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?
quote:
Originally posted by Gybesports
Hi Hardie
Have you tried any of the g-sport weed fins? Or are they too slow?
I would definately pay $$ for a proven fast weed fin as all my customs just dont seem to cut it!!
Elmo Weedies
Guaranteed to make you sail like an Elmo
quote:
Originally posted by Bender
I would definately pay $$ for a proven fast weed fin as all my customs just dont seem to cut it!!
quote:
Originally posted by elmo
Elmo Weedies
Guaranteed to make you sail like an Elmo
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
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???
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
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
.
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
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
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.
So how do you work out what size to use compared to a normal speed / slalom fin ?
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.
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.
quote:
Originally posted by yoyo
doesn't work that way mike. a 10% is still a 10% whatever the angle.
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?
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 :-))
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?
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
(Mineral1 again)
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?
quote:
Originally posted by Longreef
.
what are we calling this fin, speed weed or weed speed?
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 :-))
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.
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
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.
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!
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 interestinghttp://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
