Re: Resistance calculation

DELFTship forum Hydrostatics and stability Resistance calculation Re: Resistance calculation

John R. Coil

I’ve got a question about the Delft Series for resistance calculation: is there a limited range for prismatic coefficient that is valid for Delft Series calculations?

Marven stated earlier that it is for “sailboats” but my sailboats just seem to break the thing. Even without keels added to my model (with it managed to produce a literal figure-8 up and down the graph) it shows (for my last model) resistance actually decreasing between 8 and 9.25-9.5 knots. Sometimes these plotted shapes can be rather funky, taking a negative slope after the first peak has been reached. This seems usual for the somewhat high Cp hulls I’ve been producing (I seek to err on the side of having a Cp suited for hull speed based of statements I’ve read here and there … and a Cp of 0.6-0.62 should result in a SLR close to 1.3).

Fn is only around 0.4-0.45 for all the hulls I’ve contrived so I just don’t see the program ‘thinking’ that the thing is planing either.