How to design and make humpback whale inspired surfboard fins

This is one big rabbit hole to tinker with…be warned!

The subject keeps popping up in multiple other threads and is so interesting to some that those threads end up getting de-railed.

Here is a starter:

The Tubercles on Humpback Whales’ Flippers: Application of Bio-Inspired Technology

The whale foetus and CT flipper imae is from the above research article.

Mr. Mik, did you ever want to try a high aspect ratio fin with an outline almost exactly like the CT scan flipper? I think it would look pretty trippy. I might give it a try.

These where designed after a picture. But the leading and trailing edges are so random that they play havoc on the foil. So I cleaned them up a bit for the fins in the last pic. I have also modeled a realistic Gal porpoise and real dolphin fins. I want to do sharks and orcas too. 



WAO you keep blowing my mind with your skills. What program did you create those in? 

I did manage to trick my cam software into cutting some curved side bites. I don’t think they will be as elegant as yours though.

  Yeeeehaaaawwwwwwwww.

 

For future  reference, Post 592, in this thread seems to be in the general range of posts which inspired this tangential thread.

https://www.swaylocks.com/forum/45240/show-us-your-home-made-fins?page=59

 

The undulation patterns/concaves behind the turbucles of MrMik’s fins, are the major reason I decided I would never try to hand shape a tubercle fin.  I’ve sanded enough Gwhale fins to know that achieving any level of accuracy by hand would be excruciatingly time consuming and to prone to error.

On first inspection I thought it would make the water too busy and be draggy, but actual use proved far different.

You guys should drag over some pictures of your work from that thread to have on the first page of this thread.

I doubt that the Humpback whale pectoral fin is necessarily the best planshape for our purposes as surfers.

Evolution finds ingenious solutions, but it’s a process and we might be the catalyst to move it along into the next big leap.

‘We are one’… as in: The life form on this planet is one, it constantly re-shuffles it’s genomic knowledge base between species and then adds something, makes it even better, by combining it with something that has proven it’s value before.

So I doubt that attempting to reproduce a ‘perfect’ Humpback pectoral fin will yield the best result.

But I’m all for analysing how they work, to then integrate it into something even better.

 

 

While this fin shape might be good for an application like the drive on a Hobie peddal kayak I doubt its functionality on a surfboard.  Also, my first thought is what if that fin hits you or someone else.

super interesting. i dont doubt the claims made by the testers of this fin.  also aggree with those above its possible the humpback whale fin may not be the most efficient for surfboards…i imagine the fins of an animal that makes sharp turns in the water would be better for shorter boards.  but most these animals use their flexible spine for propulsion as well so who knows… we have humpback whale season in maui and they can be seen doing some pretty radical ‘aerial’ maneuvers, swimming on their sides with one fin out of the water, etc…  they would need to have pretty efficient hydrodynamic features for that big of an animal to maneuver so gracefully/radical at the same time…(which is something a lot of us do aim for in our surfing…) .  and the length of their body seems to be more stationary compared to the wiggling motion needed for propulsion by smaller fishes and sea mammals. (another thought…is fin area:animal size ratio applicable to fin area:board size in some way maybe?).  also sharks have went through over 400 million years natural selection before the first whale evolved.  does that mean nature has ‘modeled’ their features to be more efficient hydrodynamically?  then theres the skin texture factor…certainly thought provoking…  i was looking at the sailfish for some ideas.  always stuck in my head when i heard ‘fastest fish in the world’…dolphins and sharks mostly come to mind sure…how about animals that take to the air, if airfoils are relatable? these hatchet fins and paddle fins kinda remind me of the wingshape of a bird…the wing shape changes when the bird pulls his wings in for ‘dive position’  for max speed.  look more raked out as opposed to the main body like a keel with cutaway, highly resembles hanalei fins H3 & H5 template…in fact the sail of a sailfish almost reselmbles the wing of a bird of prey(fast) flipped on its side…natures awesome…i need to lay off the pakalolo.  can o worms opened.  props to you for testing these things…

The planshape (minus the tubercles) is quite good I think, sort of an elongated spitfire wing, not that different than any upright HAR fin like the Wavegrinder or even your Gullwhale. The more rounded tip should actually lead to a more eliptic lift distribution, so less tip vortex. I think they’d display the same stall/recovery smoothness as any tubercled fins, but the irregularities or randomness of the leading edge bumps must induce more drag, or a lesser lift/drag ratio. Not as efficient or consistent as the smooth, human designed ones. 

I designed these just for fun but I’ll make a set as an homage to the whale, they’ll look awesome on a board or my living room. I was going to machine them today, had the stock ready on the cnc but someone dropped in with beers.

Well I spent some time with a cad program and managed to make this whale fin. I’m not sure what to call it, but I’m including the fin whose outline I borrowed and modified. I plan to cut one out sometime this week, although maybe not full sized. I made it 8" tall and its over 10" long.



I did not realise before that hammerhead sharks also have bumpy leading edges - a ‘cephalofoil’.

Certainly a candidate for hydrofoil experimentation.

I decided to have another crack at learning more about fluid dynamics, especially the Reynolds number.

I found some good resources and am starting to develop an understanding of it.

This video is very good and it will help you understand why a longboard glides so much better than a short board, because of length being one factor in the Reynolds number: 

Physics of Life - Life at Low Reynolds Number - YouTube  https://www.youtube.com/watch?v=gZk2bMaqs1E

This video by the same guy is also very good: Physics of Life : The Reynolds number:  https://www.youtube.com/watch?v=rtcpMK6NpLo

And I like this short article about the Boundary Layer: https://www.grc.nasa.gov/WWW/BGH/boundlay.html

Looking good, the leading edge wave looks well proportioned.

I admit I have a mental block with long chords at the tip but that comes from my flying time. Unpowered flight requires the most efficient designs that always tend toward the same principles. But I understand that the situation is very special with surf fins because they have several functions at the same time. They’re wings to capture the wave energy, rudders to control direction and stay up the wave face, attitude control devices through drag like the ribbon tail of a kite, and aerobrakes when suddenly pushed to high AOA. I think this situation is unique among the whole range of applications of foiled objects. That explains the wide range of unlikely plan shapes that have had success with surfers, but which would be ludicrous for a flying object. So it looks like all fin designs are a blend of compromises between all the functions cited above. The situation is so complex that there’s certainly many more successful plan shapes that haven’t been discovered, which is good news.

Here are the Reynolds numbers for a range of chord lengths used in fins at speeds relating to surfing. Numbers are rounded for simplicity. Usefull when searching for foil profiles on the net.

Chord Length        Rn

Speed: 3 m/s = 10.8 km/h = 6.7 mph

10 mm, 0.4 in.        30 600

50 mm, 2 in.          153 000

100 mm, 4 in.        306 000

150 mm, 6 in.        460 000


Speed: 5m/s = 18 km/h = 11.2 mph

10 mm, 0.4 in.        51 000

50 mm, 2 in.          255 000

100 mm, 4 in.        510 000

150 mm, 6 in.        765 000


Speed: 10m/s = 36 km/h = 22.4 mph

10 mm, 0.4 in.        100 000

50 mm, 2 in.            510 000

100 mm, 4 in.        1 000 000

150 mm, 6 in.        1 500 000

Edit: These numbers are for water at 20°C or 68°F. At 10°C/50°F you can remove 20% to the RN and 40% at 1°C/33°F just above freezing temperature. Surfers in the warm tropics benefit from more friendly Reynolds numbers ! I wonder if somebody here has surfed the same board with the same fins in the tropics and in really cold water, the difference should be noticable.

So basically the lowest Rn will be at the narrowest part of the fin at your lowest speed and the highest Rn at the widest, often the base of the fin, at your highest speed. Fins that do not taper much like the Gullwhale will have the same reynold number along the depth of the fin for a given speed.

If someone can tell me the max speed of a gun on a huge wave (70 km/h ???), I can add the numbers. 

That sounds like the ‘Extended tip’ McCoy Gullwing fin is pretty much the opposite of a tapering fin, with highest Rn in the tip area. 

So how do you use the Rn’s to decide on a foil profile?

I made one but apparently I wasn’t the first. It is unlikely though that with a hydrofoil you would need the kind of AoA at which the tubercle effect starts to kick in, all busy that you are to not pierce the surface. But to be able to take off at lower speed than a conventional foil then it can be useful, that’s the reason I tried it. 


Here is a link showing a laminar  flow chamber 

Starts at 4 min

looks fairly simple to make

https://www.youtube.com/watch?v=y7Hyc3MRKno

 

The whole of this youtube vid is worth a watch.

Turbulent flow is more awesome than laminar flow.

https://www.youtube.com/watch?v=5zI9sG3pjVU

How cool is the process called periodic vortex shedding 

Looks awesome!

But it’s more of a humpback hydrofoil than a hammerhead, wrt size and number of the tubercles. Maybe it matters? I have no idea.

Check out at least the dead fish swimming upstream at 14:37