rogerthebodger
Well-known member
If you have a large single block on the bridle line and the drogue attached to that both legs of the bridle will automatically have tension kept in then and also equalise the load on the chain plates better.
Drogue Chain Plates Strength?
- Thread starter Tim Good
- Start date
thinwater
Well-known member
Have you used this method in storm conditions? I did, and found it to be a complete disaster. If the boat yaws away from the block side, the load on the block line doubles (which in storm conditions is a LOT) and the bridle pulls up close to the stern and cannot be restored to it's original position. The boat becomes stuck beam-on to waves.
The bridle angle is also far too narrow. Simple physics shows it can be no less then 120 degrees, and if the bridle is moved to either side for balance it is worse. The vector diagram makes this obvious. But try it yourselves.
At least that is what happened to me. I recommend folks test this on a rough day before they believe in it. You see the method in books, but I've never read of it being used in winds above 10 knots or seen photos of same.
(large image showing the problem)
https://1.bp.blogspot.com/-A7EoUXqFCZU/VxJWtdu44rI/AAAAAAAAMVg/mV31qQfahGQ5scvk-MQ2g0TcZYGn5t3nACLcB/s1600/Why%2Ba%2Bsnatch%2Bblock%2Bbridle%2Bis%2Ba%2Bmistake%2B%2528inpossible%2Bto%2Bwinch%2Bback%2Bto%2Bport%2Bfrom%2Bthis%2Bposition%2529.jpg
Why the funny carabiner set-up? The sling goes to a load cell. At the point the photo was taken, we were stuck; because the bridle slid to one side in a yaw, the boat was forced turning starboard, but the load was too great to crank the line back to center, and even if we could, look how narrow the angle would be, with forces 3-4 times the rode force, which was about 400 pounds at the time. Grinding 1600 pounds with winches found on a 34' boat is impractical. And this was just a nice breeze!
Most of the images of drogue testing you see are done in flat calm conditions. Guess why? In a breeze it is bloody hard work.
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rogerthebodger
Well-known member
I take your word for it.
Fascadale
Well-known member
A recent JSD thread brought me back to this great discussion
Has our cumulative knowledge on JSDs moved on much over the last few years?
I have seen YouTubes where JSDs have chaffed through, where a JSD has destroyed a vane and where JSDs are a nightmare to retrieve
I have not seen, or read much about their effectiveness once deployed and I am not aware of any commentary on JSD chainplates that have actually seen use
Is there any new information out there?
Has our cumulative knowledge on JSDs moved on much over the last few years?
I have seen YouTubes where JSDs have chaffed through, where a JSD has destroyed a vane and where JSDs are a nightmare to retrieve
I have not seen, or read much about their effectiveness once deployed and I am not aware of any commentary on JSD chainplates that have actually seen use
Is there any new information out there?
Tim Good
Well-known member
Sure. Take a look at my site below. Use the second video. It shows the retrieval and some discussion about my chainplates and deployment bag at the end.
I have plans for my chainplates on the link below:
When I had to use the Jordan Series Drogue! | Chasing Contours
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Tim Good
Well-known member
but to answer this question then here are the things I’ve learned and how things have changed.
1. chaffe can be minimised or eliminated by having overhanging chainplates like mine
2. Use solid eyes to reduce chaffe on the bridle
3. Use crosby shackles with a decent swl equal to half the boat displacement
4. If you have an early JSD with a figure 8 knot at the end of the leaders then get it spliced instead. You don’t want to do a Suzie!
5. Ensure the weight on the end is correct. Too little is worse than too much. Ideally chain.
6. Retrieval is quicker and easier than I thought providing you can get the leaders around a winch.
7. Deploy from a large drybag into which the JSD is flaked to ensure a seamless and hand free deployment.
8. Ensure it is all rigged before the bad weather comes.
All the above meant I had a very pleasant experience with a JSD were no chaffe was found at all.
Yellow Ballad
Well-known member
As the poster of the other chainplate thread could I ask what your plans are for you chainplates?
Kind Regards
Tim Good
Well-known member
See the link on my site. The plans are there.
When I had to use the Jordan Series Drogue! | Chasing Contours
Yellow Ballad
Well-known member
Ah sorry, I thought you meant you had plans as in to change/modify them rather than the plans for the plates.
I was looking at your site earlier when researching a design. Glad you started this thread, lots of good info on it.
Tom
I was looking at your site earlier when researching a design. Glad you started this thread, lots of good info on it.
Tom
Neeves
Well-known member
Be careful how you view usage.
Being caught in 55 knot winds with breaking seas is slightly different, to entirely different, to simulating these conditions in 30 knots. What you can do at 30 knots becomes a heroic effort when the winds get up. Don't under estimate how bad and awful it can be.
If possible - don't get caught in 55 knots (or more) of wind
The ideal is, like a life raft, you never ever want to use a JSD, you never want to experience 55 knots (or more). None of it is very pleasant and bragging rights really don't count for much.
Jonathan
Being caught in 55 knot winds with breaking seas is slightly different, to entirely different, to simulating these conditions in 30 knots. What you can do at 30 knots becomes a heroic effort when the winds get up. Don't under estimate how bad and awful it can be.
If possible - don't get caught in 55 knots (or more) of wind
The ideal is, like a life raft, you never ever want to use a JSD, you never want to experience 55 knots (or more). None of it is very pleasant and bragging rights really don't count for much.
Jonathan
differentroads
Active member
Really interesting to see your drogue in use and your thoughts anout it. Cheers for going to the efgort of sharing
differentroads
Active member
Helpful advice and you might just have saved me a lot of unneccesary trouble. I live in a place where westerly F7 to 8 are fairly regular (in Spain just N of Gibraltar) but the sea close inshore is deep, near tideless and fairly calm. I've managed to try my storm sail out in 30 to 35kn in these conditions and my JSD was next on the list. Your comment has made me realise how little it will relate to ocean storm conditions. I might as well rehearse deploying it under engine in calm conditions. I won't learn much more in strong winds but calm waters and hauling it back in would be a bastard - I already know that! And I'm not about to go out into the Gibraltar Strait to find the stronger winds and 3 to 4m waves and then drop a drogue over the side. The first thing I'd learn is how fast a wife's love can turn to hate ?Be careful how you view usage.
Being caught in 55 knot winds with breaking seas is slightly different, to entirely different, to simulating these conditions in 30 knots. What you can do at 30 knots becomes a heroic effort when the winds get up. Don't under estimate how bad and awful it can be.
If possible - don't get caught in 55 knots (or more) of wind
The ideal is, like a life raft, you never ever want to use a JSD, you never want to experience 55 knots (or more). None of it is very pleasant and bragging rights really don't count for much.
Jonathan
zoidberg
Well-known member
Here's a direct question, pointed specifically at those few who have actually built and used a JSD 'for real'.....
Don Jordan, back in 1980, showed in his original Proof of Concept design a 'leader' secured to another rope which had the droguelets secured into it. I have no issue with the number of droguelets, the shape/size of bridle, the chainplates concept, or the terminal 'sinker'.
I do question - strongly - the point of having TWO ropes, with a joining bend/knot/device between them. I'm aware that Don Jordan used nylon rope and other materials that, for him, were to hand and readily available in 1980. Material science/rope technology has moved on, and I see no good reason not to have the whole rope beyond the bridle constructed in one long piece.
Or does anyone have a justification for 'several sections' and the attendent weakening knots/bends....? Or 'double braid nylon' and 'tapered'....?
Don Jordan's table of recommended rope diameters vs displacement can surely be updated in the knowledge of the strength capabilities of e.g HDPE single braid, where even a 12mm single braid can give over 15 tonnes UTL.
Don Jordan, back in 1980, showed in his original Proof of Concept design a 'leader' secured to another rope which had the droguelets secured into it. I have no issue with the number of droguelets, the shape/size of bridle, the chainplates concept, or the terminal 'sinker'.
I do question - strongly - the point of having TWO ropes, with a joining bend/knot/device between them. I'm aware that Don Jordan used nylon rope and other materials that, for him, were to hand and readily available in 1980. Material science/rope technology has moved on, and I see no good reason not to have the whole rope beyond the bridle constructed in one long piece.
Or does anyone have a justification for 'several sections' and the attendent weakening knots/bends....? Or 'double braid nylon' and 'tapered'....?
Don Jordan's table of recommended rope diameters vs displacement can surely be updated in the knowledge of the strength capabilities of e.g HDPE single braid, where even a 12mm single braid can give over 15 tonnes UTL.
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Tim Good
Well-known member
The sections allow a smaller diameter along the length where less strength is required. Mine has three sections and it a total beast. 22mm, 18mm and 14mm double braid nylon. It would be totally unmanageable if it were the same as the first leader all the way along.
I got mine in around 2016 and used once in 2020. I’ve seen new ones and the construction is different. The new ones are made from hollow braid HDPE (generic dynema/spectra). A red line attached every fifth cone is to aid recovery so that the running hitch on the recovery line has something to grip onto as the main line is so slippery.
Mine has no issues with hitch or prussik slipping as it’s Nylon.
Laminar Flow
Well-known member
None of the forces alluded to are quantified in any way.
There are no shock loads.
Breaking loads for a threaded machine screw, as shown in your pic is: at the thread and in shear: 10mm - 2593 lbs; 12mm 4808lbs
A 30mm x 10mm Stainless strapping with a 10mm hole drilled through it would hold 12,656 lbs, 40mm x 10mm also with a 10mm hole would hold 20,246 lbs
Ergo, you would need a 40mm x 10mm chainplate held on by 8 10mm threaded machine screws to hold 9t.
GRP at chainplate attachment should be 1.3 times the hull thickness plus a distance of twenty times the smallest bolt diametre beyond the last bolt.
Dave Gerr, Boatstrength.
Hope this helps.
Neeves
Well-known member
For the holds defined for the strapping, 12,656lbs and 20,246lbs - at what angle are these loads applied?
The question is not what tension can this strapping accept but at what point will it yield if loaded at an angle, and some comment needs to be included at what angle the tension might be applied.
Jonathan
Neeves
Well-known member
Sorry but I missed this post - and it may have been answered.
The shear strength of the shackle pin is the strength of the shackle - assuming you buy a quality shackle.
I've only tested 3/8th" shackles, it keeps costs down, but a Crosby G209a shackles, these are the best shackles they make and are as good as the best you can buy (Campbell, Peerless and Yoke make similar qualities) and the Crosby 3/8th shackle will shear at the thread of the clevis pin at the rated strength. So for a 3/8th" shackle it will have a UTS of marginally over its min break strength of 10t. The WLL is 2t. Peerless and Campbell shackles will fail the same way, at the thread of the pin. I have not tested Yoke shackles. Most shackles you buy from a hardware store will have a maximum of half the strength of the Crosby G209a shackles - and may. fall through the eye breaking. These better shackles are classed as G80, in the same way chain is G30 or G40 and are also supplied as being Grade B shackles (the more common shackles are Grade A shackles).
Peerless and Campbell shackles are difficult to source in the UK, actually they might be impossible to source. I would not use anything but the Grade B quality (I do have Campbell and Peerless shackles but if I need to buy I source Crosby from Tecni in the UK.
For larger sizes you can use Green Pin shackles from Van Beest - but they don't make small sizes (the sizes we would use for anchoring) and I have not tested them - but am sure they will fail the same way.
However if the shackle is 'side' loaded (and Ive tested this as well; and agree) at 45 degrees strength is reduced by 25% and reduced by 50% if loaded at 90 degrees.
If loaded at 45 degrees, possible under the conditions being discussed, then the chain plates need to be considered for yield not their ultimate tensile strength. The UTS of the chain plates illustrated in Post 1 might be quite high - their yield strength will be much lower and its value more applicable. If the chain plate yield you are no longer simply considering bolt strength in shear.
Jonathan
D
Deleted member 36384
Guest
Surely all design in this context, shackles, bolts and chain plates, would be done by comparing to Yield Strength? Designing to UTS would be allowing for deformation and failure. Would the shackles, at 45 degree loading, not be selected on WLL based on the 45 degree load rating? Do you select shackles based on yield (at 45 degrees or in line) to reduce the the size of shackle, considering WLL will have a derating factor applied to Yield Strength? Trying to understand why you mention UTS, as it suggests that this would be used in design and selection of materials. Curious to understand this.
Neeves
Well-known member
In Laminar Flow's post #95 he refers to some data but he does not define what the data means. Is it UTS, is it yield.
Alloy shackles are rated on the basis of a straight line load so Crosby's G209a 3/8th" shackles is sold and embossed as a WLL of 2t BUT in small print Crosby warn that if the shackles are loaded at 45 or 90 degrees to the straight line load then note should be made of how the WLL is degraded. This warning is a blanket warning for their shackles and is not printed on the specification of each type of shackle they make - you need to find the small print. Crosby shackles are sold with a 5:1 safety rating and are Proof Tested to 2 times WLL.
When you buy shackles they are commonly sold based on their UTS and their WLL. People use a 6t (WLL 1t) or a 10t (WLL 2t) shackle.
The discussion is of a chain plate, being made by an individual, with no known characteristics. We have no knowledge of how it might actually be used - or we know the theory of the use but not what will actually happen.
With for example alloy lifting shackles some detail has been provided by the manufacturer - so we have some idea of is characteristics.
Without knowing the characteristics of the components made from 316 steel we are guessing - and that is wrong.
Laminar Flow's post gives some data, I assume from a simple (or less simple) calculation - but not knowing what the data means - its not much use. If its the UTS, where the item is torn apart - that's might not be its point of failure - failure might be when it yields. If we had a yield point a judgement could be made on what safety factor might be applicable. The problem of UTS of 316 stainless is that it is 'respectable' but its yield is low.
When I recommend shackles I do so on the basis of a tension at 90 degrees to the straight line pull. For a 3/8th" shackle this brings the WLL down from 2t to 1t and this neatly allows that 3/8th" shackle to be better than a 8mm G30 chain and similar to a 8mm G40 chain. I also know that the UTS of the shackles are factorially higher than the chain as the chain has a safety factor of 4:1 and the shackles 5:1.
To me you need all the data - because the safety factors are different and as in the case of chain and shackles a recommendation for a Crosby G209a 3/8th" shackle for 8mm G30 or G40 chain is conservative in terms of WLL AND in terms of UTS. So I'm not sticking my neck out - and its a responsible (I think) piece of advice). So unless I know all the data, what the safety factors are - I'm cautious. If we look at American G43 and G70 chain they are sold to a 3:1 safety factor (and Maggi's G70 was to a 5:1 safety factor)and G43 looks really good - you need to look at their UTS and then compare with the UTS of metric G40 to see that G43 is not THAT good - its an arithmetic fudge (and I know that there are a lot of gullible people around). The strength of the bolts for the chain plate application is in shear - but if the chain plates fail, bend, the bolts will no longer only be in shear. Now - if we know the UTS of the bolts as well as their WLL the OP can make judgements on what he can accept.
In this case I'm still trying to probe to have someone with much more knowledge than me to provide the data - Laminar Flow might have done that.
Without naming names:
A well know marine company published a specification for their component. I tested it and was genuinely surprised when it failed at about 25% of the specified data. I had tested in a way that simulated actual use. My publisher queried the discrepancy with the manufacturer.
The data had been derived by SGS and they had been asked to test the item, they tested till they tore it apart (they did not know how it was used). They had tested it to destruction but the item failed long before it 'tore apart' - because it passed its yield point and simply released the device to which it was attached. The manufacturer initially complained about my poor technique etc etc and then quietly when they worked it all out - changed their specification. As this' sort' of issue has occurred more than once - I don't commend this supplier.
So - my testing is to try and simulate how an article is used - and in this thread and the parallel thread I'm considering how the chain plates will be used - in real life. UTS of the shackles is relevant, or safety factor is relevant because the chain plate will be to a different safety factor to that of a shackle.
I tested another component from another manufacturer using a standard test technique. It failed, consistently. They complained about my testing (I've get used to it ) they then quietly changed the specification from metric tonnes to short tons (which met my data). This raised further questions as to whether they did any testing (at all) before releasing their product to the gullible public - or did they think they could get away with selling product that did not meet their spec because no-one would even use it to the limits? I will not recommend this product range.
Unless you test to UTS - these stones are never turned over.
Sorry - another of my long winded posts.
Jonathan
Alloy shackles are rated on the basis of a straight line load so Crosby's G209a 3/8th" shackles is sold and embossed as a WLL of 2t BUT in small print Crosby warn that if the shackles are loaded at 45 or 90 degrees to the straight line load then note should be made of how the WLL is degraded. This warning is a blanket warning for their shackles and is not printed on the specification of each type of shackle they make - you need to find the small print. Crosby shackles are sold with a 5:1 safety rating and are Proof Tested to 2 times WLL.
When you buy shackles they are commonly sold based on their UTS and their WLL. People use a 6t (WLL 1t) or a 10t (WLL 2t) shackle.
The discussion is of a chain plate, being made by an individual, with no known characteristics. We have no knowledge of how it might actually be used - or we know the theory of the use but not what will actually happen.
With for example alloy lifting shackles some detail has been provided by the manufacturer - so we have some idea of is characteristics.
Without knowing the characteristics of the components made from 316 steel we are guessing - and that is wrong.
Laminar Flow's post gives some data, I assume from a simple (or less simple) calculation - but not knowing what the data means - its not much use. If its the UTS, where the item is torn apart - that's might not be its point of failure - failure might be when it yields. If we had a yield point a judgement could be made on what safety factor might be applicable. The problem of UTS of 316 stainless is that it is 'respectable' but its yield is low.
When I recommend shackles I do so on the basis of a tension at 90 degrees to the straight line pull. For a 3/8th" shackle this brings the WLL down from 2t to 1t and this neatly allows that 3/8th" shackle to be better than a 8mm G30 chain and similar to a 8mm G40 chain. I also know that the UTS of the shackles are factorially higher than the chain as the chain has a safety factor of 4:1 and the shackles 5:1.
To me you need all the data - because the safety factors are different and as in the case of chain and shackles a recommendation for a Crosby G209a 3/8th" shackle for 8mm G30 or G40 chain is conservative in terms of WLL AND in terms of UTS. So I'm not sticking my neck out - and its a responsible (I think) piece of advice). So unless I know all the data, what the safety factors are - I'm cautious. If we look at American G43 and G70 chain they are sold to a 3:1 safety factor (and Maggi's G70 was to a 5:1 safety factor)and G43 looks really good - you need to look at their UTS and then compare with the UTS of metric G40 to see that G43 is not THAT good - its an arithmetic fudge (and I know that there are a lot of gullible people around). The strength of the bolts for the chain plate application is in shear - but if the chain plates fail, bend, the bolts will no longer only be in shear. Now - if we know the UTS of the bolts as well as their WLL the OP can make judgements on what he can accept.
In this case I'm still trying to probe to have someone with much more knowledge than me to provide the data - Laminar Flow might have done that.
Without naming names:
A well know marine company published a specification for their component. I tested it and was genuinely surprised when it failed at about 25% of the specified data. I had tested in a way that simulated actual use. My publisher queried the discrepancy with the manufacturer.
The data had been derived by SGS and they had been asked to test the item, they tested till they tore it apart (they did not know how it was used). They had tested it to destruction but the item failed long before it 'tore apart' - because it passed its yield point and simply released the device to which it was attached. The manufacturer initially complained about my poor technique etc etc and then quietly when they worked it all out - changed their specification. As this' sort' of issue has occurred more than once - I don't commend this supplier.
So - my testing is to try and simulate how an article is used - and in this thread and the parallel thread I'm considering how the chain plates will be used - in real life. UTS of the shackles is relevant, or safety factor is relevant because the chain plate will be to a different safety factor to that of a shackle.
I tested another component from another manufacturer using a standard test technique. It failed, consistently. They complained about my testing (I've get used to it
) they then quietly changed the specification from metric tonnes to short tons (which met my data). This raised further questions as to whether they did any testing (at all) before releasing their product to the gullible public - or did they think they could get away with selling product that did not meet their spec because no-one would even use it to the limits? I will not recommend this product range.Unless you test to UTS - these stones are never turned over.
Sorry - another of my long winded posts.
Jonathan
zoidberg
Well-known member
I find myself thinking - 'Do you want the short answer, or do you want the right answer?'
I'm also reminded of the 'Bronze versus brass' little
It emerged that the Recreational Craft Directive was the culprit. In their fervour, the architects of this load of EU 'Administratium' had cobbled together a Standard for such items which, if memory serves, required them to last merely 5 years from 'putting into service'. That the original products were traditionally made of 'naval bronze' which lasted a couple of lifetimes, and were not a problem that needed solving by the EU, was completely overlooked - but not by boatbuilders, who swiftly plumped for the very much cheaper 'brass' fittings which might last just a handful of years before 'Failing Unsafe'. And by then Out Of Warranty....
No-one noticed for years..... for they were 'CE Compliant'.
It took some publicity in HERE, some prodding of insurers and the editors of some US magazines, to bring to the surface that there was a problem. Now we have 'DZR' and engineering plastic throughhulls, and folks are just a little more willing to ask searching questions of boatbuilders, yards and chandleries.
This is one of the few good places where individuals with wide-ranging expertise can explore some boaty problems and work towards a helpful consensus on 'better'. I'm thinking of personal tethers, chain vs mixed rodes, DZR brass, chinese shackles, dripless stern glands, JSDs.....and many more topics.
I'm perfectly content to have those with questions, and those with expertise, 'debate' vigorously towards a pro bono better tomorrow. That's good for all of us.