Ship resistance

Hello There!

I would like to ask you how you deal with calculating ship resistance and end up with choosing the best propulsion for it. You need to get an appropriate estimation to decide using sails or electric motor etc. What kind of physical and mathematical formulas and concepts comes into play in this stage of design thinking?

Thanks.

 

Not being a designer, I can tell you there are distinct and reasoned differences between sailing hulls and powered hulls. There are also examples of successful transformations of a hull from sailing to power only.

Within sailing, of which I am most familiar, but mostly as a sailor, not as a designer, there are differences in hull shape that are dependent upon the type of sailing. Cruisers, monohulls, planing hulls, fishing hulls, net boat hulls, bluewater hulls, thinwater hulls,... they all have good reasons for variation in design based on how, where, and who is sailing them and for what purpose.

 

There are several methods depending on Statement of Requirements (SOR), what type of hull, and how deep are your pockets. The propulsion type comes from the SOR needs. If you give us what type of vessel you are looking at, we could point you to an appropriate method.

 

Hm, seems we've been here before...

 

You are asking for a whole course in Naval Architecture and engineering. Please don't take this as an insult, but what is your mathematical background? You will need at least proficiency in calculus and statistics.

 

You can have a rought idea of how hull's drag changes with different beam & draft combinations.
if you find the famous: Serie 64 from the David Taylor Model Basin or David Taylor Institute ?
It was very useful for me when trying to make the beakdown of all drags for a beach cat.
The models at DTMB are 20 feet long so they are "model" for a destroyer or a tanker project but pretty appropriate size to guess-estimate small boat hull's drag.

Cheers

 

For long slender hulls you can explore the MICHLET freeware available on BOATDESIGN

 

You should go on with what types of boat you are going to analyze (range of speed, linesplan, dimension, range of load, and others).
Then you can choose which approach will you use. It can be empirical formula, CFD, or towing tank test or maybe combination of three of it.

The simple one is emperical approach but you should be very careful of the limitations of the equations. Experienced user will help you to do that easily.