Advice on choosing an intermediate kite.

[knotwindy]

Again, thank you for adding your wisdom to the thread.....

[iriejohn]

To get back on topic, here is what Paul Dyer, Technical Manager at Marlow Ropes (a major rope manufacturer in the UK), had to say on the subject of shrinking Dyneema ropes. For the sake of completeness I've posted what he said in its entirety.

https://www.marlowropes.com/

We produce hundreds of thousands of metres of D12 type rope each year and the feedback for 99% of it is good. However we have have had rare reports like this one spanning perhaps 10 years, only 2-3 per year though. With such few reports it's difficult to pin down exactly what's happening. These reports cover several different industry areas and applications, D12 and D12 MAX, covered and uncovered ropes. We've never found a fault in the material or the construction suggesting that this shrinkage is due to the environment in which the rope is used/stored. The common factor appears to be that the ropes reduce in length while in an unloaded condition rather than when in use or even when new. What we can definitly say is:
-All the ropes are made from DSM Dyneema fibre, either SK75 or SK78.
-This phenomenon has been reported on both D12 and D12 MAX which undergo different stretching conditions.
-Dyneema does not shrink in water like some other fibres.
-Dyneema will shrink if it gets hot when under no tension.

As this can affect both D12 and D12 MAX I don't think the stretching process we put the rope through here at the factory is the cause. Some of the ropes have not been used until months after stretching so residual 'shrink back' is unlikely. We've also not seen this occur with rope in our factory.

DSM Dyneema (the fibre producer) have been informed of this in the past and heat is the only explanation they've been able to offer.

Therefore the most likely cause and the only one we've been able to re-produce in the factory here is that the ropes have been exposed to elevated temperatures while they are stored, the sort of temperatures required would be possible if they were in a mast in the sun for instance. Unfortunately this can only really be proved or disproved by feedback from people who have seen this issue and can report on the conditions the rope was under when it happened. Until then it just remains the leading theory. I also see from the previous post that it's happened to the Chinese UHPME fibre as well So it's not just us!

BTW: For the record: EB's Dynamic range is made from exactly the same fibres and has very similar construction and stretching process as the D12 so is unlikely to behave any differently in this respect

Sorry about the long post, hopefully it's helpful!

My highlights

[LetsFlyaKite]

Nope, that's not right either.

Everyone knows that front lines stretch, and when this happens the rear lines will be shorter. Not because they have shrunk, but because it gives the false illusion that they have shrunk as you can tell from the few on this thread that think their lines are shrinking.

Lines don't stretch and shrink like a rubber band, they only stretch. When you pull on any line with a substantial amount of weight they will stretch, that's why you want to stretch your back lines out from time to time.

This is why most people on this thread are so confused, because the longer front lines have thrown them off making them think their rear lines are shrinking.

[jeromeL]

At least everyone agree that you need to shorten power line or elongate steering line to fix issue
Common sense would say that power line stretch, the idea that you can have steering line stretch as symetrically due to kitelooping only on one side sounds weird but if someone makes a study and show number I would believe it.
Anyway at the end of the day it doesn't matter.

One thing though is that clothes do shrink after a while

[tavis]

I test flew a Union and then decided to buy a 2017 Lithium because if it ain't broke, don't fix it.

[kitesurfing2000]

I would definitely choose a North Rebel, super easy, stable, a bit slow but very predictable, huge range and forgiving when you try new tricks. The hang time helps for soft landing even if something went wrong during the process. It handle gusts as any other kite I tried. In Costa Rica we have strong and gusty wind but I don't worry with this kite!

[Kamikuza]

Nope, that's not right either.

Everyone knows that front lines stretch, and when this happens the rear lines will be shorter. Not because they have shrunk, but because it gives the false illusion that they have shrunk as you can tell from the few on this thread that think their lines are shrinking.

Lines don't stretch and shrink like a rubber band, they only stretch. When you pull on any line with a substantial amount of weight they will stretch, that's why you want to stretch your back lines out from time to time.

This is why most people on this thread are so confused, because the longer front lines have thrown them off making them think their rear lines are shrinking.

Troll knows best. Stupid Technical Manager, what does he know?

[Kamikuza]

To get back on topic, here is what Paul Dyer, Technical Manager at Marlow Ropes (a major rope manufacturer in the UK), had to say on the subject of shrinking Dyneema ropes. For the sake of completeness I've posted what he said in its entirety.

https://www.marlowropes.com/

We produce hundreds of thousands of metres of D12 type rope each year and the feedback for 99% of it is good. However we have have had rare reports like this one spanning perhaps 10 years, only 2-3 per year though. With such few reports it's difficult to pin down exactly what's happening. These reports cover several different industry areas and applications, D12 and D12 MAX, covered and uncovered ropes. We've never found a fault in the material or the construction suggesting that this shrinkage is due to the environment in which the rope is used/stored. The common factor appears to be that the ropes reduce in length while in an unloaded condition rather than when in use or even when new. What we can definitly say is:
-All the ropes are made from DSM Dyneema fibre, either SK75 or SK78.
-This phenomenon has been reported on both D12 and D12 MAX which undergo different stretching conditions.
-Dyneema does not shrink in water like some other fibres.
-Dyneema will shrink if it gets hot when under no tension.

As this can affect both D12 and D12 MAX I don't think the stretching process we put the rope through here at the factory is the cause. Some of the ropes have not been used until months after stretching so residual 'shrink back' is unlikely. We've also not seen this occur with rope in our factory.

DSM Dyneema (the fibre producer) have been informed of this in the past and heat is the only explanation they've been able to offer.

Therefore the most likely cause and the only one we've been able to re-produce in the factory here is that the ropes have been exposed to elevated temperatures while they are stored, the sort of temperatures required would be possible if they were in a mast in the sun for instance. Unfortunately this can only really be proved or disproved by feedback from people who have seen this issue and can report on the conditions the rope was under when it happened. Until then it just remains the leading theory. I also see from the previous post that it's happened to the Chinese UHPME fibre as well So it's not just us!

BTW: For the record: EB's Dynamic range is made from exactly the same fibres and has very similar construction and stretching process as the D12 so is unlikely to behave any differently in this respect

Sorry about the long post, hopefully it's helpful!

My highlights

How hot? Like, sitting in the back of the car hot?

[Brin]

Kinda OT, but info for those that are interested....

Thinking about line shrinkage....from my days, some time ago (!) as a synthetic yarn consultant, ALL synthetic fibres have the capacity to shrink when heated....as individual yarns or as components of a manufactured (woven, braided, knitted, whatever) cord, fabric or other stuff

the part of the manufacturing process that hopefully stops this being an issue is called heat setting; when made, most industrial yarns are stretched (tensioned) and oriented to a particular level , then heated very carefully and specifically to lock in dimensional stability at that temperature...

It is possible to buy unoriented, non heat set yarns...these are used by specialist cordage makers to produce their own variety of cordage with their own tech ....without having to build a yarn extrusion plant.....

But for the most part, yarns are heat set at manufacture...there is some customisation possible if you buy enough!

Heat setting is important for, for example, in yarns used to make seatblets....imagine if you have a stretchy seatbelt!

also important in ropes.....you don't want, in most cases , ropes to stretch too much (or too little in some cases....that's why climbing rope is generally not prestretched heat set polyester.....you want a climbing rope to be dynamic and stretch a bit if you fall!))

Its a fact that the factory heat setting can be 'undone' or modified by further exposure to a HIGHER temperature than the factory heat setting...thermoplastics have a weird 'memory effect' ,


Dynema is UHMWHDPE...what a mouthful...ultra high molecular weight high density polyethylene.......highly oriented polythene with very high linear strength properties...

and..........

being polyethylene, its not that resistant to heat..... it gets soft way lower than polyester......so it does limit the ability of manufacturers to heat set at (higher) temperatures which offer maximum stability

I guess if the bar was sitting in the sun on the black dashboard of your car, you might get high temperatures that may affect the lines...have to be approaching 90C or above......

someone could apply for funding to check this and publish their PhD thesis on it.....might already be out there.....