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.

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!)

Look great mike i also noticed you have beefed up the foil a bit and gave it the decrepit touch??

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

Select to expand quote

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

Ill grab that red delta 17 off you and don't tell you know who

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.

Select to expand quote

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.

Select to expand quote

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.

Select to expand quote

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.

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.

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

Select to expand quote

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.

I can honestly say "No, I have never used one" nor do I want to, after hearing how they behave

Thanks for the explanations Fangy & Decrepit..

Select to expand quote

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.

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.

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

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....

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.

Select to expand quote

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.

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

Select to expand quote

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

And Yoyo just emailed me this article,
netforum.sname.org/eweb/DynamicPage.aspx?WebCode=LoginRequired&expires=yes&Site=sname&URL_success=http%3A%2F%2Fwww.sname.org%2FHigherLogic%2FSecurity%2FnetFORUMLogin.aspx%3Fcstkey%3D%7BCustomerKey%7D%26ReturnUrl%3Dhttps%3a%2f%2fwww.sname.org%2fHigherLogic%2fSystem%2fDownloadDocumentFile.ashx%3fDocumentFileKey%3d6b7de6c7-1e9c-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.

Select to expand quote

decrepit said..
And Yoyo just emailed me this article,
netforum.sname.org/eweb/DynamicPage.aspx?WebCode=LoginRequired&expires=yes&Site=sname&URL_success=http%3A%2F%2Fwww.sname.org%2FHigherLogic%2FSecurity%2FnetFORUMLogin.aspx%3Fcstkey%3D%7BCustomerKey%7D%26ReturnUrl%3Dhttps%3a%2f%2fwww.sname.org%2fHigherLogic%2fSystem%2fDownloadDocumentFile.ashx%3fDocumentFileKey%3d6b7de6c7-1e9c-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!)

Put a fillet on my 17 delta and sanded it up this morning. Have only used it once before and hated it. Need a decent blow to test it though.

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

Nice work, swindy and keef, the more results we get the better.

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.

Great Swindy, this is the sort of stuff we need to find out, I'll be very interested in your results.