Jimi,
I have no other option then to say in so many words :"Your text book is wrong"
Numerous counterexamples are available, ranging from full sized high speed marine fregats (ever saw such a boat planing ?) to beachcats.
Your text book is providing you with a particular intepretation of Froude's Law that really only covers a particular part of the real world. Pretty much only heavy displacement hulls of low prismatic hull ratio.
What the book should have written is that a displacement hull travelling at a speed equal to 1,33 * the root of its waterlength will experience a relatively dramatic change in its growing wave-making drag. In some displacement vessels this sharp increase is so big that it prevents the vessel from travelling through the water much faster. Other displacements vessels were the total amount of wave-making drag is only a rather small of the total (beach cats) will no be held back by this increase. The reason for this is that a doubling of a 40 % drag component is really significant while a doubling of say a 15 % component is relative small compared to the total. Beach cats and Modern Navy frigates fall in the last category.
In effect the max hull speed law is nothing more then a speudo-scientific intepretation of the Froude law which only describes what happens to wave-making drag at a certain hull speed.
If you say that the waterlength for the Taipan 5,7 is 5,7 meters, that gives a theoretical top speed of 6,07 knots. This book is written by Anders Endal, a professor in Marine Technology and a legend at the department.
I don't care much for the title of professor. In my time at the university I've seen professors making the biggest of dumb mistakes. The simple fact that the Taipan 5.7 easily travels faster then 6.07 knots disproofs the max hull speed law in the way you have worded it. If prof Anders Endal did indeed word it in the very same way then he too is wrong. No-one will be claiming that a Taipan 5.7 travelling at 10 knots is in planing mode, you yourself can confirm that. Just like at how the hulls travells through the water at this speed.
Please understand that I'm not at all questioning your knowledge of hydrodynamics Wouter,
Don't worry Jimi, I'm not made of cake. I can handle my fair share of abuse (not that you are given me anything of that at all). I've had discussions with many people were the discussion have gotten alot more heated. Also I'm not unfallable either, I fully expect to be put in my place when I say something that is scientifically wrong. However in this particular case I'm certainly not wrong.
... His knowledge of hydrodynamics is great, ...
That may be his reputation, I don't know. However, are you sure that you inteprete his writings correctly ? If his writings are exactly as you presented them then I fail to see the thruth in his reputation.
I am simply stating that the myth as you call it of theoretical top speed of displacement wessels is something that marine engineers at the Norwegian University of Science and Technology learn in their first year as marine students...
I understand, hell even my own universities textbooks were less then thruthful on this subject. I had maritime courses during my studies. Later on it turned out that they knew better but thought it too much to burden the young students with the truthful situation. I think this to be on the border of what is acceptable. It would have been alot better to describe the law not as a law but as an intepretation that was only valid on a limited numbers of cases. How difficult would that have been for young students to understand ? We must give the youngster some credit, they are smarter then we
often think they are.
Jimi, if you ever see a discussion about the jib slot effect then you can again expect to be taught a myth, much like this max hull speed law.
If you really want to learn then read Marchajs book or Frank Bethwaite book or the writings of Arvel Gentry. These writers have gotten it right on max hull speed and jib slot effect.
Good luck,
Wouter
