Parachute sea anchor

[Boo2]

What happened when it got thrown forward by a following breaking wave ?

It does not.

Well, very many of the references I've read refer to single point drogues / sea anchors being thrown forwards by following breaking waves. I saw one where the crew saw some tyres weighed down by the boats main anchor surf forward on the face of a wave but can't find the reference atm.

I have explained to you...

You have explained nothing, merely repeating rubbish which contradicts elementary physics. There is nothing you can do on the end of a line which makes any difference to the way the boat behaves except the following :

1. Change the magnitude of the force exerted
2. Change the direction of the force exerted

Pictures of the SeaBrake I've seen on the web show it being dragged along on the surface, the manufacturers' recommendation to add weights to the middle of the line will do nothing to prevent it being thrown forward and very little to hold the stern down. Transferring the same weight to the rear of the boat would do about as much because the stronger the pull from the drogue the less the catenary from the weight. You want the weight after the drogue, not before it.

And this presupposes that holding the stern down is a good thing to do whereas, in survival conditions I have heard the concern expressed that continual bombardment by following seas was endangering the transom of a yacht let alone the washboards.

And you still havent addressed the key point that a series drogue tries to prevent :

How do you stop the drogue being thrown forward on a breaking wave in a confused sea ?

I am in no way saying the SeaBrake is not a good device of its kind. However, my understanding from reading the experiences of others is that basically no amount of weight will stop a single point device being thrown forwards by a big enough wave and that the JSD was designed specifically to address that issue.

Boo2

 

[VO5]

How can you talk such nonsense without being ashamed ?

The shape of the drogue / lines in the water makes no difference whatsoever to the direction of the force on the boat. The force on the boat is determined entirely by the direction of pull of the single line at the point where it attaches to the bridle.

If the forces in the line are the same then the boat will behave in precisely the same way whatever you tow.

As for the JSD "snaking" around then I would like to see a more reputable source for such a proposition than yourself, quite frankly.

Boo2

Quite frankly you need not seek a more reputable source as you call it.
What you ought to do is venture into the big wide ocean and try it yourself, frighten yourself silly in the process and then come back and we'll see.

 

[VO5]

Well, very many of the references I've read refer to single point drogues / sea anchors being thrown forwards by following breaking waves. I saw one where the crew saw some tyres weighed down by the boats main anchor surf forward on the face of a wave but can't find the reference atm.



You have explained nothing, merely repeating rubbish which contradicts elementary physics. There is nothing you can do on the end of a line which makes any difference to the way the boat behaves except the following :

1. Change the magnitude of the force exerted
2. Change the direction of the force exerted

And this presupposes that holding the stern down is a good thing to do whereas, in survival conditions I have heard the concern expressed that continual bombardment by following seas was endangering the transom of a yacht let alone the washboards.

And you still havent addressed the key point that a series drogue tries to prevent :

How do you prevent the drogue being thrown forward on a breaking wave in a confused sea ?

I am in no way saying the SeaBrake is not a good device of its kind. However, my understanding from reading the experiences of others is that basically no amount of weight will stop a single point device being thrown forwards by a big enough wave and that the JSD was designed specifically to address that issue.

Boo2

That's just it, you see.
You refer to the experiences of others.
As I advise you in my previous post on this thread the best idea is for you to go out into the wide ocean, meet a howler, a real howler............. and try it.

It is quite clear to me you are trying to pontificate to me but you have, by your own admission, no practical experience of this matter and have to rely on the experiences of others, that is, the reported experiences of others, not even first hand incisive interface.

Now if you really really would like to frighten yourself as silly as you can, go and do it on a catamaran, because that is a vessel ideal for you to understand the principles.

Why are catamarans overwhelmed in big seas ?

Because instead of having just one stern to keep down and to maintain directional stability they have two sterns........double the trouble !

All you need is for one to lift and get caught and over she goes !

And when a cat is overturned it stays like that so make sure you have a proper liferaft EPIRB and all the kit before you go.

 

[Lady Campanula]

Now, now, children! This is too important a topic to let some 'aspertions-casting' get in the way.

Of course this is controversial. And there are differing experiences, different boats and conditions, and differing firmly-held opinions. The only value in posting them on here is the 'sharing', so that someone, somewhere, in time of need will remember some of this stuff and use it. Then come back and tell us about it.

Now, can we get back to the VIP issue? Spats, stamping of little feet and 'toys out of pram' are welcome - even expected - in The Lounge.

We're here for a higher purpose....

Chill!

 

[Phoenix of Hamble]

Now, now, children! This is too important a topic to let some 'aspertions-casting' get in the way.

Of course this is controversial. And there are differing experiences, different boats and conditions, and differing firmly-held opinions. The only value in posting them on here is the 'sharing', so that someone, somewhere, in time of need will remember some of this stuff and use it. Then come back and tell us about it.

Now, can we get back to the VIP issue? Spats, stamping of little feet and 'toys out of pram' are welcome - even expected - in The Lounge.

We're here for a higher purpose....

Chill!

+1

I still have a lot to learn on this subject, so am keen to take input from as many sources as I can lay my hands on.... I'll worry about sorting out the wheat from the chafe when i'm feeling a bit more educated on the subject!

 

[webcraft]

My understanding from reading the experiences of others is that basically no amount of weight will stop a single point device being thrown forwards by a big enough wave and that the JSD was designed specifically to address that issue.

My understanding also. The whole point of the series drogue surely is that is spans more than one crest/trough, even in big seas.

VO5 obviously had a very successful experience on the one occasion he deployed the seabrake, and I have no trouble with that. Why this should now make him the world's leading drag device expert is slightly harder to understand. There are several account of the JSD being deployed with at least equally sanguine results.

- W

 

[VO5]

My understanding also. The whole point of the series drogue surely is that is spans more than one crest/trough, even in big seas.

VO5 obviously had a very successful experience on the one occasion he deployed the seabrake, and I have no trouble with that. Why this should now make him the world's leading drag device expert is slightly harder to understand. There are several account of the JSD being deployed with at least equally sanguine results.

- W

The tow line of the Seabrake is 3 1/2 ships lengths. Add to that 10 ft of 5/16" chain. Add to that the length of the Y brace....and now the drogue at the end...... and the rig embedded and under tension.

Now how can this jump out of the sea ? How ?

And what makes you think that the sample incident I have recounted off Cape Hatteras purely to illustrate a point is the only single experience I have ewver had in 40 years of sailing ? What makes you think that eh, Webby?

What is it you people really want Webby, for you to be presented with the facts, or for you to have the opportunity to obstinately contradict just for the sake of it ? What is it you really want ? Wot izzit ?

Just like Boo you now ought to go out and experience howler after howler in really deep water as I have done over the years and then come back and tell us about it because I find what you have posted above is well, astonishing.

 

[VO5]

+1

I still have a lot to learn on this subject, so am keen to take input from as many sources as I can lay my hands on.... I'll worry about sorting out the wheat from the chafe when i'm feeling a bit more educated on the subject!

I'm sure you have.
Why do you think it is imperative to keep the stern down ?

 

[RichardS]

There is nothing you can do on the end of a line which makes any difference to the way the boat behaves except the following :

1. Change the magnitude of the force exerted
2. Change the direction of the force exerted

I have no experience in a real storm and am therefore interested in the discussion but isn't there a third factor, viz

3. Continuity of the force exerted

I think that V05 is saying that his Seabrake provides more continuity / constancy / consistency than other drogues.

I've no idea whether that's true, or indeed whether that's a good or bad thing but it might be relevant!

Richard

 

[Phoenix of Hamble]

I guess the stern needs to be kept down to...

1] encourage the wave to roll past the boat rather than pick it up and surf on its face

2] To avoid the boat 'quartering' and moving into a broach situation and presenting its side to the next wave

3] In extremis to avoid the boat tripping over its bow and pitchpoling

I therefore see a device that maintains a pull on the stern as a wave approaches either the boat or the drag device as being critical. As a logical thinker, I am struggling to see the reason why the seabrake performs that role in a superior manner to a JSD. I have sympthy with Boo2's position that basic mathematics gives that the angle of the line from the stern determines the direction of the applied force, yet remain open minded to the volume of the restraining force. For me right now, a JSD seems a better proposition, but as said, I remain open minded and will listen to any argument that causes me to analyse my thoughts more robustly.

 

[webcraft]

The tow line of the Seabrake is 3 1/2 ships lengths. Add to that 10 ft of 5/16" chain. Add to that the length of the Y brace....and now the drogue at the end...... and the rig embedded and under tension.

Now how can this jump out of the sea ? How ?

Easily. The drag provided by the line is small and the actual device is well under the length of a single wave, so in the right circumstances it can either surf down the face of the wave it is in or be thrown forward by a breaking wave, thus removing 90% of the drag. If at that point the yacht is on the face of the wave ahead of that she is then free to accelerate dangerously down the face of the wave. If you can't see that and see how the JSD was designed to counteract this by having an even drag all along the length of the device then I suggest a basic course in physics.

Your consistently arrogant and rude replies to people on here and your repeated claim that only YOUR experience is valid seem to me to be verging on a psychological problem or disorder, and until you have pulled yourself together and learned to communicate with your fellow seafarers in a more normal fashion I am afraid I shall take any of your tales or assertions with a very large pinch of salt - or more likely just ignore them altogether.

I would suggest that in future if people want to have any future discussions about drag devices without you ruining them then they should consider putting you on ignore for the duration of the discussion.

- W

 

[Phoenix of Hamble]

here's a video that illustrates where i'd be wanting some extra assistance from a drag device!

 

[VO5]

First Part.

I guess the stern needs to be kept down to...

1] encourage the wave to roll past the boat rather than pick it up and surf on its face

2] To avoid the boat 'quartering' and moving into a broach situation and presenting its side to the next wave

3] In extremis to avoid the boat tripping over its bow and pitchpoling

I therefore see a device that maintains a pull on the stern as a wave approaches either the boat or the drag device as being critical. As a logical thinker, I am struggling to see the reason why the seabrake performs that role in a superior manner to a JSD. I have sympthy with Boo2's position that basic mathematics gives that the angle of the line from the stern determines the direction of the applied force, yet remain open minded to the volume of the restraining force. For me right now, a JSD seems a better proposition, but as said, I remain open minded and will listen to any argument that causes me to analyse my thoughts more robustly.

Actually you have just beaten me by seconds by making this post.
I was going to ask the question "why is is imperative to keep the stern down?" to appeal to people here, who, like me, have had real storm experience, in the hope and expectation it would filter out the armchair sailors with a lot of opinion.

But since you are making the effort, I will explain to you.

When you observe a surfer on a surf board riding a huge wave, which way is the surfboard pointing ? Is it pointing up or down ? ...Have a good look...
You will see that the surfboard is pointing up.

The surfer knows ( intuitively perhaps ) that if he allows the surfboard to point downwards, he will lose control. This he wants to avoid at all cost, so the constant effort is to remain upright and not to lose control and to find a sweet spot on the board to stand on so that the board is kept pointing up, that is, so that the bow is not allowed to drop significantly below the horizontal level of the stern.

WHAT THE SURFER IS DOING, IS KEEPING HIS STERN DOWN.

The surfer knows, that at the bottom of the wave he is riding, there is a trough.

His requirement is to remain upright and in control, throughout. When he descends into the trough, his objective is to keep going.

He cannot keep going if his bow digs in.

His priority is to keep his bow UP, not down.

 

[snowleopard]

Your consistently arrogant and rude replies to people on here and your repeated claim that only YOUR experience is valid seem to me to be verging on a psychological problem or disorder, and until you have pulled yourself together and learned to communicate with your fellow seafarers in a more normal fashion I am afraid I shall take any of your tales or assertions with a very large pinch of salt - or more likely just ignore them altogether.

+1

 

[VO5]

Easily. The drag provided by the line is small and the actual device is well under the length of a single wave, so in the right circumstances it can either surf down the face of the wave it is in or be thrown forward by a breaking wave, thus removing 90% of the drag. If at that point the yacht is on the face of the wave ahead of that she is then free to accelerate dangerously down the face of the wave. If you can't see that and see how the JSD was designed to counteract this by having an even drag all along the length of the device then I suggest a basic course in physics.

Your consistently arrogant and rude replies to people on here and your repeated claim that only YOUR experience is valid seem to me to be verging on a psychological problem or disorder, and until you have pulled yourself together and learned to communicate with your fellow seafarers in a more normal fashion I am afraid I shall take any of your tales or assertions with a very large pinch of salt - or more likely just ignore them altogether.

I would suggest that in future if people want to have any future discussions about drag devices without you ruining them then they should consider putting you on ignore for the duration of the discussion.

- W

No. And I will explain to you why you are not right, later.

 

[VO5]

here's a video that illustrates where i'd be wanting some extra assistance from a drag device!

The problem there is that there is a huge sea running but with less wind.
Now look carefully and you will see that the boat is yawing, because it lacks directional stability, but fortunately the bow does not seem to be digging in. If it did, there would be serious risks.

 

[Phoenix of Hamble]

VO5,

I think we all get that...... we're not children, or inexperienced sailors....

The question is what device, in what position is best to secure the boat against the wave action?.....

We seem to have honed in on stern too but you have not, as yet, explained why a seabrake is a better proposition to achieve this than a JSD, other than talking about drag being proportional to the pull being exerted, which as a soundbite is OK, but needs explaining to me, as right now I don't see the benefit in that statement... and ignored the point about a JSD seeming to have the additional benefit of being able to negate the risk of being swept forward by a wave, or not being correctly placed to exert any drag at all.

 

[VO5]

Second Part.

A vessel which is towing a drogue ought to keep its stern down as a matter of priority.

An inability to sustain this can lead to broaching.

The broach occurs because directional stability is lost and the sea overwhelms the vessel and rolls it over.

A broach commonly occurs if the bow is allowed to dig in or if the stern is allowed to lift, or a combination of both, which are lethal.

When the stern is held down, the wave following gives the visual impression of trying to climb aboard but in reality passes underneath and lifts the boat.
This is a surprising experience at first until you get used to it. The boat now begins its descent down the face of the wave with the bow UP, so that when it reaches the trough, the bow does not dig in. Digging in should be avoided at all cost.

As the vesel is in the trough with the bow UP, it is already positioned for the next wave to lift it at an angle of advantage, and the cycle continues.

Synchronous with this directional stability is preserved because the drogue is capable of adjusting to the pull, remaining submerged.

The JSD exerts a pull that slows down the boat, granted.

It does not provide directional stability nor does it succeed in keeping the stern down. Nor does it adjust to the pull as the cones are fixed.

 

[Phoenix of Hamble]

so you keep saying....

but WHY does the seabrake exert a downward force where the JSD doesn't?
Surely if the angle is the same on the line basic schoolboy maths means that the direction of pull on the stern is identical with either device?

and WHY does the seabrake impart directional stability where the JSD doesn't?
directional stability is surely a function of ensuring the pull on the stern is maintained?... where I could see a strong argument for a JSD achieving just this by constantly having part of the device in operation, whereas the seabrake will lose pull when their is no load on it, thus allowing the stern to wander

You need to explain the reason for your statements rather than just repeat them over and over again.

 

[VO5]

VO5,

I think we all get that...... we're not children, or inexperienced sailors....

The question is what device, in what position is best to secure the boat against the wave action?.....

We seem to have honed in on stern too but you have not, as yet, explained why a seabrake is a better proposition to achieve this than a JSD, other than talking about drag being proportional to the pull being exerted, which as a soundbite is OK, but needs explaining to me, as right now I don't see the benefit in that statement... and ignored the point about a JSD seeming to have the additional benefit of being able to negate the risk of being swept forward by a wave, or not being correctly placed to exert any drag at all.

The Seabrake drogue evolved in Australia as the brainchild of an Australian captain and was designed by him and tank tested repeatedly.

It was found that any drogue whose shape is sharply conical will spin, simple.

But a drogue whose cone is less acute will not spin, but will not have the same drag.

Then therefore a new concept evolved, which was to use two cones, less sharply conical, rigged one behind the other.

Then it was discovered that these swelled and remained normal when the speed of the rushing water in the tank was altered accordingly and additionally, that the "double bottomless bucket" arrangement if you like, did not spin.

Already for a drogue not to spin is a huge achievement.

Then the diameters of the relative buckets in relation to one another were tweaked and tank tested again.

Now something new was observed, that the swelling of the cones was proprtional to their shape, their dimensional ratios and how far proportionately they were rigged, that is, how far or how near to each other they were constructed.

So over several years of tank testing and testing in the Bass Strait, the final design evolved before these became available. Bear in mind they have been adoped by the Australian Navy and The Australian Coastguard.

Thgis is because this drogue by swelling when extra pull is exerted on it will increase the drag when needed, as for example when carrering down the face of a wave, and will relax back to a normal double bucket shape in the trough.

So this is not a sound bite, it is a reality, but in order to appreciate it, it has to be experienced.

As for a wave sweping a drogue out of the water forward, I think it must be a myth. As my Seabrake is weighted by 10 feet of 5/16" chain and it is well dug in to the sea well below the surface I cannot see how this can happen.

I will concede it might be possible if not sufficiently weighted.

But there again, the manufacturer's instructions are very specific, and the result of extensive testing, in tanks, at sea, and for different vessels, in different conditions of wind and sea state combinations..