Hydrodynamic quality comparison.

Hello everyone. What is a best way to comparison of hydrodynamic quality of two similar hull shapes?

 

Mmmm.. first I'd try to define "hydrodynamic quality", say as "the ability to carry a payload and a crew a specific distance at a given speed with the lowest power demand with acceptable accelerations and movements, including course-keeping, in a specific sea/environment condition"??

Major key qualities would then start with lift/drag ratio, vertical accelerations, roll and pitch in general and in resonance (if that may occur in the specific condition).

 

May be I am wrong. Simply I need to predict resistance for new ship from existing prototype I know resustance.

 

What you are describing is a simple scaling or geosim.
If the new ship is an exact scale of the original (a geosim), then it is a simple task to calculate.
If it is not an exact scale of the original, then it becomes a tad more tricky...

 

Simple scaling is too simple. Ship is similar, but with different hull shape…

 

"Ship is similar, but different......"!!
If the shape of both fit within the limits of a regression analysis of a known hull type, that might give an indication of the respective qualities. Otherwise a CFD simulation could be useful, starting with validation runs for the model with known performance.

 

Indeed.
I assume you can calculate the WSA, if so that is your frictional taken care of.
Then you need to find hulls which are the same or very close/similar to yours in the length-displacement ratio, with varying L/B and B/T ratios, to establish the residuary resistance.
Then you can make a very good approximation.

 

Yes, this is where the Taylor series or Series 60 data comes in handy. Blubs, however, complicate matters.

Edit: brain fluctuance 64 for 62 and back again to 60...as planing hulls were not mentioned

 

Look for MICHLET on BOATDESIGN for slender hull it seems to work fine