I will leave the numbers to someone who can do the numbers. I can't. However, there is a reason why every wing and foil that goes for high efficiency and high L/D is as long and high AR as possible and practical.   Arto --- On Wed, 5/25/11, Micha Niskin <micha.niskin@gmail.com> wrote: From: Micha Niskin <micha.niskin@gmail.com> Subject: Re: [harryproa] Re: Design your proa To: harryproa@yahoogroups.com.au Date: Wednesday, May 25, 2011, 2:11 AM   The depth-constrained condition here seems to result in the tradeoff of multiple foils with the attendant tip vortices vs. single, low aspect ratio foil. It seems possible to me that the induced drag coefficient for a single foil with aspect ratio of x might be greater than the sum of the drag coefficients of four separate foils, each with an aspect ratio of 4x. How would you analyze this? Also, induced drag effects must be balanced against structural and weight requirements, so maybe that influences the optimal design, as well. On Tue, May 24, 2011 at 6:42 AM, Arto Hakkarainen <ahakkara@yahoo.com> wrote:   Every foil, be it rudder, sail, wing, board, keel, whatever that has tip has also tip wortex. It is one of the reasons why multi mast vessel performs worse to windward than single mast (there are other reasons too). If foil generates lift it will also create tip wortex at the tip. Tip wortex adds to resistance. The added resistance which also adds fuel consumption has put airplane industry to work a lot to improve the wingtips in order to minimize the tip vortices. See more here:  http://en.wikipedia.org/wiki/Wingtip_vortices    Of course if your design goal is not maximum efficiency you may have better results with bigger number of shorter foils but the tip vortices are one design consideration.   Arto --- On Tue, 5/24/11, tsstproa <bitme1234@yahoo.com> wrote: From: tsstproa <bitme1234@yahoo.com> Subject: [harryproa] Re: Design your proa To: harryproa@yahoogroups.com.au Date: Tuesday, May 24, 2011, 2:00 AM   How so ? In what conditions? and at what cost? Cost to benefit analysis. Having four blades interconnected to work as one sure does have some merit in the way of handling ease and shallow draft. If it did work using all four of same size blades on Gardeners design. What would be the draw back. Would it even be noticed if there was a draw back. Todd --- In harryproa@yahoogroups.com.au, Arto Hakkarainen <ahakkara@...> wrote: > > four blades also get four tip vortex. > > Arto > > On Mon May 23rd, 2011 9:21 PM EEST tsstproa wrote: > > >I see, So shallowest possible draft while retaining overall helm balance in most wind cinditions. > > > >I would say Instead of the long shallow stub keel have you thought about using four steering blades instead of two? Have two leeward with two to windward. Might be able to gain a shallower draft with the four boards. > > > >Todd > > > >--- In harryproa@yahoogroups.com.au, Gardner Pomper <gardner@> wrote: > >> > >> This seems like a thread that might be able to answer a related question > >> that has been nagging at me for a while. I am mostly concerned with how > >> shallow the water can be for practical sailing (this would be, for example, > >> cruising off the south tip of florida, inside the florida keys). > >> > > > > >

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