So, you're admitting this is just your way of starting a pissing match. I thought you wanted a fully formed argument. The references I gave you have all the formulas relevent to theoretically define how foils functions underwater. The experience that sold me was working as a boatyard manager on racing sailboats. In the seventies keels had fillets and very gradual transitions into the hull.In the 90's people paid us tens of thousands of dollars to optimize the fairness of the hulls and appendages on their boats. I worked with Allan Andrews, Dave Pedrick, Bill Lee and Bruce Nelson on several optimization programs. All of them wanted the keel hull joint as perpendicular as possible. During several America's Cups, tank testing, Bernoulli's Principal and the end plate effect that Greg refered to all changed the design of how keels were faired to the bottom of state of the art racing sailboats. And guess what they did away with the fillets. Fillets on appendages disrupt the linear flow of water across a foiled surface. The primary function on glass on fins is support, not flow.
No, that's my way of saying that you pointed me to dozens/hundreds of pages of stuff, and it was taking a minute or more per page to load on my screen... I'm actually interested and not trying to start a pissing match. I still would like to know which of all this info is most pertinent. I've never worked on yachts (other than sailing them) and I accept your design experiences as very valuable input... which I've never heard before now so couldn't very well have known about.
Try 11.2 in the first link I posted. It refers to efficienies of foils and describes end plate effect as it relates to tip vortices. But, the text as a whole has alot of good stuff in there. It's just hard to interpet without a degree in math.
End plate effect: I'll admit that this is an area of interest to me yet was not familiar with the term "end plate effect." Some quick study and I may be up to speed. The "end plate effect" reduces the drag caused by the high pressure flowing into the low pressure side of a foil: like a fin, sail, or wing. In surfing this probably occurs mostly at the tip of the fin and winglets/wing tips/Starfins can vastly reduce this induced drag. A sail on a sailboat best illustrates the "end plate effect." Since most sails don't reach down the the deck the air spills under the sail into the low pressure side. Sail skirts and lower booms are used to reduce this. The boat deck becomes the "end plate" of the sail. So when a surfer mentions "end plate effect" they are probably referring to induced drag caused at the base of the fin. A major cause of fin base induced drag would be FCS fins that don't fully connect with the deck. I see fin base drag being much less of a factor than tip vortices (at the top) of the fin. How would curved fins or a Bonzer board/fin combination effect what is called "end plate effect" or fin base induced drag? Greg/Tom/others my knowledge is incomplete; please fill in the gaps. Thanks, Rob Olliges
Sorry, I can't draw on this thing. But, picture the flow of water across a hull and around a foil as parallel lines(Bernoulli's Principal). The end plate effect that Greg is refering to would have lines remaining parallel to the hull closer into the base of the foil when the foil does not have fillets. On fins with fillets the lines closest to the base of the fins compress out away from the foil and produce a greater area of distrubed flow. As you get out towards the tip end of the foil without an end plate the lines spill over the end and reduce the effective length of the foil. But, fins have a trick in that they end in a gradual turned ellipse. This minimizes the cord length and consequently the amount of tip vortices for fins. Theoretically, you could shorten the depth of a fin if you added an end plate. In practice with surface turbulence and angular transitions, how short do you really want to go. 4-5/8" is not very deep. Malcomb Campbell was addressing the first type that I described years ago. They actually routed into the board and glassed the side fins on with minimal fillets. But, the tip end really does not address the second version.
Rob, We have been considering doing a longer travel center fin box. But, we have not gotten there yet. We may consider the wider base concept with undercuts. But, alot of the give, people experience, in fins has to do with how the fins fit in the boxes. With so many single fins already on the market, it would be self-defeating to make a box that only fit one fin manufacture's tolerance. But, the industry has too wide a tolerance across the board to make one box fit all fins snuggly.Consequently, some will be too tight and some will be too loose.
If you notice newer commercial aircraft, they have what are called "winglets" on the ends of the wings. These reduce drag, and help me here tom...these would be considered end plates? Only at the tip instead of the base,right? If you notice, especially on moist days,when landing you sometimes see a swirl coming off the wing tip. This is the air depositing off the end of the wing, and because the foil ends abruptly, the air comes off irregularly, creating drag. I think.
Do glass on fins stiffen the tail of the board? if so maybe the "speed and positiveness" that some people perceive as coming from some hydrodynamic effect is actually from changed flex pattern in the tail.
i still believe you guys could all try silicone glue as a tempory fillet to see what it does when you go for a surf tommorow! however i want to throw a design in that i tested recently and really like the performance increase! it called the C-DRIVE! i really enjoyed using it and on several of my boards... i actually dont enjoy any of my boards as much since one of the guys making them took his prototype back! ive posted a pic of the fin down the bottom on my fin page on my website .. i cant seem to put a pic up here direct. im still not sure what you guys mean about end plate effect but the trailing edge on this fin really gives a lot of drive and the rather reduced tip cuts drag considerably! http://www.feraldave.com
Dave - had a peek at the html in your post - you have to stick in the path to the image itself not the page it sits in. ie http://www.feraldave.com/Images/cdrivefin1.jpg