step design question

[BWD]

For those with knowledge:
In planing hulls with step(s), how is the curve of areas handled?

I've been playing around with models of stepped hulls in freeship, and found there can be a lot of tweaking needed to get a smooth curve of areas without a dip or notch matching the step.

Having no advanced design texts, I just assumed it would be "nice" for the curve to be smooth when the hull is running at the appropriate AOA....

Any kindly advice or guidelines appreciated!

[marshmat]

Hi BWD,

Once you're on plane, the curve of sectional areas that you get with the boat sitting still has little or no significance. I don't think you'd get much useful information out of a curve of areas at the operating angle of attack and waterline, either.

Much more important, at least from my limited understanding of step hydroplanes, is the height and angle of the step (must be chosen to get a bit of air in, but without creating any weird instabilities), the deadrise and angle of attack of each planing surface (not necessarily the same ahead of the step as behind it), and the placement and shape of any strakes, air induction channels, etc.

[BWD]

Thanks. I see.

I'd supposed the curve of areas, for a planing hull in running trim, might be a useful proxy for the lift from the planing surfaces.
And that this lift, like the buoyancy indicated by a curve of areas, ought to have a certain distribution, and affect stability, although the other factors you mentioned clearly have great weight, as far as I have read (which is not too far...).

So, modeling some hulls in freeship software, starting from published lines and photos, I made some observations, summarized in the sketch below.

Playing around with the models, I figured it was "better" to have smooth curves, though I have no idea how much importance this has to "real" boat designs, since other things affect lift and pressure more (my real design is limited to more humble canoes and surfboards!).

Any reading suggestions welcome, thanks again!