|11th February 2008 01:21 PM|
50 Knots/10" has alreadt been broken by a windsurf
|9th February 2008 03:59 PM|
All together very good ideas of Michel to reduce drag. Of course surface design is the secret of nature. But first the main issues have to be solved. Main part in limiting the speed in windsurfing is the ratio between board and sail. See the kiters and you will find for speed kiting a 9 sqm kite and a very small board with moreless no fin. Additional a fast going kitebord is extremly reduceing the wetted surface. Because of the big kite and small board speed kiter have to go very deep downwind to find the balance between kiteforce and bodyweight.
Okay, conclusions for speed windsurfing:
Use a big deep fat sail, much bigger as usual recommended for your speed board. Very difficult to start but needed for the deep downwind. Next problem to solve: When reaching 80% of your top speed the fin is much to big! That means the fin is not anymore working in the field of best drag/lift ratio (polardiagram). Best would be to be able to reduce at 80% top speed the size of your speedboard down the size of a mono water ski and also reduce the area of the fin to the size needed at top speed (can be calculated by finding the are out of the best drag/lift coeffizient). A lot of points to solve to hold against the top speed of kiters.
But: I all conditions with micro waves bigger than a view cm windsurfers will be faster. Only in "pools" of extremly flat water and deeps of a view centimeter allowing no waves kiter will be faster because of there physical advantages.
|9th February 2008 05:35 AM|
These ideas are from the GPS-SS forum by Michel Miejer, what do you think about them?
First of all let me say that I'm not an expert in hydrodynamics or aerodynamics.
Being involved in science(neuroscience it is) I stumble apon a lot of intersesting literature. Recently my attention was drawn to an article in making surfaces superhydrofobic. This gave me the idea that it might be useful to decrease drag of the board/fin. So I started a small search into literature into drag and espiacially reduction of drag.
Being board, sail or fin all three suffer from multiple forms of drag.
The board from drag of the surface, the waves and the air with the biggest factor for the wave drag followed by the surface.
For the fin and the sail these are bodydrag(the shape) and surface drag.
So how could we optimzize these systems?
Well I started looking at nature and espially at aquatic animals.
How are fish like makoshark, sailfish and blue marlin able to reach speeds of 60 knots in water. Well the interesting part is the tail(the fin). Well looking at the latest designs of the fins used by Martin and others were almost there there's a lot of resemblance.
If you look at the microscopic structer of these animals you will see that it looks like a V. But then a lot next to each other running along the side of the body.
These grooves makes the water less turbelent which means less drag. This was already discovered in the 80's. 3M made a tape they called riblet tape and was used in the America's Cup of 87. The only ship using it had 13.5 % less drag resulting in 6.5% higher speed comapered to the rest. So they won. But this tape was hard to make and expensive so it was forbidden. But it is still used by the army on ships and planes. So riblet on the side of the fin could be useful.
Another strikin feature are the small fins in front of the tail, probably they act as vortex generatots therby reducing. The idea is that by placing a vortex generator you create turbelence which creates drag. But this turbelence makes the turbulent and laminar alyers shift later which reduces drag. Its like gease flying in V formation.
So this for the fin what about the board.
Michel Meijer 2-7-2008 22:15
The surface of the lotus and insectwings have common feature. On the surface there a waxknobs. The size and distance of these waxknobs create a feature called superhydrofobicity. This is measured in a so called contactangle. this the angle between a droplet of water and the surface. Teflon for instace has an angle of 110 but sperhydrofibic surfaces can go up to 170 degrees. Meaning there is almost no contact between the surface and the water(180 dgeres menas that there is no contact only air between the surface and the droplet).
Guess wat there is a company making this stuff because of its selfcleaning properties. I have asked them for a sample. First indications are 20-30% reduction in drag(wave drag). If they want cooporate as have protocls for making these surfaces bu either I have to use nasty solvents or heat the surface to 280 C. Both of with my board don't like.
What about the sail?
Michel Meijer 2-7-2008 22:24
Ok the sail.
For the sail all the same stuff I mentioned for the fin accounts. If you like at the surface of modern sail you have a rough leading edge and the rest is smooth. Actually shouldn't this be the other way around a smooth leading edge followed by V grooved surface to the end. This is how the suits of iceskaters work. Ten years some american company made a textile called Supertread. They used it for skieers in the world cup reducing up to 30% of drag.
Another thing I found was how birdwings function. When the angle of attack ofwind becomes to high the wing stalls(like spin-outs). But is delayed by placing some small flexible flaps at the end of the sail. This prevents turbelence in stalling situations and it creates 10% more lift.
Michel Meijer 2-7-2008 22:35
Then the water we are sailing in.
Based on studies on swimmers they found that rasing the watertempereture in a pool from 25C to 30C you have 5% less drag.
Warmer water is less viscous. If you calculate this for water of 5C to 25C you gain 50% reduction in viscousity!
To conclude a long story.
Improvements of the surface 13% less drag
Placing vortex generators ?% less drag
Superhydrofobicity 20-30 less drag
Improvements pf the surface ?% less drag
Placing flaps 10% more lift and deeper angles with light winds
Going from colder water(although more laminar flow) to warmer water 50% less viscous water so less power needed so higher speeds.
Probably using riblet film at underside of the board plus placing a small fin in front of the big fin would also mean you could make this fin also smaller so again less friction and you could sail in shallower waters.
Michel Meijer 2-7-2008 22:38
So if any of the experts here has any thoughts/ comments on my ideas it would be nice to here them.
Have fun and may we beat the kiters:-)
|9th February 2008 12:33 AM|
Not to late
The kite boys are knocking on the door and so is the Vot Rocket.
|8th February 2008 11:40 PM|
Soon a new king for speed.
|8th February 2008 10:29 AM|
Windsurfing needs a technological or developmental leap.......
to catch up with kiting speeds now, C'moorn starboard, Tiesda do something about this!!!!!
This needs to inspire us to go faster, hulls with less drag, fins with more lift and reduced drag