Loads for pin kit - Mountain Buzz
 



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Old 10-12-2013   #1
 
Nelson, New Zealand
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Loads for pin kit

Hi All,

What sort of loads should I be allowing for when sizing everything for a pin kit? I already have some really nice sailing pulleys left over from a boat I did up a few years back. They have a working load of around 500kg and breaking load of 1000kg. This is much less than the 4000kg typically allowed for the Petzl pulleys that most people seem to use.

Any ideas? It would be nice not to have to buy more of them if possible.

Cheers,
Chris

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Old 10-12-2013   #2
 
Nelson, New Zealand
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Just realised that finding out the breaking load for my throw line might be a good start. Turns out it is around 1000kg so no point having a pulley any stronger.
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Old 10-12-2013   #3
 
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Originally Posted by cep32 View Post
Just realised that finding out the breaking load for my throw line might be a good start. Turns out it is around 1000kg so no point having a pulley any stronger.
Doesn't your pulley need to be 2x stronger? 1000kg tension on the rope x2. I've never seen ratings in kg. usually KN
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Old 10-12-2013   #4
 
frisco, Colorado
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don't use your throw line, get a static line instead.
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Old 10-12-2013   #5
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NRS Pro Rescue Throw Bag

Looking at the specs for NRS's top of the line throw bag I see that the 3/8inch DyneemaŽ line has a Max load rating of 5239 pounds. This is of course weekend by knots in the line but it's still plenty beefy stuff. Dyneema and Spectra are Ultra-high-molecular-weight polyethylene (UHMWPE, UHMW) a subset of the thermoplastic polyethylene. It is strength to weight ratio higher than steel. It's density is .75 so it floats. It is a static rope not dynamic so it is well suited for mechanical advantage systems.(It won't stretch) If you are using it to unwrap a raft and you have several strong men pulling on the Z drag you will be glad you are using pulleys that are rated for this kind of force. Don't forget to tie a PFD in the middle of the line to dampen the snap if something in the system lets go.
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Old 10-12-2013   #6
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I've always assumed the prussic grip was the weakest link part of the system. Get appropriately sized prussic cord and if it starts slipping try something different. Kayak pins are a lot easier to pull though...
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Old 10-12-2013   #7
 
SYOTR, Tennessee
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I've always assumed the prussic grip was the weakest link part of the system. Get appropriately sized prussic cord and if it starts slipping try something different. Kayak pins are a lot easier to pull though...

This is correct. If using a traditional mechanical advantage system a prussic on a wet rope will slip first.
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Old 10-12-2013   #8
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Don't forget that the mechanical advantage will multiply the force on the line depending on how it's rigged. Could be 12:1 with two pulleys. Don't forget the PFD tied to the middle of the line in case something gives.
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Old 10-12-2013   #9
 
Searching for water....., Idaho
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Don't forget that the mechanical advantage will multiply the force on the line depending on how it's rigged. Could be 12:1 with two pulleys. Don't forget the PFD tied to the middle of the line in case something gives.
How do you get 12:1 with just two pulleys? Without using other directional changes like a bare carabiner?

I thought the 4:1 was the most bang for your buck with using just two prussiks and two pulleys.

On subject, OP, I would get the right gear. If you do need it you will be glad you have the strength and matched gear for the job.
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Old 10-12-2013   #10
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My bad! I had to look it up in RIVER RESCUE page 199. You can get 9:1 with two pulleys and two carabiners at the anchor points. This also requires two ropes. The "Z" rig works with only one rope and two pulleys or carabiners creating a 3:1 advantage. Still a lot of force. Enough force to damage the boat if not applied correctly. If I were a kayaker I wouldn't bother with pulleys. I'd just use biners and prussics. In my kit I carry a Petzl Rescucender: rescueDIRECT I also have an NRS throw bag and two lengths of blue water static line. One is 60 feet and one is 20 feet. I also carry extra biners and a Rescue 8 and a number of lengths of webbing to make anchors. Probably over kill but what the heck.

Should also mention that Avitard was correct that the pulley takes twice the load of the rope.
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