Jordan Series Drogue in Dyneema

[Afrinus]

Thanks for including those links. Definitely some interesting reading.

Pieter

Originally Posted by At Peace

I have not read through this entire thread, but there is a lot of incorrect information and thinking here. First, if Dyneema had been around when Jim Jordan designed the Drogue, he would have used it and years later, he mentioned that. The design of the Drogue has evolved since the original with heavier cloth for the cones and improved attachment points. The biggest issue is how to attach the JSD to the boat with adequate strength. Most production boat cleats are most likely not designed for the loads that could be experienced with a rare breaking wave (again, this is discussed in the link below).

I’ve added two websites that go into great detail. Anyone who has questions or interested should research.

https://www.jordanseriesdrogue.com/D_5.htm
Website explains a lot in the JSD design and has a link for the USCG report.

https://dragdevicedb.com/drogues
Website has numerous personal experiences with using the JSD on various boats. You can filter the search in the left column to find the boat you have or one similar.

[Fi2010]

You have a very real problem using any type of UHMWPE (Dyneema/Spectra) type fabric or rode. This type of fiber floats and can cause a “bunching up effect” that can lead to tangles.

More importantly, this type of fiber may cause significant shock loading, because the fiber is too light in weight; creating extra slack in the system.

Our pioneering research regarding this very real danger has been tested for approximately two years by the Dept. of the Navy. Additionally, several military contractors are currently testing several para-anchor and storm drogue designs made with UHMWPE, Dacron, and Nylon. So far, their test results are matching up to our published data.

The only advice we can provide you is what we’ve published on this forum many times. Add lots of weight to the JSD or it will likely fail. That means an average of 35 to 50 lbs. to remove the dangerous slack created by UHMWPE. It's not a guarantee to stop the problem, but it can certainly help.

[StoneCrab]

I also built a Covid inspired Jordan Series Drogue using Dyneema. The project was a lot of work but it turned out really well.

I am looking for a design guide for the chainplates that I plan on attaching to the stern of the boat. My hull is solid fiberglass. I am against just overbuilding everything and feel much more comfortable with a way of calculating the design.

I was excited to learn that Ocean Brake sells chainplates but theirs are a one size fits all affair. That doesn't take into account what you are bolting it to either.

It is fairly easy to pick a shackle and calculate the loads in the metal strap that is the "chainplate'. Where it gets mysterious is the number and diameter of the bolts needed to spread that load to the hull, the load carrying capability of the fiberglass, the size of backing plates and whether additional glass is needed to spread the loads.

As with everything bolted to fiberglass, you want a backing plate. These plates prevent the point loading of a bolt from pulling through the hull by spreading the loads. The JSD chainplates will be under a shear load at the hull to plate joint and should be able to support the weight of the boat, since that's what you will have, if you are falling off a wave but being held back by the JSD. Admittedly having the plates rip out a section of the stern would complicate the situation. But this situation is unique in that the load is almost completely parallel to the the surface of the hull... shear load.

Does anyone have a recommendation of a design guide which describes a design standard for determining minimum hull thickness and shear carrying loads of fiberglass in a chainplate application?

The emotional reaction is to beef the hell out of the plate, add as big of a backing plate as will fit, add a few more layers of glass for extra measure, and throw holding bolts at it until it looks like a turn of a century bridge. I'd prefer to know I've done it right rather than DIY "feel" like I did.

Any retired naval architects?

[At Peace]

Originally Posted by Fi2010

You have a very real problem using any type of UHMWPE (Dyneema/Spectra) type fabric or rode. This type of fiber floats and can cause a “bunching up effect” that can lead to tangles.

More importantly, this type of fiber may cause significant shock loading, because the fiber is too light in weight; creating extra slack in the system.

Our pioneering research regarding this very real danger has been tested for approximately two years by the Dept. of the Navy. Additionally, several military contractors are currently testing several para-anchor and storm drogue designs made with UHMWPE, Dacron, and Nylon. So far, their test results are matching up to our published data.

The only advice we can provide you is what we’ve published on this forum many times. Add lots of weight to the JSD or it will likely fail. That means an average of 35 to 50 lbs. to remove the dangerous slack created by UHMWPE. It's not a guarantee to stop the problem, but it can certainly help.

Is your research, the Navy, and military contractors testing published? I would like to read it, could you provide the link(s)?

[At Peace]

Originally Posted by StoneCrab

I also built a Covid inspired Jordan Series Drogue using Dyneema. The project was a lot of work but it turned out really well.

I am looking for a design guide for the chainplates that I plan on attaching to the stern of the boat. My hull is solid fiberglass. I am against just overbuilding everything and feel much more comfortable with a way of calculating the design.

I was excited to learn that Ocean Brake sells chainplates but theirs are a one size fits all affair. That doesn't take into account what you are bolting it to either.

It is fairly easy to pick a shackle and calculate the loads in the metal strap that is the "chainplate'. Where it gets mysterious is the number and diameter of the bolts needed to spread that load to the hull, the load carrying capability of the fiberglass, the size of backing plates and whether additional glass is needed to spread the loads.

As with everything bolted to fiberglass, you want a backing plate. These plates prevent the point loading of a bolt from pulling through the hull by spreading the loads. The JSD chainplates will be under a shear load at the hull to plate joint and should be able to support the weight of the boat, since that's what you will have, if you are falling off a wave but being held back by the JSD. Admittedly having the plates rip out a section of the stern would complicate the situation. But this situation is unique in that the load is almost completely parallel to the the surface of the hull... shear load.

Does anyone have a recommendation of a design guide which describes a design standard for determining minimum hull thickness and shear carrying loads of fiberglass in a chainplate application?

The emotional reaction is to beef the hell out of the plate, add as big of a backing plate as will fit, add a few more layers of glass for extra measure, and throw holding bolts at it until it looks like a turn of a century bridge. I'd prefer to know I've done it right rather than DIY "feel" like I did.

Any retired naval architects?

There’s info here to give you an idea and info on how the design works.
https://www.jordanseriesdrogue.com/D_5.htm

Doesn’t need to be able to carry the total weight of the boat. The design load of a JSD is 70% of the boat displacement.

[StoneCrab]

Thanks for your interest.

I've read the Jordan report. He does not give design data for the hull to plate joint which is my area of concern and the point of my post. It is the interaction between the steel strap and the hull that is indeterminate and under defined.

I believe he felt that a 1/4" thick chain plate was adequate. I dispute that dimension for several reasons, not the least being that with only 1/4", you are point loading the shackle, which reduces the safe working load of that piece in the chain keeping you safe.

You are correct in saying Jordan suggest the loads are 70% of displacement....but that is per leg of the bridle. My comment that the chain plates need to support the weight of the boat is just a generalization. Depending on what we are talking about, that is either too low or too much, but as a system, accurate in intention.

It is really the fiberglass failing that is my concern.

When they started building fiberglass boats they made the fiberglass as thick as they would build it with wood. Over time the hulls were thinned. Since this didn't cause any failures, they kept thinning. There doesn't seem to be any composite design guides. Perhaps due to the variable nature of the construction...chopgun, strand,mat etc. I'm starting to get the feeling that the industry is just working off of legacy thicknesses that didn't break the last time....rules if thumb, but not calculations.

In the case of a horizontal chain plate pulling on the hull just below the toe-rail, I don't don't think that section of the hull was designed for those loads. It is quite a bit thinner that high up, so out of an abundance of caution and a dislike for not knowing, I continue my search.

I've contacted two naval design schools without successful referrals or answers.

I'm hopeful though

[At Peace]

I agree with what you say here. That reference was written many years ago for a design load of 14k#, which was probably a fairly small boat 35 years ago. I did mean to say “with any addition such as this should be at least reviewed by a naval architect”.
I’ll send you a publication which may be more help.

[fxykty]

Originally Posted by StoneCrab

Thanks for your interest.



I've read the Jordan report. He does not give design data for the hull to plate joint which is my area of concern and the point of my post. It is the interaction between the steel strap and the hull that is indeterminate and under defined.



I believe he felt that a 1/4" thick chain plate was adequate. I dispute that dimension for several reasons, not the least being that with only 1/4", you are point loading the shackle, which reduces the safe working load of that piece in the chain keeping you safe.



You are correct in saying Jordan suggest the loads are 70% of displacement....but that is per leg of the bridle. My comment that the chain plates need to support the weight of the boat is just a generalization. Depending on what we are talking about, that is either too low or too much, but as a system, accurate in intention.



It is really the fiberglass failing that is my concern.



When they started building fiberglass boats they made the fiberglass as thick as they would build it with wood. Over time the hulls were thinned. Since this didn't cause any failures, they kept thinning. There doesn't seem to be any composite design guides. Perhaps due to the variable nature of the construction...chopgun, strand,mat etc. I'm starting to get the feeling that the industry is just working off of legacy thicknesses that didn't break the last time....rules if thumb, but not calculations.



In the case of a horizontal chain plate pulling on the hull just below the toe-rail, I don't don't think that section of the hull was designed for those loads. It is quite a bit thinner that high up, so out of an abundance of caution and a dislike for not knowing, I continue my search.



I've contacted two naval design schools without successful referrals or answers.



I'm hopeful though

Well, the JSD will be a (mostly) horizontal pull (roughly) parallel to the hull. The shrouds supporting the mast are a (mostly) vertical pull (roughly) parallel to the hull.

So if the chainplates for your shrouds are bolted to the hull, that should be a pretty good guide for what you will need at your sterns for your JSD. Of course, one of the variables as you point out will be the thickness and layup of the hull at the chainplates versus the hull at the stern.

Maximum loads I expect will be pretty similar for both.

We’re using the toerail on the hull deck joint (a horizontal flange that sticks out to the side well below the deck) as the backing plate for a fibreglass ‘chainplate’ for our JSD connections. As it turns out we’re covering about twice the area of hull with our fibreglass plate as our chainplates do for the cap shrouds.

Talk to an experienced boat builder - they’re likely to be more helpful as they have to rebuild structures all the time. If they’re nervous about providing guidance, then get them to refer you to the marine structural engineer they use. Don’t bother with eggheads.

[StoneCrab]

I'd like to hear more about your fiberglass chain plates. Do you have any drawings or pictures?

[BigBeakie]

Originally Posted by StoneCrab

I'd like to hear more about your fiberglass chain plates. Do you have any drawings or pictures?

For all our structural components that have expected high loads, we built carbon chainplates, attachment points etc.

We sought the advice of those knowledgeable in the dark arts of composite engineering as applied to performance multihull boat building.

For our two JSD attachment points we used high quality 450 gsm unidirectional carbon stitched and we use Scott Bader laminating Vinylester resin with high mechanical properties in a wet layup technique, taking care to roll out excess resin or to vacuum bag when possible. Surface finishing layers are 200 gsm double bias glass. The carbon is multi layer and the straps are splayed out in a uniform fashion for load path spreading, and are tied to any other structural component if possible.

The core of the structure is stainless thick walled tube, sized to take the appropriate sized rigging screw clevis pin. In the case of the JSD pin we used 19mm. We'll use 3/4" Crosby G209 shackles to take the 14mm Acera bridle eyes that have spliced in Hampidjan stainless gusseted thimbles designed for HMWPE rope. ( see Wire Thimble Stainless Steel With Gusset )

We went this way due to a healthy respect for chafe and the loads expected, instead of soft splices everywhere.

[jalmberg]

Originally Posted by fxykty

Talk to an experienced boat builder - they’re likely to be more helpful as they have to rebuild structures all the time. If they’re nervous about providing guidance, then get them to refer you to the marine structural engineer they use. Don’t bother with eggheads.

Without science there is no engineering.

[Fi2010]

Stainless gusseted thimbles are designed for cables. The mention of specifically designed for Dyneema or any other type of rode is marketing. Although we spliced nylon rode using these thimbles decades ago for Naval operations. Can be a challenge to splice the rode, because the tubes get in the way.

We have some twenty or so in stock if anyone is interested in acquiring these thimbles below wholesale price. We have no use for the stainless steel gusset thimbles sized for 5/8” (16 mm) rode.

[BigBeakie]

OK. What is your preferred method of attaching the drogue bridle to the boat?

[Benz]

Originally Posted by Fi2010

Stainless gusseted thimbles are designed for cables. The mention of specifically designed for Dyneema or any other type of rode is marketing. Although we spliced nylon rode using these thimbles decades ago for Naval operations. Can be a challenge to splice the rode, because the tubes get in the way.

We have some twenty or so in stock if anyone is interested in acquiring these thimbles below wholesale price. We have no use for the stainless steel gusset thimbles sized for 5/8” (16 mm) rode.

The shop where I work commonly has gussets welded into SS thimbles specifically so that we can make megayacht dinghy tow-bridles, which are usually Dyneema, that won't collapse the thimble. Lots of bridles come in with cracked thimbles; most of these are 1" or bigger Dyneema, and the ungusseted thimbles just can't take it.

[StoneCrab]

Morgan's Cloud has several articles on this topic. Where possible, John interviews sailors who have used their JSD's. These reports support the use of gusseted thimbles. The loads are tremendous and even the shackles can become deformed.

https://www.morganscloud.com/2013/06...launch-system/ This link goes to one of the chapters in the Attainable Adventure Cruising book on drogues.