Acquiring A Ready Made Series Drogue

[thinwater]

Originally Posted by 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?

You can also get data from Jordan's report.

A 100-cone drogue at 7 knots produces about 1200 pounds of drag. Drag goes up in proportion to the number of cones and with the square of speed, within very broad limits. 3 knots = 216 pounds, 14 knots = 4800 pounds. This will vary a little during rapid acceleration. Waves are faster than that, but you should never fully surf. The load on the drogue is defined by how fast the boat goes, not by how much water hits the boat.

The WLL of nylon is only about 9-12%, depending on who you ask (ABYC = 12%), polyester is about 20%, and Dyneema about 30%, again, depending who you ask and the life expectancy you want.

A thought and an experience.

a. There is very little market for rock climbing gear that does not meet UIAA standards.

b. I once had a hurricane swell break all over my boat in a blue sky. The water was very smooth, though there was 10-foot swell from a storm 700 miles away. You sit a glass of water on the coaming. The breeze was 10 knots, we had all sail up and all of the hatches open. A crossing wake, wave from an odd direction or something made it rare up and land on us, and in a few seconds, we gained several hundred gallons of water. I wouldn't call it a rogue, but it was an eye-opener.

[kmacdonald]

Thanks Thinwater. That's exactly what I was looking for.

Now it can get really interesting and subjective as to the engineering part. What FS to use. You say climbing ropes use a FS of 2. The rope manufacturers tell us to use 12 or more. That's a pretty big range.

[Dockhead]

Originally Posted by thinwater

. . . . The load on the drogue is defined by how fast the boat goes, not by how much water hits the boat.. .

That's the beauty of it, isn't it? It's not like being tied to an anchor.

But don't forget that how fast the boat goes will be also influenced by how much water hits the boat. That's why Don Jordan talked about designing for breaking wave strikes.

It's a hell of a thing to be hit by some tonnes of water moving at 30 knots. I suppose it could crush in the deck of coachroof, but I've never heard of this happening.

[thinwater]

Originally Posted by kmacdonald

...You say climbing ropes use a FS of 2. The rope manufacturers tell us to use 12 or more. That's a pretty big range.

You have taken what I said very, very badly out of context, and you know it. You should be able to figure it out from this. This is the perfect case with no abrasion or flexing.
* Green = nylon
* Red = polyester
* Light blue = Dyneema

[Juho]

Originally Posted by Dockhead

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"):

Attachment 167847

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.

It seems that in the conditions that you described you could see the seas building up, and you could avoid the big waves for a while. This means that if you had had a JSD with you, you could have deployed it before the waves got too dangerous and too numerous to avoid.

At night time it would be wise to deploy the JSD already if there is a risk of dangerous waves, since you can not see them coming. For this kind of situations I'd like to have good estimates on when to expect bad waves. If new research can not give us any new information on this (I can't estimate this), we must live with the existing knowledge and deploy the drogue earlier. One problem with JSD is that it could be quite tiring to take it up every morning.

Another surprise element could be waves that grow so quickly that one can not avoid them. This could happen e.g. when waves are coming from two different directions. Also here I don't know what is and will be possible (ability to se those waves, new knowledge). Maybe one should just lower the drogue deployment criteria if waves don't look like regular waves from one direction. Time will show if there will be new information on the possibility and probability of dangerous waves.

[thinwater]

Originally Posted by Dockhead

... But don't forget that how fast the boat goes will be also influenced by how much water hits the boat. That's why Don Jordan talked about designing for breaking wave strikes.

Absolutely. I just wanted folks not to get hung up on the "tons of water" and imagine only the speed the boat will attain, which is a lot more than hull speed, and considerably less than wave speed when 2 or more tons is pulling you backwards. I don't know how much less, which is a fascinating question. I only know the relationship between drogue speed and drag force.

Funny thing. I studied this for my last boat, which had a center cockpit and could comfortably handle big waves from behind. Now my boat (trimaran) is open-transom, only 8 inches above the water, and waves will slosh in rather easily if I don't keep my speed up. I would never use a drogue with this boat, even with good washboards, because the weight in the cockpit would be too much. Either run off or use a sea anchor. Always something different.

[kmacdonald]

Originally Posted by thinwater

You have taken what I said very, very badly out of context, and you know it. You should be able to figure it out from this. This is the perfect case with no abrasion or flexing.
* Green = nylon
* Red = polyester
* Light blue = Dyneema

Sorry. I should have made it clear that the FS is applied to the working load of the rode, not the ultimate strength. The working load of the rode is only 12% (nylon) of the breaking load so is about 8 times stronger than the breaking load. Fatigue life or cycle life needs to be considered also and number of safe uses of a drogue should also be considered.

[kmacdonald]

Originally Posted by thinwater

Absolutely. I just wanted folks not to get hung up on the "tons of water" and imagine only the speed the boat will attain, which is a lot more than hull speed, and considerably less than wave speed when 2 or more tons is pulling you backwards. I don't know how much less, which is a fascinating question. I only know the relationship between drogue speed and drag force.

The max speed the boat can be accelerated to by a wave strike is critical since the forces applied by the drogue are a function of the speed squared. I need to reread the CG report and see what they concluded via calculation or tank testing.

[Dockhead]

Originally Posted by Juho

It seems that in the conditions that you described you could see the seas building up, and you could avoid the big waves for a while. This means that if you had had a JSD with you, you could have deployed it before the waves got too dangerous and too numerous to avoid.

At night time it would be wise to deploy the JSD already if there is a risk of dangerous waves, since you can not see them coming. For this kind of situations I'd like to have good estimates on when to expect bad waves. If new research can not give us any new information on this (I can't estimate this), we must live with the existing knowledge and deploy the drogue earlier. One problem with JSD is that it could be quite tiring to take it up every morning.

Another surprise element could be waves that grow so quickly that one can not avoid them. This could happen e.g. when waves are coming from two different directions. Also here I don't know what is and will be possible (ability to se those waves, new knowledge). Maybe one should just lower the drogue deployment criteria if waves don't look like regular waves from one direction. Time will show if there will be new information on the possibility and probability of dangerous waves.

You learn from experience when dangerous waves will be experienced. As Thinwater (or was it Estarzinger?) said, it's not closely related to wind speed.

I would say:

* F9 or more with great fetch (thousands of miles) and duration (more than 12 hours) will make waves high enough that the risk of their breaking without obvious provocation becomes significant.

* Wind against current greatly magnifies this risk. Dashew wrote that even 25 knots of North wind in the Gulf Stream can create waves which can sink a medium sized yacht.

* An area where the sea bed comes up -- like the edge of a continental shelf or perhaps the last mile or two before shore in some places -- can make waves pile up and topple over, which were orderly swells in the open ocean.

* When two (or more) large high energy weather systems produce two (or more) wave trains which are not aligned, the area of interaction between the two wave trains can create viciously breaking seas and survival conditions, even in relatively moderate wind conditions. This is a particular risk in the high North Atlantic where at some times series of weather systems track across. The movie "The Perfect Storm" shows -- realistically! -- what can happen when two really big weather systems collide in this manner -- no hurricane can make a sea state like that. The point is not waves coming to YOU from different directions, it's waves interacting with each other and results from the physics effect of interference.

* As Estarzinger pointed out, the well known (among ocean sailors) phenomenon of dangers sea states AFTER the storm has passed. I don't understand where this comes from, but it's a fact.


Concerning tactics -- you are exactly right. Up to a certain sea state, you can keep the boat safe by steering around the bad breakers, and steering carefully at the right angle down steep wave faces (always the scary part for me) -- not straight down, or you can speed out of control, but not to crossways, either, lest you trip on your keel or get rolled if a crest breaks on you.

But the worse the sea state gets, the fewer safe paths there are, and unless you have a full racing crew, the helm rotation may start to get exhausted. This is the time for the JSD.

And you are right about night time -- a dark night in big sea conditions is absolutely terrifying, because you can't see them coming. That's also time for the JSD.

[kmacdonald]

Originally Posted by thinwater

You can also get data from Jordan's report.

A 100-cone drogue at 7 knots produces about 1200 pounds of drag. Drag goes up in proportion to the number of cones and with the square of speed, within very broad limits. 3 knots = 216 pounds, 14 knots = 4800 pounds. This will vary a little during rapid acceleration. Waves are faster than that, but you should never fully surf. The load on the drogue is defined by how fast the boat goes, not by how much water hits the boat.

The WLL of nylon is only about 9-12%, depending on who you ask (ABYC = 12%), polyester is about 20%, and Dyneema about 30%, again, depending who you ask and the life expectancy you want.

A shoestring wold hold that. If the drogue is sized properly, what is your best guess to the max worst case speed?

[gjorgensen]

Originally Posted by estarzinger

Im not sure if they are still making the galerider thou . . . seem to remember that small sail loft went out of business, but perhaps someone else picked up the product.

I'm not either. Hathaway, Reiser & Raymond closed up, but sold the rigging business off to a local yard (Service). Norwalk Cove does not list the galerider anywhere on their site, but perhaps they make them. Landfall Navigation still claims to have them in stock.

Dockhead, for an emergency rudder it would be worthwhile trolling around the sites and references for the Transpac, Pacific Cup, Bermuda, and especially Single Handed Transpac races. All require emergency rudders, and especially SHT (Singlehanded Sailing Society | San Francisco Shorthanded Racing) takes it very seriously. The forums on that site have a ton of good info, especially in years past, about emergency rudders including real world experiences (in the trades to Hawaii, not Greenland of course) of what works. By far the two most popular solutions are the Scanmar SOS Rudder and various custom solutions using a cassette and slide-in rudder. Both have been installed on numerous folding transom boats like yours, although almost all require a sizable bracket on-deck at the transom along with one lower. As mentioned, a rudder with a pintle and gudgeon setup is almost impossible to install in a seaway, but a cassette is easy and then the rudder is dropped in. There may be people making those stock now.

[fxykty]

The issue has been raised that one drogue will not work in all conditions. As an example with our catamaran, in more moderate conditions once running downwind under storm sails or bare poles is too fast and dangerous, then we could deploy a speed limiting drogue such as the Para-Tech Delta Drogue https://www.seaanchor.com/delta-drogue/. Rather than surfing into the 20s and risking spearing into a wave ahead, this should limit our speed to 6-10 knots.

Once waves get steeper and higher where potential surfs are no longer safe, the next step would be to deploy a JSD, which should slow the boat to below 3 knots.

Of course, switching from one drogue to another would be very difficult in those kind of escalating conditions. Does anyone have any experience or thoughts? I’ve certainly read that “the drogue you start the storm with is the one you’re stuck with”.

Other than cutting a speed limiting drogue loose and then deploying a JSD, are there any methods to switch from one drogue to another?

[thinwater]

Originally Posted by fxykty

The issue has been raised that one drogue will not work in all conditions. As an example with our catamaran, in more moderate conditions once running downwind under storm sails or bare poles is too fast and dangerous, then we could deploy a speed limiting drogue such as the Para-Tech Delta Drogue https://www.seaanchor.com/delta-drogue/. Rather than surfing into the 20s and risking spearing into a wave ahead, this should limit our speed to 6-10 knots.

Once waves get steeper and higher where potential surfs are no longer safe, the next step would be to deploy a JSD, which should slow the boat to below 3 knots.

Of course, switching from one drogue to another would be very difficult in those kind of escalating conditions. Does anyone have any experience or thoughts? I’ve certainly read that “the drogue you start the storm with is the one you’re stuck with”.

Other than cutting a speed limiting drogue loose and then deploying a JSD, are there any methods to switch from one drogue to another?

Drogues are not stable past about 5 knots. The loading/ft^2 is too high and they will pull out of wave faces. This has been reported many times and I have seen it it testing. The problem is that any single-element drogue will run just under the surface, even at very lond scope and with some weight, because the load will be on the order of 1000 pounds. Thus, on the weight of the water holds it down, and when a steep wave comes up behind it, it pops out. Multiple elements stops this, because they are in different waves and because the trailing element or elements run deeper.

The "drogue you are stuck with" thing is one reason to like two drogues in series. I also wonder if the JSD design could be improved to run better at higher speeds, allowing it to be used as a multi-purpose adjustable drogue. But the price would be higher and the market would be tiny. Something like a string of 12-18" diameter Delta Drogues (much more stable than cones, yet pretty simple to make). For steering, just a few, for slowing, a few more, and for a real storm, let out a total of about 5-10. Something like three 100' sections holding three drogues each. In fact, even just for slowing, 2-3 18" drogues will be far more stable at higher speeds than a 30" drogue.

[Snowpetrel]

Originally Posted by thinwater

Drogues are not stable past about 5 knots. The loading/ft^2 is too high and they will pull out of wave faces.

I am interested in this 5 knot instability thing and how it manifests itself. My folks ran off for a few days in a really nasty southern ocean midwinter blow between NZ and Tahiti with an old seabrake spring loaded plastic drogue designed for speeds of 5-8 knots depending on the setting. They found it held them nicely at 5 or 6 knots and gently decelerated them as they approached 8 knots, preventing them from surfing. I don't recall any instability being mentioned. The device worked flawlessly as advertised. Unfortunately they are no longer available.

Another friend had a homemade stainless version of a HSD300 that he used behind his tri to stop high speed surfing. He used it at 8-10 knots or so. So maybe the rigid ones work better?

[thinwater]

Originally Posted by Snowpetrel

I am interested in this 5 knot instability thing and how it manifests itself. My folks ran off for a few days in a really nasty southern ocean midwinter blow between NZ and Tahiti with an old seabrake spring loaded plastic drogue designed for speeds of 5-8 knots depending on the setting. They found it held them nicely at 5 or 6 knots and gently decelerated them as they approached 8 knots, preventing them from surfing. I don't recall any instability being mentioned. The device worked flawlessly as advertised. Unfortunately they are no longer available.

Another friend had a homemade stainless version of a HSD300 that he used behind his tri to stop high speed surfing. He used it at 8-10 knots or so. So maybe the rigid ones work better?

It is not that the drogues themselves are unstable. Some fabric drogues are stable up to 15 knots or more. It is that when there are waves steep enough to need a drogue, above 5 knots, and the rode is pulled bar tight, as it will be at higher speeds, the frequency of the drogue pulling out of the wave face goes up. This is independent of design and is simply a matter of the geometry of waves. Longer scope helps, but only to a point when the waves are steep. it is the angle of the face that matters. Drogues are stable at higher speeds in even swell.

There are numerous stories of folks using a drogue at high speeds, going like a bomb, and as the storm grows, suddenly the drogue fails and they are screwed.

Like everything expereinces vary, but the point is that as the speed increases above 5-7 knots and loads increase, the chance of sudden failure increases. Just something folks should know. The JSD is designed to avoid this, at the cost of low speed.