6kn nut strength

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whitelion
Posts: 7
Joined: Mon Nov 02, 2009 8:49 pm
Location: Cape Town

6kn nut strength

Postby whitelion » Mon Nov 02, 2009 9:03 pm

hi u guys

2 questions please

can i fall on a 6kn nut/stopper - eg number 4 & 5 size BD nut
if properly placed?

say i lead 2 - 3 meters out and then take a fall.
would the rock break (considering its a very small crack) or the equipment

question 2 -

why is the left (east, left of plattekloof gorge) side of table mountain not very popular for climbing
i never hear of ppl climbing there.
yet the faces do look clean from down below - base of platteklip gorge


many thanks
vernon

shorti
Posts: 706
Joined: Mon Nov 19, 2007 3:13 pm

Re: 6kn nut strength

Postby shorti » Mon Nov 02, 2009 11:01 pm

Yes it should be strong enough. The problem with small nuts are the small surface area that increases the load on the rock. The rock is more likely to break than the nut. Only a tiny bit needs to break out for the nut to fail. If the rock is solid and the placement is good, you should be fine. It goes without saying that you want to be sure you are save. So to give yourself a better change you can do many things, some depend on you, some depend on your belayer and some on gear. With small nuts you want to try placing them deep and spreading the load on as much as possible surface area. Also try to place more than one and if possible equalize them. You also want a belayer that can give you a soft catch. There are lots of other things to reduce the load, but I think you should worry more about the placement, quality of rock and you and your belayer's skill rather than the strength of the nut. Watch E11 (the movie about Dave MaCloud's route called Rhapsody) to see what those small nuts can take (and what not). All being said, I often wondered why BD's small stoppers seem to be inferior to Wild Country in the strength rating department. I like them both though.

mokganjetsi
Posts: 1263
Joined: Fri Dec 15, 2006 12:32 pm
Real Name: Willem Boshoff
Location: Cape Town

Re: 6kn nut strength

Postby mokganjetsi » Tue Nov 03, 2009 7:27 am

most new half ropes have a maximum impact force of below 6kn so its actually not possible the exceed the 6kn impact rating of the nut (and the 6kn nut rating is probably conservative).
as shorti said, gear is only as good as the placement. ask him about the 50-foot cam-popping whipper at tafelberg....

Nic Le Maitre
Posts: 878
Joined: Mon Apr 02, 2007 9:40 am
Real Name: Nic Le Maitre
Location: Stellenbosch

Re: 6kn nut strength

Postby Nic Le Maitre » Tue Nov 03, 2009 10:56 am

Hi

The rock will break before the nut does, you will struggle to exceed 6kN of force

If you weigh 70kgs and you are 3m above the nut with 10m of rope out from your belayer and you fall then:

The speed that you are falling at is:

Final velocity squared = intial velocity squared + 2 x acceleration x distance
V squared = 0 + 2 x 10 x 6 (The rope begins to stop you after you have fallen 6m)
V squared = 120 m2/s2
V = root of (120)
V = ~11m/s

The rope you are falling on is a dynamic rope and will stretch about 30% of the length between you and your belayer

30% of 13m = ~4m

In order to stop you, you must come to a halt in 4m from a velocity of 11m/s, and now we need to know your deacceleration
Final velocity squared = intial velocity squared + 2 x acceleration x distance
0 = 120 + 2 x a x 4
0 = 120 + 8a
-120/8 = a
a = -15 m/s squared

To create this deacceleration a force was required

Force = mass x acceleration
Force = 70 x -15
Force = -1050 N or -1.05kN (don't worry about the minus sign, it merely implies that the force was acting in the opposite direction to your fall, i.e. upwards)

So in order to stop you, a force of 1.05kN was exerted on the nut, about 1/6th of its breaking strain.

As to the second part of your question, there are routes on the faces closer to platteklip, the routes on the ledge are better and cleaner. The old MCSA journals have route descriptions
Happy climbing
Nic

whitelion
Posts: 7
Joined: Mon Nov 02, 2009 8:49 pm
Location: Cape Town

Re: 6kn nut strength

Postby whitelion » Tue Nov 03, 2009 12:44 pm

thanks very much guys for the input :pirat:


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