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Old 30-01-2011, 15:59   #16
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Originally Posted by roverhi View Post
wonder why you went with 3/8" chain on a Catamaran. For your displacement and windage, 5/16" G40 would have more than enough strength. It seems it would make more sense in a weight sensitive like a cat to go with a lighter chain and/or more of it.

The problem with line as an anchor rode is chafe. A boat dancing around in high winds has very high chaff at chocks etc that chafe gear is only marginally able to handle. I'd worry more about having any line in my anchor rode than whether it's polyester or nylon. I've had the displeasure of being anchored in 30 gusting to 50 wind conditions for several weeks. Keeping the snubber from chafing through was a 24/7 problem that I had to deal with.
Without going into a very long thread departure, let me just say that because cats always anchor with a bridle between the hulls, the chaff issues are different and considerably less, and because of the fineness of the hulls, the weight issues are greater. Thus, A different set of answers has evolved.

The reduced stretch characteristics of polyester seem better in terms of chafe and sailing around in gusts, and I've seen the math. In big waves, the nylon has greater energy absorption (strenght x stretch = energy) and will transfer less energy to the anchor, which is the weak point. But the differences are going to be very small.

Another problem with polyester double brain (Yachtbraid, Stayset) is that they cannot be spliced to chain in a manner that can pass through a windlass (an eye splice will not work)--and PLEASE correct me if I am wrong.
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Old 30-01-2011, 16:21   #17
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Originally Posted by CarinaPDX View Post
I was taught that nylon was used for its stretch. Some stretch is desirable but there is more than one way to skin a cat... (apologies to cat lovers)

In addition to choice of material, one can choose various constructions. Three-lay is the stretchiest but has the disadvantage of twisting. Next is 8-plait construction, common in Europe, which I think is a good compromise. Least stretchy is double braid. Without looking up the specs I would guess that NER's 16-plait Mega-Braid is between 8-plait and double braid.
Stretch is a very good thing in an anchor rode when big waves are involved. It reduces peak loading on the anchor, chain, rope rode, anchor cleat and any other fitting in the system.

As CarinaPDX points out there are other situations involving anchoring to shore or Med-Moor where stretch would not be very desireable.

My feeling is that most of the time most cruisers will not be anchoring in those situations, they will be anchoring out where stretch is not particularly important most of the time but where a storm coming up suddenly would make the stretch important on short notice. My thought would be to have the stern anchor rode be a lower stretch material/construction and use a regular 3-strand nylon for the main bow anchor. And perhaps the backup anchor rode could be a lower stretch plaited construction. The storm anchor rode should definitely be 3-strand nylon.

For those spending a lot of time Med-moored stern-to I would swap the main and backup rodes.

I did go look up New England Ropes' data for their lines and I don't trust the results they publish.

Their data for Polyester 12 strand Single braid, Regatta ( http://www.neropes.com/Datasheets/MAR_REGATTA.pdf ) says it has a 4.5% stretch at 30% load.

Their data for Nylon 12-strand braid, MegaBraid ( http://www.neropes.com/Datasheets/MAR_Megabraid.pdf ) says it has 3% stretch at 30% load.

Their data for Nylon 3-strand laid ( http://www.neropes.com/Datasheets/MAR_3S_nylon.pdf ) says it has 3% stretch at 30% load.

Polyester should have less stretch than Nylon for the same construction. Assuming the Nylon used a similar but better construction they should still be about equal.

Nylon 3-strand laid should have 14-15% stretch, not the 3% in their data.

On a different but related topic I saw that NER represents scope as being calculated based on water depth rather than water depth plus bow height ( http://www.neropes.com/Datasheets/MAR_megaplait.pdf )
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Old 30-01-2011, 16:26   #18
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Originally Posted by Unicorn Dreams View Post
I think you will find that the chain and swivels etc. are the weak points in strength, 3/8" cgain is only 5400 lb. working load, swivels and shackles about the same.
The breaking strength of these items are about 4x higher meaning the anchor is more likely to break or pull out of the bottom first depending on bottom conditions.
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Old 30-01-2011, 16:32   #19
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Yes that data looks very suspicious.

BTW I stand corrected: MegaBraid is 12-plait, not 16 as I wrote. My bad. It should be easy to remember: 8-plait makes a tidy square splice, and 12-plait makes a beautiful hexagonal splice - I've never seen an octagonal splice :-) (These splices are very attractive, but very time-consuming as well).
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Old 30-01-2011, 19:05   #20
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OK, OK GUYS, I SCREWED UP!!! Yah all are right on the mark, fabrics are ACRYLIC! I have to talk to Wifey, I did to many "Honey do's" today and just plain lost control of what my keyboard typed.

Anyway, polyester line is far superior to nylon.

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Old 30-01-2011, 19:28   #21
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Another problem with polyester double brain (Yachtbraid, Stayset) is that they cannot be spliced to chain in a manner that can pass through a windlass (an eye splice will not work)--and PLEASE correct me if I am wrong.
The attached eyes as well as the eye splice to the chain readily passes over the modern chain/rope gypsies and capstans. The polyester, of course, is more resistant to wear as it passes through the windlass. As a precaution is it easy to "JOG" the windlass switch to slow the retreival over the mechanical parts. Because there are no shackles in the system (previously described) everything passes through the hausepipe although some small orifices may require a pause as one might have to ease and tease large line eyes through.

The advantages are huge. I have been in the water watching several boats at anchor in a large swell where those boats having all chain would buck up and fall down having the chain rode rise from the roller onto the rail eating up nice teak. Those boats having 50 feet or more of movement back would cyclically ride the waves easily with no jerking. You could see this mechanism easily from the water level at a distance.
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Old 31-01-2011, 01:17   #22
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does anyone know why nylon is preffered over polyester when it comes to a anchor rode. it would be used after the initial 175' of 3/8" G40 chain the polyester is stronger than the nylon 3/4" mega braid nylon only has a breaking strenght of 15,000 where as the chain is 16200 so it would make nylon the weak point. 3/4" polyester 12 strand has a breaking strenght of 22,700. thoughts?
Nobody's really answered your question with any sort of definitive response, and the answer goes something like this: it isn't.

We routinely recommend polyester square or 8-plait as anchor rope, as generally superior to nylon. Multi-plaits as superior to 3-strand, as well.

The long answer has a bit to do with boat scale - nylon in long lengths is perfectly appropriate on smaller boats (let's say 40' and under for the sake of drawing a line in the sand), but not larger heavier vessels and in fact can be quite dangerous in certain scenarios. We've smoked (literally) through rope from internal heating - 25 tonnes of boat and nasty katabatic wind gusts with calm lulls in between can generate some really amazing cyclical forces, which nylon does not handle well.

(Generally however nylon is a bit stronger than polyester. Less so with the multi-plaits. Are you comparing like for like with your figures? Either way, you want the rope stronger than the chain. SWLs should match, or the rope's should be higher, and most rope manufacturers will use a 5:1 break:SWL ratio as opposed to 4:1 or 3:1 for chain figures).

Read this:
Rope (Rocna Knowledge Base)
and the article from Steve Dashew on nylon, at the bottom.
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Old 31-01-2011, 01:34   #23
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Originally Posted by Rick View Post

The advantages are huge. ....

Those boats having 50 feet or more of movement back would cyclically ride the waves easily with no jerking. You could see this mechanism easily from the water level at a distance.
OK, this jumps out at me. Words like "advantage" together with "huge" do that to me. But I'm not clear on what you're saying about "boats having 50 feet or more of movement back"
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Old 31-01-2011, 02:25   #24
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Craig that’s a good article on Nylon/poly by Steve Dashew

http://www.rocna.com/distributable/d...right-rode.pdf

Steve’s recommendations on anchoring for cruising in his books and website are invaluable.

Steve also recommends on his own site SetSail » Blog Archive » Anchoring System Logic

“All serious cruisers use chain rodes. Yes they are heavy, but you do not have to worry about chafe. We have been using schedule seven heat treated chain for 25 plus years with good results. We find that 90% of the time we use no more than 200 feet/60m of rode. We normally fit about 330 feet (100m) of chain.
We also carry a spare rope rode, with 25 foot/8m chain leads for use with the spare anchors.”
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Old 31-01-2011, 03:06   #25
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For all Steve Dashews knowledge, he has failed to analyse the problem and look at why his previous preference has been failing. His decision to stop using nylon is based on experience of nylon 3 strand breaking at well below expected breaking strains when used on parachute anchors.

If he understood what was happening with the rope he would understand that the it was not the material but the construction that was wrong.

A 3 strand nylon rope when placed under high stress will tend to stretch and to unwind slightly, when the high stress and then zero stress happens a few times, the rope tends to "knuckle" on one of the strands as it releases from pressure. This knuckle is where one of the strands turns over on itself and then will not lay back into the strand properly. When the rope comes under pressure again, the knuckle is very much a weak point, and leads to rope failure at much less than design loads. This is a fundamental characteristic of this type of rope, and thus nylon 3 strand is a very poor choice for a rope that is under continuous cycles of stress.

However, there is another type of construction where this is not a problem - known in UK as octoplait, where the rope has 4 strands woven in one direction and 4 in the the other. This does not suffer from the knuckle problem. It has another great characteristic - it is much easier to handle.

Thus my own rope of choice for both bridles, and anchor rodes is nylon octoplait
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Old 31-01-2011, 17:39   #26
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The stretch factor in nylon drastically reduces the surge impact on an anchor in a swell or gusty winds.. How to tell the difference? Nylon dissolves in strong acid ,polyester doesnt. Polyester dissolves in strong alkali, nylon doesn'.t
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Old 31-01-2011, 21:10   #27
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The stretch factor in nylon drastically reduces the surge impact on an anchor in a swell or gusty winds.. How to tell the difference? Nylon dissolves in strong acid ,polyester doesnt. Polyester dissolves in strong alkali, nylon doesn'.t
Another way to tell the difference is to boil some water and Black Rit dye. Dip the frayed end of the rope in question in the boiling water/dye for 10-30sec then immediately rinse in cold water. The nylon will absorb water and dye changing color, the polyester won't.

I got this from page 4 of a report from the Cordage Institute ( http://rtm.marine-technology.org/pre...urnal_Pape.pdf ) dealing with 'Misrepresented Imported Fiber Rope'. Apparently there has been some cordage being imported which is a mixture of fibers. Because of differing stretch characteristics the lines are not meeting expected strength for either fiber, the stiffer fiber carries all the load initially until failure, then the reduced section of stretchier fibers carries the load. The report seems to be mostly addressing commercial sized line, 2" or so and the report is of an unknown age.

Kind of makes me wonder what is coming out of all the yachting chandleries and their suppliers. In the future I will use this test when buying nylon or polyester.
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Old 01-02-2011, 12:50   #28
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A short piece of chain taking the rode overt the fair leads will eliminate chafe there.
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Old 01-02-2011, 19:42   #29
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Cyclical riding with rode stretch

Hi Minggat'
If You observe a particle that rides on waves (like a boat at anchor having enough rode "play or stretch") the particle motion describes a circle riding up, back, down and forward in a gentle motion. With all chain, the motion is mostly up and down in a jerky motion.

Obviously the larger the wave height and the longer the distance between crests the greater the rode stretch necessary to minimize "jerk".
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Old 01-02-2011, 19:56   #30
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Thanks Rick,

I think I just missed the transition your post was making from boats with chain to boats with line.

At the risk of thread drift here, sounds like that "advantage" of having heavy chain pick up and laid down on the bottom again to replace the stretch of line is no advantage at all. Obviously depending upon conditions, chain may spend more time off the bottom, but still the weight wouldn't do some work to ease the jerking?

I used to keep my anchor rode chain/line. When I got to Mexico I listened to advice to go all chain. So Now I'm all chain with serious snubbers, which have their own vulnerabilities.... Well, to be more accurate, I have 250 ft of nylon spliced behind 200 ft of chain.

Did the boats you watching of have snubbers? Or maybe a better question, is chain/ snubbers the optimum set up?
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