Acquiring A Ready Made Series Drogue

[Don C L]

Originally Posted by Snowpetrel

"Unusually steep waves are classified as rogues if either: (a) the height (crest from preceding trough), H is greater than twice the significant height, Hs (Hs = 4 times the standard deviation of the wave record); or (b) the crest height, Crx, above mean sea level (MSL) is greater than 1.25 times Hs2. Rogue waves are not necessarily huge, but they are much bigger than the surrounding waves." https://www.nature.com/articles/srep44124

Also see here https://www.nature.com/articles/srep...ink-section-61.

So in a 1 ft chop a 2 ft wave is considered a rogue event, and it's possible (but statistically very unlikely) for a 3 ft wave to exist somewhere in a 1 foot wavetrain. Of course 1.5 foot waves will be reasonably frequent in this 1 foot sea. These wave heights are not an issue for our boats, but maybe they are rogue event for a kid in a small kayak, especially since these rogue waves tend to have a much higher steepness ratio and are more likely to break violently.

I generally plan for a 2x sig wave height wave when deciding things like what hatches to close. Realising that significant wave height is only the average of the highest third of the waves, so you will often see waves much higher than the sig wave height anyway.

The Draupner wave was one of the first electronic readings and was reliably recorded at 25 meters in a 12 meter sig wave height. But plenty of earlier accurate scentific observations had been made of larger waves (eg the '69 obs by scrips reasearch station FLIP) plus numerous seafarers accounts.

https://en.m.wikipedia.org/wiki/Draupner_wave

Wave statistics were pretty well understood before the Draupner wave. My old 93 copy of Van Dorns excellant book 'Oceanography and Seamanship' has a very good discussion of large waves and and the wave spectrum. I think what the modern research is finding is that they tend to be more clumped together in certain areas and conditions rather than evenly distributed, and extra large storm rogue waves are more common deep sea than had prevously been supposed by scientists.

Wave energy increases ^4 to wind speed so if we double the windspeed the wave energy in a fully developed sea goes up 16 times. Wave height goes up by ^2 of windspeed, and wave energy goes up ^2 of wave height.

This CSS Diagram is pretty useful. Handy to have a laminated copy at your chart table for reference.

Here is a good example of its use
David Burch Navigation Blog: 100-foot Waves Expected near Aleutian IslandsAttachment 167812

One thing I have wondered about, and maybe your research found reference to it, is the presence of 2 or more moving sources of the highest wind events and changing fetches in fairly close proximity and not converging as this one did (few hundred miles apart with significant waves coming from different angles) and if there could be some accounting for that in wave height predictions for a given location. It is a rare event, but I have seen some odd things in the maps in the last year. But this is a thread drift best saved for another thread I 'spect.
BTW 1/2000 is 2x the SWH? That's pretty often in my book!
Also, any idea why some of them are reported to appear as three waves in succession?
AND I thought this article in the references was interesting!
https://www.theregister.co.uk/2005/0..._wave_rethink/

[Snowpetrel]

"In a year-long rogue hunt at three buoys off the Brazilian coast19, 442 rogues (H/Hs ≥ 2) were found in a population of 3.9 million waves. This gives an encounter probability of 1.13 × 10−4. (Snip)

From equation2 the encounter probability of rogues (Crx/Hs ≥ 1.25) is 1 in 2637 waves, which for 13.5 s period waves (like Andrea) yields a return period of about 10 hours or a 3.3% chance of finding a rogue in a 20 minute record. Maximally steep rogues (Crx/Hs = 1.7) are much more rare: the encounter probability, EPR(1.7) is 1 in 133,361 waves or return period of 500 hours. Very large targets (e.g.*ships or offshore platforms) experience shorter return periods as quantified in Eq. (2)."

https://www.nature.com/articles/srep44124

I guess this shows that there are a few differing types if rogues, big waves and steep waves. The more dangerous being much rarer. It makes sense that its the maximally steep ones that roll over yachts.

The presence of crossing wave trains at similar frequencies definately seems to me to be a big factor in the 3 sisters type waves . One interesting thing about waves is that the phase(or group) velocity of the groups of waves is around half the speed of the individual waves. This is why breaking groups of waves seem to "stand still" compared to the waves themselves, and you often get three breakers in each phase group, as the phases align then go out of sync.

But I think this is the standard linear wave theory that modern research is going way past with new non linear concepts to explain these exceptional rogues, but the science and jargon is way beyond what I can easily make any sense of. I guess in a few more years the findings will be simplifed into seafarers language.

I guess this is vaguely relevant due to the fact that a Series Drogue is really designed to deal with rogue waves...

Some more interesting stuff in here
https://folk.uio.no/karstent/waves/index_en.html

[kmacdonald]

OK, we have 1 in 133,361 waves that are "Maximally Steep Rogues". I would assume that the overwhelming majority of those are very small waves. They could be a foot or a meter tall but "maximally steep". At what height does a "maximally steep rogue" become dangerous? What is the significant wave height needed to potentially create that wave? What percentage of time is the sea state conducive to creating that maximally steep rogue wave of significant height to be of concern? I'm sure the answers varies greatly based on location and season. I wonder how many ship wakes created a rogue wave? I would guess all of them that passed near the buoys in calm seas. I'm not ready to dust off my wallet and send money for more research.

[Dockhead]

Could you guys remind me of what rogue waves have to do with the subject?

I'm not chiding -- thread drift is natural -- just that I lost the connection entirely.

[Juho]

Originally Posted by Dockhead

Could you guys remind me of what rogue waves have to do with the subject?

I'm not chiding -- thread drift is natural -- just that I lost the connection entirely.

To me the connection between rogue waves and series drogues is the question when should one deploy the drogue. (This does not really address the original question on acquiring a drogue, but is related to the use of drogues anyway.)

People say "reef early". To me the question is if one should also deploy the drogue early. We know that many boats have been abandoned due to demasting, and waves are more dangerous than wind.

It is possible that people have felt safe until one big wave has broken the mast and flooded the boat. I have read quite a number of stories where even experienced sailors have lost their boats due to wave related surprises.

If we know that rogue waves or near rogue waves are to be expected and are not rare, then maybe one should deploy the drogue already when there appears to be no imminent threat. I wonder how many boats could have been saved this way. The wave math might give us some guesstimates on when the drogue should be deployed.

[kmacdonald]

Originally Posted by Dockhead

Could you guys remind me of what rogue waves have to do with the subject?

I'm not chiding -- thread drift is natural -- just that I lost the connection entirely.

It's related to drogues and the conditions they would be used in. As you said previously you have pretty much made up your mind as to what to buy so you're right, the original question has been answered. I think it is this: Details & Prices | Ocean Brake

It is interesting that some feel that the JSD is not the gold standard in drogues. I hadn't even considered that it wasn't until thinnwater suggested it so there has been value in the extended discussion for me at least.

The design factors and considerations has also been questioned as well as the drogues usefulness given the excellent weather forecasting. Their limitations have only been glanced at.

[Dockhead]

Originally Posted by Juho

To me the connection between rogue waves and series drogues is the question when should one deploy the drogue. (This does not really address the original question on acquiring a drogue, but is related to the use of drogues anyway.)

People say "reef early". To me the question is if one should also deploy the drogue early. We know that many boats have been abandoned due to demasting, and waves are more dangerous than wind.

It is possible that people have felt safe until one big wave has broken the mast and flooded the boat. I have read quite a number of stories where even experienced sailors have lost their boats due to wave related surprises.

If we know that rogue waves or near rogue waves are to be expected and are not rare, then maybe one should deploy the drogue already when there appears to be no imminent threat. I wonder how many boats could have been saved this way. The wave math might give us some guesstimates on when the drogue should be deployed.

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.

[Dockhead]

Originally Posted by kmacdonald

. . The design factors and considerations has also been questioned as well as the drogues usefulness given the excellent weather forecasting. Their limitations have only been glanced at.

Well, two things to this: First of all, weather forecasting is certainly good enough to avoid ever being in a situation where you would need a drogue, if you are sailing along a coast less than a day or two from a safe harbor. But weather forecasting is not indeed good enough to be sure you won't need a drogue (or some other effective heavy weather tactics) if you are on a long ocean passage in higher latitudes a week or two of sailing from a safe harbor. Weather is too chaotic to be capable of being accurately forecast that far ahead.

A dangerous sea state requiring a drogue or other effective heavy weather tactics can exist from Force 9 in open ocean conditions, or even less if you have some factor like wind against a current -- the Gulf Stream in a Norther, for example.

Any breaking wave strike can produce loads near the maximum design parameters of a drogue system. Someone suggested that drogues could be more lightly designed if you're not using them in a Force 12 -- this is not true. Whenever you need a drogue at all, you can experience high loads. Even a Force 7 or 8 in a Norther in the Gulf Stream, for example, can produce a horrendous sea state which can sink a medium sized yacht.

[kmacdonald]

Weather forecasting is a lot better than a day or two out. If waters are sailed in the favorable season, much longer forecast can be relied on. Sure, some boats are too slow to avoid nasty weather but that's not the case with modern boats. In almost all accounts of drogue use, they were not used in survival conditions and were deployed to allow a shorthanded crew rest and a more comfortable ride. Given the typical uses of drogues, the design criteria is about 10% of what Jordan designed for. Designing for worst case offers marginal benefit at potentially large cost. Worst case conditions are not survivable, regardless of equipment.

The ability to receive weather forecasts is far more valuable than a drogue ever thought of being.

[Snowpetrel]

Originally Posted by Dockhead

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 dont know DH, I think almost all of our storm preparation is really about dealing with rogues (or near rogues) of some sort.

I suspect many of the casualties in the 79 fastnet and 98 sydney hobart where to some extent rogue related. There being so many boats in one patch of ocean that the chances of a percentage of boats encountering rogue waves goes up. And the only really effective defense against them is a strong, well found boat and a series drogue or equivalent. All other techniques will end up with the boat beam on to a big rogue breaking wave. Fast running might also work on a few boats capable of surfing at high speed under control, but it isn't my prefered technique for most cruising boats at night with limited crew.

[kmacdonald]

Cruisers aren't on a schedule and race course. They can decide when and where to sail and can go around bad weather systems. Racers feel the need to show their manhood and sail thru bad weather and pay the price on occasion. Cruising and racing a two different activities.

[Dockhead]

Originally Posted by kmacdonald

Weather forecasting is a lot better than a day or two out. If waters are sailed in the favorable season, much longer forecast can be relied on. Sure, some boats are too slow to avoid nasty weather but that's not the case with modern boats. In almost all accounts of drogue use, they were not used in survival conditions and were deployed to allow a shorthanded crew rest and a more comfortable ride. Given the typical uses of drogues, the design criteria is about 10% of what Jordan designed for. Designing for worst case offers marginal benefit at potentially large cost. Worst case conditions are not survivable, regardless of equipment.

The ability to receive weather forecasts is far more valuable than a drogue ever thought of being.

Well, just about everything in this post is not correct.

The design parameters for drogues are not just "worst case" -- they are for breaking wave strikes. Do you suggest that a drogue should not be designed to withstand a breaking wave strike? You seem to think that "worst case" is just a question of wind force -- that is not true. It's a question of sea state.

Second, concerning boats outrunning weather -- many big weather systems in the North Atlantic move at over 20 knots. Neither rowboats nor any modern cruising boat, even a high performance one, can "outrun" weather. Receiving weather information when you are offshore is of course very valuable, but if you are a week away from a safe harbor, news of a developing system may not save you.

As to drogues being used in "survival conditions" -- any time a vessel less than 100 feet long is involved in breaking waves higher than the vessel's beam, there is a significant risk of being broached and/or rolled. Being rolled is a threat to survival. MOST drogue deployments involve such conditions. "Survival conditions" are not any particular wind strength; they are a result of sea state, and can occur in as little as F7 or F8 in some situations, as was mentioned. Just because the crew MIGHT have coped by active steering, if the crew had not been exhausted, does not mean that the conditions were not "survival".


The one thing you say in this post which is right, is that in a favorable season, in a benign latitude, you can rely on the the weather forecast over a longer period. That is true, and that's why the great majority of cruising yachts, even those used to cross oceans, don't carry drogues and don't need them. There is no need for a drogue for a trade winds crossing (even a trade winds circumnav) outside of hurricane season.

But if you need a drogue AT ALL, there's no point in carrying one which is not designed to Don Jordan's specifications, because you may load it up near to its maximum loads in ANY breaking sea conditions.

[kmacdonald]

Originally Posted by Dockhead

Well, just about everything in this post is not correct.

The design parameters for drogues are not just "worst case" -- they are for breaking wave strikes. Do you suggest that a drogue should not be designed to withstand a breaking wave strike? You seem to think that "worst case" is just a question of wind force -- that is not true. It's a question of sea state.
The reality is it is "worst case". A cursory look at the design parameters will clearly say so. If you had had any experience with truly gigantic breaking waves you would understand the difference. Typical breaking waves don't creates the load the JSD was ultimately designed for.

Second, concerning boats outrunning weather -- many big weather systems in the North Atlantic move at over 20 knots. I never said "outrun". It's sort of like swimming out of a rip tide. You swim perpendicular to the current to get out of it, not against it. In sailing, you would sail perpendicular to the approaching weather. Sorry, I thought that was obvious but should have made it crystal clear.Neither rowboats nor any modern cruising boat, even a high performance one, can "outrun" weather. Receiving weather information when you are offshore is of course very valuable, but if you are a week away from a safe harbor, news of a developing system may not save you.

As to drogues being used in "survival conditions" -- any time a vessel less than 100 feet long is involved in breaking waves higher than the vessel's beam, there is a significant risk of being broached and/or rolled. Being rolled is a threat to survival. MOST drogue deployments involve such conditions. "Survival conditions" are not any particular wind strength; they are a result of sea state, and can occur in as little as F7 or F8 in some situations, as was mentioned. Just because the crew MIGHT have coped by active steering, if the crew had not been exhausted, does not mean that the conditions were not "survival". Again, I'm sure you don't understand just how bad conditions can be.


The one thing you say in this post which is right, is that in a favorable season, in a benign latitude, you can rely on the the weather forecast over a longer period. That is true, and that's why the great majority of cruising yachts, even those used to cross oceans, don't carry drogues and don't need them. There is no need for a drogue for a trade winds crossing (even a trade winds circumnav) outside of hurricane season.

But if you need a drogue AT ALL, there's no point in carrying one which is not designed to Don Jordan's specifications, because you may load it up near to its maximum loads in ANY breaking sea conditions.

The only point in carrying a JSD not up to specifications is that there are no examples of one being used that needed to be up to those specifications.

[thinwater]

Originally Posted by Juho

People say "reef early". To me the question is if one should also deploy the drogue early. We know that many boats have been abandoned due to demasting, and waves are more dangerous than wind....

... If we know that rogue waves or near rogue waves are to be expected and are not rare, then maybe one should deploy the drogue already when there appears to be no imminent threat. I wonder how many boats could have been saved this way. The wave math might give us some guesstimates on when the drogue should be deployed.

While not always true, like "reef early," this is a good thought to keep in mind. By the time things go pear shaped, it will be too late. Capsize happens fast. No doubt, multihull sailors are more cognizant of this.

or put another way (Dockhead); "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."

[Dockhead]

Originally Posted by kmacdonald

The only point in carrying a JSD not up to specifications is that there are no examples of one being used that needed to be up to those specifications.

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.