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Old 30-01-2014, 17:34   #1
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Jordan Series Drogue experience

Disclaimer: This is an account of a single deployment of a JSD, with conclusions drawn by a troubled mind. As such, it is presented not as dogma, but as a basis for discussion.

We recently had occasion to use our JSD in force 9 conditions off the coast of Japan. We were eastbound 5 days out of Yokohama when we were overtaken by the remnants of TS Leepi, which had become a fast-moving extra-tropical cyclone. The wind was in the high 40's, gusting into the mid 50's with seas of approximately 5-7 meters. The boat was under autopilot, our speed was 9-11 knots under bare poles and, although an occasional breaker would push the stern around a bit, the boat was handling the conditions comfortably, taking the seas in a dignified manner off the starboard quarter,. However, as the wind continued to build, the boat began to plane on the gusts. The autopilot continued to handle it well but the sun had set, the wind was building and it was time to slow the boat. We had pre-rigged both the JSD and parachute anchor prior to leaving Japan. I chose to deploy the JSD rather than the parachute anchor as we were traveling in the same direction as the weather with 4,000 miles of sea room and I expected the gale to pass by us quickly. Deploying JSD off the stern was simply a matter of dropping the chain overboard. The drogue ran out smoothly and behaved brilliantly, slowing the boat to 3.5 – 4.5 knots as the stern lifted gently over the seas. We turned off the autopilot and settled in. The gale continued for 2 hours then began to abate. By sunrise the wind had dropped to a light breeze and we retrieved the drogue and carried on.

A few points are worth commenting on.

First, the forces exerted on the boat by the drogue were truly impressive. The pull from the JSD, while gradual, would cause us to stagger if we were not holding on.

Second, one often hears that a disadvantage of the JSD is that they are difficult to retrieve, but in this particular case we found it fairly easy. Before deployment I had rigged a long pendant to one of the bridle arms. When it came time to retrieve the drogue we simply led this line forward to the bow roller, released the bridle arms and motored slowly forward, pulling the drogue in by hand. The whole operation took about 15 minutes.

Third, and most surprising, was that when we retrieved the drogue in the morning we found that most of the cones had frayed badly, particularly those closest to the boat that, presumably, were subjected to the most stress and turbulence,. The leading edges were most affected, but the trailing edges were frayed as well. This was after only 2-3 hours of gale force conditions.

Fourth, I was a bit surprised at our speed while lying to the drogue. After reading many accounts of monohulls lying to a JSD I expected our speed to be around 2-3 knots. We averaged 4 knots, which may have contributed to the rapid degradation of the cones.

Things I will do differently in the future;

I will replace the nylon rodes with Dyneema (SK-75). I believe the elasticity of the nylon rode allowed the boat to acclelerate on the gusts before all the cones were brought into play and the boat could be slowed. Many believe the elasticity of the nylon is a crucial component of the drogues function, providing elasticity and decreasing shock loads as with a parachute anchor. However, in the case of a drogue, I believe that the elasticity of the nylon is unnecessary as the resistance of the drogue is limited by it's smaller surface area in comparison to a parachute anchor. Further, as the boat is moving the rode is under constant tension so there is no shock loading even as waves strike the stern. In addition, it is possible that an elastic rode may ultimately result higher loads on the boat. Recalling that Force = Mass x Velocity squared, the loads multiply very quickly if the boat is allowed to accelerate. I believe that, in our case, this contributed to the fraying of the cones closest to the boat. I will likely keep the nylon bridle arms, but only as they serve double duty as anchor bridles and docklines. (As an aside, our 22mm, 3 strand nylon bridle arms were both badly hockled. I will replace them with double braid nylon in the future.) Weight is another consideration. Our drogue consists of 167' of 3/4” and 167” of 5/8” nylon double braid, with 45' bridle arms and 20' of 10mm chain attached to the end. This is very heavy, bulky and clumsy to move around deck. When wet, it is more that I can manage without pain medication. Dyneema would be far less bulky and much lighter, particularly as it does not hold nearly as much water as nylon. When sized for equivalent strength, Dyneema single braid can be found for roughly the same price as Nylon double braid..

I will also consider adding more cones. We used 150 cones, the recommended number for a multihull our size, but I feel that the recommendations for multihulls, with their greater windage, may be not be conservative enough. We have about average windage for a bridgedeck saloon cat our size, but the JSD still allowed an average speed of 4 knots. This speed may have contributed to the rapid fraying of the cones.

When we rebuild the drogue we will reinforce the edges of the cones. This could be done either by hemming or gluing a strip of cloth to the edge with GM 5200 or similar. It is possible that a simple bead of 5200 along the edge could be sufficient. My wife put ours together from a Sailrite kit, which uses lightweight ripstop polyester for the cones without reinforcement. Had the gale lasted longer, it is conceivable that the cones could have failed completely. This gale occurred in the first week of a five week passage and, had we needed the drogue again, it would not have been available.
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Old 30-01-2014, 17:55   #2
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Re: Jordan Series Drogue experience

Thanks for the great report and details. Unfortunate for you, but fortunate for the rest of us - these first-hand accounts are rare.

Why did you turn off the autopilot after setting the drogue? Was it no longer able to handle the boat, or was it just unnecessary because the drogue was steering the boat?

Mark
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Old 30-01-2014, 18:22   #3
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Re: Jordan Series Drogue experience

Thanks for the report. There was an active thread recently that covered (rather extensively) the issue of which line to use. Jordan himself said (to me in a letter) that stretch in the lines increases the loads, so Dyneema sounds like a good idea for the low stretch, and also the low weight for lightweight boats like cats.

Greg
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Old 30-01-2014, 18:22   #4
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Re: Jordan Series Drogue experience

Quote:
Originally Posted by mikereed100 View Post
Before deployment I had rigged a long pendant to one of the bridle arms. When it came time to retrieve the drogue we simply led this line forward to the bow roller, released the bridle arms and motored slowly forward, pulling the drogue in by hand.
Could you elaborate on how you retrieved the drogue? I don't understand what role the bow roller played in the retrieval.
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Old 30-01-2014, 18:49   #5
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Re: Jordan Series Drogue experience

In the uscg study on the JSD, their model indicated that the boat would be pulled backwards through the crests of large waves. Did you experience any of this effect (which would be greater the slower the boat was going)? Did any of the wave crests break against the back of the boat?
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Old 30-01-2014, 18:50   #6
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Re: Jordan Series Drogue experience

First off, thank you for posting this, Mike Reed.

How much slack did you leave in the pennant line, and did you lead it forward at the time of deployment of the JSD or after the wind got light?

We made a short series drogue for towing our dinghy downwind (to keep it off the boat and straight), and after the cones frayed, we replaced them with cones made of herculite, a pvc fabric with some kind of scrim, probably polyester. That totally cures the fraying problem! I wonder if using herculite for the first 15 cones would take care of your problem? or if that would be a bad solution to the fraying for some reason I have not thought of?

Another potential solution would be to cut the cones 1/2 in. longer, then turn the fabric under 3/16" or so, and zigzag a hem on both ends, then close the seam. If you think the latter is the better idea, would you please explain why?

I feel concerned that the 3M 5200 beads would get ripped off the fabric by the water. Can you explain why that wouldn't happen?

Thank you for your help,

Ann
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Old 30-01-2014, 19:03   #7
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Re: Jordan Series Drogue experience

I love your Herculite idea, Ann! I made some sand bags out of that stuff to weigh down a canopy and various other things 20 years ago. Those things were tossed around on hot blacktop and driven over at race tracks all over the southwest and never showed ANY wear. When I build a drogue it will be made of Herculite.
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Old 30-01-2014, 19:04   #8
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Re: Jordan Series Drogue experience

Thanks for taking the time to type up this great report. We're going to have a drogue on the boat we're building so first hand accounts are much appreciated.

I'll second Mark's question as to why you turned off the autopilot with the drogue deployed. Also, can you touch a bit more on exactly how you attached the drogue to your boat?

David
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Old 30-01-2014, 19:12   #9
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Re: Jordan Series Drogue experience

Quote:
Originally Posted by mikereed100 View Post
----
Before deployment I had rigged a long pendant to one of the bridle arms. When it came time to retrieve the drogue we simply led this line forward to the bow roller, released the bridle arms and motored slowly forward, pulling the drogue in by hand. ----
Mike - Great post, thank you.
I am assuming you turned the boat around so the bows were facing upwind towards the drogue? I am trying to visualize exactly how this was accomplished without fouling the pendant/bridle lines in what must have been still relatively large seas?
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Old 30-01-2014, 19:15   #10
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Re: Jordan Series Drogue experience

Actually the force on the Jordan drogue is just proportional to the square of the velocity. Mass doesn't really come into the equation except via the density of the fluid.
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Old 30-01-2014, 20:04   #11
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Re: Jordan Series Drogue experience

During our circumnavigation, we had winds to fifty knots on three occasions.

We used our parachute on one occasion 300 miles north of New Zealand with good results.

In an Atlantic gale, we used the Abbott Drogue with good results.

ABBOTT DROGUE

We carried a series drogue and never had to deploy it because we were never in winds over fifty knots. But it was ready to go.
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Old 30-01-2014, 22:39   #12
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Re: Jordan Series Drogue experience

Quote:
Originally Posted by mikereed100 View Post
Things I will do differently in the future;

I will replace the nylon rodes with Dyneema (SK-75). I believe the elasticity of the nylon rode allowed the boat to acclelerate on the gusts before all the cones were brought into play and the boat could be slowed.

....

In addition, it is possible that an elastic rode may ultimately result higher loads on the boat. Recalling that Force = Mass x Velocity squared, the loads multiply very quickly if the boat is allowed to accelerate. I believe that, in our case, this contributed to the fraying of the cones closest to the boat.

....

This gale occurred in the first week of a five week passage and, had we needed the drogue again, it would not have been available.
Actually

Force = Mass x Acceleration

Energy = 1/2 * Mass x Velocity^2

Of more interest here are the equations:

Momentum = Mass x Velocity

Impulse = Force x ElapsedTime or the integral of Fdt if the force varies over time.

Impulse and momentum are of more use analyzing in impact situations such as wave hitting boats.

Impulse and momentum have the same units so there a mathematical equivalence between the two.

When a wave strikes the stern of a boat it is imparting an impulse to the boat. If the boat is held rigid against the wave the length of time the wave acts on the stern of the boat is decreased compared to if the boat gives to the wave some and moves forward with it. For a given impulse from a wave a longer elapsed time means a lower average force acting on the stern of the boat. A springy line between the boat and the drogue stretches out the time interval of impact which decreases the force. The wave is moving and by moving with it you stretch out the time it acts on the boat.
If a stiffer line is used to connect the boat to the drogue it shortens time that the wave is acting on the transom and increases the forces experienced.

This argues for stretchy line (nylon) in the system. I would rather see fraying of some the cones at the front of the series (or even all of the cones in the series) rather than risking damage to the hull and losing water-tightness in the middle of a storm.

A stiffer line also changes the mass of the boat, the water contained in all of the drogues needs to be accelerated at the same rate as the boat. I'm not real clear on how this affects the system but my sense is it shortens the time of impact slightly increasing the forces still more.

Let's look at the damage to the cones, my understanding is that they are all at the front or boat end of the series. My guess is that because of the stretchiness of the whole line as the wave passes the load comes off the front end is briefly pulled backwards thru the water by the springiness between the front and the middle and back of the series. This collapses the forward drogues. When the load comes back on with the next wave they snap open which is when the fraying and damage happens. It may be that the rate of damage is related to the resonant period of the front of the drogues compared to the period of the waves. Changing the length of line between the boat and the front of the boat would change the resonant period and decrease the damage. Because you can't see the front of the series there is no way to match the length veered to the period of the wave. I see two solutions here:

1) Putting out the most leader (the line between the boat and the front of the series) possible would skew the ratio of stretch away from the series into the leader meaning the there is less likely to be flow reversal at the front of the series. This method has practical limitations related to how much line you can carry.

2) Alternatively during original construction the series can be assembled on a low stretch line with an eye-splice and solid thimble at the front end which is shackled to an appropriate length of nylon leader between the boat and the front of the series. Because there is no stretch between the front and middle or tail of the series there is less likely to be flow reversal and the damage that results when leader loads up again.

Finally from the description of the damage it was all to a limited number of cones at the front of the series, I do not see mention of damage to the line itself. To me this means the series would be still have been useful with some degradation in performance in subsequent gales.
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Old 31-01-2014, 08:24   #13
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Re: Jordan Series Drogue experience

Thanks to all for the thoughtful responses.
I'll try to answer some questions:

@Mark: After deploying the drogue I set the rudders amidships and let the boat move straight downwind, so the AP was not needed. We set the drogue just as I was going off watch and, after watching how the boat rode for a while, I was able to go below and get some sleep.

@Ziggy and Mike: Prior to deployment, I had tied a 90' length of 10mm Spectra to the port side bridle arm with a rolling hitch. When it came time for retrieval we led this line forward, outside the shrouds over the bow roller, then released the bridle arms. This allowed the boat to swing bow into the wind and we retrieved the bridle and drogue over the bow roller. Initially we tried using the windlass, but the cones got hung up on the drum. We then tried the primary winches, with their larger drums, but had the same problem. At that point my brother, who was at the bow, pointed out that he was able to pull the drogue in by hand quite easily. After that, I simply motored forward slowly as he pulled in the drogue from the bow as my wife flaked it in the forward cockpit.

@Don: The waves weren't much of an issue. They were relatively small as it was a very fast moving system and they didn't have much time to build. They were really more just whitecaps than breaking waves. The whitewater would approach the stern and then just pass under the boat as the sterns lifted. I was a little concerned about the dingy on davits, but the waves never reached it. At other times we did have waves break into the aft cockpit, but none while riding to the drogue and the ones that did break into the cockpit came from the side.

@Ann: I'm afraid you have far more expertise than I with regard to sailcraft so I don't feel like I'm on solid ground offering advice. I like the Herculite idea, I've never heard of that. A hem would probably be a better fix than gluing, but 150 cones is a lot of hems! I thought of gluing purely out of laziness. It would be interesting to make up a few cones using different methods and materials, then tow them behind the boat for a day or so to see what works and what doesn't.

@David: We have 1/4" ss chainplates, 12" long and 3" wide bolted to the aft crossbeam. The bridle arms are attached with 5/8" high tensile shackles.
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Old 31-01-2014, 08:43   #14
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Re: Jordan Series Drogue experience

Quote:
Originally Posted by Adelie View Post
Actually

Force = Mass x Acceleration

Energy = 1/2 * Mass x Velocity^2

Of more interest here are the equations:

Momentum = Mass x Velocity

Impulse = Force x ElapsedTime or the integral of Fdt if the force varies over time.

Impulse and momentum are of more use analyzing in impact situations such as wave hitting boats.

Impulse and momentum have the same units so there a mathematical equivalence between the two.

When a wave strikes the stern of a boat it is imparting an impulse to the boat. If the boat is held rigid against the wave the length of time the wave acts on the stern of the boat is decreased compared to if the boat gives to the wave some and moves forward with it. For a given impulse from a wave a longer elapsed time means a lower average force acting on the stern of the boat. A springy line between the boat and the drogue stretches out the time interval of impact which decreases the force. The wave is moving and by moving with it you stretch out the time it acts on the boat.
If a stiffer line is used to connect the boat to the drogue it shortens time that the wave is acting on the transom and increases the forces experienced.

This argues for stretchy line (nylon) in the system. I would rather see fraying of some the cones at the front of the series (or even all of the cones in the series) rather than risking damage to the hull and losing water-tightness in the middle of a storm.

A stiffer line also changes the mass of the boat, the water contained in all of the drogues needs to be accelerated at the same rate as the boat. I'm not real clear on how this affects the system but my sense is it shortens the time of impact slightly increasing the forces still more.

Let's look at the damage to the cones, my understanding is that they are all at the front or boat end of the series. My guess is that because of the stretchiness of the whole line as the wave passes the load comes off the front end is briefly pulled backwards thru the water by the springiness between the front and the middle and back of the series. This collapses the forward drogues. When the load comes back on with the next wave they snap open which is when the fraying and damage happens. It may be that the rate of damage is related to the resonant period of the front of the drogues compared to the period of the waves. Changing the length of line between the boat and the front of the boat would change the resonant period and decrease the damage. Because you can't see the front of the series there is no way to match the length veered to the period of the wave. I see two solutions here:

1) Putting out the most leader (the line between the boat and the front of the series) possible would skew the ratio of stretch away from the series into the leader meaning the there is less likely to be flow reversal at the front of the series. This method has practical limitations related to how much line you can carry.

2) Alternatively during original construction the series can be assembled on a low stretch line with an eye-splice and solid thimble at the front end which is shackled to an appropriate length of nylon leader between the boat and the front of the series. Because there is no stretch between the front and middle or tail of the series there is less likely to be flow reversal and the damage that results when leader loads up again.

Finally from the description of the damage it was all to a limited number of cones at the front of the series, I do not see mention of damage to the line itself. To me this means the series would be still have been useful with some degradation in performance in subsequent gales.
You want to think about the drogue in your analysis of the problem. The force exerted by the drogue on the boat is proportional to the velocity squared. It is like a friction with a dependence on velocity. It is the drag of the cones through the fluid (sea water) that prevents the boat from excessive acceleration preventing a high velocity run down the face of a steep wave.

Consequently, the force exerted by the Jorden drogue has been decribed as being attached to a rubber band. A stretchy line is not required for the Jorden drogue.
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Old 31-01-2014, 08:48   #15
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My Jordan Series drogue cones were a little frayed after 2 deployments near Chile, so I heatsealed all the edges with a soldering gun. The last deployment was for 3 days last June, S of the Aleutians, and there was no more fraying.
36' monohull, 10 tons displ. Sailrite kit 124 cones.
1.3 to 1.6 knots under drogue.
Recovery also was by a separate line, led loosely to the bridle apex, hauled in over the stern without problem.
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