Octaplait vs Doublebraid For Jordan Series Drogue

[Orchidius]

Hi there,

I'm gathering materials to start construction of my own JDS. Their site advises double braid nylon rope, but some people I talked to would rather use octaplait.

What's the best value and what would be safest (also taking into account it might sit unused in the boat for years)?

What would you choose and why?

[estarzinger]

First point: JSDs do not create large shock loads (unlike para anchors) and thus do not need extra elasticity in the rope.

Second point: chafe resistance and "stow ability" are typically the key practical rode factors . . . And if you are building your own, the easy of installing the cone tapes. Dacron double braid would have the best chafe resustance on the common lines. And brait would have the best stow ability and ease of installing the cones.

Third point: functionally, actually, the best choice is dyneema single braid. It is the most chafe resistant, stows the smallest and equal to brait in ease of cone installation. Of course it is several times the price. Dashew and I both use this.

So, all the alternatives will "work ok" but there are some trade-offs involved. Only you can set where you want to fall in the trade off between stowage space, chafe resustance, and ease on construction.

[Orchidius]

Thanks for your input, and you make some really good points there.

Even though you are right about the fact that the drogue does not generate big shock-loads on the rope, some elasticity is needed I think. That and the financial aspect made me exclude the expensive static ropes from the equation.

Secondly you can debate the various properties of the ropes all you want, in the end of the day it all comes down to wether it will break when used in harsh conditions. Of course any rope would do the trick if you got it in big enough a diameter, but would the difference between rope thickness in octaplait/double braid be that big for a given break load?

[mikereed100]

Originally Posted by Orchidius

Even though you are right about the fact that the drogue does not generate big shock-loads on the rope, some elasticity is needed I think. That and the financial aspect made me exclude the expensive static ropes from the equation.

We built our JSD using double braid nylon, but if I were building from scratch again I would use SK-75, not only for it's stowability, but for it's weight. You don't mention how big your boat is, but we have a large cat that requires, if I recall, something like 130 cones and over 300' of line with 42' bridle legs. Once this mess is wet it is more than I can carry. We stow it in a bin next to the mast then move it to the cockpit on passage. We have to do this in stages due to the weight. It would be really nice to have Dyneema, not only for the initial weight savings, but because it will hold less water than double braid.

If you compare breaking strengths and cost of nylon and SK-75 you may be surprised to find that the SK-75 is actually cheaper for an equivalent breaking strength.

I don't agree that you need some elasticity in the line. The cones are small and the line will be at least somewhat submersed due to the chain at the end of the drogue, providing some caternary. In fact, the drogue may perform better as the cones towards the end of the drogue will be brought into play sooner if there is less stretch. If it worries you, you could still use nylon for the bridle arms.

[estarzinger]

Originally Posted by Orchidius

would the difference between rope thickness in octaplait/double braid be that big for a given break load?

I am not sure what you are asking . . . . You could look the breaking strengths up yourself . . . .

In 1/2" size (from the Yale product line):
Dyneema = 26,500lbs breaking strength
Double braid Dacron = 9,600 lbs
Double braid nylon = 8,300
Brait = 8,300lbs

Regarding your other comments . . . Please do realize we have actually used this thing. I am not "making things up".

[Stumble]

I guess it depends on the size of the boat really. But let's assume a typical 40' boat with a displacement of 25,000lbs. According to JSD this would result in a max design load of 16,000lbs. So the line needs to be at least this strong, and let's assume 200' of line.

For brait this would be...
3/4" - 17,000lbs MBL at 14lbs/100' and $2.32/foot
So our line would be... 28lbs and $464.

For amsteel...
3/8" - 19,300lbs MBL at 3.6lbs/100' and $3.73/foot
So the line is 7.2lbs and $746

So the amsteel is more expensive, but a good bit stronger (10% or so). The amsteel also weighs about 1/5th what the brait would, and is half the diameter. Which means it will store in about 1/4 the space.

[CarlF]

The nylon braid also loses about 15% of it's strength when wet. I've never heard if Amsteel has a similar problem.

[Boracay]

My understanding is that the nylon rope specified has considerable stretch under load, and that in stretching it absorbs a large amount of energy.

If my understanding about "Amsteel" is also correct it has very little stretch under load and would absorb little energy.

My vague recollection of the Jordan Drogue is that it needs very substantial mounting points on the stern to take loads of the same order of magnitude as the weight of the boat.

I'm no engineer but my opinion is that using a rope that does not stretch may cause the drogue to exceed the strength of the mounting points or the adjacent structure.

[Stumble]

Carl,

Amsteel is not effected by being wet. It holds onto all of its strength when wet.


Boracay,

Amsteel doesn't stretch true. But from what I understand there isn't much need for stretch. The load is constant without a lot of shock loading because the JSD is deployed under water and is immune from most wave action.

And the flip side of stretch is that it generates a lot of internal friction, and thus heat and internal wear on the fibers. While dyneema's low stretch keeps this from happening.

[Geoff54]

If you read the coast guard report (you can find it on the web or I can email a copy if you can't) and his other writings, Jordan specified nylon double braid. He was an engineer and clearly understood the properies of the materials he used. You have to assume that he specified nylon for a reason, presumably for it's stretch/shock absorbing qualities.

Jordan satisfactorily tested the cone attachment to nylon double braid. It has been proven in use. Unless someone has a properly tested alternative (e.g. multiplait), why mess with a proven design?

BTW, although not what was asked, I seem to recall that 3 strand was tested but tended to unwind during repeated load cycles.

Just my 2 cents.

[estarzinger]

1. If you actually read the USCG report . . . you will find it says this about the rode (page 52):

"Figure 24C shows the effect of towline stiffness on

maximum load. Some sailors believe that a highly elastic towline

will reduce the drogue load. This may be true in regular nonbreaking

waves, but in a breaking wave strike the effect is small

because the boat rides the wave front and stretches the line

until the load builds up. Actually the model tests show that a

highly elastic line is very undesirable because the boat may be

capsized before the load builds up."

They did not test this, but in real world use, I would suggest that empirically there are way more failures due to chafe than to shock loading.

As an aside, one must note that all this work was done before dyneema line was widely available. Nylon double braid was 'high tech' back then, and was lower stretch than the more common 3-strand.

2. Regarding attaching the cones . . . The standard technique of sticking the tapes thru the line twice and then tying a stopper knot works just fine with brait and with dyneema single braid. As the line tensions up it more strongly holds the cone tapes. That is equally true for all these types of construction. We have done it with dyneema single braid, and used the drogue (and lost no cones); and know people who have done it with brait.

3. All these lines will work . . . some will be easier to stow (dyneema) and some will chafe less (dyneema and dacron) and some will be cheaper (dacron and nylon) . . . just pick whatever you are comfortable with. And (as mentioned in a post above) if you want to mix the characteristic a little you can use something different in the bridle than the cone line. We use a Dacron bridle (low chafe but good grip around the winches) and a dyneema cone line (easy to stow).

[toddedger]

I'm building one right now. I got about 50 cones on so far. I went with endura braid a dyneema double braid. West Marine has their own tan color that is quite a bit cheaper. I ordered it last spring when they had their one day 40% off sale on all bulk line. I was able to greatly reduce the line size to save a lot of stowage space.

The West Marine rigging shop spliced on some very nice stainless sailors thimbles on the ends. I couldn't find a source for stainless enclose thimbles that were big enough, but the West Rigging came through for me this time. Good thimbles are very important.

[Geoff54]

Originally Posted by estarzinger

1. If you actually read the USCG report . . . you will find it says this about the rode (page 52):
"Figure 24C shows the effect of towline stiffness on
maximum load. Some sailors believe that a highly elastic towline
will reduce the drogue load. This may be true in regular nonbreaking
waves, but in a breaking wave strike the effect is small
because the boat rides the wave front and stretches the line
until the load builds up. Actually the model tests show that a
highly elastic line is very undesirable because the boat may be
capsized before the load builds up."

You know nothing about me – please do not presume to know what I have or have not done. I did read the report, admittedly some years ago when building a JSD. Clearly I read it more carefully than you did.

This quote is very misleading. You have taken it out of context and presented it as if it applies to a JSD. This quote and the accompanying graph relate to breaking wave tests and the force applied by 4ft diameter parachute anchor. I believe the point is, that if the braking force (single drogue) is at the end of a long flexible line, the boat may capsize while the line is still stretching, before any significant braking occurs. Not exactly the same as a JSD, eh? Also, when quoting something, it is not regarded as appropriate to add emphasis that was not in the original, unless you indicate that it is your emphasis.

Originally Posted by estarzinger

They did not test this, but in real world use, I would suggest that empirically there are way more failures due to chafe than to shock loading.

Can you point to empirical evidence where a JSD has failed due to chafe. If so, I think it would be interesting to know the circumstances, how it was attached and how the chafe occurred.

Originally Posted by estarzinger

As an aside, one must note that all this work was done before dyneema line was widely available. Nylon double braid was 'high tech' back then, and was lower stretch than the more common 3-strand.

Agreed. But it was 1987 not 1907. Polyester was available but nylon was used. It would have been interesting to ask Don Jordan exactly why - he was a lovely man who enjoyed sharing his knowledge but regrettably we no longer have that opportunity.

Originally Posted by estarzinger

2. Regarding attaching the cones . . . The standard technique of sticking the tapes thru the line twice and then tying a stopper knot works just fine with brait and with dyneema single braid. As the line tensions up it more strongly holds the cone tapes. That is equally true for all these types of construction. We have done it with dyneema single braid, and used the drogue (and lost no cones); and know people who have done it with brait.

3. All these lines will work . . . some will be easier to stow (dyneema) and some will chafe less (dyneema and dacron) and some will be cheaper (dacron and nylon) . . . just pick whatever you are comfortable with. And (as mentioned in a post above) if you want to mix the characteristic a little you can use something different in the bridle than the cone line. We use a Dacron bridle (low chafe but good grip around the winches) and a dyneema cone line (easy to stow).

All of this may well be correct but an example or two does not make it proven. If you use attachments as Jordan described, I don’t believe chafe is a significant issue. Just in case, I have three feet of oversized polyester double braid between each bridle leg and the boat. There are heavy duty thimbles at the boat attachment end and MIT style overlapping loops, for strength, at the bridle leg end. All loops are spliced and stitched. BUT, this is not proven and is just my experimental method, as yours is your experimental method.

I stand by my previous post - Nylon double braid, sized according to Don Jordan’s chart, is the original, tested and proven method. If you want to experiment, that’s up to you but do it with your eyes open and accept that is what you are doing.

As an aside to anyone thinking about this, it’s a really good ides make sure you understand the properties of any material that you are experimenting with. For example, with Dyneema , “… like all high tech ropes, it does not easily tolerate severe curves. Knotting reduces its strength more than other types of rope”. Good thing to know if, for example, you were planning to attach a dymeena loop to a ring, with a cow hitch.

[sabray]

I can provide a example. Give me more time and I will give you more. See this excellent page of challenging sails. http://www.thesimplesailor.com a jordan series drogue fails and is lost to chafe . Also other stories that are excellent. Chafe and load point are primary when using a drogue or anchor. This can relate back to Shackleton and go forward to modern sea anchors and drogues

[Geoff54]

Originally Posted by sabray

See this excellent page of challenging sails. Introduction to the junk-rigged Corribee Mingming a jordan series drogue fails and is lost to chafe .

I've read a lot of Roger Taylor's stuff and he has always been a proponent of the JSD. I don't have time to read all this again, can you point out where he wrote about losing his drogue? Thanks
edit: I just did a site search and found only positive comments about the Jordan Series Drogue - nothing about losing one.

Originally Posted by sabray

Chafe and load point are primary when using a drogue or anchor. This can relate back to Shackleton and go forward to modern sea anchors and drogues

Absolutely! But we are specifically talking about JSDs when attached as suggested by Don Jordan. I doubt Shackleton used the same methods.