Eric,
I think I discovered the 5 knots drag issue:
I played my HullDrag, Holtrop&Mennen, and Michlet:
HullDrag:
friction drag 38 lb
wave drag 132 lb
H&M:
friction drag 35 lb
wave drag 33 lb
Michlet:
friction drag 27 lb
wave drag 74 lb
Friction drag theory ITTC-57 for 15m² wetted area:
friction drag 30 lb
O.K.
There are no significant differences in friction drag estimations. Range 27---38 lb is due to surface roughness selected.
BUT,
This 5 kn for a 24' heavy weight ketch happens to be right at the "hull speed" steep upward slope. Only say 10% increase of hull length estimates radical changes in wave drag. Also beam/draft-ratio may be of importance? Michlet is most optimistic (too optimistic?), but even in Michlet the wave drag plot right at 5 knots is really steep. On the other side, my HullDrag seems to plot the wave drag slope at a little too slow speed area?
Thanks anyway for your interest, Eric! I normally estimated drag figures of long, narrow, and lightweight hulls, but never before of a heavy ketch.
redu
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