Acquiring A Ready Made Series Drogue

[thinwater]

My feeling is that drogues fall into categories, and that each has different rules.

1. Trail warps. Done properly, it calms things down and reduces yaw, but it is not going to help prevent a pitchpole. Stable at higher speeds, up to about 8 knots. Do this when steering is getting tiresome, you want to keep going, and you still feel safe.
2. Conventional drogues. Far more drag, only stable to about 5 knots. Capable of preventing surfing in most conditions, and rigged in tandem, capable in very severe conditions. The drogue must be big enough to hold speed below 5 knots. Also the best choice for emergency steering. This seemed a lot more important after the day I jammed a rudder by striking a submerged log (I think--never saw it).
3. JSD. Survival conditions. No point in building it for less than that, since 1 or 2 is a better choice in those cases. Do not undersize because they are unstable if undersized (I experimented with this--for emergency steering).
4. Parachute. Stops the boat. Must be large enough, and IMO, the rode needs to be larger than typically speced (they loads are MUCH higher than anchoring loads). Typically used in survival conditions, although the only time I used one was to park until dawn to enter--worked well.

[MartinR]

Originally Posted by Dockhead

it is true, of course, that as a general engineering principle, then naturally, you will save money if you don't design something to be stronger than it needs to be for your specific use.

But do you know how much less strong you can design one of these, for huge breaking waves in a F10 compared to giant breaking waves in an F12? And are you happy with a drogue you think MIGHT be strong enough, assuming a lot of things?

The reality is that breaking waves in even a F8 in the Gulf Stream can kill you, and generate huge forces. If you need a drogue at all -- and most people don't need one -- you will want it to be capable of handling whatever you might encounter with it over the period of your ownership. People who sail long distance in difficult latitudes get into all kinds of situations, and not all of them are avoidable with good weather information --that's just a fact.

Under-strength drogues aren't available in the market, because -- there's no demand for them. No one would save $100 or $200 at the expense of having a drogue which might not be strong enough.

And where you do you get the idea that there are no reports of JSD's being used in ultimate conditions? There are plenty of such reports. Here's just one, a Force 12:

Prepare for survival conditions - Ocean Navigator - May/June 2011

If you are going into high latitudes and far offshore but you think you're too smart to ever get caught in bad conditions -- then by all means, have someone build you an under-specified drogue. If you're not going into high latitudes and far offshore, then you don't need any drogue at all.


Concerning "side stepping" a weather system which might develop when you're half way across the Atlantic -- good luck with that. Some of these systems are 1000 miles across.

[kmacdonald]

Yes Dockhead, there are a lot of variables and uncertainties in engineering and if you ask 10 reasonable engineers you will get 10 unique solutions. It's true that downsizing the lines for a drogue won't save a lot of money but downsizing the attachment points could. I rule out engineering for worst case because I don't think that is survivable anyway. We all take calculated risks when we sail and sail according to our own risk tolerance. All we can do is mitigate risk but we can't eliminate it.

[Juho]

Originally Posted by Dockhead

OK, thanks for tying this back in to drogues.

Rogue waves are not the main reason for putting out a drogue.

You put out a drogue in order to avoid getting out of control down the face of big waves, to avoid broaching, to avoid being rolled by breaking waves, to reduce (or eliminate) helmsman or autopilot workload.

The highest loads on the boat (and therefore on the drogue) will be imparted by breaking wave strikes. This can occur from about Force 9 conditions in the open ocean with a lot of fetch, or even less.

"Rogue" waves are a phenomenon of physics, and are defined as waves which are more than twice the significant wave height. See: https://en.wikipedia.org/wiki/Rogue_wave. They happen because of interference -- interaction between different wave trains, wind, etc.. "[R]ogue waves are not necessarily the biggest waves found on the water; they are, rather, unusually large waves for a given sea state." This principle can produce especially dangerous waves even if they are not that high, because the wavelength doesn't change. So rogue waves are much steeper than the normal waves. There is also such a thing as "rogue holes".

I don't think you can prepare for rogues. You start to think about a drogue when waves start breaking, or when you feel like you are getting out of control, or when pilot and/or helmsman are getting overworked.

I think the best outcome of this kind of discussions would be some new rules on what kind of rogue, breaking and steep waves to expect when I know the wind speed, wave height, duration of current weather pattern, history of wind direction+speed, fetch and water depth. These could be available also in weather reports, but it would be good to be able to estimate future waves also oneself.

One can see the existing average sea condition and its effects from the boat. It would be nice to know when the risk of too risky waves (that one can't see yet) grows from zero to something meaningful. No point in risking the boat if there is a clear risk of getting too bad waves. Knowing that there is no such risk would be also great.

My wish is thus to get new rules of thumb (or more exact methods) for areas where we have not had them so far. Maybe such better knowledge would save some boats. Maybe many sailors have so far lived under the assumption that all waves are roughly similar (and some lost their boat because of that).

[kmacdonald]

Maybe thinnwater would be kind enough to help us out here. With your test, can you tell us the maximum load a 100 cone JSD can exert on a boat traveling the same speed as a breaking wave? I'n not sure what that speed is but it would be "worst case" load I think. Actually a little more. What about the load of the same 100 cone JSD towed at 3 knots. That seems to be the maximum average speed people that have used the JSD have reported. Most report around 1 or 2 knots. Do the forces scale lineally with the increase in number of cones?

[Dockhead]

Originally Posted by kmacdonald

I rule out engineering for worst case because I don't think that is survivable anyway. We all take calculated risks when we sail and sail according to our own risk tolerance. All we can do is mitigate risk but we can't eliminate it.

I agree entirely with the last two sentences.

But why do you think that JSD's are designed for unsurvivable conditions? What do you think is unsurvivable? If you have a strongly built and seaworthy yacht with proper gear, you have a decent chance of surviving any storm, with good tactics. Yachts do get caught at sea even in tropical rotating storms, even cat 5 ones, and survive sometimes.

The availability of good weather information by satellite has not eliminated the risk of getting caught in extreme weather. I am facing something like this myself -- I will be sailing 1200 miles from Greenland to Ireland in the middle of August, just at the edge of the season of bad weather. I have no choice, because I can't get there in the first place until the ice breaks up, which could happen as late as the end of July. At that latitude (above 65N, near the Arctic Circle), there simply may not be a week without a gale (F8) outside of the Arctic High period. So a forecast for F8 could still be a "go" decision. The risk of that turning into a F9 or even a F10 during the week or so at sea is significant. That risk just goes with that latitude and that season. The same, except even more so, is true of those like Snowpetrel, who sail in the Southern Ocean.

[kmacdonald]

It should be noted that the number of cones required does not scale proportionately with the displacement. Larger boats require proportionately fewer cones. With that understanding, it may be feasible to use existing cleats or winches as mounting points on larger boats. Smaller boats present a greater challenge. The assumption that chain-plates mounted at the stern is required on all boats may not be realistic, especially on larger boats.

[kmacdonald]

Originally Posted by Dockhead

I agree entirely with the last two sentences.

But why do you think that JSD's are designed for unsurvivable conditions? What do you think is unsurvivable? If you have a strongly built and seaworthy yacht with proper gear, you have a decent chance of surviving any storm, with good tactics. Yachts do get caught at sea even in tropical rotating storms, even cat 5 ones, and survive sometimes.

The availability of good weather information by satellite has not eliminated the risk of getting caught in extreme weather. I am facing something like this myself -- I will be sailing 1200 miles from Greenland to Ireland in the middle of August, just at the edge of the season of bad weather. I have no choice, because I can't get there in the first place until the ice breaks up, which could happen as late as the end of July. At that latitude (above 65N, near the Arctic Circle), there simply may not be a week without a gale (F8) outside of the Arctic High period. So a forecast for F8 could still be a "go" decision. The risk of that turning into a F9 or even a F10 during the week or so at sea is significant. That risk just goes with that latitude and that season. The same, except even more so, is true of those like Snowpetrel, who sail in the Southern Ocean.

I think the JSD is perfect for what you describe. Those are definitely survivable conditions and not likely to produce "worst case" loads on a JSD. I suppose it could happen in those conditions but I wouldn't expect it to. Worst case would be to have your boat accelerated to the speed of a breaking wave. That would require an enormous and steep wave. Think 60 or 80 foot breaker. Not a frothy top 40 footer.

[Don C L]

I am puzzled by this “survivability” criteria. I don’t evaluate things that way. I tend to assume everything is survivable with the right preparation. If not, what do you do? Give up because the waves are too big to be survivable? A drogue should keep the stern pointed upstream and prevent speeding down wave face, even if it is being pulled at 8 knots and thus will have served its purpose as long as the cones hold up. One big advantage of the drogue over a parachute i can imagine is that the waves are hitting you at a slower speed. Not only is that more comfortable but it helps the boat hesitate long enough on the wave crest, and not fall down the face, to let the wave pass underneath you. Or so I imagine because I haven’t been out in big stuff with drogue yet.!

[Dockhead]

Originally Posted by Juho

I think the best outcome of this kind of discussions would be some new rules on what kind of rogue, breaking and steep waves to expect when I know the wind speed, wave height, duration of current weather pattern, history of wind direction+speed, fetch and water depth. These could be available also in weather reports, but it would be good to be able to estimate future waves also oneself.

One can see the existing average sea condition and its effects from the boat. It would be nice to know when the risk of too risky waves (that one can't see yet) grows from zero to something meaningful. No point in risking the boat if there is a clear risk of getting too bad waves. Knowing that there is no such risk would be also great.

My wish is thus to get new rules of thumb (or more exact methods) for areas where we have not had them so far. Maybe such better knowledge would save some boats. Maybe many sailors have so far lived under the assumption that all waves are roughly similar (and some lost their boat because of that).

Every sailor with a certain amount of ocean experience knows the answer to this, to probably as close a degree of certainty as any engineering.

First of all -- with very few exceptions, the only waves which are dangerous to us, are those that break. Don Jordan explains why in his paper. Storm waves in the open ocean move at something like 30 knots. But the water in a normal wave is not moving with waves -- it is going up and down. But when a wave breaks, a certain volume of water at the crest is caught up and moves at the wave speed. One cubic meter of water weighs a ton, and so three cubic meters of water moving at 30 knots is like a Range Rover running into you at 55km/h. Got it now? That's the basic problem. That's enough force to broach and roll the boat. If the wave is higher than your beam, then it has the leverage to roll you over, and that is what can kill you.

Breaking waves can happen in a variety of conditions. Waves get higher and higher the stronger the wind and the longer a distance the wind blows across, for a longer period of time. 45 knots of wind blowing across thousands of miles for a day will produce waves of about 35 feet, as you can see from the below (from Dashew's "Surviving the Storm"):



But waves don't start to break just because they are high -- they break when they are steep, or when there is interference from a cross-sea. If you have shallow water or wind against current or a continental shelf border, you can see dangerous breaking waves in as little as 25 or 30 knots of wind. There are reports of boats who went through hurricanes where the seas were not breaking.

Once the seas start to break, it is quite hard to predict how much water is going to fall on you. A higher breaking wave might dump more tonnes of water on you from higher up, but not necessarily. It depends on how you happen to get caught. There is a lot of chance involved.

I got caught by an unforecast Force 9 in the middle of the North Sea a few years ago. The forecast was only two days old, and was double checked across several sources. The forecast was for a Force 8, which without any ground effects or wind against current will not normally produce breaking waves -- we sail in Force 8 all the time. But in the event it was F9 with steep, breaking seas, in height similar to my first spreader so probably about 30 feet, which is also about what Dashew's table would predict.

In such conditions, not all the waves break -- the waves form peaks, looking something like a mountain range, some of them higher and steeper than others, and the steeper peaks tumble over. You steer around trying to avoid the big ones, which mostly works. But after some hours of this we eventually got caught by one which toppled over onto us with unbelievable force, which knocked my 20 ton boat down flat to the water and broached us. The force involved is hard to describe -- it felt like a building falling on us. Fortunately she got right back on her feet and we got back on course before the next one came, and no more peaks toppled on us. Kudos to the brave and skillful crew -- I was at the nav table at the time.

Anyone who has been through such an experience would never think about trying to cut it fine with the engineering of your life saving drogue system. The forces are awesome, and chaotically unpredictable, and you just want system to be strong as hell, period.

I was not carrying a drogue, but if I had been, I would have deployed it. The conditions were not exactly extreme, but a direct hit from a falling peak of a large wave will exert extreme loads on your boat. What would be the point of carrying a drogue which couldn't take it? None.

[kmacdonald]

Don, I think anything a rational person sails in or might be caught in is survivable. If one is foolish enough to flirt with hurricanes, all bets are off. No one should ever be caught off guard by a hurricane. A long time ago, when sailors went to sea, they had no idea what was over the horizon. A lot of ships, and sailors, were lost.

[Dockhead]

Originally Posted by Don C L

I am puzzled by this “survivability” criteria. I don’t evaluate things that way. I tend to assume everything is survivable with the right preparation. If not, what do you do? Give up because the waves are too big to be survivable? A drogue should keep the stern pointed upstream and prevent speeding down wave face, even if it is being pulled at 8 knots and thus will have served its purpose as long as the cones hold up. One big advantage of the drogue over a parachute i can imagine is that the waves are hitting you at a slower speed. Not only is that more comfortable but it helps the boat hesitate long enough on the wave crest, and not fall down the face, to let the wave pass underneath you. Or so I imagine because I haven’t been out in big stuff with drogue yet.!

Yes, just so.

So keep you from speeding down the wave face, but also to prevent your being turned beam-on to the seas, where the wave has more leverage on you because beam is less than length, but also where you can be tripped over your keel. I suppose that if it were strong enough, a drogue might also keep you from being pitchpoled even in a breaking wave higher than your length -- it will provide a lot of resistance in the pitching plane. In short, it hold you stern-on into the mass of water where you present the least resistance to the falling water and where you can't be tripped over your keel.

[Don C L]

Originally Posted by Dockhead

Yes, just so.

So keep you from speeding down the wave face, but also to prevent your being turned beam-on to the seas, where the wave has more leverage on you because beam is less than length, but also where you can be tripped over your keel. I suppose that if it were strong enough, a drogue might also keep you from being pitchpoled even in a breaking wave higher than your length -- it will provide a lot of resistance in the pitching plane. In short, it hold you stern-on into the mass of water where you present the least resistance to the falling water and where you can't be tripped over your keel.

Yes, if the drogue is strong enough to pull the stern through the breaking crest, I would say the pitchpoling risk is dramatically reduced, as is knock-down and/or roll. Clearly what becomes survivable increases.

[Dockhead]

Originally Posted by Don C L

Yes, if the drogue is strong enough to pull the stern through the breaking crest, I would say the pitchpoling risk is dramatically reduced, as is knock-down and/or roll. Clearly what becomes survivable increases.

As far as I know, there has never been a case of a boat lying to a JSD which has been rolled or pitchpoled, although people have been through horrendous conditions in them.

A hurricane, contrary to the common belief of land people (for whom there are four types of weather -- calm, windy, t-storm, and hurricane ), is not necessarily the worst conditions you can experience at sea. The winds are extreme, but because of the rotation, the fetch is limited. Two (or more) large scale frontal system interacting at higher latitudes may produce much worse sea states. Wind needs to blow for a long time in one direction in order to transfer its energy to the water. Two fully developed wave trains from two large scale frontal systems colliding at an angle is what will produce a sea state which may be pretty close to unsurvivable. Strong boats even just lying ahull in hurricanes usually survive.

[estarzinger]

Let me ramble on a bit on this topic - my thoughts are certainly not any sort of definitive answer, but just the best we came up with in the specific boats & situations we dealt with.

First factor for me was what wind angle was our course to next waypoint. If it was upwind, we basically just progressively reefed down (until hove-to under just mizzen on Silk or fore reaching under trysail on Hawk). Upwind, on Hawk, we never found a wave size or shape or pattern where we thought something other than forereaching was going to be best. And in the sydney to hobart storm (which had the sort of worst case largish breaking waves), fore reaching was the tactic which had the lowest failure rate among that fleet. We carried a para-anchor, but I did not like it (neither the procedure to set and retrieve nor the motion/loads while it was out) and only would have deployed it if forced to by circumstances.

If the wind is on the beam, you really need to change course when the wave height gets about your beam and the crests change from just some foam to an actual break. That often happens in relatively low wind speeds (gale range). We would usually reduce down to our large staysail and either come up or fall off 30 degrees or so. That would usually calm things down a lot and give the boat a large safety reserve (for squalls or the occasional really big breaker). At some point, if the waves built and got worse in shape, we would need to take another step and run off (DDW perhaps with drogue) or forereach.

Downwind, we reduced sail progressively, from the aft (mainsail) first. It is super critical to keep the sail area forward and the helm well balanced - big mistake to have too much main and have the boat want to round up. At some point in wave size/shape, about when you start surfing more regularly, the steering can becomes a bit squirrely and then drag devices add a margin of safety (even with small breaking waves = your beam in height, if you get two in a row - one that spins you quickly, and then the second to pop you on the beam, you can get into trouble). When you get bigger breaking water you start to need more drogue force so you switch from just the speed limiting single element, to a dual element or to the series, because the drogue needs to carry you thru lots of high energy water crests. This is why we explored ways/procedures to add drag (either using the 2 or 3 series, or splitting our jsd into two sections).

The correlation between the need for a drogue and the wind speed is pretty weak. You get into any sort of current, or on a continental shelf, or in two crossing wave patterns and you can develop really badly shaped waves in lightish winds.

In addition to the breaking waves, you also have to look out for the 'holes' that happen in crossing wave patterns. These can be pretty deep and just swallow the boat and do various sorts of severe damage and can happen even when the 'normal' waves are not breaking (but typically they need to be steepish).

I have never seen a good 'wave shape' sort of forecast. But if you know what sorts of factors drive bad waves you can make a decent guess; and you do want to practice 'preventive safety' and take extra care when you guess bad waves might be around because it only takes one to wreck your day. You should not wait until you get really baddly popped before taking cautionary action.

As a final note - quite often boats weather the most severe portion of a storm and come to grief as it moderates. This (I belive) is because of three factors - a wind shift as the storm passes that produces cross waves, the boat wallows a bit because sail is not put back up as the wind decreases, and the crew is fatigued and less alert. You need to focus all the way thru the storm, even when the 'worst' has passed, because even 'little' (eg 15') waves can give you serious grief if they pop you wrong and two of them in series caan ruin your day.

I dont know much about full keel boats and they seem to have distinctive traits in the above sorts of conditions. Some (the fatter ones with barn door rudders) don't seem to steer at all well downwind (the pardey's) and want to face into the wind; while others (Joshua) want to go ddw with no drag devices at all and seem to steer well ddw under wind vane even in extreme conditions. And finally some deep/narrow/well ballasted full keelers seem to lie ahull, which you dont want to do on any other design, pretty well. So there is definitely a boat design aspect to throw into this whole mix.

And Silk and Hawk acted differently. Silk hove to perfectly, while Hawk did not. Silk also ran off well with just a long rode out; while Hawk needed a drogue. But Hawk could forereach into conditions which would have stopped silk dead, and she could take a much greater wave pop and just shake it off.

What I can say is (1) there is no magic silver bullet gear or technique which will universially save you, (2) you need to get experience with your boat and try different stuff in gale sorts of conditions so you know how she responds and feels, (3) you need to stay alert thru a storm and ready and willing to do/change stuff as conditions develop/change.