJo

Rubber snubbers are a bit of a waste of time or money anyway in an anchor bridle/snubber combination , whether you (the yacht) are heavy or not.

If you use a small one they use up all their elasticity at low loads, you would need 5 x 1 inch rubber snubbers (from memory they are standard length around 15 inches) to absorb the same energy of a 12mm x 10m long piece of nylon cordage. If you simply use one small one they will become ineffective at higher loads - all the stretch will have gone - and its at higher loads you need the elasticity.

(To put another way - if you consider 'catenary' to be overrated then rubber snubbers (unless you use 5 of them!) fall into the same category - all the usefulness disappears at winds over, say 30 knots, probably lower.)

Bigger rubber snubbers are obviously better, have not worked out (nor intend to) energy absorption capabilities.

Rubber snubbers, even small ones, are heavy and very expensive, compared to 12mm nylon.

They are excellent when used in marina mooring environment as their elasticity is contained in such a short length and the loads when attached to a pontoon should not be great. But as part of an anchor snubber system - there are infinitely better options.

Jonathan

Jonathan, you are probably correct on the rubber snubber being essential useless since they aren't likely to do much that a bit more 3 strand will do. As you know, I'm experimenting with an Ultra rubber snubber, which is quite robust, on the Dyneema Dux pennant that leads to the plait nylon that forms my snubber. I'm curious to see how this works in terms of longevity, and have rigged it so it is inboard and easy to watch. Probably not going to add much, but it will be interesting to see if I can detect any value.

[Cotemar]

Originally Posted by Delfin

5/16" G43 chain has a breaking strength of 11,600#, with an inside dimension of 1/2". You can easily fit a 7mm Dyneema Dux soft shackle through that, and it has a minimum breaking strength of 15,000#, which I believe would be a great deal stronger than a chain hook of any make I know of. With the 15% or so strength reduction from forming the shackle, this should match the final strength of the shackle pretty well to the chain. I use a 9mm Dyneema Dux soft shackle on 1/2" G4 and it is a good combination.

I used to make this same mistake, so I just want to point it out to everyone.

When you look at the spec. on a 5/16 G4 or G43 chain you see an Inside Dim. Width.
It is not the dimension you would use to judge what diameter will fit through a link of chain.

You have to use the Inside Dim. Length – wire diameter x 2 = space between the links

So as an example on a 5/6 G43 chain you have an Inside Dim. Length (1.030”) – wire diameter (.329”) x 2 = .372 space between the links for your soft shackle.

[Delfin]

Originally Posted by Cotemar

I used to make this same mistake, so I just want to point it out to everyone.

When you look at the spec. on a 5/16 G4 or G43 chain you see an Inside Dim. Width.
It is not the dimension you would use to judge what diameter will fit through a link of chain.

You have to use the Inside Dim. Length – wire diameter x 2 = space between the links

So as an example on a 5/6 G43 chain you have an Inside Dim. Length (1.030”) – wire diameter (.329”) x 2 = .372 space between the links for your soft shackle.

Quite true. And that is why a 1/4" soft shackle with a breaking strength equal to the chain can fit quite nicely on 5/16" G4 chain. If you want to shove it a bit you can fit a 5/16" soft shackle with about 25% greater breaking strength than the chain. If you think about it for a moment, you will understand why.

[Cotemar]

Originally Posted by Delfin

Quite true. And that is why a 1/4" soft shackle with a breaking strength equal to the chain can fit quite nicely on 5/16" G4 chain. If you want to shove it a bit you can fit a 5/16" soft shackle with about 25% greater breaking strength than the chain. If you think about it for a moment, you will understand why.

A Soft Shackle made of 3/16" (.187) Amsteel blue line with 5,400 lbs tensile strength will work well also.

Even though the Amsteel line is 3/16" (.187) diameter.

When you finish the Soft Shackle it will be .340 inch finish diameter, which will allow you to slide it through the 5/6 G43 chain link, which has a .372” diameter hole space.

[Delfin]

Originally Posted by Cotemar

A Soft Shackle made of 3/16" (.187) Amsteel blue line with 5,400 lbs tensile strength will work well also.

Even though the Amsteel line is 3/16" (.187) diameter.

When you finish the Soft Shackle it will be .340 inch finish diameter, which will allow you to slide it through the 5/6 G43 chain link, which has a .372” diameter hole space.

Starting to understand why you post what you post.

I am listening to the Baylor game so don't take the time to draw a picture, but.....

In a right triangle, if a = .5, b = .372, than c must necessarily = .62. So, a soft shackle made of line that is 50% of .62 inches, a.k.a. 5/16", will fit just fine between the links of 5/16" chain, and have a breaking strength greater than the chain.

[thinwater]

Originally Posted by Cotemar

Rubber Snubbers in the Bridle Snubber just remove the shock load.
The snubber elements themselves possess a nonlinear stress-strain curve.
The Snubber reduces the expected peak shock load loads 50%

Without more information the graph cannot be interpreted or discussed. The first 5 items are mandatory. We could be comparing a snubber bridle to no bridle, which tells us very little.

• Which model snubber, 1 or 2.
• Bridle angle
• How much nylon line
• What diameter line
• Boat mass
• How much chain
• What boat
• How much wind
• How deep water

The wave period is suspicious. At about 15 seconds, NOAA tells me I would need a 50 kt gale with a 1600 mile fetch. The average wind load also suggests 60 kt winds. The range of no-snubber data strong suggests all-chain, short at that. So the boat was exposed to sustained (not squall) storm conditions in an open harbor, and someone was taking data? They switched from snubber to no snubber during the storm? Studly. I would have led with this data.



For this to be meaningful I would have to know that the no-bridle case is the same bridle with the rubber removed. Then, we would need to compare it to a longer bridle, which would be more apples-to-apples.



Is this your data, or some other source? Is there more?

[boom23]

The rubber snubber application on the bridle seems interesting and I may try it when I make a new bridle.

Just FYI, I've used the 1" rubber snubbers for my ex-powerboat (55ft) dock lines while in Hotel/Marina Coral in Ensenada, which has very strong tidal surges, and 3 out of 4 snubbers broke. What broke was the metal reinforced holes where the lines go through.

For the first couple of snubbers, I contacted the company and they sent me replacements. I did not feel right asking for a third one. I do not know if they changed the design since 2009.

I think the 1" rubber snubber can be a useful product for some situations but it could be more durable. I do not know about the other sizes.

Just personal experience...

[savoir]

It sounds like you are taking the snubbers beyond their elastic limit too often. Try one less turn of rope which will reduce the maximum stretch. That should extend the life of the snubber.

[Dockhead]

Originally Posted by Celestialsailor

I almost never back down on my chain around the gypsy. I always use the snubber to do so. Why stress it?

This has been discussed before. You need more than just the snubber to take load off the gypsy! The snubber is designed for shock absorption, not UTS! The chain should be belayed in some manner (chain lock, belaying strop) first, then back down. Only then, attach the snubber for shock absorption.

The chain belaying system should be designed to match or exceed SWL and UTS of the chain. The snubber should be tuned for the right stretch - a different design value. Both these systems are essential - shock loads can break the other parts of your ground tackle without the stretch of the snubber built in. But without a separate belaying system, the snubber will (if it is tuned right, unless it is extremely long) be a weak link in the ground tackle.