I found I needed two cavities in the model to get pitch stability.  With a longer hull it seems reasonable to use more longitudinal cavities.  That way the side skirts can be lower and the hull able to handle larger waves without having a deep cavity.  

At present my two cavities are separated by ramps that would suit bi-directional operation but I expect the trailing ramp leads to more air entrainment at high speed than a clean transom between the cavities but with a ramp on the forward side.  I plan to compare the transom with the double ramp when I have the model going at higher speed.

With multiple cavities I do not see any benefit in using a foil to alter the surface profile under the cavity.  On a narrow hull a foil will have considerably higher drag for the generated lift than the hull alone so it is likely detrimental.

Rick

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