Found this in Sailing Anarchy – Back to the drawing board.
Bulbous bows are designed to "cancel" out the hull's bow wave by inducing their own wave set that has the same frequency, but opposite phase, thereby reducing wave making resistance. To make this work, the boat's speed has be within a very tight specified range and the amplitude of the pitching moment has be relatively small to keep the bulb at the proper depth. Neither of these conditions can be met on a small-ish hull form. The additional wetted surface and form drag eats you up. Was tried in the 70's on 6 Meters and flopped horribly. From: dwight veinot via CnC-List [mailto:cnc-list@cnc-list.com] Sent: Wednesday, December 01, 2021 4:14 PM To: Stus-List Cc: dwight veinot Subject: Stus-List Re: Burnished bottom paint Would a bulbous bow below the waterline help On Tue, Nov 30, 2021 at 9:31 PM schiller via CnC-List <cnc-list@cnc-list.com> wrote: No, but we did add "turbulators" to the tail section of the GBU-24 Bunker Buster Guided Bomb to break up the boundary layer between the bomb body and the wing section, causing turbulent flow over the wings. Neil Schiller 1983 C&C #5-3, #028, "Grace" Whitehall, Michigan On 11/30/2021 6:05 PM, Graham Collins via CnC-List wrote: Indeed. You don't see dimples on the wings of aircraft, for a good reason... Graham Collins CS 36T On 2021-11-30 3:50 p.m., Dreuge via CnC-List wrote: 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/ Thanks to all of the subscribers that contributed to the list to help with the costs involved. If you want to show your support to the list - use PayPal to send contribution -- https://www.paypal.me/stumurray Thanks - Stu Thanks to all of the subscribers that contributed to the list to help with the costs involved. If you want to show your support to the list - use PayPal to send contribution -- https://www.paypal.me/stumurray Thanks - Stu Thanks to all of the subscribers that contributed to the list to help with the costs involved. If you want to show your support to the list - use PayPal to send contribution -- https://www.paypal.me/stumurray Thanks - Stu -- Sent from Gmail Mobile
Thanks to all of the subscribers that contributed to the list to help with the costs involved. If you want to show your support to the list - use PayPal to send contribution -- https://www.paypal.me/stumurray Thanks - Stu
