Keel Winglets?

[hellosailor]

No really. I'm not talking so much about winged keels, because that's another "revolutionary change" that came and largely went. Either because everyone is afraid of burying one under a rock, or whatever reason, they never quite took over the market.

But I've been rereading Brian Hancock's "Maximum Sail Power" and he mentions the point that when all is said and done, there are ALWAYS vortexes coming off the ends of airfoils. And even modern jetliners have now pretty much all added "winglets" to cut down end vortexes.

Which makes me wonder...wouldn't a winglet, just a piece of 1/4" boilerplate or something similarly thin and strong, capping the end of a keel, really add to the performance by cutting down those tip vortexes? Not a huge thing, but just enough to do the hydrodynamics, break the vortex, and even be designed to break off if need be, without any serious complications?

[a64pilot]

Those are called end plates in aircraft design, and yes the do work.
1930's designs I think.
Google airfoil end plates etc.
However winglets etc are largely a fashion statement and only really have an effect at high angles of attack. Would you believe that a modern airliner cruises at close to stall?
At other angles they are parasitic drag. And even when they are functional the effect is minuscule. An elliptical wing like a Supermarine Spitfire works very well, but is hard to manufacture.

No free lunch, things like this work at very specific conditions, but other than those conditions are actually hindrances, which does not stop the marketing dept from throwing them on.

I think it's a similar argument as why modern sailboats don't have bulbous bows either

[hellosailor]

Close to stall? Let me guess, that's the most fuel-efficient. It used to be that if you wer eon the last flight of the day and they were late, the pilots would routinely firewall the throttles to make up time and keep the cattle happy. These days, I understand they get rated and scored on how much fuel they burned, and the cattle have no voice in the matter. (Good thing they've armored the cockpit doors, huh?)

I know TANSTAAFL, but wonder if anyone has actually run the numbers, either on a supercomputer or better in a tank, to see if there isn't still something to be found here. You know, like you'd have to be crazy to think about hydrofoil catamarans doing the AC.(G)

[Stumble]

Fundamentally they could reduce drag and increase lift. But it isn't as simple as just bolting a plate to the bottom.

First the winglets add substantial amounts of drag so you have to be very sure that the reduction in tip vortexes are higher than the added skin friction drag.

Worse for keels is the fact that as the boat pitches the wings will progressively drag the boat to leeward (when going upwind), and pull the boat deeper into the water (again headed upwind), so there are dynamic forces that need to allowed for. This forces you to sail boats with wings far closer to upright than without.

Basically they really have never been shown to be a benefit, have a lot of downsides, increase the damage if you do hit something, and are kind of an all round pain with a very minimal upside.


Winglets on rudders however are a different issue.

[hafa]

Originally Posted by Stumble

...This forces you to sail boats with wings far closer to upright than without...

Perhaps a wing keel like the one on our Hunter 40.5 is a different animal from what's being discussed here, but on a close reach, the 40.5 sails fastest when heeled over (to a point, of course).

[Captsteve53]

The latest theory is to manufacture rudders/keels with a "whale" type fin thus breaking up the "dirty" water flow (and stall), we recently fitted a new rudder with this design but have had no feed back as yet,

[Snowpetrel]

I fitted a small triangular end plate to Snow Petrels rudder. It worked remarkably well to improve the steering control. It may have increased the drag as well, but in this case it was well worth any trade off.

[UNCIVILIZED]

Originally Posted by Captsteve53

The latest theory is to manufacture rudders/keels with a "whale" type fin thus breaking up the "dirty" water flow (and stall), we recently fitted a new rudder with this design but have had no feed back as yet,

Icon sailing, a Perry designed Racer-Cruiser had such a rudder for a while, not sure if she still does or not. ICON Sailing

[Stumble]

Originally Posted by Captsteve53

The latest theory is to manufacture rudders/keels with a "whale" type fin thus breaking up the "dirty" water flow (and stall), we recently fitted a new rudder with this design but have had no feed back as yet,

Tubercles on rudders are there to help delay stalling the rudder. The science is still a little unclear, but somehow they help increase the stall angle. For surface piercing rudders they also act as mini fences helping to prevent leading edge ventilation.

I have not seen this applied to keels, though it could be out there.

[hellosailor]

Winglets and bumps on rudders...Wait, isn't that what they call "ribbed to increase your pleasure" on another product?(G)

Surely there must be government grant money available for these studies!