dgadee
Well-known member
Are there ever side loads on a drogue? That might rip the toerail off bolt by bolt.They sometimes are. I have s/s sandwich plates to bolt to my toerail. 150 M8 bolts each side should be enough
Jordan series drogue attachement point
- Thread starter Minerva
- Start date
geem
Well-known member
I have never used it anger but I had the same thought.
I use both the 400mm long deck cleats (4x M10 fixings) and the toerail. I have some dyneema strops that tie the cleats to the toerail fixings. This limits sideways force, hopefully. The idea is to share the load. I did consider bespoke fixing to the hull but it's a lot of work since the hull is lined with teak tongue and groove in the back cabin. I would need to remove it. I am not sure how we would deal with the fixings and the teak finish. I have never been in conditions that I ever thought I needed it. Hope to remain that way
AntarcticPilot
Well-known member
I think it depends on the engineering of the toerail. Mine is an integral part of the hull/deck join, and I can't imagine any chain plate type structure being stronger. But a toerail that is bolted on and not part of the structure might not be so strong. That said, mine is probably too high to be a good attachment point for a drogue - freeboard at the stern is well over a metre, maybe 1.5m, and I suspect there would be too great a downward force. Just visualising it, I guess you want the pull of the drogue to be level with the centre of buoyancy?They sometimes are. I have s/s sandwich plates to bolt to my toerail. 150 M8 bolts each side should be enough
Theoretical interest to me; I don't intend to do the kind of sailing where it would be a useful precaution!
RunAgroundHard
Well-known member
1. Are you sure the cleats are strong enough? Do you have data for the cleat stating its strength?
2. Are the cleats in sound condition? Is there unseen strain within the cleat due to deformation or previous overloading?
3. Have you inspected the cleats for external cracks or internal flaws created when forged or cast?
4. What is the GRP like under the cleat and internally?
5. Is the cleat in the right position to allow the JSD to be attached and used in the safest and securest manner?
I think using the cleats is a shit idea, mainly because they are in the wrong position, too far forward and you have no idea of the actual condition of the cleat. Under survival conditions the load may be too much. Personally I would not rely on the existing cleats. Of course, you could remove them and have the cleat load tested, then modify the lead for the JSD by mounting them in a different position, or fitting something to deflect the JSD and protect it against wear at the pushpit.
If it was me, I would add side plates to the quarter, just below the gunwale. Inside I would build up the GRP to make a much thicker area with the GRP shaped to distribute the loading as evenly as possible i.e. tear drop shaped, tapered layers of cloth. I wonder if stronger winds, less easily predicted, and therefore more likely to catch us out, is now starting due to MMGW and therefore use of a JSD or other device is more likely, even using current prediction tools. Or, in other words, when you need to rely on a JSD, you need to be certain that it will work and not fail in a manner that puts the boat at greater risk.
Lots of information on JSD attachment points. Remove the head lining and fit side plates , or top mounted plates. Don't use the cleats.
OceanBrake
A subscription service with details on mounts for JSD Category: Online Book: Heavy Weather Tactics
zoidberg
Well-known member
I think we need a clear idea of what we're trying to achieve with a Jordan Series Drogue, before we get too far into the minutiae of how we do it.
Don Jordan was appalled at the loss of life in the '79 Fastnet Disaster. Many boats were rolled by breaking, jetting seas. People died in consequence. He set out to find a way to prevent a repetition, and came up with the 'Jordan Series Drogue'.
It's worth bearing in mind that the seas and conditions that killed so many happened in our backyard. And could again.
I've sailed in such sea states off Portland. And off the SW of Wales. Even the bottom end of the Needles Channel does, as the local lifeboat coxn will tell you. Certainly, the Celtic Sea produces such conditions, in places, quite frequently.
'A breaking sea >60% of a boat's length will ALWAYS roll a boat which is beam on....'
Those sea conditions happen quite frequently for a <30' boat ( e.g. Jesters ) in 'home waters'. They happen often for up to 50' boats on a Biscay passage....
Should you wish to challenge, or dismiss, those findings then take it up with the Wolfson Institute of Southampton University who did the research.
Now, Don Jordan calculated that a Maximum Sea Strike would impart into a boat up to 70% of its LADEN weight. That's what the JSD - and each part of its fittings and fastenings - must withstand. I've learned that few ensure the hull structure - into which that load may be imparted - is up to the task.
Sure, the steel straps and/or cleats are - or seem to be - sufficient. Sure, the JSD rode itself is usually more than sufficient ( provided the LADEN weight is factored in ). But few, I'm advised, take professional/competent advice on the local strength of the hull and its local reinforcements.
My concern is for the 'That looks about right' eyeball judgement..... and others agree that's not good enough.
I'd also challenge the 'I don't intend to do that kind of sailing' attitude. Bluntly, if you're out of sight of a weather haven, you don't get the choice......
Don Jordan was appalled at the loss of life in the '79 Fastnet Disaster. Many boats were rolled by breaking, jetting seas. People died in consequence. He set out to find a way to prevent a repetition, and came up with the 'Jordan Series Drogue'.
It's worth bearing in mind that the seas and conditions that killed so many happened in our backyard. And could again.
I've sailed in such sea states off Portland. And off the SW of Wales. Even the bottom end of the Needles Channel does, as the local lifeboat coxn will tell you. Certainly, the Celtic Sea produces such conditions, in places, quite frequently.
'A breaking sea >60% of a boat's length will ALWAYS roll a boat which is beam on....'
Those sea conditions happen quite frequently for a <30' boat ( e.g. Jesters ) in 'home waters'. They happen often for up to 50' boats on a Biscay passage....
Should you wish to challenge, or dismiss, those findings then take it up with the Wolfson Institute of Southampton University who did the research.
Now, Don Jordan calculated that a Maximum Sea Strike would impart into a boat up to 70% of its LADEN weight. That's what the JSD - and each part of its fittings and fastenings - must withstand. I've learned that few ensure the hull structure - into which that load may be imparted - is up to the task.
Sure, the steel straps and/or cleats are - or seem to be - sufficient. Sure, the JSD rode itself is usually more than sufficient ( provided the LADEN weight is factored in ). But few, I'm advised, take professional/competent advice on the local strength of the hull and its local reinforcements.
My concern is for the 'That looks about right' eyeball judgement..... and others agree that's not good enough.
I'd also challenge the 'I don't intend to do that kind of sailing' attitude. Bluntly, if you're out of sight of a weather haven, you don't get the choice......
WindyWindyWindy
Active member
You've still just eyeballed it, to call it engineering would require some adding up.
Cleats might well be designed to take the weight of the boat for all I know.
It's perhaps also worth considering the breaking strength of the rope that's transmitting the load it can't be more than that can it?
Could you put enough stretch in with octoplait nylon to significantly reduce snatch loads?
Can you say that with a bridle on two cleats that the load is halved or could it still load up entirely on one side if the boat sheared?
zoidberg
Well-known member
Er....
* That's been done for me by pros in composites structural engineering, found via Sailing Anarchy. Checked valid by another pro in the UK.
** Possible, but consider also the bolts. It would be surprising if a cleat was SPECIFICALLY designed for such. 'Welded-on' would likely suffice.
*** I have specified 11mm Dyneema. That's capable of more than the AUW of my laden boat. 12mm diameter is even easier to handle....
**** The core principle of the JSD is that the Reverse Catenary created by the far end sinking achieves the desired 'soft snubbing' effect. Don Jordan specifically ruled out the 'dynamic recovery' concept - obvious why when one watches Offroad Vehicle Snatch Recovery videos.
Nylon loses significant strength when wet. It also loses significant strength under UV exposure. It is significantly worse than polyester and other modern ropes.
***** Don Jordan's premise is that the Maximum Wave Strike load is shared between both bridle arms. The JSD concept is that a sudden asymmetric load caused by wave-strike would pull the rear of the boat in line as the load progressively increased. This is experienced in practice.
It is conceivable that one bridle-arm could part/detach through chafe or unscrewed shackle pin. Making each bridle arm capable of absorbing the WHOLE MaxWaveStrike load is easy, using Dyneema..... and anti-chafe protection.
The above represents one conscientious student's understanding, There may be scope for preferences and for use of better materials, but the mechanics of what's wanted and how to achieve it are well established.
Roberto
Well-known member
Some consideration should be given to the construction of the JSD itself, the OCC Flying Fish magazine has a picture of what was left of a commercial JSD after having been used, it has copyright but it's basically a long rope with shredded pieces of webbing and fabric all along its length. The crew praised its effects, one wonders if towing a long "dirty"rope would be much different
WindyWindyWindy
Active member
I think that's what I was saying to the other guy. To do it right requires an engineer to design it for the specific boat.
That said I wonder what weight a cleat can take, they do usually have pretty hefty attachments.
dgadee
Well-known member
I contacted West with my plan to fit two 12mm eyes to the stern of my Dehler and tie the stern to the inside of the hull. Ply and SS plates encapsulated in epoxy glass. They said "should be fine". I can send pics - am on board now.
Oceanbrake (UK) said
Oceanbrake (UK) said
WindyWindyWindy
Active member
I finally found a decent copy of the original report, which otherwise only appears to get passed around as a photocopy of a scan of a
photocopy.
Go to: National Technical Reports Library - NTIS
In "Fields" select "Accession number" and enter "ADA 188 598" (with spaces), hit return and you get a link to the PDF of the original report.
photocopy.
Go to: National Technical Reports Library - NTIS
In "Fields" select "Accession number" and enter "ADA 188 598" (with spaces), hit return and you get a link to the PDF of the original report.
WindyWindyWindy
Active member
One error is that he says Grimalkin sank, she actually survived and was re-rigged.
14K478
Well-known member
A very interesting thread.
I keep thinking about a JSD and making or buying the JSD is the easy part.
The chain plates each able to take 70% of the laden displacement are more challenging.
Ripping the stern off the boat would be counterproductive.
I can’t do the maths, so I would need someone who can.
I fancy that at the least some more glassing on an already old and very well cured hull will be needed. I really don’t want to take the internal reinforcements past the aft watertight bulkhead… the laden displacement is 24 tons, so that’s a load of 17 tons, not necessarily coming in line with either chain plate.
I want the series drogue and its gubbins stowed in the lazarette and not already secured to the chain plates but able to be secured quickly and simply to chains secured to the chain plates with their free ends held on deck.
I think we are looking at internal backing plates bolted to external chain plates, probably with some extra glassing. Certainly the deck moulding is nowhere near strong enough in tension.
I keep thinking about a JSD and making or buying the JSD is the easy part.
The chain plates each able to take 70% of the laden displacement are more challenging.
Ripping the stern off the boat would be counterproductive.
I can’t do the maths, so I would need someone who can.
I fancy that at the least some more glassing on an already old and very well cured hull will be needed. I really don’t want to take the internal reinforcements past the aft watertight bulkhead… the laden displacement is 24 tons, so that’s a load of 17 tons, not necessarily coming in line with either chain plate.
I want the series drogue and its gubbins stowed in the lazarette and not already secured to the chain plates but able to be secured quickly and simply to chains secured to the chain plates with their free ends held on deck.
I think we are looking at internal backing plates bolted to external chain plates, probably with some extra glassing. Certainly the deck moulding is nowhere near strong enough in tension.
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noelex
Well-known member
These are the rear cleats and fairleads on our boat. These have been professionally engineered to cope with the loads expected from a JSD.
The cleats are not just welded on the deck, instead the twin aluminium Sampson posts continue under the deck and are welded to multiple stringers. In addition, gussets spread the load.
This is probably overkill, but it does show how a professional design team engineer attachment points suitable for a JSD.
The photo below was taken during construction:
The cleats are not just welded on the deck, instead the twin aluminium Sampson posts continue under the deck and are welded to multiple stringers. In addition, gussets spread the load.
This is probably overkill, but it does show how a professional design team engineer attachment points suitable for a JSD.
The photo below was taken during construction:
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zoidberg
Well-known member
I came across this short video-clip, which should remind us of what the problem looks like...
dgadee
Well-known member
What would the force be of that when taken on the stern?
veshengro
Well-known member
Did the designer/seller of these Drogues go bust? If everyone who attempted to buy one was advised to uprate/rebuild their boats to the standards that some people are suggesting, I doubt he sold very many. Certainly none to the major European boat makers I would think.
Roberto
Well-known member
That was the punitive breaker wave as he had stolen the boat
geem
Well-known member
He didn't sell them. He gave away the design so others could build their own or have them made. Most European sailors don't need one if you are coastal cruising.
noelex
Well-known member
A drogue is a specialised piece of equipment that is likely to be carried only by some long distance cruising boats, so the market is quite small. A suitable attachment point can be fabricated for most production yachts. Yachts contemplating carrying a JSD will typically have already been modified with additions such as solar panels, extra shade, davits, larger battery bank, more significant ground tackle etc. Installing attachment points for a JSD is just one additional modification.
This attachment also provides a strong point should the boat need towing from the stern off a serious grounding.