9mm or 10mm SRT rope

[ObviousSpectre]

I am looking to buy a 100m of rope to start SRT with and was wondering which diameter to get. I know there are similar threads on the forum but most are about 10mm vs 10.5mm or are quite old. Thanks.

[Canary]

I would use 10.5mm if it is going to get hammered by novices, as it doesn't stretch as much making easier prussiking. For personal use, i would go for 9mm.

I think on the whole 9mm is better as it is usually cheaper, lighter and packs down smaller. I don't think there is much difference in how they wear (i.e. they probably have similar sheath thicknesses, so assuming you bin/cut them if you start to see core).

BW

Can

[Fulk]

Here are a few thoughts.

Maybe you could start by listing the pros and cons of each:

9 mm
Pros: Lighter, packs into tackle bags more easily, cheaper, easier to climb, absorbs less water

Cons: Less resistant to abrasion if badly rigged or something goes wrong with the rigging, probably less resistant to damage by grit getting in between the fibres, can be a bit scary when ‘shiny’ and new/dry as descent can be less easy to control (depending on type of descender), knots can be more difficult to untie

10–11 mm: Opposite of above

No doubt others will think of other pros and cons.

My wife and I found that the biggest advantage of 9 mm is that it makes it possible for us to do trips where we’d have struggled to carry the rope – not so much the weight, more the number of bags needed to carry it – using 10 mm.

I guess ultimately it’s down to personal preference – for what it’s worth, most of our rope is 9 mm, but we find that a length of ‘chunky’ 10–11 mm Marlow is great for places like Lancaster Hole where the rope will almost certainly get covered in mud, which will get ground into it (to some extent).

It’s perhaps also worth considering who’s likely to use your rope – if you’re confident of your pals’ ability, then 9 mm, but if it’s likely to be used (and possibly abused) by novices, then thicker rope might be a better bet. (I posted this as the above was being posted, hence the overlap.)

I notice that Canary states that thicker rope is easier to climb, when I said just the opposite; to clarify what I meant, I find that jammers run more readily on thinner rope (especially when it gets mucky) than on thicker rope, and it's easier to get started, but I accept what Canary says about stretch.

[Ian Ball]

Are you considering Type A and B?  If money were no object I would buy the Type A 9mm.

[ObviousSpectre]

Thanks for the replies Fulk and Canary. I didn't think that their would be much of a difference in pack space, but it seems as though I was wrong. I like to carry as little as is needed so that another point in favor of the 9mm. I also didn't consider water absorbency.

[ObviousSpectre]

Are you considering Type A and B?  If money were no object I would buy the Type A 9mm.

I'm not too concerned about A or B as I'm sure that B should be fine for what I plan to use it for.

[Ian Ball]

I've not bought a 10mm rope since 2006

[Fulk]

Here's a funny thing about packing rope – 100 m of 10 mm rope has a volume of ~7.8 litres, but you'll need a 35- or 40-l bag to get it in.

[ObviousSpectre]

Looks like its going to be 9mm then    Thanks all for the advice.

[Fulk]

Hi OS, if you're buying rope for the first time you need to be aware that when it gets wet and dries out, it can shrink by a fair amount.

If you soak it and allow it to dry it may shrink by anything up to 5 or 6%, but it will continue to shrink with use.

I've just checked some data on our ropes, and the maximum shrinkage I seem to have recorded is 13/2% – so you'll need to allow for this when cutting it to what you think are appropriate lenghths.

[ObviousSpectre]

Hi OS, if you're buying rope for the first time you need to be aware that when it gets wet and dries out, it can shrink by a fair amount.

If you soak it and allow it to dry it may shrink by anything up to 5 or 6%, but it will continue to shrink with use.

I've just checked some data on our ropes, and the maximum shrinkage I seem to have recorded is 13/2% – so you'll need to allow for this when cutting it to what you think are appropriate lenghths.

Will do   

[Leclused]

Hi OS, if you're buying rope for the first time you need to be aware that when it gets wet and dries out, it can shrink by a fair amount.

If you soak it and allow it to dry it may shrink by anything up to 5 or 6%, but it will continue to shrink with use.

I've just checked some data on our ropes, and the maximum shrinkage I seem to have recorded is 13/2% – so you'll need to allow for this when cutting it to what you think are appropriate lenghths.

When my clubs buys rope (on 200m rolls)  I ALWAYS dump the rope in the bathtub for a while (approx 2 days) before cutting the rope.

If you cut an unwashed rope and mark the length of it on a label on the rope  then you end up with ropes that are shorter then mentioned on the label

This can cause problems when somebody grabs a rope that says 40m but in reality it is only 35m due the shrink.

On average a shrink percentage of 10% is common.

[MJenkinson]

I also like to run new rope through a descender as it seems to squeeze a lot of the manufacturing lube (???) out of the rope and can make it a "little" less speedy on descent.  I usually then soak it again, dry it and then measure / cut.

[Leclused]

I also like to run new rope through a descender as it seems to squeeze a lot of the manufacturing lube (???) out of the rope and can make it a "little" less speedy on descent.  I usually then soak it again, dry it and then measure / cut.

So the work method would be.

- Soak the rope
- Pull the WET rope through a descender
- Soak again
- Let it dry
- Measure / cut / label the robe
- ... go caving ....

I think I'm going to take over the pull through descender step the next time a new roll comes in.

[ObviousSpectre]

I also like to run new rope through a descender as it seems to squeeze a lot of the manufacturing lube (???) out of the rope and can make it a "little" less speedy on descent.  I usually then soak it again, dry it and then measure / cut.

So the work method would be

- Soak the rope
- Pull the WET rope through a descender
- Soak again
- Let it dry
- Measure / cut / label the robe
- ... go caving ....

I think I'm going to take over the pull through descender step the next time a new roll comes in.

Will do 

[Ian Ball]

The silicon you are trying to get rid of in a rope takes many many rinses to get rid of if you are wanting non-milky water to come out of the rope.

[Simon Wilson]

The silicon you are trying to get rid of in a rope takes many many rinses to get rid of if you are wanting non-milky water to come out of the rope.

I put new rope in the washing machine. A long cool wash, no detergent, no spin.

If you get a 200m reel it won't fit in without cramming it in. To get it in loose cut it into half and do two washes.

Allowing for 10% eventual shrinkage you will end up with two ropes around 90m which is neat to cut into 60 + 30 and 50 + 40.

[Fulk]

I find that spinning rope on the lowest setting (400 rpm for our machine) works fine – it makes unloading it so much less messy.

[andrewmc]

I cut ropes based on 10-15% shrinkage from the dry rope - so I measure it before I soak it. It might shrink 5% when you soak it after purchase but it can easily shrink more in use, so even if you soak then measure you should still leave a bit spare.

I wouldn't want Class A 9mm rope - to make it class A it has to withstand more force in a drop test so it is likely to have more core and less sheath, while I want more sheath for abrasion and the rope is plenty strong enough.

[Fulk]

andrewmc:

I wouldn't want Class A 9mm rope - to make it class A it has to withstand more force in a drop test so it is likely to have more core and less sheath, while I want more sheath for abrasion and the rope is plenty strong enough.

These are interesting points you make, Andrew; can you back up your ideas with any real evidence? Of all the rope types we have, my favourite is 9 mm Gleistein, which is Class A (mind you, it looks quite thick for 9 mm, and certainly appears to be thicker than our red Beal 9 mm).

[Ian Ball]

Gleistein is superb rope.  I'm intrigued, do you use a 9mm Type B because you regard it as more abrasion resistant than a 9mm Type A? Or do you prefer 10mm Type A rope to all 9mm?

[andrewmc]

Other than that video where a guy repeatedly pulled loaded ropes over an edge until they failed (with the class B rope lasting very slightly longer than the class A rope), no I can't.

BUT on the 'other side' (i.e. climbing) it is absolutely standard that a thin single rope will have less abrasion resistance than a thinner half rope, as to pass the fall tests for a single rope they need a certain amount of core (nylon is nylon, after all) so they have less sheath - while a half rope needs less core and can have a higher sheath fraction.

My Mammut Genesis 8.5mm half ropes are 49% sheath.
Mammut Serenity 8.7mm single rope is only 38% sheath.
Edelrid Corbie 8.6mm single rope is only 29% sheath.

Different ropes will vary, but there will always be a sheath/core compromise. It may be there is actually little variation in static ropes though; I don't know.

[Ian Ball]

I think you are referring to Tor Paulins (FCSO) video, top bloke is Tor.

I would suggest that a statistically significant result can't be found from 1 test.  There is also wet v dry to consider and age/usage.

As a consideration,  percentage of mass made up by core to sheath is something I haven't seen as important, if it's sold as a type A or type B is more important to me as I know what criteria it has had to pass to achieve that grade.

Percentage wise, would a higher percentage of total rope mass made up by the sheath for 9mm simply be a thinner core, but exactly the same sheath construction as a 10mm so abrasion resistance would be near enough equal?

climbing ropes Ive not got a clue.  It's only 65 years since Edelrid invented the kernmantel rope so I guess we are still learning.

The abrasion resistance Ive always regarded as rubbish and so treat your rope with much respect and you will be alright.

[andrewmc]

I would suggest that a statistically significant result can't be found from 1 test.

I would very much agree!

[Bob Mehew]

Different ropes will vary, but there will always be a sheath/core compromise. It may be there is actually little variation in static ropes though; I don't know.

Slightly off topic but EN 1891:1998 specifies two constraints on sheath and core mass.  The minimum percentage of sheath mass must be greater than 100*(4D-4)/D*D%.  That in turn means the maximum core mass is 100 - 100*(4D-4)/D*D% for both Type A and B ropes.  Then for Type A ropes the standard specifies the minimum core mass as 100*48/D*D% and for Type B ropes 100*40/D*D%.  If you do the maths, you find that you cannot get a Type A rope of a diameter smaller than 8.9mm.  Perhaps of more significance is that for a  Type B rope, the sheath mass must be between 42% & 45% for 8.5mm diameter and 40% and 51% for 9mm.  (I have not looked into the Amercian standards.)

I accept for caving having sufficient sheath to protect against rubbing is important but the indications from some bitter expereinces out there are that sheath rub will work it's way through any sheath remarkably quickly.  I fear that extra sheath thickness (and hence extra sheath mass) has minimal impact on the rub resistance of a rope.   

I would add that the standard also specifies that the static strength (slow pull) of a Type A rope without terminations (knots) should be at least 22kN as opposed to 18kN for Type B ropes and 15kN for Type A ropes with terminations (be that knots or some other means) and 12kN for Type B ropes.  The standard's approach to dynamic strength is not a useful parameter to cite for a fall situation.

My hypothesis is that a kernmantle rope gains its strength for weight per unit length due to the sheath compressing the core and hence allowing the cord within the core to better share the load.  I had not looked at sheath v core for dynamic ropes but the values Andrewmc cites appear to reflect that.