Tubercles On Drive Fins?

Tom, thanks for bringing out a couple of very good points:
1. You never know for sure if something works until you try it.
2. Personal experience is more valid than armchair hypothesizing.

This has been a very informative thread with some excellent related applications that do apparently work and suggest possible directions for improving the fin operation. I haven't tried it out and it was premature to come across as dubious on the tubercle idea.

I'd much rather eat my words and get faster fins than be right. Please keep us posted on your progress!

PS. Here's one in a series of failed experiments on camber enhancement and boundary layer energizing -- a different approach than tubercles to a similar concept. It was fun to try anyway!

Hope you don't try the same mod to your hull RR. Agreed that this has been an informative thread.

Just had a look at your whale videos Tom. Amazing stuff. Especially love the whale calling clip and the way it surfaces vertically up backwards. What was going on there ? Is that common ?

_________________


Don't take life too seriously................it ain't permanent.

Roadrunner, perforating Turbo Fins is a bold move indeed! I was thinking about putting blobs of 5200 on my old, original drive fins, which I don't use anyway since I got Turbo Fins. I am NOT messing up my Turbo Fins for this experiment. Hobie can do that!

Your post got my mind wandering on prop efficiency. Wandered over to cupped trailing edges on outboard props, then somehow got to vortex disruptors of various types on aircraft. There has to be a heck of a vortex at the tip of each Mirage Drive fin. I wonder if molding a little T shaped tip onto them would help? Only really practical on Turbo Fins, so I'm not trying it, but you seem to have some perforated ones laying around...

Slaughter, I'm not sure what you're asking. The whales generally like to be vertical when they sing, and they also stick their flukes up in the air and slap the heck out of the surface of the water.

No doubt it would. Small winglets on rudder tips work in much the same manner. Here's one on the Hobie sailing rudder:


I haven't figured out a way to do this with Turbofins though without snagging debris (seaweed, sea grass, reeds, etc). BUT I believe there is an alternative. Notice on your Humpback pec. fin picture, three qualities (aside from the tubercles) -- a good aspect ratio (length to width), reduced chord at the tip, and rounded leading edge at the tip -- all tip vortex reducers.

If you could rake the Mirage Drive fins forward, you would make some gains in similar ways.


1. increased overall length for a better aspect ratio (and larger swept area)
2. angled tip for smaller vortex generating surface
3. the raked forward angle improves the angle of incidence along the leading edge (tubercles appear to do this also)

Does it work? Yes, it actually does.

And there is more. Notice the conspicuous gap at the fin clew (above). By adding a link (I currently use jack chain) and using the clew adjustment feature, you can play with fin pitch and improve the AOA or optimal working zone of the fins (hypothetically pictured below in the oval zones):


There is a down side or two. It almost certainly voids any warranty on your Drive and it shortens the life of your fin masts and therefore the reliability of the Drive. Can't have everything!

No updates yet on the drive fins, but I did find another use for the otherwise-obsolete paddle on an AI. Makes a great dog rest!