The need for a fast weed fin............

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General Gps & Speed Waves Foiling Gear Reviews Lost & Found WA NSW QLD SA VIC TAS

hardie

4133 posts

hardie

WA, 4133 posts

31 Aug 2007 8:30am

Particlularly for the WA crew (but otheres as well), who wanna sail Hardie's Run in summer, we are all gonna need fast weed fins to fully exploit the place!!!!

The true Hardie's Run is unsailable with a pointer, or standard rake fin, you need at least 45 degree rake or you'll just plow!!

We need to encourage people like Mal Wright and Chris Lockwood, to do some research and testing, and then put something into production.

In order to encourage these guys to invest their time and money, who would be prepared to buy a speed weed fin and roughly what sort of price would you be prepared to pay, or what price would discourage you?

Gybesports

NSW

193 posts

Gybesports

NSW, 193 posts

31 Aug 2007 10:53am

Hi Hardie

Have you tried any of the g-sport weed fins? Or are they too slow?

hardie

4133 posts

hardie

WA, 4133 posts

31 Aug 2007 8:57am

quote:
Originally posted by Gybesports

Hi Hardie

Have you tried any of the g-sport weed fins? Or are they too slow?

Never tried? Wanna send one over for a test?

Bender

2236 posts

Bender

WA, 2236 posts

31 Aug 2007 9:01am

I would definately pay $$ for a proven fast weed fin as all my customs just dont seem to cut it!!

elmo

8895 posts

elmo

WA, 8895 posts

31 Aug 2007 9:24am

Elmo Weedies

Guaranteed to make you sail like an Elmo

quote:
Originally posted by Bender

I would definately pay $$ for a proven fast weed fin as all my customs just dont seem to cut it!!

Having a preference for weedies on the estuary I did a fair bit of digging and unfortunately there is not very much to offer for Speed, there is the occasional slalom one out there but speed are rare.

Lescher do them but the carbon ones don't like rocks.

You could always grab a quick slalom or speed fin cut it and rebox it but taking a hacksaw to a $300 techtonics fin could be a bit daunting to some.

My last Weedie which I made was using a JP G10 (repairable vs carbon) which is a good slalom fin at a reasonable price which made a great weed fin.

My first attempt was with an old Finworks Pro 355 which I converted to a 22cm 45 deg weed which cracked 38knots on when I loaned it to 25.

The beauty about slalom fins is you don't have to change them apart from re boxing them for them to perform well.

mineral1

4564 posts

mineral1

WA, 4564 posts

31 Aug 2007 9:42am

quote:
Originally posted by elmo

Elmo Weedies

Guaranteed to make you sail like an Elmo

Elmo, any chance you can photograph a standard weed fin, and then your modified version, so we can see what sort of additional profile your highlighting, or Hardie is highlighting.
Gybesport, how much of a rake, compared to the normal weed has the item you indicate, may do the job.
Mineral

grumplestiltskin

2331 posts

grumplestiltskin

WA, 2331 posts

31 Aug 2007 9:51am

Maybe we could just hire a D9 bulldozer (mineral might be able to assist), and hack the weed out of the strip in one foul swoop.

Would last for a season, and if we are quick we could get it done before the council gets wind of what we are doing.

only jokin

grumplestiltskin

2331 posts

grumplestiltskin

WA, 2331 posts

31 Aug 2007 9:55am

On a serious note, I have been thinking about buying or building a CNC router for the express purpose of building fins.

I was thinking I would market them under the name "Grumplestilts-Fins".
Has a nice ring to it I thought.

What sort of market do you reckon there would be for locally produced fins???

elmo

8895 posts

elmo

WA, 8895 posts

31 Aug 2007 10:00am

quote:
Originally posted by grumplestiltskin

Maybe we could just hire a D9 bulldozer (mineral might be able to assist), and hack the weed out of the strip in one foul swoop.

Would last for a season, and if we are quick we could get it done before the council gets wind of what we are doing.

only jokin

Better Idea would be dragging the rocks out of there so as to save the ocassional fin.

We need the weed to kill the chop

and to hide the rocks, cobblers, crabs and stingrays

Bender

2236 posts

Bender

WA, 2236 posts

31 Aug 2007 10:00am

Grumps, perhaps you and all the WSP Mob could sail it with big deep pointer fins and clear out all the weed so the Mandurah Mob can have a real crack at some quick runs

grumplestiltskin

2331 posts

grumplestiltskin

WA, 2331 posts

31 Aug 2007 10:17am

quote:
Originally posted by Bender

Grumps, perhaps you and all the WSP Mob could sail it with big deep pointer fins and clear out all the weed so the Mandurah Mob can have a real crack at some quick runs.

HO HO, everyone's a comedian

I've already shredded the bottom 2cm off my favourite weedie on that bloody rock

I bet Elmtree and Hardo thought it was funny to put a marker on it AFTER I had ripped over it TWICE[}:)]
Unfortunately no amount of ploughing will remove the rocks.

Gybesports

NSW

193 posts

Gybesports

NSW, 193 posts

31 Aug 2007 12:21pm

I hadn't dealt with G-sport since 2005 but It just came back to me from this thread that G-sport do the weed fins. I'll give him a call and see what I can find out. It'll take a 3 hour conversation - they are pretty verbose.

Regards

David

Bender

2236 posts

Bender

WA, 2236 posts

31 Aug 2007 10:22am

Grumps i feel your pain my nice new 32cm Techtonics is now a 30cm as with only three runs down into hardies i hit the rock (bout 300cm round) on all runs.

Haggar

QLD

1670 posts

Haggar

QLD, 1670 posts

31 Aug 2007 1:22pm

So how do you work out what size to use compared to a normal speed / slalom fin ?

decrepit

12885 posts

decrepit

WA, 12885 posts

31 Aug 2007 1:07pm

Probably about the same, if you're railing up, tail walking, fins to big. If you're going sideways, fins too small!
I think the fastest downwind is the smallest fin that doesn't go sideways.

I like Alby's idea of remounting a standard slalom at an angle. This should come close to turning a slalom all round foil into a speed foil.

For a 45deg change in angle the chord is increased by 140% but thickness doesn't change so a 10% chord to thickness becomes about 7%. Maybe a tad thin, and the thickest part will still be around 33% instead of about 40% of speed fins. So maybe not ideal but getting close.

I'm still experimenting with speed weedy's, will see how the next one I'm making for the wavewands speed1 turns out.

Will also have to test the experimental speed twiny sometime. It's almost ready to try.

yoyo

1646 posts

yoyo

WA, 1646 posts

31 Aug 2007 1:20pm

doesn't work that way mike. a 10% is still a 10% whatever the angle.

mathew

QLD

2174 posts

mathew

QLD, 2174 posts

31 Aug 2007 4:36pm

Mal Wright is starting work on some speed-slalom fins, ie: longer/thicker than the normal speed fin and not assymetric, but still computer foiled.

You could possibly re-base one of these so that you get the required angle.

nebbian

6277 posts

nebbian

WA, 6277 posts

31 Aug 2007 3:02pm

quote:
Originally posted by yoyo

doesn't work that way mike. a 10% is still a 10% whatever the angle.

Hmmm.... Why?

I was investigating this, and came across this link:
~~http://adg.stanford.edu/aa241/drag/sweepncdc.html~~

Check out near the bottom where they 'bottle' the fuselage

Longreef

NSW

49 posts

Longreef

NSW, 49 posts

31 Aug 2007 5:56pm

Wow so in effect the bottom of the board should have negative rocker for the width of the fin, to compensate for the swept fin. I wonder if routing out the base in the shape would be enough or whether it need to be in the board too.

I can see how this is easliy done on a board with tail cut outs.

anybody know anymore about the coke bottling?

yoyo

1646 posts

yoyo

WA, 1646 posts

31 Aug 2007 4:22pm

That doesn't work either. Whitcomb coke bottle effect is to reduced wake drag at supersonic speed due to shock wave formation. This shock wave formation at the speed of sound totally overpowers the skin friction and form drag which make up the drag equation at subsonic speeds.

You must be very careful trying to translate what happens to aerofoils to hydrofoils.

In the above example, reducing the volumne by hollowing out the tail of the board will not reduce the sonic shock wave.. there isn't one. Instead it will produce a low pressure area around the fin which will lower the speed at which cavitation starts.(not an issue in air)

But you can try it if you want .. others have.. then they are puzzled why it doesn't work... they didn't read enough... a little knowledge is a dangerous thing :-))

Mike, with the thickness thing, consider the freestream flow can be broken up into 2 vectors. One going parallel to the leading edge and the other normal (perpendicular) to the leading edge. Clearly the vector flowing parallel to the LE will not have any effect on the flow over the foil so you are left with just the vector normal to the LE. ergo a 10% foil is a 10% foil whatever the angle.

From this a few other things should become apparent... see if you can figure it out :-))

hardie

4133 posts

hardie

WA, 4133 posts

31 Aug 2007 4:26pm

Che?

Is someone gonna get me a fast weed fin, or am I gonna have to stamp my feet, scream, and shout, and embarrass you all next time we are at the supermarket together?

Wineman

NSW

1412 posts

Wineman

NSW, 1412 posts

31 Aug 2007 7:09pm

quote:
Originally posted by Bender

Grumps, perhaps you and all the WSP Mob could sail it with big deep pointer fins and clear out all the weed so the Mandurah Mob can have a real crack at some quick runs.

Get the council to buy one of these

www.seabreeze.com.au/gallery/gallery.asp?imageid=5756

get a BIG RED ROCK-EATER to go with it

(Mineral1 again)

& hey presto...a clean speed strip

Longreef

NSW

49 posts

Longreef

NSW, 49 posts

31 Aug 2007 11:07pm

In my desperate attempt to get an hour on the water I went to Jamison Park on Narrabeen lake. I hadn't been there for 10 years or more and found it completely weeded up where you used to be able to get a clear run across the lake in a westerly.

what are we calling this fin, speed weed or weed speed?

grumplestiltskin

2331 posts

grumplestiltskin

WA, 2331 posts

31 Aug 2007 9:29pm

quote:
Originally posted by Longreef

.

what are we calling this fin, speed weed or weed speed?

Both of those connotations sound like something Joey Johns would take

decrepit

12885 posts

decrepit

WA, 12885 posts

1 Sep 2007 2:19pm

quote:
Originally posted by yoyo

Mike, with the thickness thing, consider the freestream flow can be broken up into 2 vectors. One going parallel to the leading edge and the other normal (perpendicular) to the leading edge. Clearly the vector flowing parallel to the LE will not have any effect on the flow over the foil so you are left with just the vector normal to the LE. ergo a 10% foil is a 10% foil whatever the angle.

From this a few other things should become apparent... see if you can figure it out :-))

Not sure I follow you Dave, surely the flow has nothing to do with the leading edge? Isn't it approximately parallel to the bottom of the board??? Thus increasing the chord?

decrepit

12885 posts

decrepit

WA, 12885 posts

1 Sep 2007 2:33pm

On the plane to Canberra had a few more thoughts, for Hardy's run we don't just want to clear surface weed, there's also the stuff growing up from the bottom!
So I think low aspect ratio to decrease depth of fin would be a good idea, but how low aspect can you go??? what's the other advantages/disadvantages of high aspect over low?

Also is Hardy's always starboard tack?
If so we could go asymmetric, which brings up the question of which way do you make it asymmetric???
I guess the starboard side has the best foil for downwind speed, but what about Port?
If you're walking the board back up wind, that can have a very minimum foil for less drag, but if you want to sail upwind, it needs more foil depending, on how fast you want to get back.

decrepit

12885 posts

decrepit

WA, 12885 posts

1 Sep 2007 2:47pm

quote:
Originally posted by nebbian

I was investigating this, and came across this link:
~~http://adg.stanford.edu/aa241/drag/sweepncdc.html~~

Check out near the bottom where they 'bottle' the fuselage

All a bit beyond me I'm afraid, I'm an intuition, trial and error sort of person.

yoyo

1646 posts

yoyo

WA, 1646 posts

1 Sep 2007 5:01pm

yep, it is counter intuitive, but it is what it is.

Think of a sail... there is only one force on it. X force at Y angle to the cord. But aerodynamicist don't think of it like that. They break that force into 2 vectors. One sideways (or up on a wing) which they call lift and the other backwards which the call drag.

Likewise when you have flow over a foil. If that foil is swept then instead of saying as you do that it has X freestreem speed at 30 degrees you break it up 2 vectors like I said. As far as the water is concerned it is still a 10% section.

decrepit

12885 posts

decrepit

WA, 12885 posts

1 Sep 2007 7:23pm

Thanks for try to point me in the right direction Dave, but this counter intuitive stuff just does my head in!
I can't cope with that at all.
Think I'm going to have to do more research to get some different angles on that, may be something will make sense!

elmo

8895 posts

elmo

WA, 8895 posts

1 Sep 2007 7:49pm

Trying to figure out fins is what made me into a Muppet

Way to testicle for me

decrepit

12885 posts

decrepit

WA, 12885 posts

2 Sep 2007 9:51am

not much to do in Canberra at the moment, I've been browsing foils and stuff, there's an old thread on the starboard forum that's interesting

~~http://2006.star-board.com/forum/starbulletin/read.asp?ID=5434&t=200512151254~~

Here's an excerpt about what I thought of chord/thickness ratio changing with rake.

quote:

94
date 10/9/2005 11:29:22 AM
message Wolfgang,

I found some NACA test for tow tanks. Using the same foil section vertical or raked 30 degrees forward or back. The section was NACA 66012. They found the drag of both the 30 degree raked tests was lower because the effective thickness was reduced. The chord was 1/cos(30) longer but the thickness was the same.

naca.larc.nasa.gov/digidoc/report/tn/20/NACA-TN-3420.PDF

Yoyo,
I've found some stuff that shows your vectors as well, but the impression I get is they're for working out the lift/drag for a particular fin at different angles.
Seems there's data for standard vertical fins that needs to be converted for any rake. So for the calculation the fin is the same % but I'm still not convinced that's the way the water sees it.

What I need to do is calculate lift/drag for a fin using the angle conversion method and compare that result with a calculation of the actual parallel to board chord and thickness lift/drag, just have to figure out how to do it!!!!

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