Weight/ displacement estimation

[dbierman]

Hello all, I'm new to the forum and also new to boat design. I have an engineering background and have read a few boat design books and want to try to design a boat but there are a few things I haven't found in the books.

Is there a way to estimate the hull weight/ displacement based on the desired length, beam and hull depth or would I have to go through and determine skin and scantling dimensions then add everything up to find weight and then go back to the hull lines to see where the load waterline would be?

[Grant Nelson]

It might not hurt to get Gerr's "The Nature of Boats", while not an engineering text, it is full of just the kind of estimates and general ranges for various design criteria you are asking about.

For your specific question, you would use the prismatic coefficient. I am surprised it was not in the books you read.

Prismatic Coefficient = Cu. Ft.Displacement / ( Midsection Area x LWL)
or
Disp. = PC x (MA x LWL)

PC for sailboats:
.54 and .56.

PC for powerboats
.60 to .70. leaning toward the higher side.

[Bito]

Parametric Analysis!

Go find boats on the Internet that are similar to the one that you are looking for. Make a plot of length versus displacement. Also, calculate length/beam and beam/depth ratios. For a given style of boat, these should be similar for all the boats. If there is an outlier, find out why.

You can go crazy and get 100 boats and really break down details like hull structural material, etc.