Rubber (tyre) snubber : to stretch or squeeze?

[Slocumotion]

I had always assumed that you would put a couple of turns of chain around opposite sides of your tyre with some slack between so that snatches would be absorbed in stretching the tyre, but a recent post suggests a few turns in line so the effect would be more of a squeeze. So which is it?

 

[Slocumotion]

Forgive me for bumping this up the list , but I didn't see it appear in the first place (possibly because I attempted to post while I was in new-user limbo)

 

[prv]

Not sure I understand how the squeeze approach would work. Like you I've always assumed it would be a stretch (never actually needed to do either).

Pete

 

[Mistroma]

I'm puzzled as well, not quite sure how it would be tied. If you pull opposite sides together it sounds as if will be unstable. Stretching sound like an easier way to get a stable system.

Can you explain?

Assuming I'm understanding the question, effort to change the shape by stretching or compressing would probably be roughly similar for initial deformation. However, I imagine that effort to squash a compressed tyre would be much greater than effort to stretch it. Perhaps someone else can do better than my guesswork.

 

[Slocumotion]

I'll try again:
System 1 A round turn of chain round one side of the tyre - a bit of slack across the centre of the tyre then another round turn. Perhaps with some wiring to keep the turns where they are. When the pull comes it's trying to pull the whole tyre into an oval.
System 2 A couple of round turns together. The pull now is squeezing the side walls together in the one place. I imagine the turns would just get cinched up tight and not relax between tugs.
(How I wish I could do diagrams)

 

[Mistroma]

Much clearer now, thanks. I'd been imagining wierd ways of tying the chain in order to compress the whole tyre. I can't see "System 2" being much use as it is only compressing one small section of the tyre. I've seen "System 1" and it does look as if it gives a lot of damping and loads would be huge before it allowed sudden snatching.

Never seen "System 2" in use. My vote (worth every penny you paid me for it) goes to "System 1".

 

[NormanS]

I'll try again:
System 1 A round turn of chain round one side of the tyre - a bit of slack across the centre of the tyre then another round turn. Perhaps with some wiring to keep the turns where they are. When the pull comes it's trying to pull the whole tyre into an oval.
System 2 A couple of round turns together. The pull now is squeezing the side walls together in the one place. I imagine the turns would just get cinched up tight and not relax between tugs.
(How I wish I could do diagrams)

You won't keep any slack "across the centre" unless you use shackles.

 

[oldbilbo]

System 2 A couple of round turns together.

I've used what you describe as 'System 2' on several occasions, and over an extended period of some winter months, completely successfully and at no cost. The 'system' emulates that used by the commercial 'Rubber Snubber' seen below - which is intended for rope - and winds chain around one segment of the tyre perhaps 4-6 times. This reduces shock loads on the boat's gear and fittings considerably when the vessel 'snubbed' hard, hour after hour, in short, gale-driven choppy seas.

One had imagined that the tyre would be shredded, but that did not happen, and the boat stayed safely moored this way a full winter. Once I'd experienced a stormy night on board, with no chafe or other damage to the boat and her normal twin mooring warps - which were left slightly slack and unloaded - I was able to leave the boat to look after herself subsequently, without worry.

It's a very low-cost but effective 'belt and braces' for boats left on moorings.

 

[Slocumotion]

Yes, I see your point Norman . Perhaps threading the chain through tight holes on opposite tread faces with a couple of shackles inside to maintain the slack would be better than stitching chain to tyre with wire.
Oldbilbo - I intend to report you to the Administrators for entering, uninvited, a forum discussion with the unfair advantage of practical experience (Smiley needed here )
Looking at your pic though, isn't it the case that with the commercial job , there is no stretch going on at all, it's all squeeze (and I can't imagine the huge force that would be required to compress to any useful extent , that centre rod of rubber) .Wouldn't it work better if there were a hitch at either end and slack turns to make for some stretching?
As an aside - where would you put a tyre-type snubber in relation to boat, float and clump?

 

[oldbilbo]

Looking at your pic though, isn't it the case that with the commercial job , there is no stretch going on at all, it's all squeeze. Wouldn't it work better if there were a hitch at either end and slack turns to make for some stretching?

As an aside - where would you put a tyre-type snubber in relation to boat, float and clump?

From the evidence of my own eyes ( one has to take a view on the reliability of that ), and AIR the manufacturers' instructions, the Rubber Snubber becomes stretched elastically under load, with the 'extra' length of rope integral to the several spiral turns effectively extending the length of the mooring line. This absorbs considerable energy. The Rubber Snubber then contracts, using the stored elastic energy to recover the 'system' to the original condition. The mechanism is explained here: http://en.wikipedia.org/wiki/Elastic_energy. If there is an element of 'squeeze', it is inconsequential.

As for positioning a tyre-type snubber.... I had it mid-way between the boat's bow fairlead and the mooring buoy. The boat was already moored using twin warps, so I did the spiral-winding of chain on the foredeck, hung one end over the bows, then got into the dinghy to complete the attachment to the buoy. I had about 4-5 metres distance between bow and buoy to work with. Should there be perhaps half that distance available, then it might be less satisfactory.

 

[NormanS]

I seldom lie alongside anything, but on one particular occasion, I lay alongside the pontoons at Tobermory in weather when it was not the place to be. The only reason I was there was because of an inoperative starter motor, so had little choice. The boat was snatching at her lines, so I went up the street and aquired two old car tyres. The springs, being slightly longer, were alright, but the head and stern ropes, being short, were snatching.

On each tyre, I tied one line from the boat, and one from the pontoon, so that tension on the lines was trying to pull the circular tyre into a straight line. The difference was excellent, but it certainly didn't look very "yachty".
I have used the same system when towing another boat in rough conditions, where I am sure it helped.

I now have two lines made up with rubber snubbers, as shown by oldbilbo, and they work very well.

 

[Zagato]

I have also been researching snubbers for mooring.. (the Mobo's create the biggest waves on my mooring! ). A small car tyre (some use scooter tyres) with the rope simply threaded through and around one side of the tyre is the best arrangement (as per Oldbilbos snubber pic but with tyre!) it squeezes the sidewall and tries to pull it straight at the same time. It doesn't have to be tied separately at either end, it's doing less of a job that way.

 

[Slocumotion]

It becomes clearer! With the tyre rigged as per diagram you take advantage of ,first, pinching in the sidewall, second pulling out the whole tyre round to oval, and third in extremis, gripping a section of tyre with the tightened turns and stretching it.
Does it really do all that though - or does it just hang on the chain, part filled with water and act as an "angel" ?

 

[Giblets]

Thanks for the pic, Zagato. All is now clear.

 

[oldbilbo]

A small car tyre (some use scooter tyres) with the rope simply threaded through and around one side of the tyre is the best arrangement (as per Oldbilbos snubber pic but with tyre!)

'Zackly!

Go try it. No cost. Not rokkitsciense...