Jordan series Drogue Attachment

[YPSILANTI]

I have a 49 ft. catamaran for which I've constructed a robust JSD comprising 155 drogues. I've read the recommendations regarding the attachment methods of straps ( chain plates ) and shackles. I am considering using my existing cleats which I will reinforce with backing plates. 1. Will this method be strong enough. 2. What preventative methods can I use for chafing. 3. Is it a bad idea? I respectfully ask that only people qualified and experienced reply such that I can obtained informed replies as apposed to sentiment and opinion. Thank you.

[kmacdonald]

The existing cleats are no where near strong enough unless specifically designed for that purpose. There is plenty of information available that will show you how to determine the max load you need to design for. Once you have that get it engineered by some one qualified, not a forum.

[Jim Cate]

I respectfully ask that only people qualified and experienced reply such that I can obtained informed replies as apposed to sentiment and opinion

Mate, it's an internet forum, and you'll get what you get!

My advice is to contact the builder/designer for this sort of information. Only those folks have any realistic idea of the structure's strength.

Jim

[Sailmonkey]

I would second or third the "NO" to the cleats. To really properly do this you'll need to add some chain plates to the quarters so that the load is taken by the hull. As to the specifics for loading and reinforcement you'll need to consult with an NA or engineer to say if your particular attachment is kosher.

Now it's up to you to decide if I'm qualified and experienced enough for your liking.

[thinwater]

If anyone (including those that are sure they are weak) has cleat working load or breaking strength data, please post it. Obviously, a large cleat can be as strong as you would like it to be. Just go down to the ship docks. But data is hard to come by, and installation details are difficult to confirm. Below are the only data I remember.

And chafe is an interesting topic, to geometry specific to discuss intelligently.

The thing about dedicated straps is that we can confirm the engineering more easily, and chafe is easier to eliminate.

As for load, the drag of a JDS at speed is given in the Coast Guard report. Pick a speed and number of cones.

---

http://www.boatus.org/findings/16/

Cleat Types & Failure Loads. 6-Inch Cleats


Test Cleat Cleat Material Fasteners 0° 45° 90° 45°/45° Average Load
Sustained List Price
(circa 1990) A Nylon 2 - #10-32 2780 1390 1590 2380 2035 $4.25 B Aluminum 2 -1/4-20 3780 3860 3800 4000 3860 $16.95 C Aluminum 2 - 1/4-20 2500 3890 3700 4770 3715 $36.35 D Zinc 2 - 1/4-20 3580 3380 3970 4760 3928 $21.00/pr. E Aluminum 2 - 1/4-20 4970 3780 4170 5360 4570 $19.25 F Aluminum 4 - 1/4-20 4170 1190 1790 4770 2980 $31.95 G Marinium 4 - 1/4-20 7160 6760 6720 5370 6503 $17.95 H Zamac 4 - #10-32 3380 2920 2380 3180 2965 $15.00/pr J Zinc 4 - #10-32 3180 2780 2880 3970 3202 $10.45 K Stainless 4 - 1/4-20 6660 6800 7550 6560 6893 $10.09 L Bronze 4 - #10-32 3180 3990 3970 4570 3928 $12.69
Fasteners Failed
Leg Failed
Feet Failed

[model 10]

I ended up using plates on the outside of the hull, it was the only way to get a chafe free looking set-up. If you imagine how the stern will move around, docking cleats would never work.

[UNCIVILIZED]

One other thing about cleats. Even if the cleats themselves, & their fasteners are strong enough. Plus that they're mounted with decent sized backing plates. Under severe loads, it's not uncommon for the section of the deck that the cleat is mount to to tear out. As usually decks aren't designed to withstand multi-ton point loadings, especially not loadings that are severe, sharp pulls. Where with a chainplate, that also has purpose built added structural laminate around & under it, they're better suited to such loadings.

We've all seen pics of cleats that have torn loose of the boats they were mounted to. And not necessarily in extreme conditions either. Which drogue deployment would definitely fall under said header.

And think about how common chafe, & or partial line melting is where docklines meet cleats on boats when the weather pipes up. Just the small amount of motion in the vicinity of the cleats in such situations can be very hard on docklines. And it'd be exponentially worse if/when a boat was tethered by a drogue.

[thinwater]

I cleaned-up the data table:



8-inch cleats will be 2-4 times this strong, and so forth for larger sizes. In other words, if they are large enough, they will probably break the rope. Interestingly, the cleats with feet, which some folks so adamantly swear by, are substantially weaker in some cases--be aware.

I won't argue the "cleat pulled out of the deck" incidents. The problem with cleats is that it is difficult to estimate the strength of the installation, particularly for the non-engineer. It's complicated. Even then, you must make educated guesses about the laminate. However, I will say that every cleat I have seen fail was...

* An old POS boat that was mat and chopper gun stuff, and...
* Hung from the dock, which is NOT something cleats are engineered for.

In fact, the average JSD strap would fail under similar load if pull sideways, for example, since only 1 or 2 bolts would have to carry the load. Vertical loads on cleats are not relevant here (the boat is already sinking).

As for a crazy range of angles and chafe, the only motion should be slightly vertical. The bridle will handle the side-to-side. In fact, bridle legs should be kept short enough to prevent single leg loading and the slack that comes with it. I've towed drogues a lot, and the bridle barely moves at all. On my boat there is very little chafe potential, but every boat is different. Yours may be horrible.

I'm not arguing against JSD straps. They are an elegant solution and are easy to engineer. That is why they are brilliant. But let's engineer from facts and understand they are not the only solution.

[kmacdonald]

Originally Posted by thinwater

If anyone (including those that are sure they are weak) has cleat working load or breaking strength data, please post it. Obviously, a large cleat can be as strong as you would like it to be. Just go down to the ship docks. But data is hard to come by, and installation details are difficult to confirm. Below are the only data I remember.

And chafe is an interesting topic, to geometry specific to discuss intelligently.

The thing about dedicated straps is that we can confirm the engineering more easily, and chafe is easier to eliminate.

As for load, the drag of a JDS at speed is given in the Coast Guard report. Pick a speed and number of cones.

---

Cleats : BoatUS Foundation

Cleat Types & Failure Loads. 6-Inch Cleats


Test Cleat Cleat Material Fasteners 0° 45° 90° 45°/45° Average Load
Sustained List Price
(circa 1990) A Nylon 2 - #10-32 2780 1390 1590 2380 2035 $4.25 B Aluminum 2 -1/4-20 3780 3860 3800 4000 3860 $16.95 C Aluminum 2 - 1/4-20 2500 3890 3700 4770 3715 $36.35 D Zinc 2 - 1/4-20 3580 3380 3970 4760 3928 $21.00/pr. E Aluminum 2 - 1/4-20 4970 3780 4170 5360 4570 $19.25 F Aluminum 4 - 1/4-20 4170 1190 1790 4770 2980 $31.95 G Marinium 4 - 1/4-20 7160 6760 6720 5370 6503 $17.95 H Zamac 4 - #10-32 3380 2920 2380 3180 2965 $15.00/pr J Zinc 4 - #10-32 3180 2780 2880 3970 3202 $10.45 K Stainless 4 - 1/4-20 6660 6800 7550 6560 6893 $10.09 L Bronze 4 - #10-32 3180 3990 3970 4570 3928 $12.69
Fasteners Failed
Leg Failed
Feet Failed

I agree with that.
I would be more concerned with the cleat pulling a chunck of the deck out than the actual cleat and fastenings breaking.

[AKA-None]

I thought they were designed to trip if the force got to great?

[kmacdonald]

Originally Posted by AKA-None

I thought they were designed to trip if the force got to great?

No they were not. If the force is to great the weakest link breaks. The objective is to design it so that the weakest link is strong enough to hold the worst case scenario load so that doesn't happen.

[estarzinger]

so, something that is perhaps not so commonly understood about series drogues . . . is that there are two distinct load cases.

The first load case would occur in a semi-typical strong gale/storm - where you have strong winds, large waves with decent breaking crests. The boat speed will accelerate a bit down the waves and when hit by the crests, but generally not be way above hull speed. In this case, the series drogue loads are actually quite manageable - on Hawk (47' mono with 150 cones) we measured peaks of 3500lbs (which is consistent with the USCG findings for this situation). We might have been doing 7ish knots and perhaps accelerated up to a max of 11. Note: as a point of reference - this is quite similar to our max #3 jib sheet loading.

A stern cleat (and deck) should (on the size boats we are talking about here) actually be able to hold 3500lbs. We actually used both cleats and our primary winches (at different times) for holding the bridle lines. We never had any problems. (our cleats were 14" aluminum welded to deck with doublers, so probably unusually strong, but our winches where just pretty typical and typically mounted).

Cruisers would consider this a quite serious storm. You can make a standard tropical circumnavigation, and summer higher latitude cruising and never encounter these conditions, but you might.

The 2nd load case is rather more difficult to deal with. It is if you encounter an enormous breaking wave. In this case the boat can possibly be accelerated to breaking crest speed (quite quickly), or understood a different way - the boat falling down a 45-foot near vertical breaking wave. The physics of this are pretty impressive. Commercial vessel experience confirms this order of magnitude loading . . . . these unusual waves can (worst case) exert a pressure of about one hundred tons per square meter and other testing has found somewhat 'common' (in extreme conditions) wave loading of about 100,000-170,000 lbs/sq meter for 7 seconds on static structures. The 1,000-foot cruise ship Norwegian Dawn encountered a 70-foot wave that broke windows designed for 5 ton/sq meter loads up to the 10th floor.

Now these sorts of conditions are (fortunately) extremely rare. We never encountered this sort of worst case in two circumnavigations, including long distances in the southern ocean and above the arctic circle. However, they do happen. In yachting terms the sydney to Hobart storm was such a situation - now, it should be noted that no cruiser should have been caught in that if they were paying attention to the weather. But if you do get caught in these sorts of worst case scenarios it is difficult to tell what will break. In the sydney to hobart storm, there were decks crushed and windows broken in. I'm guessing a typical series drogue will be shredded (no drogues were deployed in that storm). The engineering calculations for the series drogue have suggested that you need to be able to hold between 50-100% of vessel displacement (large range and take with grain of salt, but that is the best rough estimate). Essentially this means that (if you want to engineer for this worst case) you want to be able to lift the boat from the drogue attachment points.

We had drogue tangs engineered into hawk which could take this loading. However we never used them. Honestly for a typical cruising voyage, with prudent weather navigation, I would suggest engineering for case #1 is sufficient. And if you want to engineer for case 2 you have to (to be consistent) think about what else will break in such possibly crushing loading.

[kmacdonald]

I agree with estarzinger. IMHO there are no cruising boats that will survive "worst case scenarios" so designing the drogue for that is senseless.
Minimizing chafe is where the chain plates excel and cleats create problems.
Remember the boat will be bucking and a line attached to a cleat will chafe on the transom as the stern rises. Some sort of wire leader would be needed if you use the cleats and then damage to the transom could occur.

[sailormed]

Just a post to add to this thread. No opinion, no sentiment, just an expert post.

[foojin]

I would listen to Evans.

We probably overbuilt our chainplate-like drogue attachments on our last boat. I have no doubt the little Vancouver 27 could have been lifted from the attachments and bounced like a yo-yo without failing. The overbuiltness of it was comforting even if only an illusion of safety. Fortunately we never had conditions to test it.

Designing attachments on our current boat, with a canoe stern, is proving difficult.