Select to expand quotewaricle said..
Does the 12 dia have enough strength to run aground? Delrin is hard stuff. I've used it as bearing material.
Peter as per usual I flying by the seat of my pants: I chose 12mm after careful consideration, mainly its the largest drill I have got. Also it fitted in the aluminium framework of the base resonably well. I also want to create the point of failure at bolt, rather than tearing off the back of the board. I just need to do some tests and see how well 12mm of thread holds, and try to find the goldilocks strength required.
After testing two fins from the same mold with different fillets i'm convinced the fillet will do 40nts , the fins were 55deg deltas, the bigget difference i found was the ability to point, i could do a good run off the wind and hit some decent chop and sail back to the launch in one tack, the second was the ability of the fin to recover,usually when a delta lets go it's gone.
The wind was 20 to 30nts using a naish sp80 and 5/8 ev05 ,and a 17cm thicker fillet & couldn't crack 36 changed to the same fin with thinner fillet and 36.4 , my guess is in the rite conditions with a lucky gust a fillet will do 40nts ??
So Keef, you've hit on an important point here, the ideal size of fillet, too small may not work as well, too big probably slower.
Is it a fixed size for all fins, or is it a percentage of chord or depth????????
I'm guessing here, but it's probably got to do with speed of water flow and angle of attack.
Although, my bigger fins seem to have more need of it than my smaller ones, that doesn't add up.
Any clues, theories anybody?????
Ian showed me an old 45 deg weedy the other day, he'd put a very small fillet on, only between the blade and the edge of the base. Said it improved the upwind performance of the fin no end.
Guess I'll start experimenting with smaller fillets, and see how small you can go, and if they are any faster.
From what I could find in the research, the radius of the fillet should be 6 - 10 % of the chord. There is a small advantage in making the fillet a more complex compound curve in the leading edge area, but the researchers concluded the effort vs benefit was not worthwhile. Most of the benefit occurs in the first third. A fine fillet edge is important, hence the efforts to reduce the gasket width, and finishing the edge to as fine as the material and longevity will allow.
These measures are to increase efficiency and reduce drag by taming pertubed flow patterns in order to make a small surface area fin with improved lifting behaviour, not so much a speed fin. I don't know, but I suspect that at very high speed, the interference pressure waves between fin and board will overwhelm the fillet effect. I am finding it hard to find research on the hydrodynamics of turbine end plates at higher velocities - after all, the turbine engineers are after maximum lifting (power generation) efficiency, not how fast they can get the turbine to spin. I think I will need to follow Yoyo's lead and look at high speed propellor design.
The flip side: the small surface area, the friendly and confidence inspiring handling characteristics of filleted fins could be enough to see them cross the 40 knot mark. I certainly have sailed faster downhill over chop with a filleted fin than with a Delta, simply because I am confident its not going to let go. As Decrepit says, time for some more experiments! 
Thanks IanK for the tip, maybe theres something in the angle of a drill bit it makes sense to me but does it apply to a fin fillet
Select to expand quotefangman said..
The flip side: the small surface area, the friendly and confidence inspiring handling characteristics of filleted fins could be enough to see them cross the 40 knot mark. I certainly have sailed faster downhill over chop with a filleted fin than with a Delta, simply because I am confident its not going to let go. As Decrepit says, time for some more experiments!
I think the reason you can sail further off the wind is because the angle of the fillet directs the water flow to the angle of attack , where as the standard delta's leading edge is thin opposed to the chord and easy for the water flow to be directed to the opposite side of the fin , maybe to be honest I don't know
Started on the 24 today, I'm using a different sequence of metal removal.
First a coarse file to remove the large high spots, then a flat sanding board with 120 grit to fair up the shape, a linish with the scotchbrite belt and then 240 grit on an orbital which is as far as I have done one one side.
The Tuttle head was sized up first using disc sander wth 30 grit and files.
I've yet to sand the fillet and cutout and drill and tap the head.
Peter 30 Grit! I didnt know that existed - is a flap wheel? Do you reckon its that faster than a 7 inch grinding wheel?
Today's product, Bling finish for Pepe.
Select to expand quotefangman said..
Peter 30 Grit! I didnt know that existed - is a flap wheel? Do you reckon its that faster than a 7 inch grinding wheel?
Today's product, Bling finish for Pepe.
They are shinier than our cup, get polishing slugger.
Nice work Ross
Select to expand quotedecrepit said..
So Keef, you've hit on an important point here, the ideal size of fillet, too small may not work as well, too big probably slower.
Is it a fixed size for all fins, or is it a percentage of chord or depth????????
The 17cm with the larger fillet was getting lifted in the middle of the speed run, the smaller fillet settled the board down and faster My guess is the smaller the fin the bigger the fillet ,i couldn't image a 28cm fin with the same fillet proportion as a 17cm with and over sized fillet as the fin would be huge
I would say there would be a cut off size (maybe 24), a few years back when i first had a look at something like a fillet the initial idea was to fill the gap of the fin and reduce the 90deg angle of the base,so with the larger fins thats maybe all you would need
Select to expand quotewaricle said..
My bad, is wasn't 30 grit it was 24
Thanks Peter, I will keep an eye for those and try them out if it is quicker than grinding.
Select to expand quotewaricle said..
Does this Fin make me look fat?
Defo your best angle Nice job!
First attempt at using 12mm Delrin inserts for barrel nuts. Straightforward to tap with detergent and water. Tomorrow I plan to see what it takes to strip the thread.
Select to expand quotekeef said..
The 17cm with the larger fillet was getting lifted in the middle of the speed run, the smaller fillet settled the board down and faster My guess is the smaller the fin the bigger the fillet ,i couldn't image a 28cm fin with the same fillet proportion as a 17cm with and over sized fillet as the fin would be huge
I would say there would be a cut off size (maybe 24), a few years back when i first had a look at something like a fillet the initial idea was to fill the gap of the fin and reduce the 90deg angle of the base,so with the larger fins thats maybe all you would need
sounds like the 17cm thin fillet is ready to get the team rider out testing it Keef
Select to expand quotefangman said..
First attempt at using 12mm Delrin inserts for barrel nuts. Straightforward to tap with detergent and water. Tomorrow I plan to see what it takes to strip the thread.
The Delrin seems to be reasonably strong. I inserted a bolt through the full width of the delrin rod. I used a metal spacer to simulate the board width. I tightened the Phillips head M6 bolt as tight as I could with a screwdriver. The delrin appeared to be ok. So next test is durability. If durability seems ok, then delrin appears to be a useful material as a barrel nut. Cost is $6.95 for 60cm delivered.(Ebay)
My current plan insert the delrin rod and then drill and tap both the aluminium and delrin at the same time. That way the aluminium can do the bulk of the work and the delrin is only there as a backup should there be a corrosion issue in future.
Select to expand quotefangman said..
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My current plan insert the delrin rod and then drill and tap both the aluminium and delrin at the same time. That way the aluminium can do the bulk of the work and the delrin is only there as a backup should there be a corrosion issue in future.
Good thinking 99, I remember thinking the same thing for one of my fins, but then discovered that I'd drilled the holes too big to thread. Fiberglass doesn't hold a thread as well as alli anyway, so I didn't stress over it.
I now have 4 Fangy fins to choose from, the third one is now 22 cut down from a 24. Took quite a bit of shaping to try and maintain a decent foil shape at the tip but I'm happy with the result. If this is still too close to the 24 in performance in may cut 15 or20mm off the trailing edge but this will require a load of re shaping of the foil and cut out and some input from the fangman himself.
Blimey Swindy you have more fins than I do! That looks great. I will be really interested in your experience on your '22'. If we need to trim some off the trailing edge, I can easily make you some scaled down templates of the foil for you to use and shape to.
Delrin has a shear strength almost 100% of its tensile strength and great wear resistance. If 12 dia is too weak you could always up it to 20 and also 8mm screw if necessary.
Ill see how my 8 mm last in the alloy with the antseize
As there is very little difference in surface area atm I probably will do further mods so templates will be great, thanks Ross. I will give it a couple of goes first though.
Used the new 22 briefly yesterday and as I suspected still felt a bit big so I attacked it with the grinder again. My plan was to remove about 20mm off the trailing edge then cut in a new cut out and completely re shape the foil. After laying the 20 on top I decided to leave the cut out and cut a radius that ended up about 25mm in from the trailing edge at the tip giving it a more upright trailing edge a la 20. Still quite a bit of grinding to re shape the foil but no where near as much as my first plan.
As you can see there is now a more substantial difference in surface area. Hope to test tomorrow.
The only reason I am doing this is because for my purposes the gap between the 20 and 24 is too substantial and the fangman is unwilling to risk certain death by investing in a new print and mold for a real 22. All 3 available sizes are fantastic and the gap between the 24 and 28 isn't an issue.
if enough interest is expressed in a real 22 we may be able to persuade him.
Select to expand quoteSwindy said..
Used the new 22 briefly yesterday and as I suspected still felt a bit big so I attacked it with the grinder again. My plan was to remove
The only reason I am doing this is because for my purposes the gap between the 20 and 24 is too substantial and the fangman is unwilling to risk certain death by investing in a new print and mold for a real 22. All 3 available sizes are fantastic and the gap between the 24 and 28 isn't an issue.
if enough interest is expressed in a real 22 we may be able to persuade him.
....Or, you can just send them to Swindy and he will happily cut back a 24 into a super nice looking 22. Simples.
Looks really nice mate, I am very keen to see it in the flesh, because you are dead right, I really need to do a 22. I noticed it yesterday, my 24 was too big and the 20 just a tad too under-done for uphill work on the 6.6.
And then somebody will want an 18.
I was on a 16.5 yesterday, a tad small for my 5.4 uphill but nice downwind. I should have been on my 18 to be comfortable in both directions.
Select to expand quotedecrepit said..
And then somebody will want an 18.
I was on a 16.5 yesterday, a tad small for my 5.4 uphill but nice downwind. I should have been on my 18 to be comfortable in both directions.
Now you come to mention it Mike, for them realy big days.
That can go on the wish list for now though. The 22 will be my go to fin on the 100L and occasionally on the 90L.
Finally got to use the hybrid FF22 yesterday and very pleased with its performance. I reckon I have removed enough surface area to make a very noticeable difference compared to the 24. It behaved impeccably with plenty of grip giving 100% confidence at all points of sailing. I achieved a 24.99 alpha, a 24.5 knot hour with quite short runs and lots of jybes and a crash and a 34.2 2second. So in the absence of a real 22 which would have a shorter base and a thinner profile and therefore be a bit faster. I reckon its a worthwhile project for anyone who wants to bridge the gap left by the fangman.
It may be some time until a factory 22 is produced as the managing director is too busy smashing personal bests and ripping up weed with his product.
Select to expand quoteSwindy said..
....as the managing director is too busy smashing personal bests and ripping up weed with his product.
...as well as feeding the Minister For Excessive Windsurfing Expenditure massively over inflated sales figures in order to try and get the FF22 design process off the ground.
Good work on that FF22 Swindy, as soon as I get a chance I will copy it 
How do the 20 and 24 cm fins compare to regular weedies and pointer fins that have similar performance with respect to area? One extreme scenario would be that only area matters, so high-rake fins can be a lot shorter. MUF seemed to think so with the original delta, but that was not quite true in praxis. Is it true for Fangy fins?
I think it's much truer for a fangy than a delta. But we're not comparing apples with apples here. The pointer is going to win in deep water chop, no doubt about it. But the fangy fin will win hands down in thick surface weed. How the fangy compares to a good conventional weedy is more problematic. However hardie used a pepe weed 48deg and a fangy on the same day and found them very similar, but I've no idea about their area or sizes.
There's also the issue of leverage, a long narrow fin will have more leverage than a short wide one, even if they both produce the same lift. So there's going to be a difference in board trim.
