how to make a drogue or sea anchor

Gosh, this issue becomes more confusing for every page I read about it. I have excerpted some quotes which are interesting, some apparently contradictory, and some that throws out my earlier assumptions. The quotes from the coastguard report referenced above are headed with their chapter number.
Noting also two other relevant threads here: "the egotistical quest.." and "sea-anchor, parachute anchor, para-anchor" started by Eiland.

Effect of hull design:
1.1
"Although it was found that' certain design characteristics such as beam/length ratio would adversely affect capsize performance, the effect was relatively small and a slightly larger wave would capsize all the designs."

Effect of windage:
1.2
"Also, there is evidence that with all sail off the wind forces are not a very important factor. Most of the time the vessel is in the lee of large waves. The blast which strikes the boat as it passes over the crest is of short duration and in the Fastnet storm sailors reported no serious problems associated with the wind except, of course, the effect of the wind on the waves."

Hull drag:
The coast guard report (in the PDF version; there is a mixup in the html chapters) concluded that drag was similar whether the models were towed forward or backwards. They were towed at several times their "hull speed".

Breaking wave direction:
1.2
"In many storms most of the waves are irregular and unstable; that is, no single wave maintains its shape for very long. Sailors report a wave as having suddenly humped up out of a flat spot and forming a crest which cascaded down three sides of the wave. A variety of unusual shapes can be seen in photographs of storms at sea. Irregular waves as such do not pose a particular threat. It is the breaking wave which is dangerous."

From www.jordanseriesdrogue.com:
"A second optical illusion is that a dangerous breaking wave comes from a direction different from the prevailing wind and sea. "

Contradiction?

Speed of water in a breaking wave:
1.2
"The characteristic of a breaking wave which can cause capsize is the fact that a mass of water on the crest of the wave or tumbling down the face of the wave is moving at approximately the speed of the wave. For a wave with a wave length of 300 feet, this water can strike the boat at a speed of 20 knots or more. A small boat lying ahull in non-breaking waves of any shape moves more or less with the surface water. It will not be struck by a large mass of moving water and therefore will not capsize, whereas a boat struck by a breaking wave can be violently thrown into the trough and capsized."

Being pooped or not:
From http://seriesdrogue.com/designersnotes/notes3.html
"The drogue has been deployed in many storms, including at least two of hurricane strength. The record has been flawless. No boat has suffered any damage, no crewman has been injured, and the drogue has been retrieved in the as launched condition. Every skipper has been satisfied with the performance. This conclusively puts to rest the old fear of being pooped when held stem to the waves. There are simple and sound engineering reasons for this most remarkable performance."

Does this have anything to do with it?
3.4.3
"It was also noted that the monohull models developed more dynamic lift when towed from the stern and showed less tendency to "bury." A photograph of model No. 2 during testing is shown on Figure 14."

Flexibility of the tow line:
From http://seriesdrogue.com/designersnotes/notes3.html
"I believe that the Casanovas were one of the first to try the large aircraft surplus parachute. They found that the chute would hold the boat into the wind in moderate storm conditions with little yaw and would prevent capsize. The cyclic loads on the rode were very high but a solution was found by providing a long and stretchy rode to compensate for the relative motion between the immovable chute and the boat. A number of multihull skippers have successfully used the chute in moderate storms."

5.3
"Figure 24C shows the effect of towline stiffness on maximum load. Some sailors believe that a highly elastic towline will reduce the drogue load. This may be true in regular non-breaking waves, but in a breaking wave strike the effect is small because the boat rides the wave front and stretches the line until the load builds up. Actually the model tests show that a highly elastic line is very undesirable because the boat may be capsized before the load builds up."

Oscillating yaw; back and forth; forward or backwards, and when?
From http://seriesdrogue.com/designersnotes/notes3.html
""It is particularly unnerving to watch a yacht tacking back and forth on a mooring under bare poles and knocking flat at the end of each tack," reported one who watched a monohull during hurricane Bertha. If the boat had been anchored from the stern, it would ride with little yaw."

3.4.3
"When towed from the bow, the monohull models often became unstable at high speeds and would yaw from one side of the channel to the other. The monohull models were generally stable when towed from the stern. The trimaran model was stable in both directions."

From http://seriesdrogue.com/designersnotes/notes3.html
"A monohull is directionally unstable when moving backward because the center of pressure of the underwater surface is behind the center of gravity."

Keeping in mind the speed of the water on the breaking wave crest, I don't see how well this correlates with the opinion that a mono should have the drag device deployed from the stern. It might then run forward on the un-breaking wave-face, due to gravity and the slope, and be towed backwards through the water in the breaking crest. Also, the last quote doesn't seem to "rhyme" with the other two.

Jerkiness:
4.4
"The series drogue developed a maximum pull of 2500 lbs. Under the same conditions the cone drogue developed 2000 lbs. maximum pull. The boat rode better with the series drogue; there was not as large and sudden a jerk on the boat as it was pulled through the wave."

So, the max pull of the SD is larger, but the cone has both a larger and more sudden jerk? What does that mean?

bridles:
http://lists.samurai.com/pipermail/passagemaking-under-power/2005-January/000597.html

 

Curioser and curiouser

This is indeed a contentious subject. There is a great deal more opinion about than verifiable fact. But it is a topic important to many, so it is worth us trying hard to separate fact from fancy, agree on what can be agreed and agree on what cannot - due to lack of reliable info or differing preferences, differing models, differing prejudices. Then we can examine the issues and options….

Where am I coming from? 40 years’ sailing, Ocean Yachtmaster/Commercial, multihull racer/cruiser enthusiast, delivery skipper, actually many more miles on monos big and small. One-time forces survival instructor, much involved in boat safety recommendations /consultancy, last decade of 20th century. Keen on shorthanded distance cruising, monos and cats/

Boats are capsized by big breaking seas, such as are generated in storms – sustained winds of 48kts and over. The research work of the Wolfson Institute shows this: http://www.wumtia.soton.ac.uk/papers.html There is more of relevance, here: http://www.radford-yacht.com/stablty1.html , and here: http://holoholo.org/caldwell/bj_96/oceannav.html
It is curious that the more recent, authoritative and rigorous professional research is not quoted in these discussions.

There are intriguing comments here: http://www.equipped.com/avraft13.htm that are worth consideration, especially i.r.o. the positive effect of increased length of the rode. Here’s another one: http://www.multihullpages.com/Parachute_anchors.html with more useful comment based on actual experience – and adequate preparation.

The task is to prevent severe structural damage that will cause the boat to sink – killing the crew. Such damage is caused by ‘jetting’, breaking seas which throw the boat sideways into the trough ( The Smeetons/’Tzu Hang’) or roll the boat, with loss of rig and damage to coachroof, companionway hatch and windows ( Knox-Johnston/’Suhaili’ ). An upside-down multihull is a better survival platform than any rubber raft ( John Passmore/’Lottie Warren’ and Mike Butterfield/’Dazzler’ ). Any boat - including multihulls - which has been subject to severe downflooding, sinks. That happens when companion hatches and catamaran ‘patio doors’ are breached by ‘jetting’ seas, for 1 cubic metre of seawater, weighing 1 ton, moving at 30mph/50ft.sec, imparts more than sufficient energy to breach many such barriers. The cockpit also fills, and a Prout 33, Vaneema 10m, Woods ‘Eclipse’, etc. will have 5 tonnes or more in there, trying to get somewhere else. If the ‘patio door’ or companionway door is breached or lost, it goes below. So also does the water from the next breaking sea, and the next…. Many tons of it. That is why the RORC specify that such washboards are tied on ( Fastnet ’79 Report ), and we carry window boards.

There are usually no such weak openings in the forepart of a mono- or catamaran hull, unless the foredeck hatch is weak ( easily fixed with a ‘strongback’ ), and the structure is usually built to accommodate the big loads associated with anchoring ‘snatch loads’ – bitts, samson posts, etc. The bows are specifically designed to part oncoming seas. The stern is usually not so specified. Therefore the shock loads imparted to the boat and its structures by breaking, ‘jetting’ seas on the bows are less likely to result in damage . If the seas are not yet breaking, it does not really matter which end the drag device is attached to. However, I’m concerned with breaking-seas conditions which, if not present yet, may develop in the next few hours - so, for me, all anchors get attached to the bows and the very strong fittings placed there for these purposes. Including parachute and series types…..

Many of the reports of ‘failed’ sea anchor/drag devices describe parted rodes, drogues on a short scope pulling out of the face of an oncoming wave, chafe, burst fabric panels, deck fittings pulling away. Then the writer blames the gear…. All that is simply a failure to ensure an adequate mechanical strength in the gear provided, sufficiently robust for the task - and that’s the skipper’s responsibility. Look at the anchoring and mooring gear fitted on any commercial working vessel of 30’-45’, and compare that with the corresponding cleats, bitts and ropes on a comparable-size sailing vessel nearby. Fit only for marina mooring? So, let’s have no more ‘chunter’ about ¾” rope parting, when it should be 1.5” or better; let’s have no more ‘mickey mouse’ recommendations for 3’ and 4’ drogues as suitable for an ocean-going sailboat, when that’s what’s being fitted to inflatable liferafts now; let’s hear no more complaints about a system sized and suited only for a small dayboat in moderate seas not doing the job adequately on a big boat in big breaking seas.

Some of the loudest arguments for this or that seem to come from people with next-to-no experience of the sea. Some of the same people, who insist on all-chain rode and a big plough for sea-bottom anchoring behind an island, seem to believe that a couple of square metres of fabric and an old mooring line will suffice to keep big, breaking/'jetting' seas at bay – hour after hour. As Spock says – ‘Illogical!”

So, let’s have more engineering logic and less blind faith.

For those who can stand it, here are a few comments i.r.o. Sigurd’s post of 29 June, which refers extensively to a US Coastguard report from 1978. Design professionals might care to research some of the more recent papers by Barry Deakin, listed on the Wolfson Institute’s website above.

Thots:

“a slightly larger wave would capsize all the designs” – this is the central issue.

“It is the breaking wave which is dangerous." – both from capsize potential, and damage.

“dangerous breaking wave comes from a direction different” – as in the Fastnet 79 report, due to violent wind shift on passage of a front within a vigorous secondary depression.

“a boat struck by a breaking wave can be violently thrown into the trough and capsized." – capsize is ‘inconvenient’; it’s the damage and downflooding that is lethal.

“This conclusively puts to rest the old fear of being pooped when held stem to the waves” – not my old fear. If it happens once, it’ll happen several times, weighing down the stern, finding its way below, making the boat unmanageable, stopping the engine, electrics, and pumps. Sinking her.

“A number of multihull skippers have successfully used the chute in moderate storms." – and also in severe storms. Read the ‘Drag Device Database’ book.

“knocking flat” is not the same as capsize. Sufficient reserve of stability is required. There is now an ISO international standard for stability.

“models often became unstable at high speeds” – we’re considering boats at close to zero speed, not being towed. It’s not at all the same.

“"A monohull is directionally unstable when moving backward” – it will seek to pivot around the rudder. Broach in reverse, then get rolled. Consider the boat moving backwards, the big, unbroken wave advancing, and the movement of the surface water on the advancing face of the wave around the rudder….. rudder stall!

“not as large and sudden a jerk on the boat as it was pulled through the wave." – many of the series-drogue cones will be acting in water moving ‘forward’, many in water moving ‘aft’, due to the movement of surface water within a troichoidal wave, here: http://hyperphysics.phy-astr.gsu.edu/hbase/waves/watwav2.html
and some of the cones would lift right out of the water, as the rode was loaded-up to straight.

Whether one uses a single large ‘cone’ ( parachute ) or a series of smaller ones, I would want that net drag-system all to be deeply embedded in the second wave back, and the whole chosen drag-system out on the end of a long, strong, stretchy nylon line - secured against chafe - attached to massively strong anchor bits or bridles, on the bows of the boat.

With the boat stopped, and the whole drag-system most unlikely to break off - because it's strong enough - the bows penetrating through what comes our way and rising after each sea, I’ll be hiding below, content that I’ve done all I can.

 

Alternatively, and sensibly if that scares you, stay ashore and take up knitting! We gotta take some risks, 'bilbo' has the right idea if longwinded (as he said ex sevices SNCO they tend to be longwinded). So bung something heavy on a long piece of string over the stearn and go below, break out the spirits and pray! It's a s good as anything and is pretty cheep

 

Excellent post Bilbo. Very thoughtful of you to add your points.

I am still hung up on the deployment of the chosen device (no pun).

I have had enough trouble simply trying to recover a lost jib halyard...

Isn't the para harder to deploy?

That parachute v/s one line with cones and a weight at one end (ok- this is simplification but you get the idea).

 

bilbo, Nice of you to comment on some of the stuff I quoted. I tried to pick out some bits that I though might be controversial and some that left me confused.
I'll look through your links when I get time. I'm making a series drogue meanwhile (already on my fourth cone! - economical and in my eyes easier to make than a structurally sound cone or chute that won't collapse.

You say that the boat is still and not being towed. If the breaking water on the crest is moving as fast as the wave, and the boat is still wrt the ground, it is being effectively towed at tremendous speed. This is behind the reasoning in the coastguard paper that elasticity of the line does not reduce max loads. The other point being that it takes longer for the elastic line to take up the load, leading to a beam-on attitude.

There are many quotes you have left standing - don't go to rest now!

 

versitile tyre

I have to agree with you F Fred

As a former fisherman/trawerman tyres have many uses they do not seem to have taken off amonst the leisure set

Mite be those asthetics getting in the way of functionality

I used then off the bow while on anchor in a blow as a snubber-
shock absorber
Great fenders take a beating
and towed to prevent surfing

As a coaster i have not yet had to face a full blow and associated swell

But would like to raise the idea of dealing with blow on two points
First to allow the bow to rise a bridle could be attached to bollards midway between the bow and mid ships

The second, bow to weather with engines slow astern

What do ya sea dogs reckin?

lyle

 

As a former commercial drift gill net fisherman I may have spent more time using a sea anchor (the gill net) than anyone here or perhaps even than the supposed experts who have "tested" sea anchors or drogues. A 900 foot long gill net makes a superb sea anchor. But I am not suggesting you use one on a yacht of any kind.
I will heartily endorse Bilbo's recent post. If you didn't understand it read it again. If you don't currently agree with him, read it over until you do.
My only contribution to this discussion is this. Deploy the sucker (the sea anchor) early! If you are sure conditions are going to become very bad, I would suggest 35 knots of wind or 40 at most. You will then be very comfortable for the duration if you keep tabs on things. I like the large sea anchor: you'll have little leeway. If you don't mind making a couple knots of leeway per hour for the duration of the storm, go ahead and use a series drogue. But I don't know what you will do if you encounter a situation where you don't have searoom.
By the way, I have seen a 14' flat bottomed skiff planing down waves towing two car tires astern. So, forget the tire story.

 

Thanks Bilbo

bow to in a good blow has to be the way to go

lyle

 

Gilbert - out of curiosity was the gill-net attached to your boat? Perhaps when retrieving the net using a winch-system from the stern? Did this depend on the sea-state.

Deploy the sea-anchor early. Ok - It doesn't sound like the parachute sea-anchor is easy to deploy in difficult situations.

The only way to solve this (ease of deployment, lee-way whilst deployed, colapse of cones/drogues/parachute, line failures) is to test them both in the same conditions.

 

Sea anchors.....

Thanks to those who are participating ( e.g. Gilbert ) with their experience and reflections.

FWIW, I don't have a 'religious conviction' about one VERSUS another, but I am concerned to ensure that what I have with me - when it is really needed - is well up to the job. So an adequate series drogue might manage AND a parachute sea anchor might also manage. But let's reiterate - I want to STOP the boat; 'parked up' at sea; by sea-anchoring..... So far, my reading of the Drag Device database and all other stuff I can find convinces me that a parachute sea anchor has worked for others and will work for me - if it is big and strong enough.

I'm also willing to be persuaded that a series drogue MAY be arranged to so much the same - again, if it is big and strong enough.

FWIW, let me describe the setup I take with me. I have a plastic fishbox, almost 3' by 2' by 1', which contains my 900' rode - which is 16mm braided nylon ( that's what I managed to get, economically ) rated at over the AUW of my boat. I have this arranged 'doubled' so I get 450' by 32mm effectively.

Ahead of this is a BIG commercial swivel/weight rated at over 12 tons.

Ahead of this is the parachute - an ex-cargo drop chute -, which is contained in a fabric/mesh bag about 14" by 14". The 'cords' have all been replaced by webbing rated at 1500lbs each, properly sewn right up the parachute seams, then across the aperture, and down the opposite seams....

Attached to the webbing at the aperture ( the 'top' ) is about 20' of light Kevlar line, which is attached to a small drogue-chute about 15" across. This has a light wire around its mouth, holding it open, and it is this drogue-chute that goes into the water first, followed by the bag containing the parachute. The drogue pulls out the 'chute, which then fills and deploys.

Attached also to the drogue-chute is about 40' of Kevlar line and a pickup fender......

It works - it's easy to deploy. Not so easy to recover - but that's not the priority.

 

To drogue or to serial drogue

I read this thread with much interest yesterday, and lay abed thinking about it for too much of last night. Fortunately my lack of sleep did produce some conclusions by three or four o’clock this morning and I would like to share them with you here. To summarize, I have come to believe that Mr. Jordan’s serial drogue is an extremely good idea. But to understand why I think this is true I think it would be a good idea to go back and look at some fundamental issues of concern to us all. So, please bear with me and let me elaborate.

When a wave advances across a body of water and under a bit of flotsam that bit of flotsam can be seen to first accelerate in the direction of wave motion, and then when the wave passes to accelerate in the opposite direction until it regains it’s original position. The wave itself is comprised of a series of layers from the surface downward which appear to “rotate” as the wave passes. It is the centrifugal force acting on the water from this rotation that causes the “hump” of the wave over the mean level of the water, and the trough receding below it. In an extreme case, the centrifugal force from this rotation can equal the pull of gravity and the water thus unsupported is effectively weightless and breaks free. We have all either witnessed or seen pictures of surfers riding their boards down the “tube” formed when this happens. I haven’t tried it, but I have been told that it is fun to take a scale to sea with you and invite your guests to weigh themselves while you ride even gentle swells. Apparently rather large swings in weight are observed, to the amusement of all. Beer aids the amusement factor, I imagine.

I belabor this point because it has a very significant implication for the question of a serial drogue versus a more traditional drogue that is designed to hold a boat in place. Consider again that piece of flotsam riding a wave. It floats for the same reason our boats float, by displacing an equal weight of water. When a wave puts the flotsam into a motion that causes a centrifugal force, that force acts equally on the water and on the flotsam, so the change in the effective weight of the flotsam is equaled by a change in the effective weight of the water and the relative displacement is unaffected. A similar thing happens to a boat riding the surface, if it rides that surface relatively unencumbered. On the other hand, if the goal of a “stay in place” drogue is actually met, and the boat it is attached to is firmly prevented from advancing with the wave, then the weight of that boat will not be reduced by centrifugal force . . . but the effective weight of the water rushing past it will be. That is, the water supporting this tethered boat becomes less dense from centrifugal forces and therefore more of it will have to be displaced in order to equal the weight of the boat, and thus float it. In an extreme case, where the wave passing under is right on the edge of breaking, such a tethered boat will sink outright because of a lack of sufficient displacement! I am making an extreme case here, but the principle remains that any such tethering reduces the ability of the boat to rise over a wave and greatly increases the probability of it being pooped, or worse.

When Mr. Jordan’s serial drogue is properly designed and deployed the windward motion of the boat causes the long drogue line to form a shape somewhat like the body of a “J” lying with the top of the “J” attached to the boat and with the other end hanging almost vertical in the water due to an attached heavy weight, usually a chain. A wave passing under this boat will accelerate it in the same direction as the wave travel, thus pulling the “J” of the drogue out straighter than it was and more horizontal. Then, as the trough approaches under the boat, both the flow of the water and the weight on the end of the drogue will pull the boat backwards as the chain on the end of the drogue line sinks deeper and becomes more vertical. It would seem to me, then, that the key to designing a successful serial drogue is to adjust it’s proportions such that the boat is slowed sufficiently to prevent approaching a lee shore too quickly by it’s overall forward motion and also to thus encourage it to meet an oncoming breaking wave near the crest rather than in a trough, while at the same time allowing the boat sufficient forward motion as a wave passes underneath to encourage flotation. A delicate juggling act, to be sure! But one that is much easier to accomplish with a serial drogue than with a simpler, more rigid and brute approach.

There was also some question above about whether it is better to lie bow or stern to the wind in heavy conditions. Given the reduction in flotation produced by centrifugal action in large waves I would think stern to would be much better than bow to. Also, in most cases and certainly in the case of a sloop rig, there is more wind resistance forward of the center of lateral hull resistance when under bare poles. This greater wind resistance must trail the point of attachment of any resistance to be stabile. This is why Mr. Jordan has recently published an article (somewhere, sorry I lost the reference) showing that it is prudent to anchor a sloop stern to the wind in a “safe” harbor during a hurricane. Of course a ketch, yawl or schooner can put a storm sail on the mizzen and accomplish stability with a forward anchor, should the owner so choose.

One more minor point: attaching to the boat with a “Y” shaped bridle increases the lateral leverage on the boat and facilitates directional stability.

Anyway, that’s how I see the issue. Any comments or corrections will be greatly appreciated though, as my life could well depend on it!

Bill

 

Terrific discussion.

Bilbo raised an important point earlier which I'd like to re-emphasize - that is that drogues and sea anchors are different things, not different versions of one another. A sea anchor should be deployed off the bow and be big enough to stop the boat rather than get pulled through the water; a drogue should stream behind to slow the boat and, hopefully, provide some additional direction-keeping.

Further, different boats will behave differently and different conditions will suggest different tactics.

I'm stating the obvious in order to encourage the discussion away from focusing on the "best" device, because I think that there is not a "best" device - it depends.

The discussion has a lot of valuable information in it - I'm wondering if anyone has some positions on the conditions (including weather, sea-state, vessel type, depth,..) where one method becomes clearly preferred over another.

BillyDoc's point about the vertical acceleration of the water in the wave is an interesting one that I'll have to scratch my head over longer before interfering with, but it could point to one of the threshold-type conditions that I'm hoping to map out.

Regards,
JPC

 

When it's time to batten the hatches

Hi Bill

If only i had uni lecturers that put it so clearly

Yes i follow your explaination
as an old surfer who has found a few barrels (tubes) i am quite aware of the suck that preceeds a wave also the loss of bouyance experienced prior to the wave then forcing one downward when the wave breaks

We seem to forget the centrifical action of the wave as it passes by

The bridle aids the bow to lift as oppossed to a bow attachment

when towing a similar bridle should be attached to each quarter allowing the stern to rise

Plus for only one metre across the entire deck (say 13m x 2m =26t of water)

@ immersion of 2.5mm (1 inch) per tonne says most 14m vessels have zero buoyancy much like a surfer being held down by a breaking wave

When we consider 15m high ocean waves are not uncommon a vessel is much like a wine bottle cork under a household tap

The main point here is the loss of water density immediately before the wave and corresponding reductiion in vessel buoyancy

lyle

 

MarkC,
Sorry! I didn't get any messages about further posts to this thread, or I would have answered more promptly.
My gillnetting experience has been with traditional Columbia River bowpickers with live rollers, skiffs both with power reels and the 'armstrong' method over the stern, and sternpickers with reels. And, yes, the boat is always attached to the net. While fishing there is seldom any reason to be concerned about which end of the boat the net is attached to. In extreme conditions being attached to the bow would be the most comfortable in most boats. There could be boats that will not lie quietly from one end or the other, depending on the interaction of their above water verses the below water configuration.

It is quite remarkable how quietly a boat will lie to a drift net, even in very nasty weather. And just to inject a little confidence in how safely one can expect to lie to a good sea anchor I will repeat a story my father told me. One of his contemporaries who fished on the Copper River flats years ago liked to catch the low water set at the Egg Island bar at the mouth of the Copper River. In fact, a lot of guys liked to try to be the one who set their net in just the right way so at low water, the last of the ebb, their net would be right where the mouth of the River met the surf of the beach to the west. If you judged it just right the net would drift to the west a little along the beach and would be in the surf. This particular fellow, whose name I don't recall liked to know where the other end of his net was and since it was hard to see the ordinary bouy, he used an open skiff for a bouy instead so he could see it. The fisherman and his fishing boat would be outside the surf and the net would stretch off into the surf and the skiff would be either in the surf or inside the surf. This fellow followed this practice for years. The flood tide would finally push the whole works back up into the River where the fisherman could haul in the net. The surf there is very impressive at times and on the average the skiff would probably be in the surf for about an hour. Now comes the remarkable part of the story. He said the skiff rarely had more than a bucket or two of water in it after one of these sets. Often, it had none at all.

 

"loss of water density"?

I don't follow this explanation at all. Are you talking about the whitecap where there is air mixed with the water?

My four kittens are unable to tangle the series drogue.