balck project shallow water weedy

Hmm interesting stuff Jimbob. Thanks for posting it. Gets no prizes for being pretty though It looks a lot like my Deltas after a season of introducing them to the real estate on a regular basis. I am tempted to get my most mangled fin and cut out the stern part of the fin near the board to create the same effect and see what happens.

Very interesting, looks like it may have more grunt than the delta shape. Will be very interested to hear how it goes.

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fangman said..

decrepit said

Sorry Decrep, you misunderstood me. What I meant to say was, I would give the fin to you to do all the hard work on, then I would take it out and see what it was like and test its snapability on the real estate... :-)

hey fanggy are you ing again

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i have 3 coming to Port Macquarie and will send them out to our 3 lakes , budgewoi, forsters and queenslake to see how they go

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decrepit said..
I like the extra width at the tip, it's how I've made my shallow water fins. My thoughts are that the heavy weedy and close proximity to the bottom, act as an "end plate" reducing the need for a small tip to minimise induced drag. A narrow tip isn't doing very much in this scenario, only dragging in more weed than necessary. But just how wide is optimum is anybody's guess?

Indeed I wonder the same thing... ie: why are the tips so narrow? they are just creating drag, with no lift and no twist.

However the Black Project (in the pic), looks wrong as there the chord changes dramatically in the middle of the highest-lift section of the fin, where the water is least turbulent (ie: not too close to the board and not too close to the tip). I dont think I have seen a foil on any production craft, where the chord changes so dramatically.

Worth noting that there is some discussion that ventilation is often cause by air/suction from the rear of the board -> it may be that the sharp angle causes a vortex which disrupts the suction... or not... without testing by "experienced" fin guru's, I dont think we would ever know.

All that said, if the trailing-edge had an elliptic curve, then I'd be interested in purchasing one... but otherwise, not sure I'd fork out for this shape without first giving it a try.

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mathew said..

decrepit said..
I like the extra width at the tip, it's how I've made my shallow water fins. My thoughts are that the heavy weedy and close proximity to the bottom, act as an "end plate" reducing the need for a small tip to minimise induced drag. A narrow tip isn't doing very much in this scenario, only dragging in more weed than necessary. But just how wide is optimum is anybody's guess?

Indeed I wonder the same thing... ie: why are the tips so narrow? they are just creating drag, with no lift and no twist.

However the Black Project (in the pic), looks wrong as there the chord changes dramatically in the middle of the highest-lift section of the fin, where the water is least turbulent (ie: not too close to the board and not too close to the tip). I dont think I have seen a foil on any production craft, where the chord changes so dramatically.

Worth noting that there is some discussion that ventilation is often cause by air/suction from the rear of the board -> it may be that the sharp angle causes a vortex which disrupts the suction... or not... without testing by "experienced" fin guru's, I dont think we would ever know.

All that said, if the trailing-edge had an elliptic curve, then I'd be interested in purchasing one... but otherwise, not sure I'd fork out for this shape without first giving it a try.

I did not know either so I thought I would ask the designer of the Delta fin, Dietrich Hanke( aeronautical engineer) to ask him - so thank you to him for taking the time to reply. He also sent some diagrams but they seem to have got lost ( I will see if I can get them sent again ) This is an edited version of his reply:


<div>" I don't know why they ( Black Project) call it Delta because it is no Delta Wing but only a highly swept wing.
<div>The aerodynamics between a swept wing and a Delta wing are quite different.
<div>A Delta or slender wing has a chord which is larger than the span.
<div>A Delta wing produces a strong vortex from the leading edge which increases the lift a lot.
<div>There is a nonlinear behavior compared to a normal wing. The vortex allows very high angle of attack without flow separation.
<div>This aerodynamic improvement with the vortex is only given by the Delta outline, not by a swept wing.
<div>Concerning the tip. If you make the tip wider you would interrupt the vortex. The wing area from the cutting point will not contribute to the lift. Therefore all Delta wings are very sharp at the tip.
<div>There is no vortex around the tip as it is on conventional wings (induced drag).
<div>Finally for a Delta you cannot use what you know about a normal wing or fin."

So are we are all clear now?

my own experience with flattening off the tips of my deltas would agree with Dietrich, I have found them best with a relatively sharp point.

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mineral1 said..

fangman said..

mathew said..

decrepit said..
I like the extra width at the tip, it's how I've made my shallow water fins. My thoughts are that the heavy weedy and close proximity to the bottom, act as an "end plate" reducing the need for a small tip to minimise induced drag. A narrow tip isn't doing very much in this scenario, only dragging in more weed than necessary. But just how wide is optimum is anybody's guess?

Indeed I wonder the same thing... ie: why are the tips so narrow? they are just creating drag, with no lift and no twist.

However the Black Project (in the pic), looks wrong as there the chord changes dramatically in the middle of the highest-lift section of the fin, where the water is least turbulent (ie: not too close to the board and not too close to the tip). I dont think I have seen a foil on any production craft, where the chord changes so dramatically.

Worth noting that there is some discussion that ventilation is often cause by air/suction from the rear of the board -> it may be that the sharp angle causes a vortex which disrupts the suction... or not... without testing by "experienced" fin guru's, I dont think we would ever know.

All that said, if the trailing-edge had an elliptic curve, then I'd be interested in purchasing one... but otherwise, not sure I'd fork out for this shape without first giving it a try.

I did not know either so I thought I would ask the designer of the Delta fin, Dietrich Hanke( aeronautical engineer) to ask him - so thank you to him for taking the time to reply. He also sent some diagrams but they seem to have got lost ( I will see if I can get them sent again ) This is an edited version of his reply:


<div>" I don't know why they ( Black Project) call it Delta because it is no Delta Wing but only a highly swept wing.

Where you sailing to morrow fangy? local fangland or over at boat ramp?
Mineral

Aww cmon Mineral. I can't tell you that, I only just got over you wrecking all my kit last time. But I reckon a few guys will go out at Fangy's.
Some will rig in the western end car park and walk straight around to the lagoon channel. Some might rig at Wamba and tack up to the channel to walk in.

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Lessacher said..
I worked a 21cm Rake 55 degrees with 446cm² She is so thick how the box. 100% carbon. Please look: www.designlessacher.eu
on facebook are pictures. Wolfgang

Wolfy, not on torture book which one are you talking about from your product page?
Can you past a picture here of the one you describe.
Currently I run a Chamaleon down at this location. Bit shorter now days as its very shallow there.
Mineral

I dont know how I can give a pic in this forum. Wolfgang

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fangman said..

I am having the exact same problem at the moment. I am trying to post images of vortex formation on Delta wing shapes... I will keep at it but atm the moment every format I choose doesn't seem to work??

OK, this looks like it, but I had to change the file name to something simple to get it to finish saving.

Wolfgang, just below the reply pane, it says, "Add an image to my message". If you click on that, you can then select an image on your computer, it then uploads to this site, then you hit save and it's incorporated into your post.

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decrepit said..

Delta foils do indeed work... the "concave trailing edge" of our speed fins, are a similar example of a negative-pressure-gradient large enough to induce flow back onto the trailing edge of the foil (in the hope that it creates less drag overall).

But at what angle-of-attack? Do we sail at much more than 10 deg AoA ?