The drag from the windsurfer and the use of such a small sail (comparatively speaking) makes the world "Sailing" speed records so much more impressive, don't they. I think windsurfing epitomises the development of efficient sailing rigs and foils. And needless to say the ability to drive a board and rig at those speeds down a course, as well as the abilities at freestyling and true wavesailing shows the skill levels reached in windsurfing that most sports could never emulate, probably a lot to do with the mindset of windsurfing.

it's not fault I'm large and non-aerodynamic. It's the pizza and beer !!(bouyancy)

The wind shadow effect of the sailor is of minor importance in the overall scheme of things. Whats more important is how much courage, determination and skill the sailor has. The aerodynamics of sailing at a broad reach reduces any turbulence caused by the sailor.


Wearing boardies outside the wetsuit causes drag and people to question your sexuality.

waveslave said...

The problem with windsurfing speed-sailing is that there is a large non-aerodynamic body (the rider) fully exposed to the wind.....
and more importantly,
this large body is right in the vicinity of the foil and partially obscuring it.
That's called major drag.
With other speed sports, the rider is usually dressed aerodynamically and/or tucked behind some sort of streamlined fairing.
With kites, the rider is a smaller proportion of the equation,
and doesn't interfere with the flow immediately around the airfoil.
Poleys could get around this problem by sailing double-surface airfoils.....
but they would need to get 'inside' them.
lol.

Mobydisc said...

The wind shadow effect of the sailor is of minor importance in the overall scheme of things.

Even on the super maxi-yachts that sail the Sydney to Hobart,
the crew are instructed to stay low and not push air.
(This is when they are on stand-by and not busy with the rigging.)

Considering people are so close to busting the 50 knt barrier, I am surprised that more attention is not being paid to rider drag.

When I used to do triathlon, a more aerodynamic seating postion would increase my average cycling speed by up to 4 km/hr for the same effort.

I know it would be impractical for a casual sailing session, but for a genuine hard-core record attempt, I would guess that some sort of aerodynamic foil worn over the trailing edge of the legs/arms/head might get that elusive 1 or 2 more knots needed to crack the 50.

greenleader said...

sooo.......why are the fattest the fastest?

imagine training a sumo wrestler to speedsail, records would tumble!

aerodynamics pfffft.

Nahh, aerodynamics have everything to do with it. However its the aerodynamics of the sail thats important. What kitesurfer doesn't really understand is that windsurfers do not have to be pushed along by the sail. Once pressure becomes great enough, the windsurfer is pulled along.

The analogy of yachts and windsurfing is false as the forces involved are not similar. I remember reading about a French board designer talking about yacht designs when talking about no nose boards around 13 years ago. I thought it was load of crap.

One reason fattest is sort of generally fastest is that the relative righting moment goes up with the cube of rider dimension ( as does mass ) but the rider's wind resistance goes up with his cross sectional area - or the square of rider dimension. ie for their given wind resistance a heavier sailor - if he chooses the right sail etc can generate more relative power.

That's also why those BMI figures divide your mass by your height cubed.

how about combining the two ? long board, windsurfer on the back with a sail, kite guy on the front with the kite/spinnaker????

Ah, Mr. Slave's just bored. No wind today? Gone fishing?

Thanks for raising an interesting topic though!

In windsurfing - having the rider opposing the force of the sail, and creating leverage through a triangle formed by the riders weight being transferred down onto the board as mast foot pressure - and the third part of the triangle being the riders legs and body leaning out providing the leverage against board and fin is integral to making windsurfers go as fast as they do. I believe that the rider is largely out of the direct lift creating windflow around a sail - but I agree that drag associated with the rider, and all the peripheral things like harness, boom, ropes could be looked at to reduce overall drag etc.
Having said that - re. kitesurfing - again the rider is out in the airflow creating a large amount of drag - not to mention those little lines to your kite - I reckon youd be surprised at how much drag they'd contribute - considering how long they are.
I guess if in fact kites were substantially more aerodynamic than windsurfers then shouldnt they then be quicker - which we know theyre not at this stage.

Im sorry to disagree with you Mobydisc; but Im yet to see any evidence regarding windsurfers being pulled along at certain speed. I have heard this one bandied about at times - but I think this is fallacy. A sail - whether a yachts sail or a windsurfers sail - both are reasonably crude airfoils when the wind gives them shape - whether the wing be horizontal as in a planes airfoil or upright in a sails - lift is created; and that lift or pressure difference is used in the sails case to provide the forward momentum. Take it a step further than windsurfing - some of the fastest land yachts use an upright rigid wing - basically an aircraft wing - to create their incredible speeds.

Mobydisc said...

When a windsurfer is going faster than the wind then there must be some other force at work beside the pushing force of the wind.

All sails are wings, unless it's a spinnaker, then it's just a big bag of wind. The forces are opposite to an aeroplane's wing - in an aeroplane, the forward thrust generated by the engines creates lift upwards at 90 degrees. With a windsurfer's sail, the wind generates lift resulting in forward thrust delivered at the mast foot (balanced by the opposing lift of the fin).

This is how we can easily sail at twice the speed of the wind. Like pinching an orange pip, and it fires out of your fingers. If you're on a beam reach in 12 knots of wind doing 24 knots, your body's wind shadow is well behind the trailing edge of the sail.

A sailboarder's and kiteboarder's body creates equal amounts of drag without disrupting the air flow over the wing.

what if I smother myself with KY gel ? (again) Or wear a wettie with the texture of a golf ball (dimpeled) ??? Maybe the speed record will go to a greased up person with a pointy nose and a huge arse???? Only time will tell.....ok back to the serious conversation.

I thought only kiters were dragged along behind their kit?

A bit of a branch from the topic: was looking at the x-ply on my sail and wondering how much all the little bumps affect the air flow. Then I wondered if you couldn't take advantage of this, lot's of little mini foils... somehow. What if you put thousands of micro foils into the actual fabric of the sail to create more surface area and even more "lift"? (I'll put it out now, I've smoked enough)

Bails said...

The future: hydrofoil windsurfers. No doubt.

Nah, even more drag than skimming across the top. Smoother ride though: