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Thread: Thin hulls have less wave drag than fat ones. Are you sure?

  1. #41
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    Default Re: Thin hulls have less wave drag than fat ones. Are you sure?

    I would love to know why he thinks he is able to "teach" everyone, while also being unable to accept logical arguments, backed up with evidence without melting down into rage rather than doing some legitimate "teaching"? The last thread he bumped up is a real gem too! He was called out almost immediately when he quoted incorrect rules of thumb regarding catamaran "size" VS stability. Tried to use logical fallacies to prove his case like usual, (argument from Authority) even when presented with actual proof from other professionals in the field.

    If I post my hobbyist level understanding of a subject on bd.net so it can be held up to scrutiny by the many highly trained and successful experts which frequent that forum, I expect exactly that. Scrutiny. My explanations may be confirmed so I know I am on the right track, or my ideas will be corrected in a logical debate backed up by evidence. Perhaps people that are already successful can rebut helpfully not only because they don't have anything to prove but they also actually know what they are talking about?

    No expert has told me I am compelled to believe them simply because they are an expert over there. Its laughable that someone with no real accomplishment thinks their statements should be held free of being constructively criticized, yet accuses others of being arrogant, while real experts seem fine with responding with actual relevant advice.
    Last edited by dennisail; 13th January 2015 at 06:33 AM.

  2. #42
    Join Date
    Nov 2013
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    Brisbane AUS
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    419

    Default Re: Thin hulls have less wave drag than fat ones. Are you sure?

    I just checked Skenes Elements of Yacht design (which BigCat only added later in his edits). I can not find any mention of the claim high Cp hulls have more wave resistance. I am only human, so I may have missed it.

    Which page is it?

    I doubt I will get an answer to that. Providing evidence is much harder than using logical fallacies. The book is 111 years old, and although that does not mean its not a great book still today, there are more relevant sources of information out there on this subject. Like the following.

    http://eprints.soton.ac.uk/46460/1/086.pdf

    This paper done by the University of Southampton is literally EXACTLY on the subject of prismatic coefficient in high speed catamaran hulls.

    And I quote paper page 10 (pdf page 12), paragraph one, which talks about catamaran hulls.

    At higher speeds there is clearly a lower wave resistance for 5e
    5e has the highest Cp of the hulls tested.

    Also a few wild card tests where thrown in where the DLR was changed as well. Article 6.7.1 mentions how "overriding" the importance of DLR is to the residuary resistance compare to Cp. Residuary resistance is the leftover resistance after frictional losses are subtracted, and consists overwhelmingly of wave making resistance.

    Also my interpretation of the results seem to show the opposite of the old chestnut you hear so often circulated "low Cp creates more resistance at high speed than high Cp does at low speed". The results appear to me to be not exactly like that at first glance. The tests seem to show that the hulls with a non optimum Cp have a lot more resistance at low speed, and the low Cp hulls do have more resistance at high speed, but the difference is not huge.
    Last edited by dennisail; 13th January 2015 at 09:31 AM.

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