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KB
Knud Benedict
Dear Louis, I am very sorry that I could not be of help for you. Maybe I missed to underline in that movie that I was only focusing on the wind effect and took aside the small disturbances which need corrective steering – I found them not worth mentioning because I felt it would be self-understanding for professionals that this is obviously necessary. From my 45 years of experience in lecturing and simulator training for students to become navigators, and also for captains and pilots I know that there are two groups of professionals: those who are relying mainly on their “gut feelings” (and they can be very good at it), and those who try to understand the nature of processes and apply their knowledge to think ahead for avoiding critical situations (which you describes as “that made your hair stand on end”…) to be expected around the corner. And in that movie, I wanted to explain when bigger drift angle and another rudder angle is waiting for you after the next bend.
By the way: Your sample with the car is failing this most important effect I was talking about: If you would have very strong wind from abeam then even a car would need a drift angle and an additional steering wheel angle to compensate the wind effect – much stronger than the normal corrective steering you mentioned.
Finally I like to thank you for your offer to the academics / hydrodynamicists - I would be open for any remaining question and kind of ideas... Maybe you could have a look on our YouTube platform (search for ISSIMS) where are more movies which might be of help – the next one will be on wind effect on turning circles…
Best regards, Knud Benedict
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MP
Marko Purwin
Dear Louis,
I am an active marine pilot, and for me this video has a practical use! Therefore I would like to point out that you should not speak for everyone here ("basically this video tells us nothing at all"). I believe that the people on this platform are able to develop own opinions and assessments.
I have experience as an instructor and I know that it is a proven method to investigate effects first separately. Only after single effects/forces have been understood, it makes sense to become more complex (with your words "variable forces"). For example, if you want to train a boxer, you start with individual techniques and footwork before everything comes together in sparring. There are just different levels of professional development in training.
In our case of ship operations, mathematical theories and models make the difference between our ancestors in their rowing boats and today's modern technology. Such mathematical models are the accepted background of every modern simulation, no matter which manufacturer. In my opinion a denial of such models means the denial of scientific knowledge and stands for backward thinking.
If you have constructive ideas, questions and remarks, it could be an option for you to contact the author directly on youtube. Maybe he is even not aware that his video was posted here.
Capt. Marko Purwin
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LV
Louis Vest
If this is to be a forum for actual marine pilots there should be some practical use to a pilot for the information being presented. Basically this video tells us nothing at all. The basic failing point is that in an academic world one can put the rudder at a certain carefully calculated angle, hold that angle, and the ship will maintain course. Such an idea can only exist in a mathematical world. Variable forces constantly act on the ship nudging it one way or another and the heading must be corrected with opposite rudder to regain the course and then with a shift of the rudder to check the swing when the course is regained. This is a constant back and forth between the helmsman and the ship. Left only to her own devices the ship will get a little off, the forces change, she gets a little more off and you find yourself in a turn. If you think she will eventually find a stable heading you are mistaken. I have never tried it (being constrained by real world considerations), but if you leave the rudder in a constant position I suspect she will eventually settle into a large sine wave course many miles wide or a circle/oval turn. I know some that would quite quickly begin turning so fast that control of the vessel is lost.
For those who don't drive ships try driving your car with a constant steering position. Even on a desert road running straight and level for as far as the eye can see you can't just let go of the steering wheel and stay on the road. The driver is constantly making small adjustments.
Add to that the complications of narrow channels and an uneven bottom and you are already outside the known math models.
Lastly, every ship is different, every rudder is different and even the same ship can have an infinite variety of steering conditions depending on the current, wind, trim by the bow or stern and how deeply she is loaded. A pilot can come inbound on a ship and sail out the next day on the same vessel and she will steer totally differently.
If hydrodynamicists would like a useful project, give pilots a way to predict which ships will steer easily and which ones arrive at the sea buoy at the limit of controllability. I bet every pilot on this forum has had ships that made their hair stand on end. We only found out when making the first turn of the transit that she would begin turning sweetly but full over rudder was barely enough to stop her from turning. I have my ideas but it would be off topic. Let's see if any of the academics contact me about it.
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