Select to expand quoteFrancone said..
Superhuman skills do not exist , therefore beach starting at ..
Perhaps, but like infinity in maths that is not the point, it is very relevant, because a real sailor's skills are somewhere between zero and superhuman.
As an extreme example weight has actually has nothing to with BS or WS, it simply a function of being able to get your weight and the sail over the board so that you can stand up. Weight only becomes relevant once you consider less than perfect agility and balance.
as Sparky said 'You are trying to make science of what is an art. Not easy!'
Back to your 52lb, then consider the following polars, even approaching this aerodynamically its not so simple...
Not sure where you got the 52lb, but if it is the reaction force from air hitting a flat surface, then it might be worth considering a guy called newton tried a calculation like that once, it didn't work out...
For a beach start, IMHO the limit factors are, possible damage to your precious fin, shoredump, fin length and skill, or its not a beach at all.
Select to expand quoteracerX said..Francone said..
Superhuman skills do not exist , therefore beach starting at ..
As an extreme example weight has actually has nothing to with BS or WS, it simply a function of being able to get your weight and the sail over the board so that you can stand up. Weight only becomes relevant once you consider less than perfect agility and balance.
Not sure where you got the 52lb, but if it is the reaction force from air hitting a flat surface, then it might be worth considering a guy called newton tried a calculation like that once, it didn't work out...
I do not agree with the statement that weight has nothing (?) do with B.S. or W.S. and that it is a question of getting the weight and the sail over the board. Exactly, but isn't getting the weight on the board in function of ( and affected by) your weight, too?
Perhaps in B.S. weight is irrelevant, but for W.S. it is not.
Everything being equal, it stands to reason that a normal, well fit 145 lbs sailor , because of his/her weight, is more advantaged in W.S. than an equally well fit , 250 lbs 6.4 individual: I am not arguing that, in the end the heavier sailor won't be able to waterstart. Both will, but in terms of energy expenditure and ease, the lighter sailor is advantaged.
Years ago, I was learning hang -gliding and I had first hand experience of the dramatic difference the weight makes wind-wise: I weighed about 75 kg at the time and I was trying to get airborne in a light wind.
No matter how fast I ran for lift-off, it took a long , fast run, sometimes unsuccessfully, to get airborne, while a tiny girl next to me, probably 60 kg or less, could lift off in a few steps .The wind literally snatched her up in the air!
At the other end of the scale, there was a big guy, taller and heavier than me. However hard he tried, he could never lift off. After the first week he gave up!
I agree that windsurfing and hang-gliding are not the same, but wind is wind and weight is weight! Yes, weight matters !
Having said this, I find your polar diagram interesting and telling. It quantifies what we already know from experience: the wider the angle of incidence , the higher the drag and the lower the lift( forward thrust) and viceversa. This is why on an upwind course the craft attains less speed ( lift ) for the same windspeed than on a downwind course .
The diagram shows this very precisely : for a given A.R. of the sail , for inst for AR=6 , a 90 deg. angle of incidence ( the wind blowing directly across the sail) produces the highest drag coefficient on the X axis ( approx. 1.3) , while the lift on axis Y is 0.
Conversely at 15 deg. incidence , the drag coefficient decreases to approx 0.2, while the lift rises to approx. 1.3.
I must say, though, that from a " pragmatic" standpoint, which seems to be the standpoint that everybody advocates in this Forum, and perhaps rightly so, this diagram has perhaps just as little relevance as my bringing in Newton on a beach start issue.
By the way, regarding Newton, I wouldn't argue too much with him : he is still the foundation of our science and physics to day and practically all of today's technology rests on his equations, with the only exception of advanced physics involving velocities approaching the speed of light. For this , Einstein's Special Relativity has replaced Newton for more accuracy, but both Einstein's and Newton 's equations yield exactly the same results for objects moving at normal velocities , i.e. a fraction of the velocity of light ( airplanes, spacecrafts, satellites, etc..)
Indeed, if it was not for A.Einstein's totally counter-intuitive theories, yet validated by experience in almost 100 years ( namely, space and time shrink (!)and stretch (!) depending on the observer's frame of reference and on gravitational forces), the GPS calculations would be entirely off , possibly by kilometers.
Francone
Select to expand quoteFrancone said..
I do not agree with the statement that weight has nothing (?) do with B.S. or W.S. and that it is a question of getting the weight and the sail over the board. Exactly, but isn't getting the weight on the board in function of ( and affected by) your weight, too?
Perhaps in B.S. weight is irrelevant, but for W.S. it is not.
Everything being equal, it stands to reason that a normal, well fit 145 lbs sailor , because of his/her weight, is more advantaged in W.S. than an equally well fit , 250 lbs 6.4 individual: I am not arguing that, in the end the heavier sailor won't be able to waterstart. Both will, but in terms of energy expenditure and ease, the lighter sailor is advantaged.
Years ago, I was learning hang -gliding and I had first hand experience of the dramatic difference the weight makes wind-wise: I weighed about 75 kg at the time and I was trying to get airborne in a light wind.
No matter how fast I ran for lift-off, it took a long , fast run, sometimes unsuccessfully, to get airborne, while a tiny girl next to me, probably 60 kg or less, could lift off in a few steps .The wind literally snatched her up in the air!
At the other end of the scale, there was a big guy, taller and heavier than me. However hard he tried, he could never lift off. After the first week he gave up!
I agree that windsurfing and hang-gliding are not the same, but wind is wind and weight is weight! Yes, weight matters !
Having said this, I find your polar diagram interesting and telling. It quantifies what we already know from experience: the wider the angle of incidence , the higher the drag and the lower the lift( forward thrust) and viceversa. This is why on an upwind course the craft attains less speed ( lift ) for the same windspeed than on a downwind course .
The diagram shows this very precisely : for a given A.R. of the sail , for inst for AR=6 , a 90 deg. angle of incidence ( the wind blowing directly across the sail) produces the highest drag coefficient on the X axis ( approx. 1.3) , while the lift on axis Y is 0.
Conversely at 15 deg. incidence , the drag coefficient decreases to approx 0.2, while the lift rises to approx. 1.3.
...
Except that's not what I said, nor my point
Weight is only irrelevant, if you have infinite agility, and perfect balance, if you have zero agility and no balance you need the sail to do all the work, with a big board.
Your hang gliding example is much simpler, in non-accelerated flight lift = weight.
Regarding the polar, what I meant was I did not know where you got the 52lbs from, but if we assume a flat plate perpendicular to the wind has as drag coefficient of 1.15, then a sail with AR of 1 might have a lift coefficient as high as 1.5 and drag coefficient 1.2, so if you combine the two coefficients geometrically to your advantage you get a coefficient of 1.92.
Enough from me I am off to windsurf
Select to expand quoteracerX said..
Enough from me I am off to windsurf
Lucky you! We still have snow here..Probably another two months.
Windstarting will be my next challenge for the incoming season, (probably not many left, though (windsurfing-wise, of coarse, because for the rest I still count on as many seasons as possible..).
All the insights I gained by chatting on this forum, even while occasionally disagreeing, will have certainly been beneficial.
Thanks for your input and have a a good wind..
Francone
