Jordan Series Drogue experience

[cburger]

Originally Posted by Geoff54

Although not completely without value, they only used a short, high mounted line without a bridle and then seemed suprised the drogues tended to skip or ride high in the water.

Also, did you notice the moaning and negative attitude to all the drogues, except the Shark, which they just happen to sell? Do you think when they kicked the JSD over, they deliberately tangled it so it didn't perform as well as it might?

There seems to be only three things to learn from this video: It's a good idea to weight any drogue; despite the mishandling, the JSD still worked well; if you lauch a drouge on a single short line, you can't expect it work properly. Nothing much new there.

Absolutely, lines way to short, not following manufacturers instructions, believe it is also required to have a rated swivel at attachment points to drouges to prevent twist.

[ontherocks83]

Originally Posted by captain58sailin

I suppose this will bring a storm of a different kind. I was raised, that if you encounter too rough weather that the safest strategy is go head on into the seas, or quarter them if they are standing too steep. On this forum, I have frequently read of vessels here that put the seas to the stern, which I believe is a most dangerous thing to do, yet, I have yet to see a thread relating to the time they pitch poled due to a following sea, perhaps those vessels never survived to tell the tale.

If you read the history of how the jsd was developed you will see why he came up with this design and why he made it to be used stern to. The multiple chutes not only lessen the sudden shock loads but also allow there to always be chutes in the water in big wave scenarios. The theory that he tested with the cg was that a breaking wave may hit you from the stern but most of the chutes will be already behind the wave and will tether you so that you don't pitch pole.....now as far as old school goes yes I do personally agree that I wouldn't hang 1 large chute off the stern but the jsd is a different story all together.

[cburger]

Originally Posted by ontherocks83

If you read the history of how the jsd was developed you will see why he came up with this design and why he made it to be used stern to. The multiple chutes not only lessen the sudden shock loads but also allow there to always be chutes in the water in big wave scenarios. The theory that he tested with the cg was that a breaking wave may hit you from the stern but most of the chutes will be already behind the wave and will tether you so that you don't pitch pole.....now as far as old school goes yes I do personally agree that I wouldn't hang 1 large chute off the stern but the jsd is a different story all together.

Correct, Jordan was an aeronautical engineer that was looking for a solution to the loss of boats to heavy weather, being thrown down the face of breaking waves, etc. extensive tank testing done to prove the validity of the theory and ultimately endorsements by the US Coastguard, seem to recall Mr. Jordan gave the ideas to the world for free.

[mikereed100]

@Suijin: Actually, 4 knots was perfectly comfortable, it's just that I believe that the speed was the main cause for the fraying of the cones.

@RDW: I let Sailrite know about the issue with the cones when we returned. They replied that they consider the JSD a single-use device, and implied that the frayed cones were not an issue but rather an expected consequence and a small price to pay for the survival of the boat. I disagree, as I feel that a safety device like a drogue or parachute anchor should be capable of multiple deployments, or at minimum of surviving a single deployment. Further, we were not in "survival" conditions, just uncomfortable. Had we been in true survival conditions I feel the drogue would have been reduced to a 340' streamer that would not have provided enough drag to pull the boat through waves. To be fair, in our case it may be a simple matter of sizing (number of cones) rather than the cones being too lightly engineered.

@Brad: I believe one could attach the cones to single braid much the same as double braid, i.e. pass the tape under a couple of strands and tie a figure 8 in the end. I don't think is necessary to use a reduced diameter line for the final portion of the drogue, but it would save weight and cost. On the other hand, at some point the diameter of the dyneema may become too small to accommodate the tapes from the cones. Maybe Evans Starzinger will weigh in as I believe he has used Dyneema in a JSD.

@ontherocks83: The motion wasn't that bad before deployment so there was not a big change, but the lower speed was far more comfortable. We went from white knuckles to peace and relative quiet almost immediately.

[Adelie]

Originally Posted by LakeSuperior

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.

Poor analogy, the nylon leader between the boat and drogue is like a rubber band, force varies linearly as a function of percent elongation and length of line between load and resistance. The resistance of the drogues varies as the square of the velocity, that distinction makes a huge difference in the loads experienced. An analogy to this would be the difference between a bungy and a laid nylon rope when doing a bungy jump off a bridge. Both will provide spring, but I would rather jump with the bungy than the nylon.

[DumnMad]

Contrary to what some are saying, the drag force on the series drogue is not proportional to square of velocity.
The standard drag equation does not work on a shape where length is so much longer than cross section. Friction is dominant and the drag force more like proportional to velocity only.
Shock loading is therefore not an issue and Dyneema is best because the lack of stretch means the whole drogue length comes into effect earlier and the lunge forward has the full brakes applied before the boat can reach max speed.

[Adelie]

Originally Posted by DumnMad

Contrary to what some are saying, the drag force on the series drogue is not proportional to square of velocity.
The standard drag equation does not work on a shape where length is so much longer than cross section. Friction is dominant and the drag force more like proportional to velocity only.
Shock loading is therefore not an issue and Dyneema is best because the lack of stretch means the whole drogue length comes into effect earlier and the lunge forward has the full brakes applied before the boat can reach max speed.

Actually the resistance load is the sum of

1) The friction between the series line which follows the square of the speed but because of the comparatively low area of the line is a minor component.

2) the form drag of the cones which follows the equation 1/2 * Fluid Density * Velocity^2 * Coefficient of drag for a cone * Frontal area of each cone * number of cones

3) force required to accelerate the water contained in the cones which follows the equation
1/3 * pi * Radius^2 * Length of cone * density of seawater (64pcf) * Change in speed / Time to change speed.

Form drag will easily dominate this sum in steady state conditions and water acceleration forces will be zero.

In dynamic conditions when a wave hits and starts to accelerate the boat, series drogue and the water contained in the drogue, the inertia forces may almost equal the form drag, the mass water in the cones will be a significant fraction of the weight of the boat if the series is sized appropriately for the boat.

[DumnMad]

The cones are slipstreaming each other so the drag equation does not work in this case.

[Adelie]

Originally Posted by DumnMad

The cones are slipstreaming each other so the drag equation does not work in this case.

I went an looked up the standard design and I can see your point but I don't think it changes the result by more than 10% or so given that the spacing of the cones is 4 times their diameters. If the spacing were 1.5 or 2 times their diameters the effect would be a lot more pronounced.

Going back to my original assertion: in support of my argument that stretchy line is better as a leader is figure 24C, pg 53 of the USCG evaluation report for the Jordan Series Drogue which shows increasing peak load in the leader with increasing stiffness. http://www.jordanseriesdrogue.com/pd...uardreport.pdf

For 3/4" nylon line 250' long they indicate a spring coefficient (k) of 200 lb/ft stretch. (E = 2-4 GPa, Breaking strength = 12,780lb Nylon Rope - Strength)

For 5/16" Dyneema, 250' long
(E = 55-172 GPa, Breaking strength = 13,700lb, SAMSON ROPE AmSteel-Blue Dyneema SK-75 Single Braid at West Marine) k should equal something like 2000-4000 depending on exact properties.

Assuming the graph for load can be extrapolated linearly, then the peak load in the line doubles or triples by using Dyneema instead of Nylon. Upsizing the dyneema line to 7/16" or 1/2" would take care of line breaking issues, but does nothing for the boats structure which would also be experiencing increased loads.

[RainDog]

Originally Posted by mikereed100

I let Sailrite know about the issue with the cones when we returned. They replied that they consider the JSD a single-use device, and implied that the frayed cones were not an issue but rather an expected consequence and a small price to pay for the survival of the boat.

Wow. That is very discouraging to hear. Kind of makes me re-evaluate my prior opinion of Sailrite.

[JPA Cate]

Rain Dog,

Consider it a warning, and use your hot knife to heat seal all your cones. It really won't take too long, and will provide an easy reinforcing. You could also turn down very narrow hems (like on a handkerchief), on all the cones (yikes!), even by hand, while you were chatting, or something. Once done, the protection is there. I still worry about making the cones smaller. Would you have to add a tail with a few cones to make up for the area lost, even by such small hems? Boy, I would like to know that! :-)

[JPA Cate]

Pacifica,

Thank you also for your posts. I'm still wondering whether adding hem allowance to the cone size, and making them hemmed is a viable option. Whaddaya think?

Most specifically, do you think that if you hot knife the cones in the first place that that would take care of the fraying issue. Because if that is the case, there are a bundh of non-checkbook cruisers who would just go buy the ripstop, and cut and sew their own cones..... Leave it to the big buck guys to buy the one use ones! OMG! That's a huge investment to make for just one time! Ooooooh MY!

Ann

[captain58sailin]

Okay, well nothing presented here alters my belief that stern "to", strategy is dangerous, so you all carry on and I'll withdraw from the conversation. I don't see how filling your cockpit with water is a good idea.

[Dockhead]

Originally Posted by captain58sailin

Okay, well nothing presented here alters my belief that stern "to", strategy is dangerous, so you all carry on and I'll withdraw from the conversation. I don't see how filling your cockpit with water is a good idea.

If you have reasonable buoyancy in the stern, getting pooped will be very rare. Remember when running off trailing warps or a drogue, your speed is subtracted from the speed of the wave, giving more time for your boat to ride up the front faces of the waves. Lying bow to the waves, nearly stopped, to a para-anchor, will give you much more violent encounters with the waves, and since your bow is less buoyant, a lot more green water on deck. And running off, your forward motion gives you steerage and control, and protects your rudder. It seems to me that the JSD is the way to go for survival conditions.

[conachair]

Originally Posted by captain58sailin

Okay, well nothing presented here alters my belief that stern "to", strategy is dangerous, so you all carry on and I'll withdraw from the conversation. I don't see how filling your cockpit with water is a good idea.

Some designers notes are worth a read here...
http://www.oceanbrake.com/jordan'snotes.html
Getting completely pooped by a breaking wave is possible but apparently an extremely rare event.