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FangyFin MkII Theory for insomniacs

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Created by fangman 9 months ago, 20 Feb 2017
sailquik
VIC, 3572 posts
8 Nov 2017 1:16AM
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Questions Mr Fangman:

Have you seen any evidence of corrosive pitting on you oldest fins? Do you anticipate that this could occur? Do you think anodising would be a good idea?

Reason I ask is I have an fantastic aluminium assy speed fin made by Mal Wright way back in the mid 80's and it shows signs of pitting, even though it has been painted with 3d primer paint. I have to get it out every now and then and refinish it to prevent it progressing. It may well be a different grade of alloy of course.

fangman
WA, 611 posts
8 Nov 2017 10:35AM
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sailquik said..
Questions Mr Fangman:

Have you seen any evidence of corrosive pitting on you oldest fins? Do you anticipate that this could occur? Do you think anodising would be a good idea?

Reason I ask is I have an fantastic aluminium assy speed fin made by Mal Wright way back in the mid 80's and it shows signs of pitting, even though it has been painted with 3d primer paint. I have to get it out every now and then and refinish it to prevent it progressing. It may well be a different grade of alloy of course.



Ah, an excellent diversion from exam study Daffy :-) When the fins come from the foundry there are small amounts of pitting present. I have noticed they tend to be on one side only. I guess this has something to do with the temperature of the aluminium in this spot and the orientation of the moulds when poured. ( Someone who knows a lot more about casting, please jump in here :-). I think Fred's attention to detail and sprueing have resulted in Fred's fins having far less pitting than my originals. However, I haven't had Fred's handiwork for very long, so I can only really use the originals for assessing 'long' term change.

The Aluminium alloy I requested is from the 6000 series - I don't know specifically which one, it is a balance between various attributes; but hardness, corrosion and casting pitting resistance were paramount. At the moment with use in heavy weed the surface is holding up extremely well, with the weed appearing to polish the leading edge. Although the hardness of G10 and aluminium are not markedly different, there is no doubt the aluminium is far more resistant to weed wear and touch downs in the mud.

I cannot see any corrosion pitting in the fins yet. That may mean I need to get better glasses, but I did use cheap and nasty Bunnings barrel nuts that have corroded aggressively. I wonder if they have acted as sacrificial anodes. Fred's versions are tapped directly into the aluminium, so it will be interesting to see if there is a difference. Also, I seem to remember reading somewhere that, the higher the polish on the surface, the greater the resistance to corrosion.

One of the FF DIY'ers is investigating back yard acid-free anodising on his fin. I am really interested to see the results and long-term outcomes. In the early stages, I approached several commercial anodising companies. I did not proceed with anodising because the cost of the fin per unit would have doubled. One of the companies suggested because it was a cast aluminium, anodising was not possible. Another would not touch cast aluminium because it would 'stuff up' their baths, which is probably more likely the reason for the high per unit cost.

Finally, from the research I found, the effect of pitting on the performance seems to be less than expected. When I was investigating how to keep the flow laminar for as long as possible on a foil, I found a paper that concluded that whilst a perfect surface was best; pitting did not have the expected deleterious effect. The authors found that bumps in the surface were potent triggers for loss of laminar flow, but pits much less influential, and if the pits were not on the leading edge, they were inconsequential. Hence I have asked Fred to concentrate on making the leading edge as close to perfect at the expense of elsewhere on the foil.
So in short, all good so far, but time will tell.

fangman
WA, 611 posts
10 Nov 2017 10:27AM
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Woohoo a floor full of new toys The next batch of fins, 20,24,28cm, all hollow, have arrived. Some don't already have good homes to go to, so pm me if you want one. If you want them finished by me, you will have to wait until exams finish so I can catch up on existing jobs.



fangman
WA, 611 posts
10 Nov 2017 10:57AM
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Well that was quick. I have just sold out of the 28 cm hollow fins. Doh, I knew I should have cast more! If you are after a 28 please let me know and when I get an order for a few, I will pass it on to the foundry. ( I still have a heavily discounted 28 solid if you want to cut/drill it out yourself )

decrepit
WA, 7756 posts
10 Nov 2017 6:36PM
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Wow 30m to sell out, there must be heaps of needy sailors stalking this thread.

fangman
WA, 611 posts
10 Nov 2017 7:41PM
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decrepit said..
Wow 30m to sell out, there must be heaps of needy sailors stalking this thread.


I wish Decrep, but it was just the 28 cm version, and there was only four of those

fangman
WA, 611 posts
22 Nov 2017 8:37AM
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Fred has squeezed into his busy schedule a pour of a few 28cm fins for me. They should be here by the weekend. I now have a full compliment of fin sizes available again, so pm if you missed out last time. I have finished exams and will be devoting time to finishing existing orders. A big thank you for your patience :-)

www.fangyfins.com

Roo
535 posts
22 Nov 2017 9:04AM
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Probably a stupid question on my part Fangy, but has anyone just done a basic clean up of the fin after casting and tried it on the water. Would be interesting to see how much difference there is between rough and smooth.

fangman
WA, 611 posts
22 Nov 2017 11:56AM
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Roo said..
Probably a stupid question on my part Fangy, but has anyone just done a basic clean up of the fin after casting and tried it on the water. Would be interesting to see how much difference there is between rough and smooth.




Hey Roo, there aint no dumb questions on this thread :-). Choco asked the same question a while ago and I did not have a sensible answer back then. To the best of my knowledge no one has tried it yet. Part of the problem is that when you get the fin from the foundry, there is a bit of work to be done to fit the box section and fillet to achieve a snug fit. You also have to knock off the dags and trim the edges of the casting on the foil itself. At the end of that stage I always end up a foil with varying degrees of roughness, some areas are still virgin cast surface, some are 40 -60 grit like, and asymmetrical on each side. So I think from a practical point of view, the roughest finish you could try would be after you had done the entire fin with your first pass grit.
The problem I have, is that the bling is addictive. With each pass of each grit, the increase in the degree of finish, makes me want to do 'just one more' grade...and I end up with a shiny fin. My own worst enemy

waricle
QLD, 529 posts
22 Nov 2017 11:12PM
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The polishing part part once done needs to be maintained, that stuff they use on alloy truck bodies any good?

fangman
WA, 611 posts
23 Nov 2017 7:22AM
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I dont know anything about it, I will have to go and do some research...

pepe47
WA, 1019 posts
23 Nov 2017 8:17AM
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I think autosol would maintain it. Most motorcycle owners would be familiar with it.

pepe47
WA, 1019 posts
23 Nov 2017 8:24AM
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Roo said..
Probably a stupid question on my part Fangy, but has anyone just done a basic clean up of the fin after casting and tried it on the water. Would be interesting to see how much difference there is between rough and smooth.


Purely speculation here Roo, but a shiny surface should take longer to oxidise than a surface with minute blemishes. And should be easier to maintain.

fangman
WA, 611 posts
23 Nov 2017 8:44AM
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pepe47 said..
I think autosol would maintain it. Most motorcycle owners would be familiar with it.


Thanks Pepe

autosol.com.au/product-range/aluminium-polish-75ml-2/

decrepit
WA, 7756 posts
23 Nov 2017 11:17AM
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I have a feeling that the weed will keep most of the fin polished, maybe just the rear of the fin will need a bit of attention?

Jonski
WA, 9 posts
23 Nov 2017 12:46PM
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decrepit said..
I have a feeling that the weed will keep most of the fin polished, maybe just the rear of the fin will need a bit of attention?


Can't wait let the wife know "I'm off to polish my fin" before hooking the trailer up and disappearing for a few hours

waricle
QLD, 529 posts
23 Nov 2017 9:31PM
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Tried the 28 out on the 75wide slalom with a 7.3 koncept In marginal conditions. Didn't really get going till the second hour when the wind picked up a bit.


Once I got going the Fin was fine, didn't notice any assy and it felt good in the light conditions. I'm loving it. The weed we have is just floating sea grass but it's enough to slow down a straight Fin. Looking forward to trying it in some wind. So far so good.

ZeeGerman
48 posts
23 Nov 2017 10:00PM
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waricle said..
The polishing part part once done needs to be maintained, that stuff they use on alloy truck bodies any good?


Nevrdull will do the trick.
But watch it: this stuff is addictive and you might find yourself polishing kitchen untensils, motorcycle rims etc. for the sake if it.
www.ebay.com.au/itm/NEVR-DULL-Magic-Wadding-never-Polish-Metal-Auto-truck-house-cleaning-rust-shine-/121394360363vrdu

fangman
WA, 611 posts
28 Nov 2017 10:41AM
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Based on the emails I have got, here is the current version of the:

FangyFin FAQ

Why aluminium ?
It has the best blend of hardness to cope with weed, toughness to cope with touch downs, corrosion resistance, lightness, least damage to the wallet and 100% recyclable.

How fast will they go?
The fins were not designed to be fast. They were designed with lift and efficiency as the paramount objective. Expected top speeds will depend on your weight. For a keg monster like me, I can hold the 24 happily at 36 knots, and I think that may be close to its limits. The 20 will happily exceed that but as yet I haven't had a chance to find out where its upper limit lies.
What size sail?
I have some really rough estimates based on my experience and that of fellow sailors:
20cm < 6m ( I have used a 6.6 okay, and Swindy used a 7.1!)
24cm 28 cm < 10. (My biggest sail is a 9.5 Race and it was fine)

Do I need a gasket?
That depends on your board rocker. I designed the fillet with enough thickness that it should be able to be shaped to fit most rocker shapes in front of the fin box.However if your boards have different rocker shapes you will need a gasket. I am using a very thin layer of silicone/silastic, but adhesive rubber tapes can be very effective when a greater amount of variation is required.

What about the surface pitting?
For the most part these have little or no effect. You can spray the fin using Dulux etch/primer, then a spray putty and sand back if you want a perfect surface.

What if I strip the thread ? I have changed my mind on the direct tapping because of concerns about corrosion, differences in Tuttle boxes and long term thread wear. Currently I am trying Delrin rod. Very cheap on Ebay to make barrel nuts and epoxy in place.

I like the fins but can I have one made in a different size?
Yes, but you need to be seriously loaded. The cost to develop and tool up for each fin is approx $3000. I would suggest instead you buy the next size up and trim the tip in a horizontal line to the length you want. Get in touch for hints on shaping the foil at the tip.

Can I change the foil shape?
Yes, there is plenty of latitude in the aluminium thickness to polish a thinner foil. However be aware that casting the hollow is really difficult and it is often not located dead centre of the fin, so one side will be thinner than the other.

What finish is the best?
I have a family of girls and they tell me there is no question that a shiny bling finish is the best. A highly polished surface does resist corrosion better, is slightly harder and easier to maintain. Whether its faster is a debate for another thread. However, the fin was designed for lift efficiency, not outright speed, and has the aim of keeping a laminar flow for as long as possible. i.e. getting the most lift for the least drag. A highly polished surface does this better.

What is the website address?
The webserver is a very low capacity virtual unit ( loads slowly) and it's a very basic site that may not run very well on mobile devices. As I learn more about this stuff I will improve the site and its capacity.

www.fangyfins.com

fangman
WA, 611 posts
29 Nov 2017 9:17AM
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FangyFin FAQ


What size sail?
I have some really rough estimates based on my experience and that of fellow sailors:
20cm < 6m ( I have used a 6.6 okay, and Swindy used a 7.1!)
24cm 28 cm < 10. (My biggest sail is a 9.5 Race and it was fine)





Hmm a few typos there - Take two:

What size sail?
I have some really rough estimates based on my experience and that of fellow sailors:
20cm < 6m - I have used a 6.6 okay, and Swindy used a 7.1!
24cm < 8m - I have used my 8.5 - it was ok, but upwind ability was lacking.
28 cm < 10 - My biggest sail is a 9.5 Race and it was fine.

sboardcrazy
NSW, 6027 posts
29 Nov 2017 1:01PM
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fangman said..


FangyFin FAQ


What size sail?
I have some really rough estimates based on my experience and that of fellow sailors:
20cm < 6m ( I have used a 6.6 okay, and Swindy used a 7.1!)
24cm 28 cm < 10. (My biggest sail is a 9.5 Race and it was fine)






Hmm a few typos there - Take two:

What size sail?
I have some really rough estimates based on my experience and that of fellow sailors:
20cm < 6m - I have used a 6.6 okay, and Swindy used a 7.1!
24cm < 8m - I have used my 8.5 - it was ok, but upwind ability was lacking.
28 cm < 10 - My biggest sail is a 9.5 Race and it was fine.


I didn't think you needed a sail over 7m in WA..

Stuthepirate
WA, 3146 posts
29 Nov 2017 1:21PM
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^^ Have you seen the size of Fangman

fangman
WA, 611 posts
29 Nov 2017 7:07PM
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Stuthepirate said..
^^ Have you seen the size of Fangman




Peeps will you ever learn?
Again, ala Seinfeld's Soup Nazi,
'No Fin for You...Stu'

R1DER
WA, 990 posts
3 Dec 2017 8:07PM
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fangman said..
With the success of the FangyMkII seeming to be something other than my imagination, I thought I had better start a new thread and explain my thinking for all the souls who have trouble sleeping. Nothing in this fin is original. To paraphrase the famous quote, I simply stood on the shoulders of giants to peer a little further in the direction of improvements that could be made in fins designed for shallow and weedy water. Thank you to all those fin gurus out there who were email stalked or pestered by me. I would particularly like to acknowledge the help of Wolfgang Lesssacher who was generous with his time, sharing his vast experience and knowledge. This fin is an amalgamation of the wealth of knowledge that was shared and in a small part, a tribute to the boffins in the windsurfing community.



My starting point was to consider the fin and board as one in a hydrodynamic system, rather than concentrating separately on what makes a board fast and what makes a fin fast. The final design is not a supercavitating design and I am not expecting it to be really fast. What I wanted to create, was a fin that worked in moderate breezes to provide enough lateral lift to allow good upwind sailing and then perform predictably and safely on the downhill in heavy weed, shallow water and small chop. At the moment the upwind legs and spin outs on a conventional 55 degree fin are frustrating at times, I wanted to solve that problem. So the brief I gave myself, was a short, high lift fin that was reasonably slippery.

After a lot of researching, reading scientific papers, watching videos of fluid dynamics, my solution was the MkII. A fin designed for the everyday conditions, rather than the epic days, but with increased hydrodynamic design efficiencies to allow comparatively good speeds in less wind. All that follows are my conclusions and they maybe considered alt-facts only. The designs have not been tested scientifically, so this is an opinion piece. There is a good chance your opinion may be different.

The increase in efficiency is primarily from reduction of energy loss from cavitation. My solution was to try to keep the flow laminar for as long as possible and reduce sources of cavitation. In considering the board and fin as one, I looked for research showing the interaction between a foil and a flat surface. Happily the US military, did a bit with their hydrofoils. There are some videos showing that the junction of the foil and its support, cavitates very easily and early at the leading edge. This is made worse with decreasing depth. A windsurfing fin is immersed, but only just, so it presents the worse case scenario for cavitation. Their research showed that a blended fillet, 6% radius, of the chord was the most effective way to reduce cavitation. So the fillet on my fin was born.





The extension of the fillet to the front serves also as very effective weed catcher stopping weed getting underneath fin. The broad base stops pressure marks/ damage to the board surface where fin touches.
The cut out is a result of Wolfgang Lessacher's work and observations of fin behavior in real time on the water through a plexiglass surface panel. I used this in conjunction with the aforementioned research papers on hydrofoil behaviour that clearly showed that the junction of the board and fin created interference pressure and as a result cavitation starts very early on the leading edge. This cavitation plume, plus any air entrapped between the board and the water may join with ever present trailing edge surface cavitation. The resultant supercharged cavitation then rapidly progresses forward across the foil and engulfs the entire surface. This is spin out. Wolfgang showed that, with the fin at an angle of attack 10 -15 degrees, the cut out swept this plume to leeward before it had an opportunity to attach to the trailing edge.



A front view of the Fangy MkII shows a large taper from base to tip. This allows very strong and hollow aluminium design. However its main purpose is elsewhere. Research shows that only 15% of the total drag is from the fin. A much larger portion of the drag comes from board contact with the water. The fin acts like a very sharp v-hull speedboat, so as speed increases there is a small amount of span-wise thrust pushing down the fin, which in turn pushes the board up and reduces the draggy wetted area sooner. This effect is self limiting. The fin might have more drag than a conventional shape, but its ability to lift the board and reduce the much greater wetted area drag more than compensates for this.


The leading edge itself, is very highly polished but blunt. It is highly polished to remove as many cavitation triggers as possible( this applies to the entire foil surface). It is blunt for several reasons: The first is to create a bow wave ahead of the fin. The intention is to try and push the weed out of the way with water pressure rather than let it abrade the fin itself. The second is to create more lateral lift at lower speeds allowing transition to planing to occur sooner. The third is to provide a speed boat bow effect and create thrust down the fin to push the board up. The effect being earlier planing because of reduced wetted surface drag. Consequently, it is expected that making the fin finer in entry will not improve its performance, rather it will be detrimental. There is one piece of research that shows the fillet does contribute to this effect also, albeit only in a small amount.

The elliptical outline is theoretically the most efficient wing shape. The leading edge is shallow ellipse, the trailing edge a deeper ellipse. Inspiration was drawn from what is regarded as the most beautiful wing design ever, the Supermarine Spitfire. The rake varies from 50-55degrees over the ellipse. Extensive crash testing has shown this is the minimum rake that weed-bergs can be safely tackled. And finally, the foil has a long roof with mid point a long way back to encourage efficient laminar flow for as long as possible.

So all that remains now is the tweaking of design and trying to get the foundry to cast them hollow. Stay tuned for updates. Oh and congratulations for staying awake until the end!


Great read, very interesting. im a bit late but Thanks.

fangman
WA, 611 posts
3 Dec 2017 9:14PM
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Glad to hear it R1der, and I hope you sleep better because of it
See StuthePirate, that's how you do it

decrepit
WA, 7756 posts
6 Dec 2017 9:04PM
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So did somebody ask how well FFs gybed?
If so here's Swindy had a 26 alpha today using a 20
www.gpsteamchallenge.com.au/sailor_session/show?date=2017-12-06&team=2

fangman
WA, 611 posts
6 Dec 2017 10:02PM
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decrepit said..
So did somebody ask how well FFs gybed?
If so here's Swindy had a 26 alpha today using a 20
www.gpsteamchallenge.com.au/sailor_session/show?date=2017-12-06&team=2


It was a pretty good session for the FF20 alround today.

sboardcrazy
NSW, 6027 posts
7 Dec 2017 1:17PM
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I've got my demo 24cm to try and if it copes with Budgy weed it will be available to test ( if you can pry it from my fingers.. ) . It's a solid version so not the same as the production ones,..it's a weapon and as it's solid quite heavy!
So I reckon I'll win the Budgy cup this month..I can either hit contenders over the head with it or run through their boards till there's no competition left..

Swindy
WA, 78 posts
7 Dec 2017 11:54AM
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Either option above will work well, just don't drop it on your toes when removing it from the board.
yes the solid proto is heavy and you do notice the weight in lighter winds but once you are nicely powered up the lift generated negates the weight and the upwind ability and grip come into their own and if you get seriously overpowered it will try to break your ankles as I found out in a squall.
Go smash some bergs and have fun.

fangman
WA, 611 posts
Friday , 8 Dec 2017 10:01AM
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This is Hardies review in the Gear Review Forum of the FF24 from last week. I thought I would re-post it here cos it gives me a serious head swell. Since then we have both been able to give the FF20 a run and given we both got PB's I think he was pretty happy with the FF20 too

" Just got my Fangy Fin 24 yesterday and had 2 hrs out on it, so here's my review.

First thing you notice, is that it planes immediately like a normal fin, unlike the Delta Fin's I have which need some momentum build up. This is a significant improvement compared to delta fins.

Next thing you notice is its upwind ability, it flies up wind at a decent speed. This also appears to be a significant improvement on the Delta's.

Weed: It planes through very Thick surface weed, this it does equally as well as the Delta Fins which was their strength. Enables you to sail in the thickest of weed, accessing the glassiest of water, which was never accessible with past weed fins. If you want to sail FangyLand, Albany Lilacs or Liptons and Point Grey, this fin is a must. In this area it's brilliant and the best fin of its type that I have sailed., , particularly for thick weed.

Speed: for the winds it felt moderately fast, you certainly don't buy the Fangy 24 as your clear water speed fin. For the thickness of weed I would rate it very fast. Particularly, given that most fins would come to an immediate halt. I believe there is a significant improvement on Deltas for speed.

Chop, wow, unlike the Deltas which would spin out easily particularly going down wind, these just hang on and give you confidence to keep going and going. Excellent and probably the most significant design and performance advancement here.

Toughness, I managed to smash a rock at decent speed, and was expecting it to be totally obliterated like a carbon or G10 fin would be with a similar impact. No....... just minor surface denting, which was sanded out easily by Mr Fangy, and looks as good as new!! Another significant improvement here.

I highly recommend this fin for thick weed, surface weed, shallow waters, and general weedy waters. Its been designed by a highly intelligent man, who did his research and made it come to reality. It meets its design brief perfectly and does everything well as intended.

I urge you to support this local developer/designer/producer/manufacturer.



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"FangyFin MkII Theory for insomniacs" started by fangman