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Jordan Series Drogue attachment point engineering


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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.)

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  • Jud - s/v Sputnik changed the title to Jordan Series Drogue attachment point engineering

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.  

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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.

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2 hours ago, estarzinger said:

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 :-)

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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. 

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4 hours ago, European Bloke said:

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%?

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33 minutes ago, DDW said:

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...

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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.

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7 minutes ago, hdra said:

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...)

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31 minutes ago, Elegua said:

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.

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Just now, Jud - s/v Sputnik said:

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.  

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11 minutes ago, Elegua said:

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.”

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4 minutes ago, Jud - s/v Sputnik said:

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. 

 

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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).

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18 minutes ago, Elegua said:

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.

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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. 

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On 11/28/2021 at 6:25 AM, estarzinger said:

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?

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Hi Jud,

My back of the envelope number for guestimating welds is 1 kN per mm of "6mm fillet weld", so a 10mm long weld can lift 1 ton! In other terms, in theory 2 x 50mm long welds would be enough to lift a 10 metric tons boat Impressive isn't it? Don't design a heavily loaded weld like this as doing it properly is a bit more complex than my dirty techniques to scheme design stuff.

My worry wouldn't be the attachment itself but that the loads effectively spread to the primary structure as the actual risk is bending out of shape the steel plate you are welding to. Thus I would attach the anchoring point close to the boat inner structure. In practice, the stern cleats are probably at one of the best place as this is where hull and deck meet. Just above the small chine below where the windows are would also be a good spot. A crease in a shell structure is always a strong point especially for "out of plane" loads.

If you use a bridle, it needs to be quite long otherwise you are creating a "catenary" and increasing artificially the loads.

For holes in a steel plate, there are edge distances, 3 times the diameter of the hole is plenty enough!

 

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4 hours ago, Panoramix said:

Hi Jud,

If you use a bridle, it needs to be quite long otherwise you are creating a "catenary" and increasing artificially the loads.

For holes in a steel plate, there are edge distances, 3 times the diameter of the hole is plenty enough!

 

 

Hey Pano - I’m not considering the stern cleats/fairleads idea any longer (I.e., weld strength) as a JSD attachment point.  Honestly, I’ve never looked into a JSD (but I have a contact to get one cheap) - and now that I have, just a little bit, I see that the loads are potentially enormous - which I hadn’t fully appreciated. 

Instead, I’d follow JSD’s guidelines and install chainplates.  From their site: 

Drogue Design Load
The design load for each drogue configuration is adjusted for the displacement of the yacht. The design load is the ultimate, once in a lifetime, peak transient load that would be imposed on the drogue in a “worst case” breaking wave strike. The working load during a severe storm is about 10 % of this value.

20,000 lb displacement [a bit more than my boat] = 13,000 lbs. design load

Attachment:
“For a load of 14,000 lbs, a strap ¼ x 2.25 x 18 inches attached with six 3/8 bolts would provide a conservative design.”

Pretty easy to fabricate and install this on my boat.  The remaining questions seem to be:

1) how far aft of the transom at a maximum should chainplates extend

2) how much material at a minimum should be left between the hole for the shackle (1/2” shackle seems to be recommended for the loads above)

3) mounting bolt pattern seems to be staggered holes (based on looking at a few pics and reading online).  Need more details on this.  (JSD recommends x6 3/8” bolts for a “conservative design”).

(I suppose these aren’t questions for the JSD folks, but instead are standard materials engineering type questions?)

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1 hour ago, Jud - s/v Sputnik said:

 

Hey Pano - I’m not considering the stern cleats/fairleads idea any longer (I.e., weld strength) as a JSD attachment point.  Honestly, I’ve never looked into a JSD (but I have a contact to get one cheap) - and now that I have, just a little bit, I see that the loads are potentially enormous - which I hadn’t fully appreciated. 

Instead, I’d follow JSD’s guidelines and install chainplates.  From their site: 

Drogue Design Load
The design load for each drogue configuration is adjusted for the displacement of the yacht. The design load is the ultimate, once in a lifetime, peak transient load that would be imposed on the drogue in a “worst case” breaking wave strike. The working load during a severe storm is about 10 % of this value.

20,000 lb displacement [a bit more than my boat] = 13,000 lbs. design load

Attachment:
“For a load of 14,000 lbs, a strap ¼ x 2.25 x 18 inches attached with six 3/8 bolts would provide a conservative design.”

Pretty easy to fabricate and install this on my boat.  The remaining questions seem to be:

1) how far aft of the transom at a maximum should chainplates extend

2) how much material at a minimum should be left between the hole for the shackle (1/2” shackle seems to be recommended for the loads above)

3) mounting bolt pattern seems to be staggered holes (based on looking at a few pics and reading online).  Need more details on this.  (JSD recommends x6 3/8” bolts for a “conservative design”).

(I suppose these aren’t questions for the JSD folks, but instead are standard materials engineering type questions?)

1) As little as possible to avoid bending the the chainplates by out of line loads, so just enough to fit the shackle. I would also make sure that the "chainplates" are in line with the bridle so that they work mostly in tension. make them thick (like 12 mm)...

2) I wsould draw a 80mm diameter around the centre of the shackle hole, that's more than 3 diametre edge distance, good enough.

3) Don't bolt it, you have a steel boat, 13000 lbs is about 6500kg that is a force of 65 kN, in theory you need about 2 x 35mm 6mm fillet welds, welding is cheap, make it 2 x 100mm 6mm fillet welds and your boat is still watertight and you know that the drogue will break before the attachment. I would only use bolts on a GRP or wooden boat.

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If you are expecting a 13,000 lb load on one chainplate, dinner napkin calcs:

The bearing stress on the fixing bolts is 13000/(6 bolts x 0.25 plate thickness x 3/8 diameter holes) = 78ksi. That is beyond the yield of cold rolled mild steel and well beyond the yield of annealed 316SS.

The shear stress on the bolts is 13000/(6 x area of one bolt minor dia) = 30ksi. Near the yield of 316SS but the six bolts will not carry the load evenly.

If the 1/2" hole is 1" from the edge of the plate, 13000/(1" x 2 (because there is material on two sides) x 0.25) = 26ksi. Below the yield of 316.

The bearing stress in the 1/2" shackle hole, 13,000/(0.5 diam x 0.25 plate thickness) = 104ksi. Way above the ultimate of 316. 

Welding on is a better connection than bolted as the stress is more evenly distributed, but larger bolts or twelve 3/8 bolts should be enough bolts. The plate has a bearing problem at both the fixing bolts and the shackle hole. More fixing bolts will mitigate that, but not solve the shackle hole bearing problem. A standard 1/2" shackle actually has a 0.650 pin diameter, that only gets you to 80ksi. You could weld a sleeve in the hole to increase the bearing area, 1/2" shackle could accommodate about 3/4" sleeve length, that gets to you ~26ksi bearing. 

Working load on an alloy 1/2" shackle is 6600 lbs, so ultimate is probably above 13,000. My idea of a conservative design (especially since weight is of little concern and the cost difference is nil) would be 3/8 plate, ten 3/8 bolts (or better welding), a 5/8 shackle and weld a 3/4" long sleeve into the hole. Note that there are bearing considerations for the fixing bolts on the hull plating as well which would need to be looked at. The 5/8" shackle is a big sucker, to have room for the chainplate and large rode thimble you need some space. 

But I have been accused of overbuilding things. 

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12 hours ago, Jud - s/v Sputnik said:

Evans - have you any idea about two particulars details of JSD attachment chainplates?  

I'm not the best guy here for those questions, and I think they guys answering are giving good advice.  Welding is better . . . but I understand that will create paint issues and might create interior issues depending on what is inside in that area (Dashew once had a fire inside his boat because a welder working outside did not look inside ).  As little sticking aft as possible while allowing the bridle connection.  I used huge steel shackles but if I were doing this today I would look at using soft shackles - much lighter/easier to stow/handle/make/replace.  The loads you are talking about are dead easy for soft shackles - its amazing stuff - a 'button with buried tails' design made from 1/4" amsteel would do it but I would go one size up to deal with wear and such.  For direct soft shackle use, you would want the hole to have a nice bend radius - probably thicker (say 2x soft shackle line diameter) than you would want the whole chain plate, so locally thickened right around the hole and radiused.  This would also help with your other question - providing extra beef around the hole.

Bridle - you want the 'length' (eg the distance back along the center line of the apex of the two bridle lines) to be 3 times your transom width.  That makes the angles on the connections relatively small, closeish enough to a straight line pull to not worry about.  It will however yaw around a bit in use, so you do need to make each bridle arm able to carry the full load.

And yea, and with drogues the typical loads are like an order of magnitude less than the 'worst case loads'.  And those worst case loads are really low probability - we never saw them, but they do occasionally/rarely happen (sydney to hobart and golden globe).  You can either think a bit about how rare as asteroid strike you want to plan for, or just bike the bullet and go for the jordan worst case (but then you are way over building for like 6 sigma of situations).

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If the intent is to use soft shackles, would it be a good idea to have several holes and pass the shackle loop through all of them? I'd be worried about bearing on the steel at very high loads. In theory it could deform the steel. 

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On 11/28/2021 at 8:33 AM, DDW said:

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. 

Take some measurements of the weld sizes and diameter of those cleats and I'll give you pretty accurate WAG. :) Is there a doubler/insert plate at the base?

Don't forget the weld of the bitts to the deck is in bending. Simple tensile calcs will overstate the strength. You have to calculate the bending moment and then resolve it to forces at the deck. You can't assume the rope is right at deck level. It's at least 1/2 diameter above the deck and in the real world probably 1 diameter above deck.

I have to keep convincing the younger engineers that the answer is NOT to FEA everything. It is more conservative and is required for complex structures, but sometimes you can get a useful answer with simple hand calcs.

Yes, the underdeck structure counts. If you are welding to 4mm deck plate and there is no under deck stiffening, you may just bend the plate. Good idea to pull down lining and check if you are not sure.

I'm not a fan of those round bar fairleads; they do look like they will bend under high load. I agree with Evans - just a big diameter dyneema bridle. Maybe even dyneema chafe sleeve at the fairlead and around the stern for 1m. Sew it to the bridle.

7 hours ago, Panoramix said:

For holes in a steel plate, there are edge distances, 3 times the diameter of the hole is plenty enough!

Well it does depend on the thickness :)   Generally we want a minimum of 1.5x hole diameter to the edge.

For highly loaded lifting lugs usually we weld on cheek plates where the pin goes through. Bearing stress will govern the thickness required if you are using alloy shackles. So cheek plates are usually smart, otherwise you end up with stupid thick lug.

The shackle in this drawing weighs 318 lbs.  The failure load is 945T. 

 

image.png.11ea838505928fa034cd0762452de212.png

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A long enough soft shackle might allow you to install the chainplates on the transom to avoid chafe, without requiring you to bend over the stern to fasten the bridle to the chainplates.  You could leave the soft shackles either permanently rigged or install them when going offshore or expecting dirty weather.

27 minutes ago, DDW said:

If the intent is to use soft shackles, would it be a good idea to have several holes and pass the shackle loop through all of them? I'd be worried about bearing on the steel at very high loads. In theory it could deform the steel. 

I'm having trouble picturing this, DDW.  Are you suggesting a lashing with something like one of these (see below) spliced into the bridle?

STpr+1.jpg?format=750w

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35 minutes ago, Zonker said:

I have to keep convincing the younger engineers that the answer is NOT to FEA everything. It is more conservative and is required for complex structures, but sometimes you can get a useful answer with simple hand calcs.

Different continent, different industry and same phenomenon here!

37 minutes ago, Zonker said:

Well it does depend on the thickness :)   Generally we want a minimum of 1.5x hole diameter to the edge.

Yes, I was a bit generous, but then it is also a good idea to start wide when doing back of the envelope stuff and optimise after, it is always easier to tell your client that you've sharpened your pencil and optimised your structure :D but then if you overdo it, it is easy to end up without a project :rolleyes:

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On 11/29/2021 at 3:58 AM, Jud - s/v Sputnik said:

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.

There's a reason I didn't line/insulate the lazarette locker area from frame 17 to the transom, and the pointy end between frame 1 and the stem. I knew those were the areas I'd most likely want to do more cutting & welding at some point.

My advice - bite the bullet and weld on fittings. Bolts are bad for a steel hull, you're introducing potential leaks and rust problems.

As for weld strength, old rule of thumb was 25mm of say 3mm fillet weld was good to hold a tonne. These days things can be better calculated of course.

I don't like your chocks, they're just bent round bar. Strong enough for shore line guides but I'd not put any load on them myself.

Attached pic of the stern quarter of my boat. The posts & cleats are welded to stainless doublers to get them up off the deck and increase the weld area. Some plug welds as well. I'm pretty confident that you could pick the entire boat up from those.

The fairleads are welded stainless pipe sections. Bit more of a PITA running a line through a closed oval but you know it's not coming out on its own no matter how much the boat is pitching & rolling.

FKT

stern.jpg

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2 hours ago, Zonker said:

I have to keep convincing the younger engineers that the answer is NOT to FEA everything. It is more conservative and is required for complex structures, but sometimes you can get a useful answer with simple hand calcs.

I'd like to be counted in the class of "younger engineers" but I think that opportunity has flown several decades by. :wacko:

If you are welding a loaded tang or cleat in the middle of some unsupported deck plating with stiffening nearby but not under, you will either need FEA or some very complex and dubious math to predict what will happen. That is a complex structure. At the corner of the transom you make the assumption that that corner is infinitely stiff and then the world gets simple. 

MFH125: yes something like that is what I was thinking. I do not know how dyneema acts when pulled above the yield strength in a hole. If the dyneema was steel, you would calculate the bearing stress as I did above (note that this is a charitable calculation with the assumption that all of the pin engages the hole, which cannot be true, nonetheless how it is routinely done - FEA will say something different there...). Perhaps Evans has a feel for how things actually happen from his rope testing binge (or he could be convinced to test it). 1/4" Amsteel could cut through 1/4" steel plate, if both achieve their rated specs, at only about 2500 lbs load.  

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If I have a cleat in the middle of unsupported plate and stiffeners some distance away I'll tell the guy to weld in a stiffener under it :). The owner of a 33' steel boat is not likely going to pay me a few hundred $ to set up a proper FEA model..

Radius:

I have a piece of dyneema eye splice in my office about 65mm in diameter (thanks Samson). It was pulled against a larger diameter pipe (~225mm) at under very high load. Then they poured some somewhat-flexible resin into the fibers from the outside while still under load. This took place about 15 years ago when dyneema was still a new rope material.

We were trying to understand how wide a contact area was applied to the pipe. (It's about = rope diameter; the rope does not spread out laterally). The fibers on the inside were so tight that very little resin got into the inner layers; almost all stayed on the outside. 

We had found on tugboat towing fittings that if the pipe wall was not thick enough then the rope would just crush the pipe ("meridional stress"). We needed to increase the steel pipe wall thickness to 25-40mm depending on the size of the rope.

Suggestion:

I would say you want the radius >= rope diameter to avoid damaging the fibers and achieving the highest strength of the rope. Often that is not practical with an eye splice in your bridle, so having an eye splice with a thimble shackled to the metal chainplate would be a good option.

Alternatively belay the rope around a double bitt with lots of figure eights to obtain enough friction to hold it.

 

20211130_131233.thumb.jpg.885df28b2bf1748b140938a110b97f5e.jpg20211130_131318.thumb.jpg.b0c8d56d14033366badfd2bd7869c92e.jpg 

 

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2 hours ago, Zonker said:

If I have a cleat in the middle of unsupported plate and stiffeners some distance away I'll tell the guy to weld in a stiffener under it :). The owner of a 33' steel boat is not likely going to pay me a few hundred $ to set up a proper FEA model..

......

Suggestion:

I would say you want the radius >= rope diameter to avoid damaging the fibers and achieving the highest strength of the rope. Often that is not practical with an eye splice in your bridle, so having an eye splice with a thimble shackled to the metal chainplate would be a good option. 

Nor, without some testing, could you blindly believe the results of the FEA. Certainly if there is already a guy underneath holding a welding torch the solution is easy and cheap. 

At those loads you want to make sure a thimble is the high strength variety, not a stamped bit of SS or galvy. I guess you could connect the thimble and shackle with a soft shackle, another link in the failure chain. The 1/4" amsteel would have a better chance against an alloy steel shackle than soft SS. 

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You do want it in the shackle, or you are going to have to use a 18 or 25mm shackle. Ductility can save you from big shock loads only if the ductile movement is significant, it will not be in a shackle. In a series drogue, you better hope the nylon rode serves that purpose. It can stretch several meters, the shackle only a couple of mm. 

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On 11/30/2021 at 3:52 PM, DDW said:

Perhaps Evans has a feel for how things actually happen from his rope testing binge (or he could be convinced to test it). 1/4" Amsteel could cut through 1/4" steel plate, if both achieve their rated specs, at only about 2500 lbs load.  

I know rather less about steel behavior than dyneema . . . but I would think if the steel had the proper D/d (you need 2:1 to match the efficiency of the stronger soft shackle) we dont have much to worry about.

The soft shackles are 'two line designs' so have double bearing area/half bearing load.

The loads (even in a severe storm) are going to be typically 10% what Jud is quoting,  with occasional peaks to 25% . . . . and the max loading only a 'once in a lifetime' '5 second peak load' (as the jet of that worst shaped wave hits you just at the worst moment). So, we are not going to see sustain of the max loads for anything more than a few seconds.

I have done a whole lot of testing around 10,000lbs and seen (at the test lab) a lot at +20,000lbs. I have certainly seen dyneema do modest 'flattening' of steel, and I have bent some grade 9 bolts when the span was a bit too long, but these were under sustained and repeated very high loads. I have not (yet) personally see a steel total failure or 'cut thru' (of any reasonable match to the loaded dyneema) under dyneema loading.  The steel might well modestly deform in the very worst case, but I would personally call that a success.

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Evans, were the bits of steel you where using 316 (which can be quite soft at 35 ksi yield) or cold rolled steel (which can be pretty hard at nearly twice that)? Alloy shackles are often in the 100 ksi range, gr9 bolts are probably 140 ksi. 

The good news about 316 is that being a badly work hardening material it gets harder as it deforms and resists more before tensile failure. That makes the failure more elegant than brittle materials as it telegraphs its intent. 

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Mild steel is around 36 ksi yield. Hence "A36" steel designations. Ultimate is around double that.

But nobody is using cold rolled steel for any chainplates are they? It will be hot rolled 316 or A36 flat bar if you are a steel boat. 35/36 ksi yield.

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1 hour ago, Zonker said:

Mild steel is around 36 ksi yield. Hence "A36" steel designations. Ultimate is around double that.

But nobody is using cold rolled steel for any chainplates are they? It will be hot rolled 316 or A36 flat bar if you are a steel boat. 35/36 ksi yield.

No, not suggesting that. Wondered what Evans' experience on the test rig was. Often they will be built with some pretty high grade steel because you want the material under test to fail, not the test rig. And as you point out it will be 316 on a boat which starts out quite a bit softer. If using steel (not ss) for chainplates (why would you?) I'd use cold rolled, because at least it is the dimensions it says on the label. Hot rolled will have an ugly finish and be (usually) oversize. 

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4 hours ago, DDW said:

Evans, were the bits of steel you where using 316 (which can be quite soft at 35 ksi yield) or cold rolled steel (which can be pretty hard at nearly twice that)? Alloy shackles are often in the 100 ksi range, gr9 bolts are probably 140 ksi. 

I have used a variety of steel bits at different times.  I have deformed some Harken and wichard HR shackles - not sure what actual grade that is.  I have used some standard HT anchor shackles (g4 and g7 I guess). My default standard are Crosby® 2130A ("Alloy Grade 80), which I have a collection of assorted sizes.  As you say, my aim was for the steel bits not to break - but in the early days I did not realize how strong some of these dyneema creations would be so I probably pushed some edges before i caught on.

On Hawk we deformed steel rings on the clew of the mainsail with/against a dyneema lashing - I dont know what grade these were but they had previously deformed HR shackles and shown no effect on themselves.

The test lab I use for bigger pulls can do 100ton pulls and I am sure knows quite a bit about the behavior of steel on dyneema at high breaking loads but is something we have never talked about - for my tests all the metal bits are way over dimensioned so it has never really come up.

One thing about the worst case drogue scenario - even if the JSD saves the boat there is still likely to be some significant damage.  We had a breaking wave hit Silk once (over the top of a seamount) and it broke our windvane, drove water into all our cockpit electronics (instruments, autopilot head and engine panel), and took our dorades clear off.  Friends had similar down the argentine coast, and it smashed their boom, washboards and dorade boxes.  And neither of these were even close to the worst case jsd scenario.

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The Harken and Wichard HR stuff is 17-4PH, usually investment cast so probably around 110 ksi. "Alloy Grade 80" is a loose term, but usually this means it is 80 ksi steel. 

I'd agree (just from reading - not been there) that a survival wave event is rare and you could size the hardware to withstand it once. If you use 316 at around 60 ksi stress, it will probably survive but probably be bent a bit. Some people seem to be expecting 80 ksi which is the usual typical ultimate value, but that means a 50/50 chance of complete failure. I design to 35 ksi which is supposed to be minimum yield for ANSI material, and use 2 - 2.5x safety on top of that for working load. All the 316 I use comes with a material certification which means theoretically they tested that particular plate, and it is usually around 45 - 50 yield. But these days it almost all comes from China so hard to know how much to trust the cert. 

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40 minutes ago, DDW said:

The Harken and Wichard HR stuff is 17-4PH, usually investment cast so probably around 110 ksi. "Alloy Grade 80" is a loose term, but usually this means it is 80 ksi steel. 

I'd agree (just from reading - not been there) that a survival wave event is rare and you could size the hardware to withstand it once. If you use 316 at around 60 ksi stress, it will probably survive but probably be bent a bit. Some people seem to be expecting 80 ksi which is the usual typical ultimate value, but that means a 50/50 chance of complete failure. I design to 35 ksi which is supposed to be minimum yield for ANSI material, and use 2 - 2.5x safety on top of that for working load. All the 316 I use comes with a material certification which means theoretically they tested that particular plate, and it is usually around 45 - 50 yield. But these days it almost all comes from China so hard to know how much to trust the cert. 

Yeah - this. A problem for sure.

Another forum I hang out on, there are some horror stories about Chinese sourced material. Cold rolled with inclusions from what looks like a partial melt, aluminium that machines in a totally shitty fashion with terrible surface finish etc. Some of the shops only use material source from Canada or Europe, won't have Chinese.

Anyway when I 'design' something I ensure the weak link is the bit that's easy to replace and/or won't result in structural damage. So I'd have the hard attachment points at say 2X the breaking strain of the drogue line or attachment soft shackle/whatever, so in the worst case, the drogue would break free without taking a chunk of my transom with it.

EDIT: And I prefer hot rolled to CRS because it distorts less when welded and you lose the benefits of the CRS anyway. But I always blast the HRS to get rid of all mill scale and give a good 'tooth' for the epoxy to stick to. You'd be advised to blast the CRS anyway for this reason. I've had epoxy paint failures when the surface prep was too smooth/shiny.

But really I'd be using 316 plate 12mm to 16mm thick depending on shackle pin size/bearing, welded to a 316 doubler plate, then fillet & plug welded to the boat hull plate, over some internal continuous welded frame members. It's impossible to keep paint on the inside of pin holes and a mug's game trying to. Pretty much every place where there's a shackle pin on my boat is bushed with a 316 insert or is solid 316. I hate rust bleeds.

FKT

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Agree with your approach on using 316 and welding.

CRS has residual stresses from rolling so yeah it relaxes when heated. Also you can't bend it to a tight radius because it is already work hardened. But hot rolled is pretty nasty for something that needs to be finished, either a ton of grinding or take a facing cut. 

I've given up on Chinese or Russian aluminum and for 6061 I specify domestic cast only. It costs me about twice as much to begin with but I'm better off in the long run. The Chinese stuff can be horrible to machine, inconsistent to anodize, and generally nasty, Russian not much better. Most of what I do I use 6013, it used to be cast only in Indiana, USA and was good quality. Then I started getting some stuff from Italy, OK too for the most part although I began to suspect the cert when some material just happened to barely meet the minimum. Last delivery was from Austria, stuff seems OK but is off dimension: 0.500" (-0/+0.030) actually measures 0.492", same with other thicknesses. Supplier shrugged and said he'd inform their IQC people. My guess is it was 12mm they substituted. At least it met strength on the cert and machined OK.

While we are at it, Chinese fasteners: the only thing I can buy anymore in SS fasteners comes from China. Occasionally Taiwan which is sometimes OK. The stuff out of the PRC has horrible quality: head is visibly non-concentric and not square with the body, thread and head sizes all over the place, strength is pretty much unknown. Haven't been able to get USA made for about 10 years, European disappeared a couple of years later. I'm considering having fasteners custom made by a specialty house here. Price is 10 - 100x but at least it will screw into a hole without wobbling all over the place and the head hitting on one side only. 

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22 minutes ago, DDW said:

While we are at it, Chinese fasteners: the only thing I can buy anymore in SS fasteners comes from China. Occasionally Taiwan which is sometimes OK. The stuff out of the PRC has horrible quality: head is visibly non-concentric and not square with the body, thread and head sizes all over the place, strength is pretty much unknown. Haven't been able to get USA made for about 10 years, European disappeared a couple of years later. I'm considering having fasteners custom made by a specialty house here. Price is 10 - 100x but at least it will screw into a hole without wobbling all over the place and the head hitting on one side only. 

Hmmm, interesting. I use a shit-ton of button head screws in 316. If anything is going to show problems, they will as the head recess is pretty shallow WRT a standard SHCS. I've not had a problem, nor with rounding out. I just bought a box of M6x30 today, will take a look & see if there's a country of origin on them. The quality has been very consistently good.

Your experiences with aluminium match what I've heard elsewhere. The Chinese & Russian stuff is just so inconsistent in quality that it's not worth using. If material cost is only 5% to 10% of the finished article cost after machining, anodizing etc - why take the chance? Maybe the importers will get the message if enough people stop buying.

EDIT: I wonder if you're using those ancient non-standard dimension fasteners. All mine are metric. Maybe nobody cares about the quality of anything else seeing as there's only 1 country on the planet that uses them.

FKT

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The fasteners are all metric, and all SHCS though no button heads - standard and low profile heads (which have the same drive size as button heads). I've not had too much trouble with the drive socket size, though it will be well off center on many of them. I thin the heads of the low profile further for the product I build, this requires chucking each of them in the lathe and the horror makes itself very apparent there. I've taken to turning the heads concentric otherwise they sometimes crash the spot face they go into - but that just makes the off center drive socket all the more obvious. The last hundred I bought were country of origin Taiwan and weren't as bad. 

When you are turning a Chinese aluminum bar, and getting a dramatic cyclical change in cutting noise each revolution, and the finish on one side of the bar is completely different than the other side, one side makes chips and the other strings, well.....

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2 hours ago, DDW said:

The fasteners are all metric, and all SHCS though no button heads - standard and low profile heads (which have the same drive size as button heads). I've not had too much trouble with the drive socket size, though it will be well off center on many of them. I thin the heads of the low profile further for the product I build, this requires chucking each of them in the lathe and the horror makes itself very apparent there. I've taken to turning the heads concentric otherwise they sometimes crash the spot face they go into - but that just makes the off center drive socket all the more obvious. The last hundred I bought were country of origin Taiwan and weren't as bad. 

When you are turning a Chinese aluminum bar, and getting a dramatic cyclical change in cutting noise each revolution, and the finish on one side of the bar is completely different than the other side, one side makes chips and the other strings, well.....

Are you using a collet to hold the screws? Just curious. I've got a Pratt Bernerd lever actuated collet chuck for small (less than 35mm) diameter round work.

As for the Chinese ally bar - erk.

WRT steel, for machining round bar I vastly prefer CRS to HRS. You have to get the SFM way, way high and use an aggressive cut to get a decent surface finish. HRS tears quite badly IME.

FKT

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On 11/30/2021 at 12:44 PM, Fah Kiew Tu said:

There's a reason I didn't line/insulate the lazarette locker area from frame 17 to the transom, and the pointy end between frame 1 and the stem. I knew those were the areas I'd most likely want to do more cutting & welding at some point.

My advice - bite the bullet and weld on fittings. Bolts are bad for a steel hull, you're introducing potential leaks and rust problems.

As for weld strength, old rule of thumb was 25mm of say 3mm fillet weld was good to hold a tonne. These days things can be better calculated of course.

I don't like your chocks, they're just bent round bar. Strong enough for shore line guides but I'd not put any load on them myself.

Attached pic of the stern quarter of my boat. The posts & cleats are welded to stainless doublers to get them up off the deck and increase the weld area. Some plug welds as well. I'm pretty confident that you could pick the entire boat up from those.

The fairleads are welded stainless pipe sections. Bit more of a PITA running a line through a closed oval but you know it's not coming out on its own no matter how much the boat is pitching & rolling.

FKT

stern.jpg

I hear ya, but I’m actually not too worried about bolting through the hull and leaks.  Nylocks with lock washers properly tightened, and the plates well bedded - I trust it.  My windvane is (of course) bolted to the hull and no leaks/rust issues.  Not ideal, but welding (at this point) would  introduce a host of “repair” issues.  Accessing inside to remove enough liner and foam insulation to avoid fire, and the nonskid on deck would also be burned.  Love the idea of welding, but I think it’s too destructive at this point.  It would really be a lot to deal with at the stern quarters (pic: mock up for radar post from a few years ago, now installed - among many things that would have to be removed outside and inside) for welding.

But when I start mocking up chainplates in the new year, I may change my tune :-)

CA19DC2E-EFDE-4AAC-8EA9-F9A56C2433B3.jpeg

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11 hours ago, Fah Kiew Tu said:

Are you using a collet to hold the screws? Just curious. I've got a Pratt Bernerd lever actuated collet chuck for small (less than 35mm) diameter round work.

No, they are screwed into a tight tolerance thread in a bar chucked in a collet chuck (Sjogren speed chuck). The screws are threaded full length, thread major diameter somewhat variable and that seemed to give a more reliable result. PITA to load/unload them though. And facing them leaves a burr on the drive socket, also a PITA to deal with. I can have them custom made for about $5 each in 100 qualtity, would probably be better off doing so, could also get higher grade material than 316 or 18/8, like 17-4 or Inconel. 

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Anyone have any thoughts on using a toe rail - that’s welded to the deck along the entire length from bow to stern - as an  attachments means for a JSD?

The article below some people wrote about Dyneema chainplates for rigging, and their application of that idea to attachment for a JSD to their boat —via bulwarks/toe rail got me thinking.  (Article “Simplifying fitting a Jordan Series Drogue”) Seems like, as they note in their case, the key is figuring out how to spread the load over the toe rail (assuming, first off all, that it’s strong enough!).  I can see how shackles could be attached on the toe rail at the quarters, but it’s attaching the bridle elsewhere along the toe rail on each side of the boat (and easily/quickly), and that prevents chafe, that seems to be the challenge.

Just curious if anyone had any quick thoughts.  I’m gonna start brainstorming it more fully, before surrendering to the traditional idea of chainplates.

I suppose the biggest challenge is probably eliminating any source of chafe of using this toe-rail attachment method.  (Sketch below is from the article linked above.)

288D6942-5A75-4B72-BB9C-115D9B0772EB.jpeg

91E857E2-9D9E-4B15-B462-53974330A6C4.png

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What is the direction of pull in a worst-case strike? I have not heard that mentioned, and unless the design is symmetrical, it matters. I think we can assume it is not exactly horizontal and that it is strongly toward the inside, probably on one plate only, due to yaw which allowed the wave to hit you from the side ... unless you want a assume one bridle leg failed (not a crazy assumption), in which case the load is primarily outwards (pealing), since the boat will be angled to that side, leading to a side strike.

Not an easy thing to optimize, afterall.

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2 hours ago, Jud - s/v Sputnik said:

Anyone have any thoughts on using a toe rail - that’s welded to the deck along the entire length from bow to stern - as an  attachments means for a JSD?

The article below some people wrote about Dyneema chainplates for rigging, and their application of that idea to attachment for a JSD to their boat —via bulwarks/toe rail got me thinking.  (Article “Simplifying fitting a Jordan Series Drogue”) Seems like, as they note in their case, the key is figuring out how to spread the load over the toe rail (assuming, first off all, that it’s strong enough!).  I can see how shackles could be attached on the toe rail at the quarters, but it’s attaching the bridle elsewhere along the toe rail on each side of the boat (and easily/quickly), and that prevents chafe, that seems to be the challenge.

Just curious if anyone had any quick thoughts.  I’m gonna start brainstorming it more fully, before surrendering to the traditional idea of chainplates.

I suppose the biggest challenge is probably eliminating any source of chafe of using this toe-rail attachment method.  (Sketch below is from the article linked above.)

 

 

Just wanted to comment on that idea, I have seen this be quite effective.  The one that blew my mind the most was a boat with a heavy walled aluminium pipe with feet welded on bolted down the length.  Essentially a boat with a built in bull rail!    

big blue polysteel mooring bridle, to smaller 3/4" line spiralling around the rail back 5 mounting feet(not measurement feet) then a loop a short piece of the same pipe welded at 90 degrees to create a point to fasten to.  I will try to find a picture for you.  

The rail was attached with #14 screws!  Into a glass ply boat.   It has broken many things, including chains, mooring rings, anchor lines etc when left on a mooring or at anchor over the years.  no maintenance has ever been done to the rail or the bridle, in at least 10 years, and I don't think anything was done to it before that since at least the early 90s.

 

152407E3-D338-4B54-8FB6-A5097489A4E4.jpeg

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5 minutes ago, Startracker said:

Just wanted to comment on that idea, I have seen this be quite effective.  The one that blew my mind the most was a boat with a heavy walled aluminium pipe with feet welded on bolted down the length.  Essentially a boat with a built in bull rail!    

big blue polysteel mooring bridle, to smaller 3/4" line spiralling around the rail back 5 mounting feet(not measurement feet) then a loop a short piece of the same pipe welded at 90 degrees to create a point to fasten to.  These points are distributed around the boat.   I found a picture for you, the same exact fitting is holding a fender in the photo, but the forward ones have been used for the bridle for decades.

The rail was attached with #14 screws!  Into a glass ply boat.   It has broken many things, including chains, mooring rings, anchor lines etc when left on a mooring or at anchor over the years.  no maintenance has ever been done to the rail or the bridle, in at least 10 years, and I don't think anything was done to it before that since at least the early 90s.

 

152407E3-D338-4B54-8FB6-A5097489A4E4.jpeg

 

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On 12/3/2021 at 3:32 PM, Jud - s/v Sputnik said:

I hear ya, but I’m actually not too worried about bolting through the hull and leaks.  Nylocks with lock washers properly tightened, and the plates well bedded - I trust it.  My windvane is (of course) bolted to the hull and no leaks/rust issues.  Not ideal, but welding (at this point) would  introduce a host of “repair” issues.  Accessing inside to remove enough liner and foam insulation to avoid fire, and the nonskid on deck would also be burned.  Love the idea of welding, but I think it’s too destructive at this point.  It would really be a lot to deal with at the stern quarters (pic: mock up for radar post from a few years ago, now installed - among many things that would have to be removed outside and inside) for welding.

I get that welding would bring major hassle, but but but but ...

But if you need to deploy a JSD, then you have committed to that mode of storm survival so you really really need it to not fail.  And if the drogue fails in extreme conditions, there is a significant chance that the result will be you entering a world of pain .. and a non-trivial chance that you will be starting a new career in as fish food.

So I reckon that if you are gonna do this, then do it right.

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On 12/9/2021 at 9:35 AM, TwoLegged said:

I get that welding would bring major hassle, but but but but ...

But if you need to deploy a JSD, then you have committed to that mode of storm survival so you really really need it to not fail.  And if the drogue fails in extreme conditions, there is a significant chance that the result will be you entering a world of pain .. and a non-trivial chance that you will be starting a new career in as fish food.

So I reckon that if you are gonna do this, then do it right.

Bolted structures are not always a compromise. A lot of bridges, buildings, and even airplanes rely on bolts. There are advantages both ways that are not about price.

 

I'm still waiting for a discussion about the probable direction of maximum pull. I'm pretty use it is not straight back. That would be too easy.

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Just now, thinwater said:

Bolted structures are not always a compromise. A lot of bridges, buildings, and even airplanes rely on bolts. There are advantages both ways that are not about price.

 

I'm still waiting for a discussion about the probable direction of maximum pull. I'm pretty use it is not straight back. That would be too easy.

... and just because there is a cat in my avitar does not mean I am thinking about cats. I'm actually thinking about a mono that is laid over a bit, getting hit sideways.

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2 hours ago, thinwater said:

Bolted structures are not always a compromise. A lot of bridges, buildings, and even airplanes rely on bolts. There are advantages both ways that are not about price.

 

I'm still waiting for a discussion about the probable direction of maximum pull. I'm pretty use it is not straight back. That would be too easy.

Yeah, I’m actually pretty comfortable drilling bolt holes in the quarters of the boat and bolting chainplates on so that they don’t leak.  At least not in my lifetime. With adequate sealant and the bolts/nuts firmly tightened, I can’t see it being an issue.  Moreover, it’s only a potential issue along the top edge, where water would collect, and there will be access inside the boat to the nuts.

(Considering that it’s pissing cold rain just a few degrees above 0*C right now here, this will be a summer project.  Which means I’d better start at least planning it all out now!)

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3 hours ago, thinwater said:

I'm still waiting for a discussion about the probable direction of maximum pull. I'm pretty use it is not straight back. That would be too easy.

i'm not sure we need a discussion - answer: about/very roughly 20 degrees 'inboard' off (centerline) axis - given the bridle will have a normal roughly 10 degree angle thats about 10 degrees more than 'normal' - all load on one bridle arm.

We got hit enough to be pretty sure that would be the most probably direction of pull.  You can ofc create scenarios with other directions.  A peeling load would be pretty unusual, probably need a broken bridle arm - should really size them so that just will not happen because it (motion and yawing up into the waves) really sucks to have the bridle only attached to one quarter (as you know well, a drogue off one quarter will 'steer' the boat)

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31 minutes ago, estarzinger said:

i'm not sure we need a discussion - answer: about/very roughly 20 degrees 'inboard' off (centerline) axis - given the bridle will have a normal roughly 10 degree angle thats about 10 degrees more than 'normal' - all load on one bridle arm.

We got hit enough to be pretty sure that would be the most probably direction of pull.  You can ofc create scenarios with other directions.  A peeling load would be pretty unusual, probably need a broken bridle arm - should really size them so that just will not happen because it (motion and yawing up into the waves) really sucks to have the bridle only attached to one quarter (as you know well, a drogue off one quarter will 'steer' the boat)

Yes, this is the discussion!

A broken bridle arm is bad. I've done that intentionally in testing (playing with adjustable suggestions, most of which didn't work in field conditions), and recovery is tough.  Oversize the bridle. That, combined with over building the attachment in general, solves the peal force dilemma.

I do wonder about about the vertical range if a boat suffers a partial knock-down. Perhaps we expand the +/- 20 degrees to +20/-30 degrees. That is still a wide range for those that believe the bolts act in a row, In fact, at 20 degrees of line, only the last few bolts do anything meaningful, so I believe the optimum design is wider than a chain plate. IS the best angle horizontal; the good hits I took were always at a down angle, as the wave rose behind me. A down angle seems beneficial. Of course, this also depends on the underlying structure; if the strap is along a strong hull edge area, that is important. Just sayin' that that last few bolts must be able to hold the load on their own. Every boat I have owned had acceptable inside access to this area, so I would obviously lay a big reinforcement down the side and around the corner. On a steel boat, I would add something on the inside, or possibly just a wrapped patch plate on the outside.

I drew this image once, just as a thought exercise. The angles are exaggerated and the shape is only for discussion. But it is obvious that only the last 4 bolts carry load at severe angles (and the rest are just for a little added stability). And should we move the holes outside a straight line?

drouge+chainplate+design+1.jpg

 

 

 

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6 hours ago, thinwater said:

I do wonder about about the vertical range if a boat suffers a partial knock-down. 

Two cases - without and with knockdown. Generally, if the drogue has 'worked' you would hope not to be knocked down.  In that case I would think planning for a horizontal perhaps +- 5 degrees . . . .but mostly I believe when we have been hit hard the peak loads were close to horizontal (to the boat's axis) . . . . on big waves the boat is pointing down already a bit when hit so the angle is horizontal relative to the boat's axis but from above/behind relative to earth surface

For the knockdown case . . . . I believe in the majority of cases the peak loads are before the peak knockdown angle.  But yea, knockdown is a case where you could definitely get loads from odd angles - perhaps even  say from the 2nd wave in a set.  I only know of one boat that has been knocked down with a properly set series drogue, and that was after the storm peak, when the solo sailor was too fatigued to do anything and the boat was wallowing - would probably have been ok if he had gotten a little sail out.  But it can happen.

The structural engineering/design I leave to you and others with more knowledge.

As I have mentioned above - you do have to determine how rare a meteorite hit you are going to plan for with this.  If you really want to plan for ALL potential cases you need a hell of a structure, but in all likelihood most (even including even most of the high latitude folks) of us will never even see 25% of worse case in our lifetimes.  We built a structure which could lift the boat . . . but that is easy when you are building it in new metal construction.

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14 hours ago, estarzinger said:

Two cases - without and with knockdown. Generally, if the drogue has 'worked' you would hope not to be knocked down.  In that case I would think planning for a horizontal perhaps +- 5 degrees . . . .but mostly I believe when we have been hit hard the peak loads were close to horizontal (to the boat's axis) . . . . on big waves the boat is pointing down already a bit when hit so the angle is horizontal relative to the boat's axis but from above/behind relative to earth surface

For the knockdown case . . . . I believe in the majority of cases the peak loads are before the peak knockdown angle.  But yea, knockdown is a case where you could definitely get loads from odd angles - perhaps even  say from the 2nd wave in a set.  I only know of one boat that has been knocked down with a properly set series drogue, and that was after the storm peak, when the solo sailor was too fatigued to do anything and the boat was wallowing - would probably have been ok if he had gotten a little sail out.  But it can happen.

The structural engineering/design I leave to you and others with more knowledge.

As I have mentioned above - you do have to determine how rare a meteorite hit you are going to plan for with this.  If you really want to plan for ALL potential cases you need a hell of a structure, but in all likelihood most (even including even most of the high latitude folks) of us will never even see 25% of worse case in our lifetimes.  We built a structure which could lift the boat . . . but that is easy when you are building it in new metal construction.

I bring it up because I believe crossing waves are the greater hazard for most sailors. These can happen in less than huricane conditions when you get caught between two weather systems. I'll avoid a predicted storm at all costs, but I've been caught by lows that came together more than expected. I've seen troubling waves, but never the regular waves Pacific sailors find common place. We get waves from the side, which is the scary part, and one of the things a JSD is uniquely suited to (other drogues are set too far away). In the case of a regular wave train, breaking waves are very unusual and the JSD isn't needed. But of course, in this situation, the hit will be no more than that 25% figure.

Smaller boats were Jordan's main concern. He began his discussion with a story about a 30-foot boat. His examples center on 30-foot boats, and he mentions that over 60 feet capsize is rare, and suggests that 40-50 feet is lower risk. Of course, people with 40- to 50-foot boats will likely risk conditions that people with 30-foot boats avoid. 

It could be that the concerns of smaller boats are a little different. Smaller storms with more crossing waves.

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Are the loads imposed by the Joran Series Drogue really all that great?  The whole point of the design is to eliminate shock loads and gradually increase the resistance as the boat builds up speed down a wave.  I am not suggesting that attachment points not be engineered well.   But it would seem that loads on your cleats in a harbor with "surge" would be higher, etc. and certainly a parachute type drogue would cause large shock loads.  

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On 12/10/2021 at 12:19 PM, thinwater said:

Bolted structures are not always a compromise. A lot of bridges, buildings, and even airplanes rely on bolts. There are advantages both ways that are not about price.

 

I'm still waiting for a discussion about the probable direction of maximum pull. I'm pretty use it is not straight back. That would be too easy.

I used to think welding was better than bolting things together.  But since I have found that a bolt together design will "absorb" forces while welds will tend to crack because there is no give like a bolted connection.

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2 hours ago, jzk said:

I used to think welding was better than bolting things together.  But since I have found that a bolt together design will "absorb" forces while welds will tend to crack because there is no give like a bolted connection.

Not.

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19 minutes ago, DDW said:

Not.

I have had 2 powered parachutes.  One was bolted aluminum tube framed.  The other welded steel.  The steel one was constantly popping welds from hard landings and such.  The Aluminum bolted one just absorbed everything.  I saw some really hard landings with the aluminum bolted ones, and you could see them absorbing the forces.  Same when we would do a vertical spin.

This is a comment from an engineering discussion of welds vs. bolted connections:

"Joint Flexibility Comparison

Welded joints are more rigid than bolted joints, due to the continuity of the cross section. On the other hand, bolted joints are connected with plates or angles, and the deflection of these elements during load transfer adds flexibility. For this reason, bolted joints allow more movement with less structural stress."

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5 hours ago, thinwater said:

 

It could be that the concerns of smaller boats are a little different.

Yes, could be, I cannot personally talk to anything under 37'. 

There have been a huge number of miles done in difficult conditions by smaller boats - like webb's moore 24, and Alessandro's (di Benedetto) mini. . . . most of them that I have been on board have not had distinctively massive construction (compared/scaled to bigger boats).  But other people can talk to that with more personal experience than I.

On the whole attachment/chainplate discussion . . . I will make two comments (1)  I have never heard of any failing in use. Other failures - bridles & cones especially, but not the attachment points.  and (2) in 'less that survival conditions' (but still real actual storms) we typically brought the bridle to our main genoa winches rather than the strong points - it was just easier and I have measured enough loads to know it would not be a problem (and it was not).

Cross waves/multiple wave trains . . . pretty common in the southern ocean.  We would try to split the wave angles with our transom, perhaps putting the more severe a little more directly behind (a lot of people are reluctant to go off their rumbline course, which is generally a mistake in these situations, seamanship requires you to keep pretty much any potentially significant breaking waves off the beam), and usually use a single element drogue rather than the series in these situations - at least with Hawk (pretty powerful with high righting moment) most of these situations could be a bit uncomfortable getting knocked around and you needed to manage the course and the speed correctly, but if you did they were not that dangerous.

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Bolted vs welded performance depends entirely on how each is designed. Both can be poorly designed. A well designed welded connection will transfer full moment, compression, and tension into the next element without exceeding material stress limits. A poorly designed one will not. Same goes for a bolted connection. 

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