My Hurricane Mathew rope experiment

[Clever screen name]

What we are going to do is on my buddies sailboat down the end in the wide slip is put a thin length of rope from the bow to the dock shorter then the heavy ones and see if it breaks. If it does of course the fat ones going to that heavy piling will still be there.
1/4" 3-Strand Nylon
1,490 Lb. Breaking Strength


I guess that boat is like a 40 footer and my weather here in Tampa bay so far is saying 31 mph winds tomorrow.


When rope says 16% stretch does that mean 17 % is broken ? Thats what I think.


So measure and make it about 20 % shorter ? That is the plan.



Will it or wont it break, any bets ????


I can pull 150 lbs in the gym so I know in that wind from the last tropical storm was tugging way over 150 but was it pulling 1,490 lbs ? I have no idea.

 

[Clever screen name]

That would be funny if a 1/4 inch line held up and we are all bugging out hoping our webs of 5/8 are good enough for this one.

 

[shrew]

Lines snap most commonly due to shock-loading, combined with other factors, such as:

1) They are old and no longer have elasticity left in them. Nylon lines have a duty cycle and won't stretch and rebound forever, they will eventually stretch and become static lines.

2) Chaffing

3) Undersized for load. Lines sized for normal use may be inadequate for storm conditions. Doubling lines helps. In storms I had 16 lines on my boat at a minimum. The secondary line was tied slightly longer than the first line. The second line comes on tension about 50% into the stretch of the primary line. This reduces shock load on the first line and when enough force is used, both lines are holding in together.

I've seen large lines snap on boats in storms. I've seen chocks and rail stanchions ripped out. I've seen cleats ripped out (commonly due to lateral loading such as with breast lines, which is the weakest direction for a cleat to hold).

 

[Clever screen name]

I don't have enough wind here to do the experiment. The boat is pointed right into it .


I also have at least 16 lines out , looks like a spider came to eat this boat.


The toughest known spider silk is produced by the species Darwin's bark spider (Caerostris darwini): "The toughness of forcibly silked fibers averages 350 MJ/m[SUP]3[/SUP], with some samples reaching 520 MJ/m[SUP]3[/SUP]. Thus, C. darwini silk is more than twice as tough as any previously described silk, and over 10 times tougher than Kevlar" - WIKI

Spider dragline silk possesses high toughness―the ability to absorb energy before breaking―due to an unusual combination of high tensile strength and elasticity. These properties are typically negatively coupled in synthetic polymers such that spider silk outperforms even high energy absorbing polymers such as Kevlar by ∼300% in terms of toughness.


It attaches the web to substrates on each riverbank by anchor threads as long as 25 meters. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2939878/

 

[Clever screen name]

We are yet to be able to fully understand how spider silk is made. An attempt at commercialisation through "spider goats", where a genetically modified goat produced milk containing an extra protein that could be extracted and spun into spider silk thread, resulted in bankruptcy. http://phys.org/news/2013-06-spider-silk-nature-stronger-steel.html


Should we be messing with nature like that ?

 

[Scott Danforth]

depends what the rope is made of. we use Dynex Dux at work 6mm has a breaking strength of 6.8 metric tons IT IS STRONGER THAN STEEL CABLE. I prefer the samson blue as it has some stretch to it, however is only about 80% as strong)

 

[Ned L]

Hmmmm,..... Unfortunately your "experiment" won't tell you anything other than maybe you found an unknown combination of stresses that caused it to fail,... Or not.

 

[fhhuber]

Weight of boat?

Estimate speed it can achieve from the line "rubber banding it toward the line's anchor point and then rebounding.

You'd be amazed at the force you can achieve with just a few MPH....

That's the simplified version of what breaks 3000 lb rated lines used by 180 lb mountain climbers.

Its not the weight... its the shock load.

 

[Ned L]

..............Which is one reason why you want to use Nylon for anchor rodes and initial dock lines. Nice and elastic to mimize the shock load.

Which is also why the storm anchor on the family boat I grew up on (46', 27 tons gross) was a 35lb Danforth, chain and 3/8" Nylon. A big rubber band, gave a nice soft motion. Spent the night aboard during a couple of hurricanes.

 

[RGrew176]

Did the experiment work for your boat?