rick,
i very much like your starting point on hull design-- lw hull shape to minimize drag at high speed and high payload, ww hull shape to minimize drag at low speed and high payload.
i was surprised to find that with this design strategy, 250 kg hulls come out roughly the same length, just different shapes. this is about the displacement of elementarry. how would things scale up at 2500 kg, the size of visionarry? still the same length??
would you mind giving us details and the dimensions of your boat? LOA, BOA, etc??
as a scientist, who spends most of his time engineering new experiments, i very much appreciate the quantitative aspect you've brought to this discussion. thanks.
ben
--- In harryproa@yahoogroups.com.au, Rick Willoughby <rickwill@...> wrote:
> The total displacement is 250kg. Static condition is 200kg on ww hull.
>
> The shape of the windward hull is the lowest drag displacement hull
> for 6kts carrying 200kg having a flat bottom.
>
> The ww [LW?] hull is the lowest drag displacement hull for 200kg at 16kts
> with a flat bottom although at that speed and load it will be planing
> so the displacement aspect is somewhat meaningless at that point but
> it has to get there and above.
>
> The ww hull ends up longer than the lw hull for this size boat based
> on my starting point.
>
> The shapes are distinctly different and highlights the advantage of
> the proa configuration over a catamaran. The fine entry and long
> waterline length on the ww hull reduces wave drag in displacement mode.
>
> The full bow and deep draft of the ww [LW?] hull works to reduce wetted
> surface when viscous drag dominates overall drag at high speed. The
> full bow gives high KMl for the waterline length and the wave
> pressure at the bow creates buoyant lift once under way. This nose-up
> attitude assists transition to planing.
>
> Both hulls have narrow flat bottoms that will plane at shallow angle
> of attack once speed gets over 10 to 12 knots. This means the lift
> to drag is high once in planing mode. There is no hump to planing
> just a gradual transition.