Mike, I have a question about this. When I am on my big gear I use a 36cm F/O Weedster (125 ltr board and 7.8) and it goes well upwind but for some strange reason it lets go on bear aways and off the wind. You bear off and suddenly it lets go with no pressure on it at all. I can understand what you are saying about lift but why would a fin let go off the wind especially when its flat???
Cheers,
Larko.
Check the leading edge of your fin, how blunt is it? Further back in the thread, Sausage and I had a similar discussion.
If it's not blunt, is it a nice even curve over the first centimeter of the leading edge.
You can be the test of this theory.
Larko, here's my answer to sausage, on the previous page. Select to expand quotedecrepit said...
Why a fin lets go when it's suddenly loaded up is fairly obvious. Why it lets go when unloaded is a bit of a mystery, it could be due to the leading edge being too fat.
I've had a similar thing with wave fins as I first take off and drop down the face. Absolutely no fin pressure, but you can just feel it let go. You know if you try to bottom turn, you'll just go sideways, but a slight upwind turn reestablishes the flow and you can get back into the wave, (if it hasn't got too far ahead). I solved this problem by sanding off the blunt leading edge making it sharper.
I think what I'm not sure about is the reduction in lift being the fin's problem. I think it's more the change in angle of attack itself, a blunt leading edge can handle a large angle of attack, (that's why I had originally shaped my wave fins that way), but flow coming from directly ahead has to separate rapidly in both directions, I think this can produce a large separation bubble just back from the leading edge, but that's all theory as far as I'm concerned. Next time you get a fin letting go when you rapidly bear off, try thinning the leading edge a bit and see what happens.
Hey sorry to get a little self indulgent here, but I have just noticed that I have been red thumbed posting this thread. I am new to this and I am wondering if I have inadvertently crossed a line somehow. If I have, my apologies, but it would be nice to know what I messed up? ( oh and if it is actually a green thumb - I am full on red green colour blind so I really do find it hard to tell)
Select to expand quotefangman said...
Hey sorry to get a little self indulgent here, but I have just noticed that I have been red thumbed posting this thread. I am new to this and I am wondering if I have inadvertently crossed a line somehow. If I have, my apologies, but it would be nice to know what I messed up? ( oh and if it is actually a green thumb - I am full on red green colour blind so I really do find it hard to tell)
Its probably a shop-owner feeling your taking business away from them, however, i'm not sure what u r doing is against the spirit of forums though, becuase Forums are about information sharing and helping each other out (which is what u r doing), if there was a shop in Perth that stocked these Delta Fins and they were a sponsor here, then maybe they might have a legit gripe? Thats the only thing to be careful about I suppose, that windsurfing shops (sponsors) are probably struggling to survive and cant afford to be losing business to the internet, but thats also a reality of modern life................. shops have to realise that the This Forum, and its association with GPS Sailing and the GPSTC have also given them a lot of business so maybe its swings and roundabouts
Some History:
The other issue here is that this "GPS Speedsailing SeabreezeForum" is the official Forum of the GPSTC, Ben & I decided not to create a forum for the GPSTC as a loyalty issue to Seabreeze & Laurie, so if these posts are red flagged or a complaint made, then it becomes an incentive for the GPSTC to have its own forum, and all this traffic will be lost to Seabreeze, and shops get less exposure........... So if it is a shop red thumbing, my advice is to think carefully about the consequences of registering negative vibes about the GPSTC community on this Forum, as you've made money and benefitted out of GPSTC............ I'm so glad I'm out of the admin side of things, and I was always an appeaser, but the new GPSTC Committee may not take so kindly to negatives about the GPSTC's forum activity......... This issue might need its own thread initiated by the new GPSTC Committee........... Sometimes people need a little reminder of the facts,......Now its goodbye from me for a while.........I'll go quiet again
Thanks Mike, missed that so will give it a go (if we ever get wind again). I have a 32 as well which is great so will compare the leading edges and probably do some sanding.
Fangman, the thumb thing is a weird one. Red thumbs appear on some of the least innocuous topics, take it with a grain of salt. It happens to all of us.
Wait for it.
Thanks to Fangy, I've been reading Fran Bethwaite's book "High Performance Sailing". It's got some interesting stuff on foils, sails and hulls.
here's an excerpt from the "foils" section. Mainly applying to rudders, but I think the principle is still there.
So as you can see (fig 19.10) he's saying that a thick foil will ventilate even going straight ahead and on both sides, once a critical speed is reached, and any leading edge blemish can make it happen earlier.
I find the bottom one, "reversal of steering force" especially interesting, not only do you loose all leeward lift, it actually reverses, and gives you windward lift! When it does that there's no hope of recovery!
Ok thank you guys. I will be more careful in future. When I wanted to buy a delta I did a search on the internet and the nearest shop was 3000kms away. I emailed Maui to see if there was someone closer. They replied with the two businesses on the east coast. If there a local shop out there that does have them please let me know as I would be more than happy to support them and save me the hassle of organising this.
Keef I look forward to reading what you have to say because if there is a commercially available alternative to the Deltas that work better and handle touching the dirt at speed without slamming you to a dead stop then I am interested to say the least.
Interesting, the article doesn't mention Larko's problem, spinning out at 0 angle of attack. they're only saying there will be a problem if the leading edge is too sharp, not if it's too thick. And this is where I went wrong with my wave fins ages ago.
I don't think fig 19.10 is appreciated enough by some fin manufacturers.
You can still have a fairly thick fin (9% chord thickness ratio), and go fast, but the thickest point needs to be around the 40/45% of chord, not 30%.
Hey fangy, I'll show you what I think Keef's talking about, he sent me one of his MXR inspired fins a while back, unfortunately I haven't been able to give it a good test yet. I was hoping Lake George would give me the opportunity, but it wasn't quite smooth enough for me to feel confident pushing it.
(it's only 17cm)
mike the fin i'm referring too is the short base, have a look at the video at 024 you will see the lift the fin has , mudskipper was on an old-style fanatic with an old 6mt areotech wind was 30knts , at the end of that run there is some decent chop and if you hit that stuff with a weed fin with any sort of flex it will end in a massive spinout , mudskipper prefers to use that fin in chop compared to the wide base , for one its faster and second it give more lift, the rake is 47deg and at speed it will go through some fairly heavy weed
gpsteamchallenge.com.au/sailor_session/show?date=2014-01-17&team=34
forgot to mention first sailor is Alex and the second is Elli shes 8 years old and wind speed was 20 to 30knts 
Select to expand quotekeef said...
mike the fin i'm referring too is the short base, have a look at the video at 024 you will see the lift the fin has , mudskipper was on an old-style fanatic with an old 6mt areotech wind was 30knts , at the end of that run there is some decent chop and if you hit that stuff with a weed fin with any sort of flex it will end in a massive spinout , mudskipper prefers to use that fin in chop compared to the wide base , for one its faster and second it give more lift, the rake is 47deg and at speed it will go through some fairly heavy weed
gpsteamchallenge.com.au/sailor_session/show?date=2014-01-17&team=34
forgot to mention first sailor is Alex and the second is Elli shes 8 years old and wind speed was 20 to 30knts
Keef,
I had a look at 024 and all I saw was him shrugging his shoulder 
lucky you mistakenly posted this vid and not those other ones. That was one criptic post and I'm still scratching my head.
PS - I know you're referring to the vid on the GPSTC session post.Select to expand quotekeef said...
Select to expand quotedecrepit said...
Thanks to Fangy, I've been reading Fran Bethwaite's book "High Performance Sailing". It's got some interesting stuff on foils, sails and hulls.
here's an excerpt from the "foils" section. Mainly applying to rudders, but I think the principle is still there.
So as you can see (fig 19.10) he's saying that a thick foil will ventilate even going straight ahead and on both sides, once a critical speed is reached, and any leading edge blemish can make it happen earlier.
I find the bottom one, "reversal of steering force" especially interesting, not only do you loose all leeward lift, it actually reverses, and gives you windward lift! When it does that there's no hope of recovery!
Decrepit,
Isn't figure 19.10 assuming detachment very early on and at much slower speeds. Wouldn't a windsurfing fin (being thinner than say a rudder) not exhibit these traits? Interesting reading though.
Select to expand quotesausage said...keef said...
mike the fin i'm referring too is the short base, have a look at the video at 024 you will see the lift the fin has , mudskipper was on an old-style fanatic with an old 6mt areotech wind was 30knts , at the end of that run there is some decent chop and if you hit that stuff with a weed fin with any sort of flex it will end in a massive spinout , mudskipper prefers to use that fin in chop compared to the wide base , for one its faster and second it give more lift, the rake is 47deg and at speed it will go through some fairly heavy weed
gpsteamchallenge.com.au/sailor_session/show?date=2014-01-17&team=34
forgot to mention first sailor is Alex and the second is Elli shes 8 years old and wind speed was 20 to 30knts
Keef,
I had a look at 024 and all I saw was him shrugging his shoulder lucky you mistakenly posted this vid and not those other ones. That was one criptic post and I'm still scratching my head.
PS - I know you're referring to the vid on the GPSTC session post.keef said...
snags fangman is quick on the draw , I remember reading one of his posts on the gps site where he was playing on words referring to hall and oats 
It was a sarcastic dig at the delta's
, they have been around for a few seasons now and at that time there wasn't a great choice of weed fins , most of the fins were reboxed slalom fins at 45deg and basically dumped weed , the bigger you went the more flex in the fin and a better chance of spinout (hardly what you would call a speed fin )
then boogie brought out the slingshot , it was my first weed speed (21cm), this fin was great it was reasonabley fat and stiff compared to what elese was around at the time but as decrepit would say it wouldn't cut the mustard in heavy weed
then the shallow water delta at 55deg and a great fin but had its limitations and needed a different technique, the advantage was for shallow sailing and that's about as far as it goes, the disadvantage was they would let go even in small chop , in most cases they wouldn't totally explode , the tail would let go and stay there and in a lot of cases you could jump it back when reaching
down wind and I mean off the wind and going for it it was a different story , and something you can relate to when your jibing on open water swell and you loose the pressure in your fin , that's what a delta is like off the wind at say 40knts with no pressure on your fin
now a few years later most fin companies are on the wagon , they have figured that a fin that is fat at the base and raked between 50 and 45deg and is stiff will give you lift and keep the board flatter and is much safer at speeds over 40knts
with my weed fins I have found I get much more lift if the fin is filled in between the fin and the base , so instead of the base being at right angles the base it becomes apart of the fin
this is noticeable on some aero plane wings , im not sure if it works with slalom fins but im sold on the idea for a weed speed
Yep, the diag refers to a rudder at lowish speed, and yes windsurfing fins are much thinner, but the principle holds true.
Making a fin thinner doesn't mean it won't ventilate, only that the ventilation happens at a higher speed.
I had a fin that would spin out reliably once I hit 32kts, yep leading edge too thick.
May be easier to understand, if we turn the diag on it's head, and instead of viewing it as a flow over the foil, look at is as a foil moving through a fluid. In this case as the leading edge of the foil impacts on the fluid, the fluid is accelerated away from the fin, as the fin passes, the fluid has to slow down and then move back to where it was. So the faster the fin is moving and the blunter the leading edge the greater the acceleration away from the fin. Separation occurs when the momentum away from the fin is too great for the pressure of surrounding water to slow it down enough to stay in contact with the foil. So the more gradually the water is accelerated around the front of the foil the greater the speed before separation.
Of course to go upwind at low speed almost the opposite is needed, a big angle of attack needs a fairly blunt leading edge.
So a compromise is needed, depending on what sort of sailing you're doing.
Select to expand quotekeef said...
mike the fin i'm referring too is the short base, have a look at the video at 024 you will see the lift the fin has , mudskipper was on an old-style fanatic with an old 6mt areotech wind was 30knts , at the end of that run there is some decent chop and if you hit that stuff with a weed fin with any sort of flex it will end in a massive spinout , mudskipper prefers to use that fin in chop compared to the wide base , for one its faster and second it give more lift, the rake is 47deg and at speed it will go through some fairly heavy weed
gpsteamchallenge.com.au/sailor_session/show?date=2014-01-17&team=34
forgot to mention first sailor is Alex and the second is Elli shes 8 years old and wind speed was 20 to 30knts
If that's the same as the short base you sent me, I showed it to fangy today, he was quite impressed, hopefully I'll get to give it a good run soon.
mike yes its the same fin, fat all the way to the tip (3mm ) stainless so im guessing 2mm at the thickest part of the foil at the tip
conan used the same fin the last time we were at primbee,
gpsteamchallenge.com.au/sailor_session/show?date=2014-05-04&team=5
I have noticed you guys using 26cm fins in 20+ knts with 6/0mt+ sails, just try that fin , because its 90% carbon and stiff you can load it up heaps in moderate chop
if you still have those cheep Bunnings barell nuts in the fin I would put a couple of spring washers underneath as I have found they can loosen
Select to expand quotekeef said...
".......then boogie brought out the slingshot , it was my first weed speed (21cm), this fin was great it was reasonabley fat and stiff compared to what elese was around at the time but as decrepit would say it wouldn't cut the mustard in heavy weed
then the shallow water delta at 55deg and a great fin but had its limitations and needed a different technique, the advantage was for shallow sailing and that's about as far as it goes, the disadvantage was they would let go even in small chop , in most cases they wouldn't totally explode , the tail would let go and stay there and in a lot of cases you could jump it back when reaching
down wind and I mean off the wind and going for it it was a different story , and something you can relate to when your jibing on open water swell and you loose the pressure in your fin , that's what a delta is like off the wind at say 40knts with no pressure on your fin
now a few years later most fin companies are on the wagon , they have figured that a fin that is fat at the base and raked between 50 and 45deg and is stiff will give you lift and keep the board flatter and is much safer at speeds over 40knts ...."
Hey Keef, I am not a speed sailor by any stretch but I did ask around here, the guys who have done 40 knots plus on a Delta and their experience is quite different to yours. I am wondering which model you used, the Ride or Slalom or Speed? They all have different chord thicknesses and therefore different in their handling of conditions and very high speed.
If you last used a Delta some time a go, you might have been using what is now referred to as the Delta Ride which has the thickest of the chords and it is my understanding that it was the first brought to market.
Of course I dont want to tell 'grandpa how to suck eggs' and would happily concede I know bugger all about fins, but I just wondered whether you are comparing current Delta shapes in your discussions?
When the first Deltas came out,bought I three. tried they ,downwind okay but not fast. Upwind say I nothing. I
worked malls ,worked they asymmetric,that was better,but I stopped there. For me not good enough. There I have the Rake 30? , the 22cm made 50 knots topspeed , was the system Delta nothing for me.When they need here in Strand Horst or in Fehmarn for big boards and big sails weedfins than say I please use 28cm Duo Weedfin,but 5cm wider.
For 140 liter and 9m? Wolfgang
Select to expand quoteLessacher said...
When the first Deltas came out,bought I three. tried they ,downwind okay but not fast. Upwind say I nothing. I
worked malls ,worked they asymmetric,that was better,but I stopped there. For me not good enough. There I have the Rake 30? , the 22cm made 50 knots topspeed , was the system Delta nothing for me.When they need here in Strand Horst or in Fehmarn for big boards and big sails weedfins than say I please use 28cm Duo Weedfin,but 5cm wider.
For 140 liter and 9m? Wolfgang
Wolfgang the reason we are interested in Deltas, is becuase of their 55degree rake, we have many highly infested weed areas in shallow water here, particularly in western australia, and its a rare opportunity for us to speedsail in flat water. In these waters even 45 degree weed fins, do not work well. I remember you sent me a prototype weed fin at 50degrees in about 2008/9, and it worked very well. My wife used it recently at Albany (2014) a highly weed infested water location, and she said it worked brilliantly. Where is your development of 50 to 55 degree weed fins? Send me one if you have any, and I'll test it over here, and compare it to a Delta, I've just ordered a 21cm Slalom. A friend of mine has developed a 48 degree weed which has excellent properties, fast at all angles, but we seem to want to sail in thicker and thicker weed, and the 55degree rake of the delta works.
It's not just the rake hardie it's also it's lack of depth. the less weed your in, the less the drag.
But out of weed these fins are inefficient because of the extreme rake and lack of depth.
There's no point in testing them unless it's in a venue that's extremely flat because of very heavy weed all the way to the surface.
In strong winds, the inefficiency of the fins is canceled out by the ability to get into dead flat water. The heavy weedy also seems to inhibit the flow from high to low pressure side of the fin, that makes them inefficient.
In lighter winds there might not be any advantage, because the weed adds more drag, and out of the weed it's not that choppy.
Quote from Blackdiamond article:
"Depending on speed and fin profile lift will decrease with an angle of attack of 15? at the latest. The point of detachment will then begin to move towards the leading edge and the flow on the windward side of the fin will begin to come off the surface. "
This is the first thing I have read that might help explain why we sometimes spin out at high speed just as we back off at the end of a run!
By the way, Wolfgang's 30 and 40 degree fins work extremely well in 'normal' weed like at Lake George and on annoying floating weed strands like we often get at Sandy Point these days. It is hard to comprehend the weed thickness of Albany and L. Illawarra if you have not experienced it (as I have not - but those who have tell me it is very different)
What speed make they in Albany...,.. I worked the Delta in carbon 176 mm vertical deep. I worked the Prototyp out a Delta in G10. Tried the fin,
and hoped that she is in carbon better, she was in carbon better, but for me not good enough. I have a mould. They are here for twinser okay. I can
work enough weedfins in Rake 50?, but why should they go faster in Albany,or work better. When you have enough time to go back,okay.Now I start to work some fins with Rake 50?. I designed today one with 21cm and 460cm?. In front 10cm over the box. Please say what boards and sails (m?)
the most use, and the speed.When Hardie or you send me a mail that I can give you a look what I try to work. Wolfgang
I looked what Black D. over TRAILING EDGE wrote. A sharp edge is dangerous,okay for my body. But is the edge 1mm thick, the fin makes music.
the edge must be sharp. Wolfgang
Hardie: Plkease send me a mail to: Wolfgang.Lessacher@t-online.de I tried it with youe adress, it comes always back.I made some Pics.
Wolfgang
