# Additional resistance due to wave of 1.2 m height for a boat with a Froude 0.6

Discussion in 'Hydrodynamics and Aerodynamics' started by Surfer Naval Architect, Nov 11, 2020.

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### Surfer Naval ArchitectNaval Architect

Hello everyone,

Do you have a solid approach to calculate additional resistance due to waves height of 1.5 m for a boat with a Fr of 0.6?

Thank you very much!

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### DCockeySenior Member

Interesting question. Why specify the wave height and Froude number but nothing about the size of the vessel?

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### Surfer Naval ArchitectNaval Architect

Hi DCockey,

you are right, vessel size: L 38 m, B 7.5 m, draft 3.2 m

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### jehardimanSenior Member

Way too little information to even start. Wave height is meaningless without other period, spectra, and direction information. The answer could be anything from zero to the vessel is lost. Start with a copy of Theory of Seakeeping by Korvin-Kroukovsky or Dynamics of Marine Vehicles by Bhattacharya.

Edit to add; FWIW, normal sea margin is 20 to 25% See below
NTNU Open: Rational calculation of sea margin https://ntnuopen.ntnu.no/ntnu-xmlui/handle/11250/2453425#:~:text=The%20sea%20margin%20is%20an,in%20environmental%20and%20deteriorative%20effects.

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### rxcompositeSenior Member

I usually start with Fn to make sure I am designing at minimum wave resistance. For a given Froude number, I will be guided by ratios and coefficient, including waterlines, shape of hull, entrance angle, ect. There are many published ratios and coeff like Watson and Gilfillian lines. Lindblad and Todd, Saunders, MARIN.

Right away I can see that you are designing a very fast ship, more than the category of Naval vessels like warships. destroyer, and frigates. Your wavemaking coefficient is downhill but still high.

Wave height is the area of operation so you start with defining the length and displacement after the Froude number.

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