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​No.49  Rigging with Class Ⅱ Fiber

The rope that you never knew that you wanted (until I told you)

Class II refers to the material type, not the ropes construction.

Class II ropes are made in whole or part from any of the following high modulus fibers: Dyneema®, Vectran®, Technora®, and Zylon®.

Technora and Vectran were originally developed for telecommunications and are also sometimes used for winching operations.

Both these fibers are abrasive and have a tendency to wear themselves out to the point of weakening the rope.

Dyneema is a soft rope so you can safely use it for repeated rigging cycles without it wearing out.

Dyneema itself has a low melting point but when used with a protective cover in a double braid construction it becomes a super strength and incredibly light weight option for a variety of uses.

If you use a Tree Motion harness you will already be using a Class II rope (green bridge).

Its strength to weight ratio is unbelievable.

Constructed into a double braid with a polyester cover protects the lightweight, high strength dyneema core from any heat damage. 

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I became personally interested in Class II ropes after following rigging stories on the Tree Buzz forum in 2005.

At that time people were discussing ways to improve efficiency and how to choose and implement the correct tools for specific problems.

A lot of the conversation was based around using lowering devices with a marine winch (Harken).

Today marine based rope technology is stratospheric in its development and tinkering.

Even twenty years ago there were a lot of different types of rope available. 

Class II rope offer various advantages:

 

• Heaps of efficiency when winching. It stretches less so the load is pulled almost immediately.

• Less weight and stretch means that highlines and speediness need less initial input tension.

• Lightweight means less work for you when carrying into difficult (slopes)and far away work sites.

• Very low stretch ( 1.5% )

• Polyester cover protects the dyneema core from heat. It also allows it to be used in a Harken winch.

• Easily spliced. 

Those of you that have been rigging for a while with a Harken winch may have tried a variety of Class I ropes by now.

Do you have a favorite rope?

Surely your choices fall into one (or all) of the following categories.

 

• Price

• MBS

• Knotability

• Hard wearing cover / coating

• Good balance of static and dynamic nature (around 4% stretch at 20% MBS / 5:1 SWL)

 

But like me I am sure that you have found most Class I ropes to be fairly similar in nature.

I am at the point now that I simply do not care which kind of Class I rope that I use as the similarities are too close.

For any ‘dynamic rigging’ I will certainly use a Class I rope and for anything else I choose Class II. 

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It is initially startling to buy a Class II rope because the price difference makes you sweat, ¥1287 compared to ¥708 in the above example.

But please study the data a little, You can see that while the rope is more expensive you should not compare a 14mm Class II to a 14mm Class I as the MBS is vastly different.

So, we can compare a 10mm to a 14mm and still have more strength in the thinner rope, 5600kg / 5000kg.

A 10mm Class II is lighter than a 10mm Class I and vastly lighter than a 14mm Class I, 64g/M compared to 140g/M.

Low elongation is the reason to use a Class II rope, it is like wire, stretching only 1.5% compared to most Class I at 4%.

This figure may not sound like a lot but it is noticeable even when pulling the rope by hand.

Finally, the price.

Comparing a 10mm Class II to a 14mm Class I results in a price increase that I am sure you will find palatable when weighed against the benefits in efficiency, which of course have a direct consequence to efficiency at work and base line profit.

For static rigging, highline and winching jobs a Class II rope will simply earn more money than a Class I.

 

 

I would like to add one more thing, which is my opinion, but valid I hope.

We ordinarily work to a ropes Safe Working Load (SWL) and at this particular point a Class I rope stretches 4%, so must recoil the same amount.

I often find situations were the recoil is a cause for concern because it must always be managed by a human hand.

The power of recoil is so strong it can break bones.

Comparing it to a Class II, when releasing a winch for example, the recoil is noticeably absent and makes this particular aspect of rigging smoother, and in my opinion, safer.