> On Nov 30, 2021, at 1:47 PM, Doug via CnC-List <cnc-list@cnc-list.com> wrote: > > This is the reason golf balls have dimples. Aides in better flight, less > resistance. > > >
Yes (if spinning) and No (as it adds lateral resistance). Going with a smooth surface is the overall best approach as it promotes smooth laminar flow. There are times when a ruff surface helps maintain laminar flow. For example, the dimples on a golf ball create a thin turbulent layer which drags air and helps keep the lamina flow closer to the surface behind the ball. The dimples add resistance to the flow but reduces the air wake behind the ball which reduces the overall drag force. The laminar flow around a smooth ball does not wrap around the back of the ball as well and leaves a larger wake. The larger the wake, the larger the drag. I think it would be foolish to add dimples or an orange peel bottom, unless you have the resources to model and measure the effect for a particular boat. Maybe adding some aft ruffness as the hull as turns inward, but this will strongly depend on the individual hull shape and likely have a positive effect at high water speeds (and a negative effect at low). Of course, a great way to reduce one's wake is to foil. Most may recall that dimples of a spinning golf ball help in another and bigger way by providing lift(i.e. aids in better flight). The spinning dimples drag air towards incoming flow and drag air away from the flow on the opposite side causing a high/low pressure difference (i.e. lateral lift force). This latter effect has not yet been exploited by sailors. Who knows, maybe we’ll see a spinning belted keel in the future driven by Kiwi’s pedal power. - Paul E. 1981 C&C Landfall 38 S/V Johanna Rose Fort Walton Beach, FL http://svjohannarose.blogspot.com/
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