I am debating on experimenting with different keel configurations, specifically the wing keel. From my modest understanding of aero and hydro dynamics the greatest contributors to the induced drag created by a wing is the air that slips from the high pressure side of the wing to the low pressure side. This slipping occurs at the wing tips for airplanes, on the foot of sails (hence the deck sweeper headsail), and on the 'wing' tip of a fin keel i.e. the bottom. The slipping creates a circular motion that creates what are called tip vortices. The vortices can become quite large and significantly increase the drag created by the air foil. Is this basic description pretty much correct? My modest understanding of the wing keel is that they increase the hydrofoil efficiently by reducing the area where water can slip from the high pressure side to the low pressure side and hence reduce the tip vortex hence reducing drag. Much like the winglets seen on some airplanes. My Hunter 25.5 has a shoal fin keel which is a very low aspect ratio hydrofoil which allows a large area for water to slip from high to low and to create large vortices. I believe this is why low aspect ratio keels (and sails) are not as efficient as high aspect ratio keels. Well I have been thinking that it wouldn't be to difficult to build a plywood wing that I can clamp to the bottom of the keel for experimentation. I would fashion a wood block that would fit over the bottom of the keel and have screw in clamps, much like the clamps used on outboard motors. The wing section would be made from plywood and would be attached to the block that is clamped to the keel. Obviously this would not be a permanent modification, but could be used as a platform to experiment with the benefits of the wing keel design. Any thoughts? Is this a crazy idea? Thanks for all your comments.
- Status
Sounds interesting...
And much more fun than testing on scale models in a water tank or a CAD station! Maybe you should use something metal instead of plywood to cancel out any bouancy issues. It would be interesting to hear what (if any) difference you notice. Happy testing!
And much more fun than testing on scale models in a water tank or a CAD station! Maybe you should use something metal instead of plywood to cancel out any bouancy issues. It would be interesting to hear what (if any) difference you notice. Happy testing!
i'm all for experimenting so i'd say go for it as long as you can undo any modifications should it not go as you hope. while i've done nothing sailboat related i've done a fair amount of experimenting w/ RC model gliders. i certainly didn't reinvent the wing but i had a blast doing it all the same. the most applicable of my experiments would be the addition of wing tip plates which were 2x the size of the airfoil section. the result of this was that in straight flight i noticed a slightly better L/D but all that and more was lost while turning. i'm guessing that as the wing yawed the leading tip plate was made to mush sideways thru the air flow which caused a huge bubble of turblence. something to test would be if you are more slick on flat water and less slick in chop since your keel plate would see the same motion as you pitch as my tip plates did as i turned. either way it's going to be difficult to get a reading of the drag since it won't be practical to tow the boat w/ a spring scale as i did w/ the gliders. i have thought about this myself and hence started working a 1/5" H18.5. then i remembered back to college days and how complex the math can get when using scale models. good luck all the same --let us know how you proceeded and what you discover 
Tim Taylor "Carried Away"
Tim Taylor "Carried Away"Wing keel vortices
Be aware that another effect of a wing-keel is the degraded pitching performance of the boat because of the “trapped water pockets” on each sides of the keel creating a less-pitching boat and by that less overall drag when in pitching circumstances.
Be aware that another effect of a wing-keel is the degraded pitching performance of the boat because of the “trapped water pockets” on each sides of the keel creating a less-pitching boat and by that less overall drag when in pitching circumstances.
- Status