Hi Mike & Rick,
thanks for the comemnts and thoughts.
I was familiar with the proa comparisons - but reading again was insightfull. Surprised to see that there was no/limited drag difference between equal-length-harry and HP - The rounding-up forces were not discussed.
Also like the beating to windward effect - although there is the question of what happens at the end of the wave... seems you would get the opposite effect - lw hull stays much longer on the passed wave. Guess specific comments from current HP sailors if it is indeed 'calmer' upwind is best answer.
So aligning drag and drive may be a separate topic including the question of narrower with waterballast may be a worthwhile thought exercise. (next to sail and rudder configuration).
and will see if I can find the ITTC friction formula.
--- In harryproa@yahoogroups.com.au, Rick Willoughby wrote:
>
> I have not checked your calculation however aligning drive and drag
> is a significant factor as you have determined. A harryproa gets
> forces close to being aligned when the ww hull is lifting. At other
> states the windward hull is trying to round it up. This can be
> counted with rig as well as rudders.
>
> The best way to analyse the performance of different combination of
> hulls, rigs and rudders is to generate polars using a good prediction
> model. There are are many interactions that are too complex to wrap
> the brain around unless they are dealt with sequentially in an
> iterative closed loop that can balance all the forces. As a first
> approximation the hull drag for a harryproa can be determined using
> the ITTC friction formula based on wetted surface and waterline
> length for the hull under different load states. My VPP approximates
> hull drag using a polynomial of best fit for data produced by Michlet
> over a range of displacements for each hull. This takes a few hours
> to generate.
>
> For a performance boat the ultimate speed is a bit easier to
> determine because the ww hull only contributes windage - no water
> drag. The righting moment is known so the maximum drive for a given
> point of sailing can be determined. The trim needs to be checked to
> ensure the hull is not bow down under the maximum drive. If there is
> moveable ballast such as crew on a small boat then this could correct
> trim. A light boat will have a tendency to plane if the sections are
> conducive to that state - just another complication or simplification
> if you are only interested in top speed potential.
>
> The preferred length of the lw hull may not be controlled by minimum
> drag but rather resistance to pitching.
>
> A flat bottom on the ww hull will result in slapping when it is
> lightly loaded. It is not an issue from hull loading perspective but
> could be reduced with some V in the bottom.
>
> Rick
> On 28/02/2013, at 3:22 AM, fvonballuseck wrote:
>
> > Baring stupid calculation mistakes and wrong assumptions it seems
> > that optimizing WW hull shape could change around 10% of total drag
> > and 10% of rotating momentum challenge?
> > Rick would it be a lot of work to guess/analyze what say the drag
> > curve of the WW hull of Harry is?
>
> Rick Willoughby
> rickwill@...
>