What is the blue filler you're using Swindy?

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ducati said..
What is the blue filler you're using Swindy?

Its west systems epoxy resin with a bit of dye mixed in. Then mixed up into a fairly thick bog using q cells.
The first one I done I added the hardener before the q cells, as the q cells take a bit of mixing in and it was a hot day it started to go off before I was finished and nearly stuffed up. So now I get it to the right consistency then add the hardener and another t spoon of q cell. Gives you more time to work it.

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Dezza said..
I had a go on keef's 17 delta fillet yesterday, only light wind and underpowered but it held well in deep choppy water and went upwind with no problems

Can see a PB coming Dez so far a 35+ and smokes to windward, upgrading the bunnings barrel nuts tomorrow

this HTML class. Value is https://www.gpsteamc
32knts not to bad for a 7mt and 17cm fin??

I've used" unkneedit " on my weed fin, I formed it on the board with some plastic conduit and once it firmed up took it off and sanded it smooth- easy peasy. I put wide sellotape on the board and coated it wth vasolene to stop it sticking to the board.

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waricle said..
I've used" unkneedit " on my weed fin, I formed it on the board with some plastic conduit and once it firmed up took it off and sanded it smooth- easy peasy. I put wide sellotape on the board and coated it wth vasolene to stop it sticking to the board.

That's a damn good idea, simple is good and just a trip to bunnings.

Yep, good thinking, you can churn them out by the thousands that way.

Interesting. I had seen the positive reports about the Fangy fin, but had not realized that the fillet plays a big role. Makes a lot of intuitive sense, though. The best normal weed fin I ever sailed was developed by CNC fins with lots of computer simulations (now sold by Tectonics as "Weed Demon"). The front-edge of the fin is rounded like a fillet, and I recall the designer mentioning that it is a very important design aspect. IIRC, the fin only has a 47 degree angle, but it sheds stringy weed very nicely, while other weed fins do not. It also had better spinout behavior than most other weed fins.

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boardsurfr said..
Interesting. I had seen the positive reports about the Fangy fin, but had not realized that the fillet plays a big role. Makes a lot of intuitive sense, though. The best normal weed fin I ever sailed was developed by CNC fins with lots of computer simulations (now sold by Tectonics as "Weed Demon"). The front-edge of the fin is rounded like a fillet, and I recall the designer mentioning that it is a very important design aspect. IIRC, the fin only has a 47 degree angle, but it sheds stringy weed very nicely, while other weed fins do not. It also had better spinout behavior than most other weed fins.

When Fangy handed me the proto type to test, I was dubious. I thought it would be slow ( fillets, and thick leading edge) and if it did go fast would spin out. But to say I was pleasantly surprised is an understatement!

So I was very interested in just what was going on, was it the lescacher rear cutout or the fangy fillet.
Having a couple of my own 55deg fins that were a bit "wishy washy" I endowed them with fillets, low and behold they became nice and solid.
So that's when it became obvious we needed to try fillets on a delta, to see if they would improve them.

I haven't messed about with the cutouts, I don't like the way they mess up the rear foil shape, and to keep a good foil is a structural nightmare, the point of max load becomes the weakest. But it may be worth trying on a delta if anybody wants more than the fillet offers

Iain has already tried it.

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sailquik said..
So your next marketing opportunity Fangy is to make plastic printed 'Fillet' 'shoes' for all of our current fins.

...and sell the range @ 'Fangy's Fillet O Fin Emporium'

Nice job legless

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pepe47 said..
Nice job legless

It was not me it was Iain work......but yes it looks like a really good job.

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Spotty said..

sailquik said..
So your next marketing opportunity Fangy is to make plastic printed 'Fillet' 'shoes' for all of our current fins.

...and sell the range @ 'Fangy's Fillet O Fin Emporium'

...which is slowly submerging in a pile of aluminium dust and polishing compound. But I do have forearms like Popeye now.

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fangman said..
...which is slowly submerging in a pile of aluminium dust >>>>

If you mix that dust with gunpowder you can make a really bright silver firework.

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decrepit said..

fangman said..
...which is slowly submerging in a pile of aluminium dust >>>>

If you mix that dust with gunpowder you can make a really bright silver firework.

Brilliant! It just so happens I have a bottle of gun powder handy, in the kids bathroom.

no, sorry, my mistake, it's a bottle of Baby Powder. I only really used that after brown explosions.

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decrepit said

"....So I was very interested in just what was going on, was it the lescacher rear cutout or the fangy fillet.
Having a couple of my own 55deg fins that were a bit "wishy washy" I endowed them with fillets, low and behold they became nice and solid.
So that's when it became obvious we needed to try fillets on a delta, to see if they would improve them.

I haven't messed about with the cutouts, I don't like the way they mess up the rear foil shape, and to keep a good foil is a structural nightmare, the point of max load becomes the weakest..."

If if anyone is having trouble sleeping, rather than hijack this thread, I have detailed as to why a Lessacher cut out is part of the design on the 'FF insomniacs' thread.

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fangman said..

If if anyone is having trouble sleeping, rather than hijack this thread, I have detailed as to why a Lessacher cut out is part of the design on the 'FF insomniacs' thread.

OK, I'm convinced, but I still don't like the idea, especially for my timber carbon fins.
Bbut maybe I'll pick one that I think will stand the strain and give it a try.

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Swindy said..
Also done a 21 and sanded it up this morning and now doing a more conventional weedie. Its a BP weed speed raked back to 50 deg actual length 22 and will sand it up tomorrow. Will be interesting to see how it compares to my custom 22 fangy fin.
This fin would normally be unusable in my 100L board but may just hang on now and the FF may still be a bit big as it still has the base and thickness of a 24.

How do you measure your rake angle?

The fin was originally 40deg and I re boxed it at 50deg. I use one of these $20 from bunnings . The reading is 40deg from the base of the fin so 50 deg from vertical.
Hopefully with the addition of the fillet it will increase grip enabling me to push harder on it to get back up wind.

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Swindy said..
The fin was originally 40deg and I re boxed it at 50deg. I use one of these $20 from bunnings . The reading is 40deg from the base of the fin so 50 deg from vertical.
Hopefully with the addition of the fillet it will increase grip enabling me to push harder on it to get back up wind.

Thanks for the info

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fangman said..
>>>> I have detailed as to why a Lessacher cut out is part of the design on the 'FF insomniacs' thread.

Hmmm very interesting vid, I'm going to have to rethink my theory of how the fillet works. I thought it was because of the spanwise flow along a highly raked fin. But those bubbles at the end plate aren't traveling down the foil, (which isn't really raked anyway). So why is there a much lower pressure at the foil end plate junction? Is it because the flow wants to go along the foil but can't because of the end plate?

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decrepit said..

fangman said..
>>>> I have detailed as to why a Lessacher cut out is part of the design on the 'FF insomniacs' thread.

Hmmm very interesting vid, I'm going to have to rethink my theory of how the fillet works. I thought it was because of the spanwise flow along a highly raked fin. But those bubbles at the end plate aren't traveling down the foil, (which isn't really raked anyway). So why is there a much lower pressure at the foil end plate junction? Is it because the flow wants to go along the foil but can't because of the end plate?

I will see if I can find a good animation of the horshoe vortex effect at an endplate junction in turbine blades - a picture might be worth a thousand words.

I found this on Junction Flows Horseshoe Vortex Dynamics, its very interesting reading IMHO:

arrow.utias.utoronto.ca/~ekmekci/research/Junction_Flows__Horseshoe_Vortex_Dynamics.html

Quote: "The drag induced by the wing-fuselage junction is estimated to be 10% of the total drag in modern civil airplanes. Hence, the design of wing-body junctions or empennage-fuselage junctions is important for aircraft makers."..

Why did we windsurfers not think of this before?

Your work on the delta-fillet makes very good sense! I will make one on my Delta19 also and test it!

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ClausF said..
I found this on Junction Flows Horseshoe Vortex Dynamics, its very interesting reading IMHO:

arrow.utias.utoronto.ca/~ekmekci/research/Junction_Flows__Horseshoe_Vortex_Dynamics.html

Thanks Claus, that's a nice find. I will get in touch with them and see if they interested in a collab for more research :-)

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ClausF said..
Quote: "The drag induced by the wing-fuselage junction is estimated to be 10% of the total drag in modern civil airplanes. Hence, the design of wing-body junctions or empennage-fuselage junctions is important for aircraft makers."..

Why did we windsurfers not think of this before?

Your work on the delta-fillet makes very good sense! I will make one on my Delta19 also and test it!

We did - metric-truck-load of testing: www.thereefjournal.com/files/7._Lavery_Foster_and_Carswell.pdf

Basically, there is a measurable difference - but it is on the order of a few percent (or less, when comparing the whole-board and not just the fins). But it adds a significant production effort, and the fillet needs to have "ideal contact" with the board (aka no edge or gap).

Mathew, were you're tests for standard speed fins, or highly raked weedies? Because there is a feeling here, that the lower the aspect ratio and the higher the rake, the more difference the fillet makes

First thoughts after reading the paper (remembering that it was done with a specific goal related to surfboards):

They tested at significantly lower velocities than windsurfers. Benefit of fillets seemed to increase as speed increased.

Even a 10-12% reduction in fin drag is very significant for a windsurfer. I think most fin designers would give their right arm for half of that!

Their figures of only about 3% overall reduction of drag (at surfboard speeds) is misleading for windsurfers. The opening paragraphs of the paper describe the 'degree' of planing of sufboards and it is much more in the planing/displacement transition stage than a high speed windsurfing board (not always a wave board though). The hull drag contribution is much higher in this transition zone, decreasing the contribution of the lower fin drag to overall drag. So fillets should have more (much more?) benefit to overall drag on a speedy windsurfer.

I contend that windsurfing fins at speed very seldom have more than a few degrees of angle of attack. certainly not 15-20 degree when planning with a suitable sized fin, so results on those high AOA ranges are meaningless for us. Next time you stand in front of a windsurfer traveling at speed directly towards you, , note the 'crabbing' angle of the board. That is the AOA of the fin. (It will also be noticably less with a good assy fin)

Hull drag can be slightly increased by a fillet, but far less than the decrease of fin drag produced by the fillet.

They showed pretty emphatically that, as I have always known, toed in angled Tri Fins (and twin fins) produce a LOT of drag. It's quite noticable even on a surfboard, but especially at higher speeds on a windsurfer. I have proved this to myself a number of times by removing the sidefins on my surfboards (and using a larger single fin) and especially by doing the same on a windsurfer. (It should be even easier to prove now with a good gps) The only advantges of the side fins are to increase grip in sharp turns and on a very steep wave face (same thing really) and maybe to help 'steer' the board on the inside fin in a turn. If you want more speed on the wave, get rid of side fins, or angle them more along the centreline axis of the board. Parallel twin fins may be good?

Decrepit. Without looking up the specific fin model they tested, I would guess that it was a pretty standard shaped surfboard fin which by windsurfing standards are actually pretty low aspect with a high rake leading edge angle, but not as low aspect and raked as a full on 'Delta' type windsurfing weed fin. They did no testing to show if the effects if a fillet are more, or less significant on very high AR fins, which is disappointing.

I might get some better insight after I have read it a few more times.

This post tells you a lot about how boring I am on New Years Eve!

Thanks for a very nice article Mathew.
I would argue that most (gps-speed)windsurfers can travel at twice the speed used in the experiments and that the total drag of the board is relatively irrelevant for windsurfers as windsurfboards at speed only touch the water surface with 1/3 or less of total board length..
Even a bit less drag and a bit more lift are important parameters for gps-speeders, but I understand that its not an easy task to make a standard fillet on productions fins that will work (be tight) on all types of boards.. However if the classic MUF Delta works better with a custom fillet than with the neoprene-tape used to close the gap between the board and the front of the fin, I think its worth the work effort anyway.
Actually I like the Delta as its quite fast and takes stress away in very weedy and shallow waters.

Interesting article. Figure 11 shows that the fin drag could be reduced by about 15%. The only source that I know that estimates drag contributions at high speed is at the Maui Ultra Fins web site; it has the fin contributing about 10% of the total drag, while the board contributes about 50% (mauiultrafins.com/wp-content/uploads/2015/10/How_fast_can_we_go_25_04_2017.edited-1.pdf). I have no clue if the number is correct, but it's clear that board, sail, and sailor also contribute drag.

On the other hand, the fin in the study is a low-speed surfing fin which will have significantly more drag than a speed fin. It's possible that the drag reduction from a fillet is larger on a high performance fin at higher speed. It would be nice to see the results of simulations.

Whatever the drag reduction is, however, may be almost irrelevant. The reports from comparisons of the filleted fins (both Fangy's and modified deltas) emphasize the reduction of spinouts, not higher speed. The idea seems to be that the turbulences created at the board-fin interface travel along the fin, and carry air bubbles with them, which can increase spinouts. If so, the mechanism is somewhat similar to Lessacher's cutouts at the trailing edge. Such "spinout inducing air bubble travel along vortices" would be most pronounced with short fins with a long cord length, i.e. deltas. If the travel is along the front edge of the fin, higher angles seen in deltas would also make the problem worse.

It would be very interesting to see what effect fillets have on regular weed fins and speed fins. But since those have fewer spinout issues to start with, the effect will likely be much less pronounced than for a delta. Still, a fillet may allow for the use of a 2 cm shorter fin and a bit less drag. Nobody would even consider using a original, swept-back fin shape for speedsurfing. Who knows, maybe in the future, using a non-filleted fin would seem just as crazy? The issue Mathew raised about production efforts is currently a big one - but one could envision different fin boxes that leave a bit of room for a fillet.