www.chocofins.com/range/flowing/

Chocoblock Weedcatcher

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elmo said..
Chocoblock Weedcatcher

Not as good as your foil but!

Makani makes a similar fin, supposedly they work pretty good, but I have no idea.

Great on a loaf of fresh bread!

I remember 3 or so seasons back i heard a 16ft skiff was doing this but never saw it so maybe they didnt. If you bother to google you may find wind farms info on it.
I was interested at the time but then forgot about it. Would like to try it

Yes .I SAW that.
It's a Bush design.

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JustinL said..
If you bother to google you may find wind farms info on it.

Google is your friend. They're called tubercles. Humpback whales have been exploiting the advantages for millions of years.

Lots of research going on. The advantages look like being real. Harder to manufacture than straight leading edges though.

en.wikipedia.org/wiki/Tubercle_effect

I recall AMAC trying them a number of years ago on Moth foils. From memory his conclusion was they worked at low speeds but not at high speed. Humpback Whales don,t do 40 knots. Interesting idea though and keen to see how they work out.

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mr love said..
I recall AMAC trying them a number of years ago on Moth foils. From memory his conclusion was they worked at low speeds but not at high speed. Humpback Whales don,t do 40 knots. Interesting idea though and keen to see how they work out.

Yes but the Reynolds number of a humpback fin doing 10 knots is greater than a windsurfing fin doing 40. And the Reynolds number is what you use for a best guess when scaling these things up and down. There's a lot of combinations and permutations to try out in tubercle spacing and shaping. Might still have promise? The whale might go slow but what's the tip speed when he flaps the flipper in anger?

Choco (Dani) should have read the scientific articles by Dr Fish before he made his fin.
Then he would have realised it increases lift by producing vortices which increase the AoA before stall. As there is a pretty much linear relationship between angle of attack and lift coefficient ( up until stall) then increasing stall from say 15 degrees to 25 gives a huge increase in lift. But slalom windsurf fins work at only a few degrees AoA. At that AoA the lumpy leading edge creates more drag and is less efficient. May work on the wave fin tho.

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I have a Slalom fin that now looks like that

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yoyo said..
Choco (Dani) should have read the scientific articles by Dr Fish before he made his fin.
Then he would have realised it increases lift by producing vortices which increase the AoA before stall. As there is a pretty much linear relationship between angle of attack and lift coefficient ( up until stall) then increasing stall from say 15 degrees to 25 gives a huge increase in lift. But slalom windsurf fins work at only a few degrees AoA. At that AoA the lumpy leading edge creates more drag and is less efficient. May work on the wave fin tho.

Yup agreed- and the last thread about them went this way also.

Shame they try and pimp this stuff and the scientists show them wrong.... its nice to hear from those who actually know the physics of this stuff.

So after the last 6 months I can see now I need a tubercle fin (made out of thermoplastic that is just as good as G10 apparently), in a peanut board that looks like a snowboard outline, with an MW sail.


Cos we see so many humpback whales snowboarding with a rigid foiled double skinned sail

Stick it with one of the golf ball bottom boards if you want to get seriously heckled at the beach!

I'll give him 15 out of 10 for the shirt, though.

?t=1

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Chris 249 said..
I'll give him 15 out of 10 for the shirt, though.

?t=1

Yup. The shirt is a winner.
Edit. Man! Those were the days.

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Ian K said..
en.wikipedia.org/wiki/Tubercle_effect

Wiki excerpt: "was analyzed extensively by Frank E. Fish et al in the early 2000 onwards".

Is this a wind up ? . Maybe it was Wanda or Nemo ?

One from Oliver for MxR back in 2013

Laird Hamilton has a semi-new line of boards (2015) that incorporate the serrated theory.
The "Surrator" board, would they work for windsurfing ????????

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JustinL said..
I remember 3 or so seasons back i heard a 16ft skiff was doing this but never saw it so maybe they didnt. If you bother to google you may find wind farms info on it.
I was interested at the time but then forgot about it. Would like to try it

I remember why i was interested in this type of fin now. It was for the Raceboard class and it was before the World Championship held in Australia. I was making sails for the class and ran out of time to test fins. BTW my sail design was well received at the event and later went into production, at the last national titles the sail won 10 of the 15 races!

In RB you can have 2 fins. RB race in all winds and often low winds. Humpback whale speeds i suspect. BTW i have seen a whale motoring along fast in Sydney harbour!! Not sure what species it was that day though.

I am designing a RB hull now so the fin has to wait but could it work for RB?

Do sailfish (allegedly the fastest fish in the sea) or dolphins have tubercles?

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yoyo said..
Choco (Dani) should have read the scientific articles by Dr Fish before he made his fin.
Then he would have realised it increases lift by producing vortices which increase the AoA before stall. As there is a pretty much linear relationship between angle of attack and lift coefficient ( up until stall) then increasing stall from say 15 degrees to 25 gives a huge increase in lift. But slalom windsurf fins work at only a few degrees AoA. At that AoA the lumpy leading edge creates more drag and is less efficient. May work on the wave fin tho.

Dr Fish references the wind tunnel experiments of Dr Miklosovic.
academic.oup.com/icb/article/51/1/203/636829



All you want is lift without drag. The open circles are for the foil with tubercles, solid for those without. 5 degrees sounds a bit high for a windsurfing fin. I've yet to see experimental results of the lift to drag of a windsurfing fin on this forum - or anywhere else? If no one can show an experimental curve beating an L/D of 24.5 to 1 maybe smaller fins with tubercles should be investigated. Just sail a bit more sideways? (Shouldn't bother those already comfortable using weed fins)

I didn't see Dr Fish as completely burying the application to windsurfing.

Confused... are we talking tubercles or testicles?

from the same article of the above graph...

The effect of leading-edge tubercles was investigated on the performance of two-dimensional foils based on NACA 0021, 634-021 and 65-021 sections (Johari et al. 2007; Hansen et al. 2009, 2011; Custodio et al. 2010). Foils with tubercles on the leading edge did not stall like foils with a straight leading edge. The best performance was observed for tubercles of small amplitude (Johari et al., 2007; Hansen et al. 2009, 2011). Stall was delayed to higher ? with CL over 50% higher for foils with tubercles compared to the baseline foil, but with greater CD in the prestall regime (Johari et al. 2007).The results on two-dimensional foil sections point out limitations for the use of tubercles under conditions in which the ends of a hydrofoil are bounded by walls or the hydrofoil is considered to be of an infinite span (Miklosovic et al. 2004; Johari et al. 2007; van Nierop et al. 2008). Tubercles have a largely three-dimensional benefit (Miklosovic et al. 2004, 2007). Foil sections with no wing tip that emulate infinite wings do not demonstrate reduced drag and increased lift, although stall is still delayed. Effects of the tip occur as a consequence of generation of lift when a fully three-dimensional wing is canted at an angle of attack to an incident flow. Induced drag is produced in generation of lift from kinetic energy imparted to the fluid from differences in pressure between the two surfaces of the wing as there is leakage of fluid from high pressure to low pressure around the distal tip of a lifting surface, resulting in spanwise flow and the formation of vortices at the tip (Vogel 1981). The flow pattern set up by the tubercles is considered to maintain a chordwise flow and reduce the induced drag due to tip vortices.

So at slow speeds and high angles of attack there may be a benefit. i.e. wave sailing or humpback whale turning. But slalom and speed fins operate at very low AoA where tip vortex induced drag is low.

^^^ Please don't say they may be OK for wavesailing.

I can see in another year or two I will need to buy 4 of the buggers to fit in with the in crowd.........

(Well, 12 of them..... )

Google Roy Stuart, he has been going on about these for years he was even selling 3d printed versions of these for surfing.. never caught on.. though he did sell one of his wooden boards for 1.5mil.....lol google it and the internet WILL tell you its true..

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mikey100 said..
Confused... are we talking tubercles or testicles?

Tubal ligations, not fast but worry free.

The same controversy in the bike world www.cyclingweekly.com/news/product-news/wheels-inspired-by-whales-dont-work-because-they-create-more-drag-302735

Zipp came out with the NSW 454 wheel a couple years back.

I know Danny was testing them in W.A. back in 2012/2013, from memory they were to eliminate spinout(don't quote me on that).
They looked like a foot/shin hazard to me