Sizing Dynice SK75 for standing rigging.

[GILow]

Hi all,

I’m putting together the materials for the new synthetic standing rigging and I’ve hit a speed bump on the first day.

I have been referring to the Equivalent Stretch Sizing Chart from Colligo Marine, and their recommendation is for 13 mm Dux to replace my 10 mm stays. But the material that seems most recommended for the job, Dynice SK75 from Hampidjan straddles that size.

I phoned them and they tell me the stretch is so low in the SK75 that I can use like for like size.

Is this now the case?

This is for a pretty conservatively rigged Kelly Peterson 44. Definitely a cruiser, not a racer.

Matt

[GILow]

It’s ok, I just figured it out I think.

Turns out their naming conventions are a bit odd. They do the Dynice DUX in 13 mm, which allows me to follow Colligo’s recommendations.

Not sure why the guy in the Australian office didn’t mention the Dux version?

Matt

[Benz]

Originally Posted by GILow

It’s ok, I just figured it out I think.

Turns out their naming conventions are a bit odd. They do the Dynice DUX in 13 mm, which allows me to follow Colligo’s recommendations.

Not sure why the guy in the Australian office didn’t mention the Dux version?

Matt

You have just encountered one of the oddities of rope that makes one tear his hair out: the inconsistency of rope measurement. One would think that a 5/16" rope would not only fit through a 5/16" hole, but be the same diameter as every other 5/16" rope from other manufacturers. But it is not so; I have what is called 6mm rope from two different manufacturers, and one is 30% larger than the other!
Part of it is that manufacturers cram more fibers into a nominal rope size so it rates stronger, then everyone thinks their offering is better than the other guys'.
With DUX, MAX, and other pre-stretched options, it gets worse, since 13mm DUX is made by taking 14mm SK75 and stretching it while applying heat. This compacts the fibers, packing them together super-tightly to get more material into a smaller diameter. I have 7mm DM20 MAX from Marlow that measures closer to 9mm. This becomes a problem when trying to assemble a system with thimbles or low-friction rings, and you're counting on the sizes being as published.
If you get all your supplies from Colligo, then their hardware will match the line diameter, so it won't be a problem. If you're matching other hardware, get the rope first, then take measurements from it.

[s/v Jedi]

The heat setting is not done to make it appear smaller and stronger. It is done to eliminate constructional elongation, or at least for the part that is not disturbed by splicing.

I’m not sure if it reduces creep but I think not. Creep is dealt with by oversizing, i.e. you don’t size for strength but for creep.

[Benz]

Originally Posted by s/v Jedi

The heat setting is not done to make it appear smaller and stronger. It is done to eliminate constructional elongation, or at least for the part that is not disturbed by splicing.

I’m not sure if it reduces creep but I think not. Creep is dealt with by oversizing, i.e. you don’t size for strength but for creep.

I agree that the heat-setting is not done for appearances: it is simply a fact that when heat-set under tension, a 14mm line becomes a 13mm line. When you splice it, the splice fattens up more than plain line because there's more material packed in.
The fact still remains that diameters are often merely nominal and not consistent across manufacturers.
One of the purposes of heat-setting, as well as eliminating constructional elongation, WAS to mitigate creep somewhat. That it didn't work as successfully as was hoped is why they developed DM20. Jury is still out on creep with that.