I did a little testing of a shortened JSD and some other drogues over the weekend (8 years ago--publication was delayed due to agreement with Good Old Boat Magazine). It seems that the notion of a short JSD as a steering or speed limiting drogue is a failure. I have corrected that post.
It seems there are four fatal flaws:
The characteristic JSD "droop" does not occur at high speed. It is not a design characteristic, just a low speed characteristic. At higher speed (6 -7 knots) a JSD runs along the surface.
Cones are inefficient shapes. The Seabrake or Shark are about 50% more form efficient.
Cones are more unstable near the surface.
Small drogues are less stable near the surface.
The cones are too close together.
The result of these factors is that a good drogue design (Galerider, Seabrake, Fiorentino Shark) is more stable and far easier to use than a series drogue for emergency steering and speed reduction.
A real survival storm? I still think that drogues in tandem, well-spaced, have a lot of merits, right up there with the JSD. For more discussion and data, read either "Faster Cruising for the Coastal Sailor" or an up-coming Practical Sailor article (though it will surely by hacked to size). A tandem drogue is easier to manage than a JSD, gives more options, provides the same drag (braking power), and runs just as deep.
[Note. The secondary rode is NOT attached to the primary drogue, it is attached to the primary rode. It passes through the center. The drogues can be of other types--the illustration simply shows the pair I use. The Fiorentino Small Shark is excellent. The Delta Drogue is also good, although it is a bit less stable when near the surface.]
According to Don Jordan, the max load on a JSD (Jordan Series Drogue), during that worst survivable hit, is about the displacement of a monohull, and about 150% of a light trimaran, like the folding Farrier and Corsair trimarans. The problem is, the folding mechanism and floats are not designed to withstand that sort of wracking force. I'm pretty sure far less would pull them right off. I'm pretty sure attaching a JSD or parachute sea anchor to the floats is a failure waiting to happen, and most likely, one you would not survive.
However, the akas (beams) are very strong in compression. That is their design basis. Let's think of this as a truss.
One scenario is anchoring the bridle to the winches (applicable to conventional drogues). The max bridle tension is about 50% displacement, or 3x less than a JSD. A turning block is attached to the beam (sling) or float (reinforced point), and the bridle extends aft from that. Chafe should be minimal if the bridle is polyester. The aft load on the akas is minimized. The bridle is adjustable (angle and length). The compression load on the aka is high, but well below the design load. See notes below.
The other senario is a JSD that is braced forward. It could be above or below the tramp (above is probably more workable). The brace could be separate or it could be a continuous line. The compression load on the aka is larger, but still within limits. See notes below.
Thoughts? The designer never envisioned these as ocean boats that would use sea anchors, so the engineering is not documented.
Don Jordan, the father of the series drogues, suggested a chainplate of conservative dimensions, but did not detail the design. He wanted to keep it simple so that people would use them. Most commonly, these plates are installed horizontally, because that looks right. But what if the pull is not horizontal?
The angle are exaggerated to make a point. Tank or model testing would could refine this. But I'm pretty sure that not all of the strike sure horizontal and thus the first few bolts are carrying most of the load.
In my limited experience, and based on what I think is common sense, the strongest pulls are from a downwards angle. From basic engineering statics, the largest bending forces are near the transom end, and the largest shear loads on the bolts will be when the load is off-axis. That suggests either more or larger bolts near the transom, but more will better distribute the shear stress load to the laminate.
Hardly a detailed analysis, just thinking. In practice, it would be simpler just to build it oversize, though internal reinforcement of the laminate might be avoided by this sort of design.
Described in the link below, a sail boat became disabled when their rudder sheared off, 3/4 of the way from Texas to Mexico. The US Coast Guard contacted the Mexican Navy, and the Mexican Navy sent a 180-foot cutter to provide a tow.
Without getting political, it's something to think about. Things do go both ways. I like to get along with my neighbors. It seems to work out better.
Of course, a proper steering drogue would also have solved the problem, just as quickly and with less drama. After my own experience with bending a rudder on a submerged log (repair described in "Keeping a Cruising Boat for Peanuts"), I did considerable research on drogues for emergency steering and storm management, learning that a good drogue is a solution even a singlehanded sailor can make work in minutes, with just a little preparation and practice. In the above situation, I would have had a steering drogue in the water within 5 minutes, and we would have been on our way, a knot or two slower, but with certainty.
A failed rudder is simply not a valid cause for rescue or loss of your boat; I've sailed hundreds of miles with no rudder or worse, a rudder jammed to the side. It's quite manageable.
See "Faster Cruising for the Coastal Sailor" for the details. Also, and up-coming article in Practical Sailor will describe the details of rigging and using a drogue. In "How Much Drag is a Drogue" (Practical Sailor, September 2016) I tested, reviewed, and list the relative drag and performance characteristics of most popular drogues.
Why the interest in drogue if I'm not going to cross an ocean? "As a coastal sailor, why should I care?" Because a little over two years ago I bent a rudder on a submerged log. Only because I had a catamaran did this avoid becoming a serious problem (I have a spare rudder). Other wise, take your hands off the wheel and tell me how you plan on getting back home. It's not that easy.
However, this post is not about emergency steering. I'll get to that later. This is about drogues for speed limitation is serious storms. It turns out that they have not been telling us the who story.
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Parachute sea anchor, speed limiting drogue, or JSD (Jordan Series Drogue). Sailors that have never used them will argue, and even those that have used them generally remember what they saw but don't understand it. My nature is to expereiment until I understand.
How many people have a full collection of 1/3 scale drogues? [Cone, Small Shark, Delta Drogue, Gale Rider, Sea Brake]
Small Scale Testing
The trouble with testing full scale drogues is that you need a full-scale storm to test them in, and mistakes have full scale consequences. Not a forgiving classroom in which to demonstrate things things that fail, and only by knowing what fails can we understand what works. It is also a mistake to build a scale model and believe everything you see, without understanding the theory and how scale up works for engineers. But that is how I have spent the last 30 years, so I know a few tricks.
These drogues are 1/3 scale, run at 80% speed, in smaller waves, and at reduced scope. Combined, these scale factors give a realistic picture of how a speed limiting drogue functions in gale conditions. In the first example I show a Seabrake 8 standing in for the real-world Seabrake 24. Like all drogues, it pulls out of the water only when a following wave catches it; at that moment, the angle of the rode to the water suddenly becomes steep, like an anchor on short scope, and out she comes. As soon as the wave passes, she settles back into the wave face. The conditions were mild.
In the real world the danger here is three fold:
A wave may strike the boat while the drogue is out of the water. Not very likely in a moderate storm.
In a serious storm, the drogue may spring out of the wave and be thrown far forward. Sailors often claim the wave threw it forward but they are only 1/3 right. The greatest factor is actually the contraction of the nylon rode (think rubber band) as the tension comes off, and that of the wind. This effect was minor in the video because the rode is oversized compared to common practice. This is also part of the case for using a polyester rode with a drogue and not the more common nylon. Several manufacturers specify non-stretch rodes.
As the storm builds, right when you most need the drogue to work, it will fail. That is when the load is peak (required to pull the drogue out) and that is when the waves get steeper.
I then added a second drogue in tandem, 30 feet farther back (Delta Drogue 24, standing in for a Delta Drogue 72). The conditions are also now near gale force (sustained over 30 knots with heavy rain). As you can see, the first drogue runs closer to the surface, the result of the secondary rode tension. On the other hand, the secondary rode stabilizes the primary drogue when it does pull out of a wave, pulling it back in quickly. The first drogue may take slightly more of a beating on the surface, but the pull, measured by load cells, is far more stable (15% fluctuation vs. 60% fluctuation). A fair trade-off.
These waves are only about 5 feet, but considering the scale factor, these are 15-foot breaking waves. Pretty tough.
It is worth remembering that both of these trial were at the same speed (4 knots). In reality, adding a second drogue will slow the boat significantly, also making the tandem drogue far more stable. Another way of looking at it is that a tandem drogue can handle 40% more wind (70 knots vs 50 knots sustained) before the first drogue begins pulling out--a pretty big difference--and far more if we consider overall stability of the combined system.
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Gale Rider 30. A little small as a speed limiting brake (they make larger sizes), but my favorite for emergency steering. Very smooth and easy to handle.
The other things to consider are these:
Redundancy. You have two.
You can adjust to the strength of the storm.\
Smaller drogues can be carried. This is no joke on a larger boat, since large drogues get very physical to handle in a blow. I later tested full scale models in gale conditions, and it was a workout.
A smaller drogue is more useful for emergency steering. This gives you the ability to transition between emergency steering and speed limiting.
However, full-scale speed limiting drogues and emergency steering are for future posts.
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A detailed treatment and more data are included in "Faster Cruising," which I should complete in a month or so.
Galerider 30. My favorite, at least at this point. Very smooth and easy to recover. But you need a huge size to generate serious braking (this one is too small for the PDQ--we needed a Galerider 36). I have a Seabrake 24 for that purpose--smaller, but twice the drag because it is solid.
... which led to more 1/3-scale models (not factory authorized, but as faithful as I could make them). Cone, Shark, Delta, Galerider, Seabrake.
Interestingly, the 1/3-scale models behave exactly like their big brothers. Drag is proportional to cross section, so the models product 9 times less drag. Drag ~ velocity^2 up to 14 knots, the limit of our testing. They also have very similar surfacing behavior, which lead to the premise that testing these with scale rode in Force 7 conditions, with steep waves and a little engine assist, is equivalent to gale conditions with a full scale drogue. Instead of loads approaching a ton, they stay below 150 pounds, and hand-over-hand recovery is 5-20 pounds instead of 50-200 pounds; makes a real difference when there are 100-300 feet of line out! The result is practical testing at more speeds and with more combinations, allowing full-scale testing to focus on the right questions.
I since made a few scaled to my F-24 trimaran, primarily for emergency steering experiments . In proportion, they perform right in between their big and little brothers. Very scalable.
If you want to try DIY, the Delta Drogue is by far the simplest. Basically, it is a triangle of fabric of the dimensions of the model number (a Delta Drogue 72 is made from a triangle 72inches on a side). Cut about 20% of the length off each corner, rim the fabric with strong webbing, and then sew the edges together up into a balute (Google it) with about 50% of the edge sewn and 50% open (there shdould be three long slots for the water to blast out). The webbing along the sides should be long enough (about 50% of the length of a side before cutting) to joint at the apex. Complicated to describe, but easy to fabricate.
After testing full scale drogues at speeds up to 7.5 knots and confirming scalablity, I built a universal cross reference table (Practical Sailor) so that you can pick a drogue for your boat, whether for steering or speed reduction. Generally it agrees with manufacturers, but they often have different theories regarding how much drag is best.
Now I am starting to focus on tandem drogues; does it make sense to trail 2 drogues on the same rode, as conditions get worse? The answer seems to be a resounding yes. Unlike anchors where rode forces destabilize anchors, in this case they seem to stabilize each other. Doesn't a second drogue add a lot of expense? Not really. Because stability is less of a problem, less expensive drogues like the Delta or Seabrake are valid. The rode and bridles are already paid for. Basically, you get the advantages of a series drogue, with more adjustability, flexibility, and easier handling.
The real bargain? It may be a surplus aircraft drogue I bought on E-Bay 15 years ago for $40. To my eye it is just as well built as the Paradrogue, and it gives a lot of stopping force for the buck. Too much for steering, too much for running a bar, but maybe just the thing for parking to drift fish.
Don't let anyone convince you that blocks work for making bridles. They just get stuck on the back of the boat, the obvious conclusion of a simple vector diagram. There are a lot of images in books and on the net that disregard the simple fact that the the block line must bisect the bridle angle.
A bit over a week ago I blogged on emergency steering. Since then I've plunged headlong into research for several articles on drogues for steering and storm management. I've got sample from the major players which I've been dragging around the Chesapeake, collecting some baseline data and learning their basic traits. Not under storm conditions, mind you--writing doesn't pay that well!
I've been able to learn about full-size drogues at higher load with 2 tricks. First, pulling them at short scope (actually the best method for emergency steering) gives insight relating to pulling out of a wave face, since a following wave also changes the rode angle. Second, getting a running start at a drogue, hitting it at as much as 7.7 knots (with extended transoms and a clean bottom, that is my best speed) with a non-stretch rode gives some high forces, but I wanted something a little easier to manage and some thing that I could pull continuously at storm-like loading. Like the tandem anchoring trials (coming in 2017 in Practical Sailor), I went to models.
3 times smaller, but faithful in performance characteristics.
From left to right, 1/3rd scale models of Seabrake 24, Delta Drogue 72, and Jimmy Green Marine 60cm Drogue. Sewn from scrap Sunbrella and 1500-pound bull tape. I saw as much as 200 pounds drag out of the mini Seabrake/Delta combination at 7 knots! I later added a mini-Galerider.
(note. These are NOT official copies and any statements should not be taken as such.)
For anchors, I was able to get roughly 8 inches across, I was able to find 2-pound surrogates in the form of a 2-pound Guardian, 2-pound Claw, and a 2-pound Mantus Dingy Anchor (very nice--get one!). But for drogues I was out of luck. So I sat down with a pile of old canvas, a roll of pulling tape, a palm, scissors and tape measure and made my own. Roughly 8 inches in diameter, if towed by a small diameter rode with mating scale chain, they perform just like their big brothers!
Drag is about 9 times less (expected to vary as the square of diameter)
speed/drag relationship is consistent (varies with V^2), like the larger versions, but now proven through a larger speed range
Pulsation behavior is similar (load varies at about the same range and frequency as larger drogues)
Behavior--yawing and surfacing--is just about identical
Because they perform to scale, I can accurately predict how larger models will behave, without testing models beyond the capabilities of my boat.
And so now I have a set of tiny scale drogues I can test at scale in small craft advisory conditions, as through it were a gale.
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The really weird part is that I have already learned some things I that either the manufacturers don't know or are in denial about. Failure patterns--both mechanical and performance--seem to come from pretty basic errors. Not the better manufacturers, though; they seem to know and communicate better.
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The early take-aways?
Anyone can need emergency steering when they hit a log. It is not a black art, but you need the right gear. I tried warps and chain, and it aint' going to work for you. No way.
Towing warps is not much of a storm strategy. The drag is perhaps 10 times lower than recommended drogues.
You get what you pay for. So far, the more money, the more stable and rugged the drogue.
There is a speed limit. All drogues have stability problems over ~ 5 knots in big waves, and my gut at this point is there is no engineering solution. You either carry enough drogue to stay below 5 knots or the risk of the drogue pulling out of a wave face goes up when the waves get steep.
Fun stuff!
I have one article on drogues in Practical Sailor, with more on the way.
So what, it snowed yesterday. Testing does not wait.
This grew into a number of articles for Practical Sailor and Good Old Boat. Later articles focused on emergency steering drogues you assemble in minutes from gear on hand: An anchor, some chain, and a fender. Hang the anchor from the fender, with some chain in front of it, and then use as a steering drogue as below. It works and people have sailed 1500 miles with that rig and no rudder.
That said, I repeated the test with a commercial drogue (Delta Drogue) the same day, and the Delta Drogue was much easier to handle and very compact to store. If I were crossing an ocean I would pack a commercial drogue. More importantly, I would take a test day, as below, and try it out in a breeze. There are lots of ways to rig it wrong and screw up. Best to learn near home.
This past fall I jammed a rudder on a submerged tree. Two loud thumps, the helm did not answer at all, and the boat was turning left. To reach my destination I adjusted sails (genoa in, traveler down) and even lowered one engine (just for drag--not running) and played the traveler as though it was the helm. Maneuvering into the harbor under power was made reasonable by having 2 engines. Once anchored, I disconnected the jammed rudder and enjoyed the rest of the cruise on one rudder with slightly mushy steering. The autopilot even worked , so long as I kept the sail balance fair.
Towing SeaBrake 24GP under power at 4.5 knots. Should be 7.4 knots at this throttle.
What if I had only one rudder, like most half-boats? A rather expensive tow would have ensued, perhaps anchoring for a time when I reached shallow water. The cruise would have been ruined for certain. I always thought emergency steering and drogues where for ocean crossing and storms, but now I realized that even on the Chesapeake, a bent rudder can lead to trouble in short order. And so my closet interesting in drogues (I actual have 2, leftovers from my Stiletto off-shore days) has exploded into full-on testing for Practical Sailor. So far I have 4 brands lined up and one factory team that wants to help me play. What fun. The intention will be to try them all on all courses and hopefully in several wind speeds, seeing what works and creating drogue speed polars. There will also be some high-load testing related to storm use, but that is separate article.
Though I have had these for years, I never tried them for steering. A few tips:
For storm use, of course, they go farther back, 150 feet-250 feet.
But for steering, bring it in close, as little as 20 feet off the stern. Much more responsive.
Spinnaker sheets work well for a bridle. You can actually steer by sitting next to a winch and playing just one leg.
Attach the sheets at the widest point, particularly on monos. Near the stern is fine for cats, but a little forward is better (more responsive).
Observations:
100-110 true with the rudders jammed 65% to leeward. I was surprised. The wake was reasonably straight and leeway less than I feared.
70 true with rudders straight.
Very slow in light winds. You are going to loose about 1-3 knots. The Seabrake is too large for this boat. We'll have to see how the Small Shark works. I also need o try the Seabrake in close, partly out of the water, to reduce drag. I forgot.
Pretty stable. I can imagine using it for days, with crew. Not as good as autopilot, but not bad.
There is a tendency to round up if sailing to weather in variable winds; when the genoa looses pressure, the drogue is still pulling, and the boat comes up. But if you catch it before it stalls, by releasing the windward bridle line a few feet, it recovers well.
Rudder 65% port requires the drogue full to windward to maintain anything close to a beam reach. Without the drogue we would be going in tight circles at best, stuck.
With the rudders straight we could make some ground to windward... but slow. Only about 70 degrees true course over ground, and slow. Notice that the drogue is nearly centered. The drogue is clipped to the sheets with only 8' of 3/8" BBB chain as an extension.
Slower than sailing, but much faster than sailing in circles, faster than waiting for help, and more comfortable than drifting beam-to-waves. Good for parking the boat transom-to-waves while making any sort of repairs (they will be easier if the boat is not rolling).
