Jordan Series Drogue experience

[Dockhead]

Originally Posted by CarinaPDX

No, it is the other way around. More stretch allows the stern to be pulled off to the side more, resulting in a greater load due to the greater cross section. I don't know all of the considerations, or certainly the formulae, behind the design but I'm pretty certain that the difference in stretch is not going to be a major issue.

Greg

Exactly. The original design called for nylon, but I think the stretch and vulnerability to chafe are very undesirable.



The other issue is weight and bulk. For the same strength, dyneema is almost 6x (!) lighter. For example, 10mm SK78 single braid weighs 6.3kg/100m and has breaking strength of 12.6 tonnes. That is comparable to 24mm (!) nylon, which weighs 35.5kg/100m.


When I made my drogue, I oversized the cordage by strength, using 14mm Acera Amundsen (UHMWPE comparable to SK78 Dyneema) with breaking strength of 20 tonnes (stronger than 32mm nylon), for the bridle, leader and first section, but still 3 times lighter than nylon would have been. This makes a huge difference in how well you can handle the drogue. I can launch mine by myself if I need to; I would need help or mechanical aids to launch one made from nylon, and how would you store it?


Lastly, splices in UHMWPE are easier and more reliable than they are in nylon.

[CarinaPDX]

I had forgotten: I was comparing 8-plait nylon to the double-braid nylon DJ had recommend, because I was in Europe and double braid nylon was not available, but 8-plait was. The world has moved on, with the newer Dyneema, etc.

Greg

[Talbot]

I think some of you are missing a major point here. One of the biggest issues we face is a breaking wave. while the design will help to minimise the shockload, there will still be significant loading. Nylon will allow that load to be absorbed by a stretch and then recover,
Dyneema would not and thus the shockload will need to be taken by the parachutes and the fittings onboard.

If you must use dyneema, make the parachutes and their straps out of heavier material and beef up the onboard fittings even more.

Most designs for this system end up with a significant risk of chafe at the attachment point. In my boat it was possible to add a fitting that eradicated this potential problem.

I am delighted that I have never had a reason to need to use mine, but I put a lot of thought into the fitting, deployment and recovery.

[wsmurdoch]

You all might want to look at CarinaPDX's earlier
http://www.cruisersforum.com/forums/...ml#post1414172 and http://www.cruisersforum.com/forums/...tml#post215527 for DonJordan's later thoughts on UHMWPE rope.

Bill

[Dockhead]

Originally Posted by Talbot

I think some of you are missing a major point here. One of the biggest issues we face is a breaking wave. while the design will help to minimise the shockload, there will still be significant loading. Nylon will allow that load to be absorbed by a stretch and then recover,
Dyneema would not and thus the shockload will need to be taken by the parachutes and the fittings onboard.

If you must use dyneema, make the parachutes and their straps out of heavier material and beef up the onboard fittings even more.

Most designs for this system end up with a significant risk of chafe at the attachment point. In my boat it was possible to add a fitting that eradicated this potential problem.

I am delighted that I have never had a reason to need to use mine, but I put a lot of thought into the fitting, deployment and recovery.

This is what Don Jordan said about it, in the post referenced by WSMurdoch:


"The increased stretch will not reduce the load, in a breaking wave strike. In fact it will increase it a bit. The drogue must pick up the load quickly before the boat broaches and must turn the boat into the wave. The cones near the boat perform this function and THE LESS STRETCH THE BETTER [emphasis added]." http://www.cruisersforum.com/forums/...ml#post1414172



So on the contrary -- if the line stretches, the boat will yaw more and pick up more loads. Heavier cones are not needed; all the shock absorption needed is provided by the way the cones move thorough the water. Stretch in the line is undesirable. I wouldn't use anything BUT UHMWPE for building a drogue.

[conachair]

Originally Posted by Talbot

I think some of you are missing a major point here. One of the biggest issues we face is a breaking wave. while the design will help to minimise the shockload, there will still be significant loading. Nylon will allow that load to be absorbed by a stretch and then recover,
Dyneema would not and thus the shockload will need to be taken by the parachutes and the fittings onboard.

Can't quite understand the mechanics there, the jsd design concept generally seems to be keep the speed down and then stern towards the wave. So as a non engineer other than a keen interest as is popular on forums......

Breaking wave hits a boat with best ever dyneema which has no stretch - the boat speeds up surfing down the wave, as this happens the jsd exerts an increasing force until it equals the force from the wave and the boat stops accelerating. As per design.
Same boat with nylon, boat speeds up, jsd exerts a force but the nylon stretches so the boat speeds up more than the dyneema boat, maybe with the stern getting kicked nround a bit. Now the force from the jsd has to still equal the breaking wave force but will continue to increase as it tries to slow the boat down, extra energy being proportional to the extra velocity squared. So overall the force is greater.
Maybe....

[CarinaPDX]

There are really two disasters that the drogues are intended to prevent: the first is accelerating down a wave face, burying the bow and going ass-over-elbows, and the second is a broach-and-roll. The first is prevented by simply keeping the boat speed down, well below the wave propagation speed. The broach-and-roll is harder to prevent. When a large, esp. breaking, wave hits the stern at a slight angle it pushes the stern over, and as the hull yaws the forces on the quarter initially increase, resulting in accelerated yaw. If the yaw gets too great the top of the wave hitting the boat can cause a roll. Any stretch in the line will increase the initial yaw, and ultimately the maximum yaw - which leads to increased loads on the drogue system. To prevent this the line should not have any unnecessary stretch, to hold the stern into the wave.

Greg

[transmitterdan]

There is a common (apparently) misconception that stretchy line reduces maximum force. That is only true if the thing being restrained is allowed to move in the opposite direction of the restraint. Then when direction reverses there is acceleration until the restraining line is taut and sudden deceleration is needed to restrain the motion. That describes a boat lying to an anchor.

It does not describe a series drogue being used in anger. The boat does not typically drift backwards putting significant slack into the line. The boat is generally always moving forward and the line has little or no slack.

Also, I agree with the need to prevent stern yaw as this puts much more stress on the attachment points.

Stretchy line is not a good thing for a series drogue.

[DumnMad]

The forward motion at the top of the wave will push forward any part of the drogue that is near the surface and can produce slack if the drogue is too short relative to wave length.
The idea is to have the tail end of the drogue in the trough where it will drag backwards.

[Lula Mongo]

Originally Posted by mikereed100

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.

Hi Mike, I once had to use a Gailryder and noticed that the slack/tensing of the line, decreased a lot if the drouge was beyond the second wave. as your JSD also beyond the second wave?
Thanks

[Dockhead]

Originally Posted by conachair

. . . Breaking wave hits a boat with best ever dyneema which has no stretch - the boat speeds up surfing down the wave, as this happens the jsd exerts an increasing force until it equals the force from the wave and the boat stops accelerating. As per design.
Same boat with nylon, boat speeds up, jsd exerts a force but the nylon stretches so the boat speeds up more than the dyneema boat, maybe with the stern getting kicked nround a bit. Now the force from the jsd has to still equal the breaking wave force but will continue to increase as it tries to slow the boat down, extra energy being proportional to the extra velocity squared. So overall the force is greater.
Maybe....

I think this is spot on.


Or to say in a different way -- with no stretch, energy from a breaking wave strike is being dissipated from the first millisecond, and so is spread out over a longer time period -- ergo, less force. With nylon, much of the energy of the breaking wave strike is converted to momentum.


Also, I think Don Jordan was saying this -- the stretch may allow some yawing, which may increase the force of the wave strike, maybe greatly. Whereas if there is no stretch, yawing is better prevented.

[pbmaise]

I have begun the thought process of a new vessel and this thread has a lot of my attention. I plan to do more adventuresome travels. While my previous multi at 65ft by 40ft wide was equipped with 2 paratech and 3 JSD I never had to employ them.

My JSD was made using 1 inch nylon. It took up a large amount of room and was quite heavy. So heavy that there were three separate sections and the bridle. Therefore, I like how many on this thread concluded the best way to go is to utilize Dyneema lines.

I should note that the previous owners appear to have tested the JSD and then made the mistake of placing the fittings on the lines into plastic bags without first washing out the salt. As a result the salt in the lines attracted moisture and rotted out thimbles, swivels, and shackles. Don't repeat this mistake and wash out this type of equipment when next in port and allow it to air dry. Never store metal inside plastic bags. We all know this don't we? That is why I was surprised the previous owners of my vessel didn't.

I want to document feedback I had about switching between paratech and JSD or vice versa mid-storm. I failed to envision taking one of them out of the water in the middle of a storm, turning the vessel, and then moving the bridle to the rear or front, installing it, and then deploying it. If anyone else has this question...the answer is NO. You can't change mid-storm. You have to pick your method ahead of the storm.

Which brings up now my questions.

Even my vessel, which was set up very well to handle a paratech had no provision to employ the JSD that was on board. Yes I had massive winches, however, they were not out on the ama. Yes, I had massive docking cleats, however, docking cleats are meant to handle lines without chaffing that go in the wrong direction, towards the dock. Not to the centerline. Any JSD attached to the docking cleat that pulled from directly behind the vessel would damage the ama and create chaffing. There simply was no provision to install a JSD.

Thinking about this now, I can envision that I could have added two chainplates onto the aka. (The aka connects to the ama). To handle the loads of a big multihull I have been looking at the charts. Yes, the chainplate would need to be about the same size as the rear chainplates holding the mast. And I would be constantly worried that this section of the vessel was not beefed up to handle 10s of thousands kg pull.

And don't be fooled. Any big multihull owner must recognize there are 10's of thousands of kg force in play. Full 1 inch D galvanized shackle loads.

Today I don't need to be concerned about my old vessel. It is sold and hauling tourists in a place where it will never need to be concerned.

I am instead worried about buying a new vessel. I have concluded the way to go in my case is JSD. I simply don't like the idea of having the bows facing the weather.

I have yet to find a single multi-hull that is equipped with a properly engineered stern attachment for a JSD. I have found tons of "bluewater" advertise catamarans however, zero that detail how they survive.

The closest I have come is a custom vessel in South Africa where the owner seemed concerned about the giant rear facing doorwall on almost every single modern condo-cat. He utilized two relatively narrow thick lexan doors and a tall step to get over before reaching inside. The lexan doors were set on hinges that swung outwards.

I am thinking of working with a small manufacturer to build a new vessel and asking them to install proper chainplates, small rear facing doors, a step, and a winch to help recover the JSD.

Has anyone seen examples of a greenwater ready multi-hull?

[pbmaise]

Ooops I need to backtrack over something I implied.

For big vessels a 1 inch D shackle may not be large enough. Remember, vessel gross tonnage is what we are looking at and it is a volumetric measurement. Despite being less than 25,000 lbs, my vessel was a 76 gt vessel and off the JSD charts. Looking at the charts now, I can see that the owners should have gone with an even larger shackle.

Consult the charts for ratings on shackles and building the bridle and attachments for a JSD.

Further, just a note about using Dyneema under high loads. I have watched forces aboard my vessel crush typical thimbles like they were tissue paper. Taking thick stainless steel thimbles to the welding shop and welding in a brace within the shackle helped. However, it didn't change the turning radius. The narrow turning radius damaged the Dyneema line. Therefore, aboard my vessel I learned the hard way to go to the big fishing boat supply house and buy thick galvanized steel thimbles that were 1 inch or larger. Nothing in the typical yacht supply store was adequate.

[fxykty]

Originally Posted by pbmaise

Ooops I need to backtrack over something I implied.

For big vessels a 1 inch D shackle may not be large enough. Remember, vessel gross tonnage is what we are looking at and it is a volumetric measurement. Despite being less than 25,000 lbs, my vessel was a 76 gt vessel and off the JSD charts. Looking at the charts now, I can see that the owners should have gone with an even larger shackle.

Consult the charts for ratings on shackles and building the bridle and attachments for a JSD.

Further, just a note about using Dyneema under high loads. I have watched forces aboard my vessel crush typical thimbles like they were tissue paper. Taking thick stainless steel thimbles to the welding shop and welding in a brace within the shackle helped. However, it didn't change the turning radius. The narrow turning radius damaged the Dyneema line. Therefore, aboard my vessel I learned the hard way to go to the big fishing boat supply house and buy thick galvanized steel thimbles that were 1 inch or larger. Nothing in the typical yacht supply store was adequate.

One of the benefits of using Dyneema for the rode is that you can get rid of all metal. The only metal we have is the thimble at the very end of the tail to which the tail chain is attached. There’s not much load at that end of the JSD. Everything else is either direct connections or soft shackles.