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Drogue Chain Plates Strength?

northcave

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So..... is it reasonable to say that when we buy a drogue ( Jordan series or 'Jimmy Green' single) we must fit a set of drogue 'chain plates' or risk loosing anything we attach the drogue to?

Interesting to read the comments on securing tow rope bridles and 'sharing' the load etc. I have always wondered how this is achieved. As we all know a single turn around a cleat is enough to absorb most of any load.


Also I guess that when chain plates are fitted as originally designed equipment the hull area strength will have been assessed/beefed up
From my reading, the loads on a single drogue are, "in most cases", much less than a JSD. A single would be regarded as a way to slow down and let you steer. A JSD is a hands off approach which you go below and hang tight.

Additionally and from reported experiences, chafe is a much bigger issue so leading lines over, under and around things is not great. Cases have been shown where JSDs are deployed for multiple days, so chain plates overhanging the stern limits that risk to almost zero. We then only need to concern ourselves with the strength of the chain plates to which I'm still non the wiser.

I have equal numbers of people saying my 10mm solid layup hull is totally capable of withstanding the loads, given a good size chain plate and backing plate. The other half say I need substantial reinforcement is required, with various ideas of how to do this.

Thanks to all on this thread for their advice and views.
 
Last edited:

Andy Doughty

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I am not being rude. But sailing should be about enjoyment and relaxation, not pondering about chain plate pul out values. Why not just go sailing when and where you can just derive pleasure not anxiety. If you make a bridle that can be fixed to all cleats on the side deck, from 20/22 m/m from good quality rope that has some stretch capacity, it can allow a drogue to be launched from bow or stern. Good luck.
 

thinwater

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Does anyone have documentation of cleats pulled out by a drogue?

Not sayin' it can't happen. There are some poor cleats out there. But there are also some excellent ones, and most drogues cannot exert forces that exceed fairly common anchoring forces. The first thing I would do is take a good look at the cleats (strength and chafe). It might be simpler to fix that, depending on access and location. Might not.

And though I like the JSD chain plate idea to a point, they will be useless if bridle needs adjusted either for steering or attitude. What if you decide to cut the drogue loose (can't reach them)? They are an "ultimate storm" thing and perhaps not best for even a pretty strong storm. Unless you believe the forces will exceed ~5000 pounds, not needed. That is LOT for a drogue. Most have to go over 30 knots to get there.
 

northcave

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I am not being rude. But sailing should be about enjoyment and relaxation
That is one very narrow minded definition of what sailing "should be". It entirely depends on the person.

For me it is:

- Seeing the world in a sustainable way
- Adventure and elation
- True exploration beyond normal cruising routes

For this I need a solid and safe boat and if it means me pondering over chain plates now to reduce anxiety down the line then so be it. Later this year my boat will be in the North Sea on the way to Norway. In the coming years it could see Patagonia, Greenland and Northern Pacific to Alaska.

Do I want a solid and proven system for short handed crews in storm conditions. Hell yes I do! And do I want to make sure I understand it will work when I chuck it overboard. Hell yes I do.
 

Scotty_Tradewind

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That is one very narrow minded definition of what sailing "should be". It entirely depends on the person.

For me it is:

- Seeing the world in a sustainable way
- Adventure and elation
- True exploration beyond normal cruising routes

For this I need a solid and safe boat and if it means me pondering over chain plates now to reduce anxiety down the line then so be it. Later this year my boat will be in the North Sea on the way to Norway. In the coming years it could see Patagonia, Greenland and Northern Pacific to Alaska.

Do I want a solid and proven system for short handed crews in storm conditions. Hell yes I do! And do I want to make sure I understand it will work when I chuck it overboard. Hell yes I do.
well done!

S.
 

Neeves

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That is one very narrow minded definition of what sailing "should be". It entirely depends on the person.

For me it is:

- Seeing the world in a sustainable way
- Adventure and elation
- True exploration beyond normal cruising routes

For this I need a solid and safe boat and if it means me pondering over chain plates now to reduce anxiety down the line then so be it. Later this year my boat will be in the North Sea on the way to Norway. In the coming years it could see Patagonia, Greenland and Northern Pacific to Alaska.

Do I want a solid and proven system for short handed crews in storm conditions. Hell yes I do! And do I want to make sure I understand it will work when I chuck it overboard. Hell yes I do.
+1

And this location gives an ability for a whole variety of views some of which are useful and might not have been considered previously. But it is also true you can invoke some very odd responses :)

Jonathan
 

thinwater

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Really, this is not anxious for engineers; it is fun and relaxing. No one should stress over any question of fact; instead, calculate the answer. Stress is for hazards coming your way that defy calculation (most of these are people).

And be thank full engineer fussed over your keel bolts and standing rigging... and the brakes on your car and the bridge you drive over.
 

thinwater

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Really, this is not anxious for engineers; it is fun and relaxing. No one should stress over any question of fact; instead, calculate the answer. Stress is for hazards coming your way that defy calculation (most of these are people).

And be thank full engineer fussed over your keel bolts and standing rigging... and the brakes on your car and the bridge you drive over.

---

* Millimeter is mm, not m/m. I had to guess on that. It would also be 20-22mm.
* If the line has stretch, load cannot be equalized. It can also not be equalized to the mid-ships cleats. We covered this. It is an illusion.
* Not all manufacturers recommend line with stretch. Jordan and Seabrake are among these.
* A drogue cannot be launched from the bow. At least the manufacturer will explain that is a mistake. Sea Anchor, perhaps--different topic, and by the way, the forces are WAY higher there.
 

Neeves

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Its vaguely appropriate and unlikely to appear anywhere but Oz.

They suggest they deployed a drogue (and then sails) - I'm not sure what they mean by a drogue. Its not a normal item of equipment (?) on a racing yacht involved in 'inshore' or 'coastal' races. The yacht would not normally be considered as one for cruising, there are much better choices, IMHO. I'm amazed they had a long enough piece of cordage suitable for a drogue, but it could have been a halyard. They certainly would not have had dedicated chain plates - cleat maybe, one of the winches.


http://www.mysailing.com.au/latest/dramatic-account-of-the-attempted-rescue-of-m3-by-marine-rescue-port-stephens?utm_medium=email&utm_campaign=Enews Feb 2 2016&utm_content=Enews Feb 2 2016+CID_f59adde513c10653a52d40a3ebd423cb&utm_source=Email marketing software&utm_term=Dramatic account of the attempted rescue of M3 by Marine Rescue Port Stephens

Jonathan
 

Graham_Wright

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Does anyone have documentation of cleats pulled out by a drogue?

Not sayin' it can't happen. There are some poor cleats out there. But there are also some excellent ones, and most drogues cannot exert forces that exceed fairly common anchoring forces. The first thing I would do is take a good look at the cleats (strength and chafe). It might be simpler to fix that, depending on access and location. Might not.

And though I like the JSD chain plate idea to a point, they will be useless if bridle needs adjusted either for steering or attitude. What if you decide to cut the drogue loose (can't reach them)? They are an "ultimate storm" thing and perhaps not best for even a pretty strong storm. Unless you believe the forces will exceed ~5000 pounds, not needed. That is LOT for a drogue. Most have to go over 30 knots to get there.
Those are very good points.

I have huge confidence in my cleats but do backing plates come into the argument? The drogue load will be along the deck with no vertical component. All we are looking at here then, is shear. My cleats are fixed with four through bolts in line by pairs so the in-line load is split sideways. (They do also have substantial stainless backing plates).

A good point about cutting free and steering.
 

northcave

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I have huge confidence in my cleats but do backing plates come into the argument? The drogue load will be along the deck with no vertical component. All we are looking at here then, is shear.
That is a good point and from what I am told the backing plate is still very important but to ensure it is flat on the inside of the hull and clamped down like buggery, therefore spreading the load of where the outer plate is fixed.

I.e it strength is not just in the bolts but loaded across the entire backing plate.

Is my engineering correct on that one?

If not the it goes back to my OP about increasing the total length of the chain plate with more bolts?
 
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Those are very good points.

I have huge confidence in my cleats but do backing plates come into the argument? The drogue load will be along the deck with no vertical component. All we are looking at here then, is shear. My cleats are fixed with four through bolts in line by pairs so the in-line load is split sideways. (They do also have substantial stainless backing plates).
Not strictly true as the line attachment is above the deck by the height of the cleat rope notch you are applying a turning moment which is trying to rip the cleat and backing plate out of the deck.

The loading on the bolts are shear but the bolts on the opposite side to the pull are also in tension and thus the backing is being pulled upwards and trying to rip the backing through the deck thus the opposite side of the deck to the load is in shear upwards.
 

Graham_Wright

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Not strictly true as the line attachment is above the deck by the height of the cleat rope notch you are applying a turning moment which is trying to rip the cleat and backing plate out of the deck.

The loading on the bolts are shear but the bolts on the opposite side to the pull are also in tension and thus the backing is being pulled upwards and trying to rip the backing through the deck thus the opposite side of the deck to the load is in shear upwards.
Agreed, but if you do the trig, I'm sure there is not a lot of upwards tension left.
I should have added that the exit over the stern would be through fairleads.
 
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Agreed, but if you do the trig, I'm sure there is not a lot of upwards tension left.
I should have added that the exit over the stern would be through fairleads.
Yes it depends on the size of the backing plate, the bigger the better. Then again if you look at the base of the average cleat the tension and crushing of the fixings and bearing on the deck it can be greater due to the base being smaller than the load height



https://www.google.co.za/search?q=deck+cleat&biw=1280&bih=685&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwiMtvX0zNvKAhUD6xQKHeTDAJAQsAQIGQ

This is one of the reasons I fabricated my own.
 

thinwater

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Those are very good points.

I have huge confidence in my cleats but do backing plates come into the argument? The drogue load will be along the deck with no vertical component. All we are looking at here then, is shear. My cleats are fixed with four through bolts in line by pairs so the in-line load is split sideways. (They do also have substantial stainless backing plates).

A good point about cutting free and steering.
This is why I often prefer FRP backing plates that are bonded. It then use oversize washers cut from 1/8" or heavier plate (fender washers serve zero purpose--they bend).
 

thinwater

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Solid fiberglass is good for about 25000 PSI in compression . At the point of compression failure all that happens is that you lose shear strength, but the bonded backing plate can carry that. You are not going to get forces nearly that high. Finally, all cleat failures I have seen in the end, become pull-out failures. The backing plate prevents that. Do the numbers.

Cored decks, depending on the core and skins, begin to crush at about 2000 PSI if there is no epoxy plug. With an epoxy plug they easily handle full bolt tension, and in this case, full compression. I've broken many bolts against plugs in testing. When in doubt, you could add a small backing plate on the top.
 

northcave

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Solid fiberglass is good for about 25000 PSI in compression
@thinwater - You seem to know your stuff. If you were me with my 10mm thick 45cm ling chain plate and a 10mm solid GRP hull.... would you think such a chain plate would be suffice against approx 8 Tonne of breaking wave force?

Or if you were me what additional measures would you take? More epoxy inside? Longer chain plate? Backing plate with right angle up against the transom also?

Note that my Hull is lloyds standard and the layup as good as it gets from building in Falmouth back in the good old days.
 

pcatterall

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"Why not just go sailing when and where you can just derive pleasure not anxiety.?"

Some good answers to that question already posted! We just want the pleasure of sailing, and certainly don't need anxiety! however part of the pleasure is in knowing that you have the equipment ( and a plan) for unexpected eventualities. Some of the very techy stuff is over my head but I do learn bits from our experts so keep it up all of you!!
 
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