9mm or 10mm SRT rope
- Thread starter Oscar D
- Start date
andrewmcleod
Well-known member
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.
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.
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.
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.
andrewmcleod
Well-known member
Ian Ball said:
I would very much agree!
Bob Mehew
Well-known member
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.)andrewmc said:
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.
