# resistance comparison between different hull lines.

Discussion in 'Boat Design' started by Brian.Lin, Feb 4, 2018.

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### Brian.LinJunior Member

dear all,
we have an idea to compare hull resistance between different lines.
we create a chart as follows.
X-axis is froude number.
Y-axis is kw/disp.
is it suitable for resistance comparison between different lines?such L/B ratio, bottom sharp...etc.

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### TANSLSenior Member

The resistance of a hull is a sum of components not all of which depend on the Froude number. Therefore the comparison that you intend, besides other possible considerations, will not be totally correct.
The best thing you can do is check, with some power prediction software, the resistance of all the hulls you want.

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### Brian.LinJunior Member

Dear TANSL,
our idea is coming from we have some existed vessels sea trial data and model test data.
but, they have different Lwl, Vs, L/B ratio....etc.
we want to compare the different lines and to judge which line is better.

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### daiquiriEngineering and Design

Question: how do you measure power?

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Better for what?...each boat has different parameters and only you can decide which is better given the ever changing parameters.

The design of a boat is greater than the sum of its individual parts....ergo...a design that has a certain L/B ratio, for example,...may be wholly unacceptable for another design - despite all other parameters being acceptable.

So, better for what:...seakeeping..carrying weight...speed...deck space...etc etc...???? Pick one or more..??!! then comparisons become very difficult.

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### Brian.LinJunior Member

Dear
thx for your opinion.and sorry for my misexpression.
our question focuses on hull resistance.

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Then you either need to ask a naval architect to show you, or, just look at any typical paper by Molland, where this is exactly what has been done, to highlight such features of a hull form series.

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### baeckmoHydrodynamics

That basis for comparison is not valid, since you use a non-dimensional factor for the X-axis, and a combination of dimensional factors for the Y-axis. A common non-dimensional unit for resistance evaluation is drag/lift (resistance/weight) ratio.

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