Jordan Series Drogue attachment point engineering

[Jud - s/v Sputnik]

After stumbling across this engrossing thread in Fix-It Anarchy on how to engineer the laminate schedule on the inside quarters of a boat to take the potentially significant loads on the mounting points of a Jordan Series Drogue, I’m wondering about how to determine the (theoretical) strength of an existing structure - the likely potential JSD mounting points on my boat.  That thread is all about questioning the “well, it looks pretty strong and it probably is” approach others have taken when bolting beefy stainless plates on the stern quarters of their boats to attach a JSD to - and instead asking, “how do you actually KNOW it’s strong enough, and what should I do to make mine strong enough in terms of beefing up the laminate schedule inside?”
 

In that thread, @estarzingerdescribes how aluminum Hawk was built with specifically engineered, reinforced points on the transom for a JSD attachment.  
 

With a steel hull, mine, how to determine the theoretical strength of welded deck fittings?  Specifically my stern cleats and chocks - obvious places to attach a JSD.  Presumably, if one knew the materials involved and other relevant details, this would be a simple matter for a trained engineer to determine - i.e, weld strength?

Secondly, assuming the stern cleats and chocks are stout enough, presumably it would make sense to devise an attachment system that would use both fittings, cleat and chock, to spread the loads?  (Sorry, the pictures aren’t great.)

 

[Startracker]

Jud, count me in as well.  FKT had some good observations on steel boat JSDs in the thread about the steel sailboat I am fixing up, though part of me is still very reluctant to not add a few bolts and a backing plate spanning several frames, I have visions of welded on exterior fittings peeling the hull like a can.  I'm finding a big comfort level loss in dealing with steel vs fibreglass.

 My basic working theory at this point is with enough measurements of the hull sides, I can calculate an approximate number of frames, or key structures I need to span to give me a safe working load of the breaking strength of the rope, which would be comforting if I'm ever using it as long as the rope is still attached.  

 

[European Bloke]

The advantage of the fittings discussed in the other thread is no chafe on the lines. You're not going to be able to achieve that with your fittings which is a key reason people add an external fitting.

 

[estarzinger]

Jud, those cleats 'look' strong enough (someone here, like Zonk, could do a better back of the envelope than I to confirm that), but I would guess in the 'worst case' a series drogue could spread open the tops of those fairleads (they are 'open' at the top - right?)

I would only add the comment that I preferred not to have to lean over the side of the boat and fiddle with a screw shackle when deploying a drag device.

 

[Jud - s/v Sputnik]

Jud, those cleats 'look' strong enough (someone here, like Zonk, could do a better back of the envelope than I to confirm that), but I would guess in the 'worst case' a series drogue could spread open the tops of those fairleads (they are 'open' at the top - right?)

I would only add the comment that I preferred not to have to lean over the side of the boat and fiddle with a screw shackle when deploying a drag device.

Thanks, Evans - it’s something I’ve never gotten around to thinking about closely, since I haven’t looked seriously into drogues.  And it’s also stupidly never occurred to me to actually consider how that hardware works: I.e., what’s behind/under the cleats, what they’re attached to.   I mean, I “know” they’re strong.  But are they really?  How strong?  I’ve spent enough time in that (actually relatively spacious) stern lazarette running wire, etc that it’s occurring to me I ought to see what is actually below the deck cleat - can easily Dremel/oscillating saw cut out a bit of 3/16” plywood hull liner under it to have a look.  That would be a start, anyway.

Then, someone who understands the engineering of welds, etc. could make a better estimation of the cleat’s strength, knowing what’s underneath too.

Re: fairleads, an idea - I feel like maybe something could be devised that could be attached (when needed) and span the gap of the fairleads to prevent them from opening if loaded up - but any load would presumably be lower down, at the bend in the 3/8” stainless rod (where it’s less prone to bend open).  

Idly thinking through a bridle once, I was kinda thinking a bridle would be cleated to each stern cleat and prussik hitches, with their free ends tied (double fisherman’s?), or spliced together if stronger, would be left “installed” on the legs of the bridle, could then be slid a little bit into position along the bridle so that the tied/spliced ends (i.e., loops) could hook on the fairleads, and the prussiks then snugged up, backing up/spreading the loads on the stern cleats.  (The aft “horn” of the fairlead is in line with the cleat.)

Aternatively, another idea, although it gets more complicated/messy - each bridle leg has an eye spliced into it.  A line runs through each eye; it connect between the hoop that’s welded on over the toe rail (see pic below, a bit forward of stern cleat), and the stern cleat, theoretically self-equalizing the load between the two points (bridle end with eye can ride along the other line between the two anchor points)...even though self-equalizing anchors maybe sort of a myth...this might load up the “sub-bridle” (where it passes through the eyes in the main bridle), or it may not (since it may slide back and forth a bit with the motion of the boat).

I’m not 100% against installing —bolting on— some sort of plates with eyes on the quarters but would really like to avoid if possible.  Don’t wanna destroy the lines of the svelte yacht

 

[DDW]

It is very difficult to be certain without dimensions and thicknesses, but I'd be wary of those deck cleats and chocks. The chocks aren't a very strong section, looks like simply bent round stock. The cleat arms look like they are tubes welded to the deck plating, you will concentrate high stress in a very small section. With dimensions, it would not be terribly difficult to calculate a SWL for the fittings themselves and the welding, but much will depend on the deck plating and how it is supported, probably requires FEA to get a meaningful answer. 

Those are the reasons to weld on purpose built tangs. They can be positioned at a strong point in the hull (like the transom corner), be aligned more or less with the load (which makes strength calculations more reliable) and backed up if necessary. Adding something like this is one of the big advantages of a metal boat. 

 

[Jud - s/v Sputnik]

The advantage of the fittings discussed in the other thread is no chafe on the lines. You're not going to be able to achieve that with your fittings which is a key reason people add an external fitting.

I can’t see any chafe points - curious what you’re seeing/thinking.

Option 1) JSD bridle ends are cleated to stern cleats

Option 2) same as (1) above, but some means is devised to use the fairleads (somehow prevent them opening up/secure their ends) as a back up attachment point/load spreading point

Option 3) As described in my previous post, a sort of “riding” bridle that has an eye in each end; the main bridle rides on a rope that attaches between stern cleat and that hoop welded over my toe rail.  (Whether this is a crazy idea or not - just an idea at this point.) 

I can’t see any (bad) chafe points in these options. But maybe you’re simply saying that JSD bridle ends shackled to hard points (plates or suitable padeyes attached to the hull, as in that other thread) basically eliminates chafe 100%?

 

[Jud - s/v Sputnik]

It is very difficult to be certain without dimensions and thicknesses, but I'd be wary of those deck cleats and chocks. The chocks aren't a very strong section, looks like simply bent round stock. The cleat arms look like they are tubes welded to the deck plating, you will concentrate high stress in a very small section. With dimensions, it would not be terribly difficult to calculate a SWL for the fittings themselves and the welding, but much will depend on the deck plating and how it is supported, probably requires FEA to get a meaningful answer. 

Those are the reasons to weld on purpose built tangs. They can be positioned at a strong point in the hull (like the transom corner), be aligned more or less with the load (which makes strength calculations more reliable) and backed up if necessary. Adding something like this is one of the big advantages of a metal boat. 

100%.  I’ve never given this any serious thought.  (Had to look up FEA - didn’t know the acronym but have heard of the concept.)

Then, yesterday reading that other thread, kickstarted my brain (which is currently thinking about details of a warehouse power upgrade from 800A to 2400A I’m doing for work, figuring out rigging for drifter and heavy air Solent jib, upgrading old cabin lights to LEDs, installing a new larger/easier to access and service fuel filter this winter, etc etc etc etc )

Ultimately, as you say, probably the easiest and most sensible option would be tangs at the quarters.  Would be fairly easy to do, but I’d possibly bolt something on given the real messiness of prep for (inside), and welding, there.  Preventing fire would involve removing quite a bit of inside liner and foam insulation in a tight area, I think.  Will have to double check today.

I’d just like to investigate and understand alternatives first to see if they’re viable.  Attaching sh#t to the hull...ugh...

 

[Elegua]

So does one have to go full JSD with the loads that brings or do products like a Galerider provide enough drag to keep the boat under control? 

 

[hdra]

Hey Jud,

The chafe point in your setup would be the fairleads, assuming you're running the bridle through them, or the stanchion bases and rest of the hardware if not.  I've only deployed a JSD in practice in calm weather, but I have had some experience with mooring lines in hurricanes, and can tell you that even very large radius fairleads can cause a lot of chafe when the line is under a lot of load and moving around.  In an ideal world, the bridle lines would go straight off the back of the boat and not touch anything anywhere.  When I was trying to figure out where to attach our JSD on our aluminum boat, I imagined the bridle / boat yawing back and forth 40 or 50 degrees, as well as up and down a similar amount (steep wave faces) and then tried to ensure that the bridle lines wouldn't touch anything in any of those angles/positions.  Didn't quite manage it as we have a crowded stern, but think we got close.

We ended up making our bridle out of large diameter dyneema so that it would relatively chafe resistant, and even if it sustained some damage it would still be significantly stronger than the max load the rest of the drogue was built for.

Haven't had to use it yet on two boats and 40,000+ ocean miles, but definitely the kind of thing that if you are going to use it you want to make sure it is figured out in advance.

 

[Jud - s/v Sputnik]

Hey Jud,

The chafe point in your setup would be the fairleads, assuming you're running the bridle through them, or the stanchion bases and rest of the hardware if not.  I've only deployed a JSD in practice in calm weather, but I have had some experience with mooring lines in hurricanes, and can tell you that even very large radius fairleads can cause a lot of chafe when the line is under a lot of load and moving around.  In an ideal world, the bridle lines would go straight off the back of the boat and not touch anything anywhere.  When I was trying to figure out where to attach our JSD on our aluminum boat, I imagined the bridle / boat yawing back and forth 40 or 50 degrees, as well as up and down a similar amount (steep wave faces) and then tried to ensure that the bridle lines wouldn't touch anything in any of those angles/positions.  Didn't quite manage it as we have a crowded stern, but think we got close.

We ended up making our bridle out of large diameter dyneema so that it would relatively chafe resistant, and even if it sustained some damage it would still be significantly stronger than the max load the rest of the drogue was built for.

Haven't had to use it yet on two boats and 40,000+ ocean miles, but definitely the kind of thing that if you are going to use it you want to make sure it is figured out in advance.

Hey hdra - Cool; thanks for the “reality check”! .  I’ve never encountered hurricane mooring or serious conditions like that, so sitting here, Sunday morning at home planning out my day, it’s easy to kind of forget how many possible areas of (incremental) failure there are.

Now that I’ve got my head screwed on straight , I can appreciate how you really do have to think “worst case scenario”, the bridle not touching anything in most angles of yaw.  I’m not quite there yet, I’ve got other stuff to think through and figure out (finalizing light and heavy air set ups is key this winter), but this thread is giving me great preliminary food for thought - a great way (for me) to hash out (sometimes possibly bad) ideas without being flamed

I definitely grasp that these are issues you want to figure out in advance, and actually hands on, in calm weather.  This, and heavy weather/hurricane-type mooring.  (But, is one ever really ready for that...)

 

[Jud - s/v Sputnik]

So does one have to go full JSD with the loads that brings or do products like a Galerider provide enough drag to keep the boat under control? 

Elegua- Not to hijack my own thread , but let a hundred flowers bloom, let a hundred schools of thought contend.  John on Morgan’s Cloud has some good, in-depth thoughts on Galeriders (not set conventionally).

Lots to think about.  I haven’t really thought through heavy weather drogue/sea anchor stuff - just kinda assumed that the JSD was the “way to go”.  That said, Fatty Goodlander has some interesting alternative ideas that he’s clearly put a good deal of thought into.

 

[Elegua]

hundred flowers bloom

Ok, but let's not go kill or jail everyone that raises their head to comment afterwards...

I've been thinking about this, (always a dangerous activity). JSD seems the go-to answer these days. But, it seems a more passive method that generates huge loads and in a space constrained environment, the JSD one use/purpose. 

A drogue generates high loads, but not as much as the JSD and you retain steerage. It also has a dual use for emergency steering (which strikes me as a much more likely failure).  A drogue probably does not protect you from that extreme breaking wave event that a JSD would.  

 

[Jud - s/v Sputnik]

A drogue generates high loads, but not as much as the JSD and you retain steerage. It also has a dual use for emergency steering (which strikes me as a much more likely failure).  A drogue probably does not protect you from that extreme breaking wave event that a JSD would.  

Carry both?!?  
 

From the Fatty Goodlander article I linked to above (which looks at old car tires, etc etc): 

“Of course, slowing devices are only limited by your imagination. Once I had my Gale Rider (made almost entire out of webbing) and a JSD aboard—I quickly had Carolyn sew me up an experimental Fat Flat drogue with JSD-type cones sewn onto webbing. We’ll soon be testing this not-patented (enjoy!) device off the Cape of Storms, and will get back to you with the results.

“Here’s the simple truth: I sailed twice around the world on a $3,000 boat that carried more offshore safety gear than almost any vessel out there.”

 

[Elegua]

Carry both?!?  
 

From the Fatty Goodlander article I linked to above (which looks at old car tires, etc etc): 

“Of course, slowing devices are only limited by your imagination. Once I had my Gale Rider (made almost entire out of webbing) and a JSD aboard—I quickly had Carolyn sew me up an experimental Fat Flat drogue with JSD-type cones sewn onto webbing. We’ll soon be testing this not-patented (enjoy!) device off the Cape of Storms, and will get back to you with the results.

“Here’s the simple truth: I sailed twice around the world on a $3,000 boat that carried more offshore safety gear than almost any vessel out there.”

Both might be the answer.  I've never figured out how much Fatty is for real. Yes, he does do it all, but what he writes seems a bit glossed over for the starry eyed magazine readers. 

The way my particular boat behaves, I get the feeling it needs some way on. It's also not as strong as yours. 

 

[estarzinger]

I personally was thinking that the best drogue solution was a 'few elements series' - that is like 3 or 4 'single element designs' in series which you can put out incrementally - be able to put out one, or two, three or four depending on the conditions and what you think will be best.  In my mind this had a couple advantages - obviously variable drag suited to the conditions - easier recovery than the jsd because you have more bare rode you can just put on a winch and winch in without worrying about cones - I would use pretty long rode between the elements and so extra long length when you have 3 or 4 out and we found 'longer than suggest' was beneficial in real big waves (the wave length can be like +600' long).  I tried it out in a few mild blows and liked it but never got a chance to try in severe conditions (fortunately I guess).

 

[Jud - s/v Sputnik]

Both might be the answer.  I've never figured out how much Fatty is for real. Yes, he does do it all, but what he writes seems a bit glossed over for the starry eyed magazine readers. 

The way my particular boat behaves, I get the feeling it needs some way on. It's also not as strong as yours. 

Agree.  He’s hard to “get”.  Undoubtedly lots of experience- but how much of that actually makes it through in his consumer-oriented magazine writing is hard to say.

 

[DDW]

Never been in survival type conditions, but from extensive reading, the drogue is an active management type of thing while the JSD (fully deployed) is more of a passive "we are exhausted" kind of solution. I imagine each has conditions that favor them. I considered the JSD as first priority because it seemed like the ultimate solution, less optimum in lessor conditions but still useable. Something like a galerider doesn't weight that much or take much space so might as well add it to the quiver. A full JSD is pretty heavy and takes some storage space. 

Regarding Estarzingers comments, it seems to me you could have a JSD built in segments to allow deployment of say 1/3, 2/3, or full. You'd have to think out the process of switching between them when the shit has already hit the fan, but I think there would be ways to accomplish. 

 

[Jud - s/v Sputnik]

Jud, those cleats 'look' strong enough (someone here, like Zonk, could do a better back of the envelope than I to confirm that), but I would guess in the 'worst case' a series drogue could spread open the tops of those fairleads (they are 'open' at the top - right?)

I would only add the comment that I preferred not to have to lean over the side of the boat and fiddle with a screw shackle when deploying a drag device.

Evans - have you any idea about two particulars details of JSD attachment chainplates?  Specifically - shackle hole location relative to the end of the chainplate (how much “meat” at a minimum should there be between the shackle hole and the end of the chainplate); and, how far aft of the transom at a maximum should attachment chainplates extend?  (Browsing around the web a bit I came across your informative post on the CF site re: attachments [about realistically designing chainplates for most common, most-case scenarios, not a single worst-case scenario] -  which got me wondering.  
 

This is the first I’ve ever really looked in any detail into JSDs, and I see the helpful Design Loads and Attachments page on the JSD site - but, surprisingly, there’s nothing on these two aspects of attachment chainplates engineering (shackle hole location relative to the end of the chainplate/minimum material left there; and chain plate maximum extension past transom).  Any clues?