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Filleting a delta

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Created by decrepit Two weeks ago, 8 Oct 2017
decrepit
WA, 7664 posts
12 Oct 2017 6:17PM
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sanded the bog, (epoxy plus Q-Cell), back, spray puttied, and wet and dried, doesn't look a million dollars but it's good enough for a test.
Front view,



side view.


This pic doesn't show it that well, but I was amazed how lumpy the delta finish is. Sanding the spray bog through to the G10, creates some very interesting patterns, All you can see here is the scratches, mostly from me sanding with 89grit paper. (Don't worry Paul, they'll wet and dry out).

So all we now is a test run by an experienced delta sailor.

fangman
WA, 541 posts
12 Oct 2017 8:03PM
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In my experince, this process doesn't seem to be right Decrepit. No bits have gone missing, no bits have melted or sagged, and you haven't done jury duty. It all seems far too straightforward for some reason...
(Fillet looks really nice too - good job!)

keef
NSW, 1965 posts
13 Oct 2017 9:38AM
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Look great mike i also noticed you have beefed up the foil a bit and gave it the decrepit touch??

keef
NSW, 1965 posts
13 Oct 2017 1:27PM
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Almost finished my version by useing a mold of a delta 17 then laying up the leading edge and glueing it on, just need to trim the tale off and a lite coat of resin





Dezza
NSW, 465 posts
13 Oct 2017 1:55PM
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keef said..
Almost finished my version by useing a mold of a delta 17 then laying up the leading edge and glueing it on, just need to trim the tale off and a lite coat of resin






looks good captain

keef
NSW, 1965 posts
13 Oct 2017 2:00PM
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Ill grab that red delta 17 off you and don't tell you know who

Jetlag
NSW, 41 posts
13 Oct 2017 2:07PM
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Great looking prototypes Mike & Keef. I'm wondering whether for such a fillet you're better off using something elastomeric. There are only small loads and you could generate a pretty good seal to the board if you put a bit of pre-curve into the fillet, so it squeezes flush when you tighten the fin.
You wouldn't be able to sand something elastomeric so it'd have to be made nett shape. You can 3d print in elastomer and make a skirt. I'll have a go at photoscanning in my delta and giving it a go.
I've had good success in using photoscan to scan in small objects and using a lazy susan to rotate the object. I recently scanned in a complex cast iron verandah bracket (90 photos one side), to print out a spare and it worked a treat. It would work better if you have some visible texture on the fin, so I might lay on some "contact" film with a textured image.

decrepit
WA, 7664 posts
13 Oct 2017 11:25AM
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keef said..
Look great mike i also noticed you have beefed up the foil a bit and gave it the decrepit touch??


No mate haven't touched the foil, apart from sanding out a few lumps. 'ken had already sharpened the leading edge a bit, apart from that it's virgin delta.

decrepit
WA, 7664 posts
13 Oct 2017 11:34AM
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Jetlag said..
Great looking prototypes Mike & Keef. I'm wondering whether for such a fillet you're better off using something elastomeric. There are only small loads and you could generate a pretty good seal to the board if you put a bit of pre-curve into the fillet, so it squeezes flush when you tighten the fin.
You wouldn't be able to sand something elastomeric so it'd have to be made nett shape. You can 3d print in elastomer and make a skirt. I'll have a go at photoscanning in my delta and giving it a go.
I've had good success in using photoscan to scan in small objects and using a lazy susan to rotate the object. I recently scanned in a complex cast iron verandah bracket (90 photos one side), to print out a spare and it worked a treat. It would work better if you have some visible texture on the fin, so I might lay on some "contact" film with a textured image.


It's the leading tip that's the problem, weed seems to be able to work it's way in there unless it's a very tight fit. Your pre-curve may just do it, well worth a try.
But I'm not sure it's worth going to a lot of trouble until we know if a fillet works on a delta. The delta is supposed to work in a different way to a normally foiled fin, it's supposed to rely on a vortex at the leading edge. I have no idea how this works, so if the fillet kills the vortex, it may actually make the delta worse. I think this is highly unlikely, but I wouldn't just advise assuming, it's going to solve all the delta's problems.

fangman
WA, 541 posts
13 Oct 2017 11:44AM
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decrepit said..

But I'm not sure it's worth going to a lot of trouble until we know if a fillet works on a delta. The delta is supposed to work in a different way to a normally foiled fin, it's supposed to rely on a vortex at the leading edge. I have no idea how this works, so if the fillet kills the vortex, it may actually make the delta worse. I think this is highly unlikely, but I wouldn't just advise assuming, it's going to solve all the delta's problems.


Agreed 100% Mike.

decrepit
WA, 7664 posts
13 Oct 2017 8:55PM
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Ken's just picked up the fin, with any luck he'll get to test it Monday arvo.
He's a bit of a fillet skeptic, so if he gives rave reviews, it has really worked.

elmo
WA, 7645 posts
13 Oct 2017 9:22PM
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He needs two fins, one original as a benchmark and the filleted.

It's hard to establish if there is any difference without comparison between the two

decrepit
WA, 7664 posts
13 Oct 2017 9:40PM
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elmo said..
He needs two fins, one original as a benchmark and the filleted.

It's hard to establish if there is any difference without comparison between the two


Alby, have you ever used a delta????????????.
Believe me, if the fillet does what it's meant to the difference will be obvious as soon as he starts planing.

elmo
WA, 7645 posts
14 Oct 2017 7:17AM
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I can honestly say "No, I have never used one" nor do I want to, after hearing how they behave

sboardcrazy
NSW, 5970 posts
14 Oct 2017 11:46AM
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Thanks for the explanations Fangy & Decrepit..

decrepit
WA, 7664 posts
14 Oct 2017 5:35PM
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elmo said..
I can honestly say "No, I have never used one" nor do I want to, after hearing how they behave


I'm hoping with a fillet, they'll be more "normal" but we'll see.

decrepit
WA, 7664 posts
14 Oct 2017 8:59PM
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I did one of my own today without using rovings, everything the same except substituted q-cell/epoxy bog for the rovings.
It worked much better than my crappy rovings, much easier to move around, also easier to taper the front and trailing edges.

PaulWA
WA, 11 posts
Monday , 16 Oct 2017 9:59PM
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I managed to get on the water for a quick test run this evening after work.

Headed down to Fangy's with the recent reports of it looking like a golf course and all, sounded perfect for the delta. Looked more like moguls today, with chop up to waist high in places. I did manage to find a smoother areas way upwind and got a couple runs in.

Guess today wasn't the best day for it. But I can say, right from the very start, it felt like a very different fin. Now it is worth understanding that for the most part I treat my delta as a 'necessary evil' and try to avoid it unless all else fails. Today, I really didn't mind it, which is a huge improvement.

I can't really talk for the top speed as I was a bit too overpowered and the water was mostly too rough but the upwind performance was remarkable and even in the choppiest it hung on really well. I did get it to let go a couple times, once pushing hard up wind in the chop and twice just picking up speed on a run but overall I was a lot more confident on it and it felt a lot more like riding a normal fin. I think probably in the right condidtions this fin will be able to go faster than before because of the improved confidence but I got a couple 36knot peaks on the dial wihich is easily as fast as I've even been on the fin before.

For the purists, who have noticed, the fin was not quite standard before the fillet, I have modified the outline with some encouragement from the bottom of the estuary and tweaked the foil a little over time after various conversations.

It is hard to be sure, without the side-by-side suggested by Elmo or just a more normal day sailing but subjectively I'd say that the fillet makes the delta a way more usable fin. Totally surprised as I still don't intuatively understand the science around this.

gpsteamchallenge.com.au/sailor_session/show?date=2017-10-16&team=2





yoyo
WA, 1504 posts
Tuesday , 17 Oct 2017 9:32AM
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Encouraging report Paul. I guess we will all be adding fillets to our Deltas now...
Just when i thought Slowies plan form was the way to go....

fangman
WA, 541 posts
Tuesday , 17 Oct 2017 3:04PM
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Just as an adjunct to Yoyo's post about Slowies planform. Although I am pretty confident about the science behind the fillet improving the efficiency and behaviour of water flows at board fin junction, I do not know whether they are 'faster' than conventional design. My initial aim was to get the most lift possible with the least drag. A really fast fin will sacrifice lift in order to reduce drag. These two aims are different and I have not yet done enough research to suggest a fillet is a good thing for very high speed fins.

decrepit
WA, 7664 posts
Tuesday , 17 Oct 2017 8:24PM
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PaulWA said.. Totally surprised as I still don't intuatively understand the science around this.



You're not alone Paul, both Pepe and I were very surprised after our first test of a fangy fin.
That fillet just looks wrong, until you experience it.

keef
NSW, 1965 posts
Thursday , 19 Oct 2017 9:56PM
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Managed a 34+ on my 25cm version on a AHD92 with a 6.4mt, i was getting heeps of lift and well over fined ,would have been happy with less wind and a 7mt sail for the fin setup, mite try a fillet on a 18cm see if theres a difference

decrepit
WA, 7664 posts
Friday , 20 Oct 2017 3:24PM
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keef said..
Managed a 34+ on my 25cm version on a AHD92 with a 6.4mt, i was getting heeps of lift and well over fined ,would have been happy with less wind and a 7mt sail for the fin setup, mite try a fillet on a 18cm see if theres a difference


Nice going Keef, the case for a fillet is looking better all the time

decrepit
WA, 7664 posts
Friday , 20 Oct 2017 3:31PM
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And Yoyo just emailed me this article,
www.sname.org/HigherLogic/System/DownloadDocumentFile.ashx?DocumentFileKey=6b7de6c7-1e9c-4fd1-b1db-7e62c333758f
I'm not sure if Fangy used this in his research, but Yoyo condensed it down to say we are doing it exactly right.

fangman
WA, 541 posts
Friday , 20 Oct 2017 5:34PM
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decrepit said..
And Yoyo just emailed me this article,
www.sname.org/HigherLogic/System/DownloadDocumentFile.ashx?DocumentFileKey=6b7de6c7-1e9c-4fd1-b1db-7e62c333758f
I'm not sure if Fangy used this in his research, but Yoyo condensed it down to say we are doing it exactly right.


Fantastic work Yoyo - that is a great find! ( and no I have not read that paper - wish I had seen it sooner!)



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