Just for the fun, I am trying to calculate what is the total wind force ( lbs/sqft) produced on a sail of a given size, given the wind speed in knts. The ultimate end of this exercise is to determine ( approximately) how much of my total weight ( 85 kg) can be pulled up by the wind on the sail during a beach start or a waterstart.
According to a chart at forum.woodenboat.com/showthread.php?69064-Wind-pressure-on-sails , a 15 mph wind would produce 1lb/sqft pressure on the sail, i.e 40 kg on a an 8.0 m2 sail . If I weigh 85 kg, this means that about half of my weight can be pulled up by a 15mph ( 12 knts) wind when beach or water starting.
By the same chart, a 23 mph ( 20 knts )wind will exert a 2lbs/sqft force on the same sail , i.e. an 80 kg pull on the sailor.
If he or she weighs 80 kg, this means that the wind will have done all the work.
I'll test this on the water in a few months. In the meantime, I'd like to have comments.

Thanks

Ittiandro

This will be tricky to work out, remember in the initial waterstart position the sail is almost horizontal so most of the wind is just going over the top without hitting the sail. Probably a few other factors to consider too.

And the water start relies on you using your legs and moving your body closer to the board to get up. Not the sail using its lift to pull you out. At 85 kg with an 8.5 sail I can water start in 6/8kts. As just a maths exercise it would be just vectors and moments with a distribution load

The velocity and direction of flow over the foil (sail) is critical as well. A small change in wind flow often brings about a large change in power/lift.

This is one of the reasons why it is a lot easier to stay planning, than get planning. As soon as the board has speed, that speed is added to the apparent wind flow over the sail. Conversely, you may often be powering along feeling like there is plenty of wind, but as soon as the board slows down in a Gybe, it feels like the wind has dropped and you struggle to keep planing out. Well the true wind may not have changed, but the apparent wind may have dropped by 10 knots!

Air temperature is a factor too. A cold wind exerts more force for the same wind speed than a warm wind.

Select to expand quote

kato said..
And the water start relies on you using your legs and moving your body closer to the board to get up. Not the sail using its lift to pull you out. At 85 kg with an 8.5 sail I can water start in 6/8kts. As just a maths exercise it would be just vectors and moments with a distribution load

Good point. I overlooked Newton's 3rd law : when you either step on the board from the beach or rise off the water ( W.S.), you first push down on the board with the rear leg while pushing the rig upwards and this creates an additional momentum with a force equal to the one with which you push down, but in the opposite direction, i.e, upward. This force combines with the wind force.
I think I understand now why you can W.S. at 85 Kg with only 6/8 knts!

If not for the physics, I never would have thought it possible! As a matter of fact, I started learning B.S. only towards the end of last summer, but I promptly went back to uphauling because even at 12 knts I was unable to B.S. I'll try again next season.
Looking at the theory from various instructional sites or videos on the Internet, I think my error was that I wasn't keeping close enough to the board and that, instead of of pushing up the rig with extended arms, I ended up in hanging down from the boom!

I am now practising the B.S. at ..home. Not that my home is flooded! It is just that I want to strengthen my legs by hopping up on an 18" high chair, with a scale on it. Since the first leg rests on the scale when rising up , I noticed that when I begin weighing on it, the reading is about 40 kg, indicating ( by the same Newton's 3rd law) an equal upward pushing force of of 40 kg which combines with the wind's force to raise me up completely on the board.



Ittiandro

What about clew first water starts.
More lift.

don't need much wind to do a beach start, basically step on board n go in shallow water
not much wind = NOT much force required
(more about balance & counter-balance ??)
- i don't follow laws - i break em

?t=12

or my shabby methodology ...

Select to expand quote

joe windsurf said..

not much wind = NOT much force required
(more about balance & counter-balance ??)

Thanks for the videos.Very nice
I don't understand the equation, though:it appears to me that the less the wind, the more you have to compensate with your own force to hoist yourself up. Unless there is something I am missing...

I noticed the ease of your B.S., but it looked pretty breezy, too. By the way, what was the approximate wind speed ?


Francone

Select to expand quote

Francone said..
Just for the fun, I am trying to calculate what is the total wind force ( lbs/sqft) produced on a sail of a given size, given the wind speed in knts. The ultimate end of this exercise is to determine ( approximately) how much of my total weight ( 85 kg) can be pulled up by the wind on the sail during a beach start or a waterstart.
According to a chart at forum.woodenboat.com/showthread.php?69064-Wind-pressure-on-sails , a 15 mph wind would produce 1lb/sqft pressure on the sail, i.e 40 kg on a an 8.0 m2 sail . If I weigh 85 kg, this means that about half of my weight can be pulled up by a 15mph ( 12 knts) wind when beach or water starting.
By the same chart, a 23 mph ( 20 knts )wind will exert a 2lbs/sqft force on the same sail , i.e. an 80 kg pull on the sailor.
If he or she weighs 80 kg, this means that the wind will have done all the work.
I'll test this on the water in a few months. In the meantime, I'd like to have comments.

Thanks

Ittiandro

I think what your trying to do is actually very hard, and maybe a little misguided, especially if you are approaching it aerodynamically.

Just for starters if you are stationary, does sail drag count? is there in fact any sail drag? Depending on your frame of reference the answer could be Yes or No. What happens when you move the sail?

Select to expand quote

racerX said..

Francone said..
Just for the fun, I am trying to calculate what is the total wind force ( lbs/sqft) produced on a sail of a given size, given the wind speed in knts. The ultimate end of this exercise is to determine ( approximately) how much of my total weight ( 85 kg) can be pulled up by the wind on the sail during a beach start or a waterstart.
According to a chart at forum.woodenboat.com/showthread.php?69064-Wind-pressure-on-sails , a 15 mph wind would produce 1lb/sqft pressure on the sail, i.e 40 kg on a an 8.0 m2 sail . If I weigh 85 kg, this means that about half of my weight can be pulled up by a 15mph ( 12 knts) wind when beach or water starting.
By the same chart, a 23 mph ( 20 knts )wind will exert a 2lbs/sqft force on the same sail , i.e. an 80 kg pull on the sailor.
If he or she weighs 80 kg, this means that the wind will have done all the work.
I'll test this on the water in a few months. In the meantime, I'd like to have comments.

Thanks

Ittiandro

I think what your trying to do is actually very hard, and maybe a little misguided, especially if you are approaching it aerodynamically.

Just for starters if you are stationary, does sail drag count? is there in fact any sail drag? Depending on your frame of reference the answer could be Yes or No. What happens when you move the sail?

As explained in my original post, the purpose of this exercise is to determine approximately(!!!) the lb/sqft wind pressure on a sail of a given size when the wind is blowing into the sail of a stationary board at beach start, at a given speed.

I still think therefore that it is possible to get an approximate answer to my question without striving for mathematical precision and safely ignoring the complex of physical forces acting on a moving sail( drag, the angle of attack of the wind, etc ) .

At the time of this reply, I have just found a site that answers my question with the formula: P=V^2 x .0043, where P= pressure/sqft and V=windspeed in knts : for V=12 knts, P on an 8M2 ( 85 sqft) sail would be 52 lbs.

The site is forum.woodenboat.com/showthread.php?69064-Wind-pressure-on-sails&p=1640890#post1640890

They may be just as misguided as I am, or are they?

Love to hear comments

Thanks

Francone

Select to expand quote

Francone said..

At the time of this reply, I have just found a site that answers my question with the formula: P=V^2 x .0043, where P= pressure/sqft and V=windspeed in knts : for V=12 knts, P on an 8M2 ( 85 sqft) sail would be 52 lbs.

The site is forum.woodenboat.com/showthread.php?69064-Wind-pressure-on-sails&p=1640890#post1640890

They may be just as misguided as I am, or are they?

Love to hear comments

Thanks

Francone

No, their problem is much simpler, as an extreme example, with an 8M sail you can beach start in LESS than 0 knots, if you have superhuman skills you could water start a 5m sail in say 5knots, with less than superhuman skills your result will differ but by how much? How does your 52lbs fit into that?

Maybe you could come up for a mathematical formula for a windsurfer with no skills but what use would that be? Not saying it can't be done.

My suggestion is too approach this empirically, by going for a windsurf and just see what happens

hey Francone:

checked my notes - winds were 20-30 kph on that day (prob average only 12 knots !!)
wanted to use my JP SLW92 with a 10 meter sail, but buddy wanted to try the JP
and so, I was out with the Mistral Equipe One and MS TR-6 8.4 ...
...
as I have said before, do NOT over analyse the beach starts - just do it
we need to make a bet - will you nail your beach starts or will i get in the straps first this year ??

JE

Select to expand quote

racerX said..

Francone said..

At the time of this reply, I have just found a site that answers my question with the formula: P=V^2 x .0043, where P= pressure/sqft and V=windspeed in knts : for V=12 knts, P on an 8M2 ( 85 sqft) sail would be 52 lbs.

The site is forum.woodenboat.com/showthread.php?69064-Wind-pressure-on-sails&p=1640890#post1640890

They may be just as misguided as I am, or are they?

Love to hear comments

Thanks

Francone

No, their problem is much simpler, as an extreme example, with an 8M sail you can beach start in LESS than 0 knots, if you have superhuman skills you could water start a 5m sail in say 5knots, with less than superhuman skills your result will differ but by how much? How does your 52lbs fit into that?

Maybe you could come up for a mathematical formula for a windsurfer with no skills but what use would that be? Not saying it can't be done.

My suggestion is too approach this empirically, by going for a windsurf and just see what happens

Superhuman skills do not exist , therefore beach starting at ..0 knts or W.S. at 5 knts windspeed on a 5 m2 sail should be left out of a mathematical exercise, however imprecise it may be .

If the formula P=V^2 x .0043 is correct, as you seem to think, then the 52 lbs solution does fit into my quest . How?
Well, however theoretical ( and possibly approximate) this finding may be, it tells me that, even at that relatively low windspeed, the wind will lift a big chunk of my weight, about 30% .

In other words it would be as though , for the purpose of beach starting, my weight was even less than what it was in my 20's, when I was a ..thin, athletic youth, perfectly able to do 15 chin ups on a pull up bar, which I cannot do anymore now at my age and my weight, 20 kg after..
The wind would now take over for a few moment the extra lbs I have picked up in 50 years!
Kind of reassuring, a far cry from the strain on my back caused by the uphauling I have been doing so far !

This is how 52 lbs fits into all this!

But I do agree with the suggestion to adopt an empirical approach, on the beach. Of course!
Unfortunately it still winter here, although, at the tail end and it won't be before June that I can finally practice at the beach..

Francone

Select to expand quote

joe windsurf said..
hey Francone:

checked my notes - winds were 20-30 kph on that day (prob average only 12 knots !!)
wanted to use my JP SLW92 with a 10 meter sail, but buddy wanted to try the JP
and so, I was out with the Mistral Equipe One and MS TR-6 8.4 ...
...
as I have said before, do NOT over analyse the beach starts - just do it
we need to make a bet - will you nail your beach starts or will i get in the straps first this year ??

JE

Looking at the chop, I thought the windspeed was more than that.

Regarding analyzing (or ..overanalyzing) , I am a bit of a theoretical bent and this is my best way to learn : once I have everything clear in my head, then " doing" will become easier.

For the moment, my back FEELS as good as it can possibly be, although it IS NOT good , according to the verdict of the DXA scan machine at the hospital.

In my condition, I need learning B.S. and possibly W.S. much more urgently than you need getting into the straps. I have to nail B.S. ! I cannot afford not to, because I risk serious problem with my back, possibly fractures, if I continue uphauling as wildly (and , often, as wrongly )as I have been doing so far.

So far I have been lucky, I guess. Some days , especially on choppy waters, I was doing more uphauling than sailing (!) and often the wrong way: arching the back! Yet, I never suffered more than slight back aches, lasting a couple of days at most.

Fortunately, with the Windsup, I fall much less now . I am glad I bought it.

Now doctors warn me against vertebral compression fractures ( sometimes unnoticed!) from even minor falls or excessive spinal torsions or flexions of the trunk. If I ever had a burning desire to do skydiving, skiing , bunjee jumping or judo, I'd certainly think twice, unless I was suicidal..

I still think, though, that windsurfing ( except wave jumping or sailing in 30 knts winds) is still relatively safe, at the leisurely way I do it, once I avoid uphauling.
In fact there are no excessive torsions or flexions and we stand upright on the board . If we fall, we fall in water and all doctors agree that swimming is absolutely no problem for the back , as the water supports the body.

I think that the wetsuit and the harness already support the back . May be I can slip on a lumbar brace.. It is relatively stiff, but thin enough not to hamper the movements. It may be a bit bulky under the harness, though. I'll see.

Take care

Francone

Beach starting in 0 knots doesn't take superhuman skills. It's doable by nearly anyone who can beach start. As long as the board is floaty enough.

Select to expand quote

Sparky said..
Beach starting in 0 knots doesn't take superhuman skills. It's doable by nearly anyone who can beach start. As long as the board is floaty enough.

So how much water under the board are we talking about here? And sailor height?

300/400mm of water no worries...

Select to expand quote

Subsonic said..

Sparky said..
Beach starting in 0 knots doesn't take superhuman skills. It's doable by nearly anyone who can beach start. As long as the board is floaty enough.

So how much water under the board are we talking about here? And sailor height?

300/400mm of water no worries...

A bit more difficult if your fin is over 40cm, but yes, average fin depth. Easy, no worries, as you say. Sailor height is all proportional, smaller sailor, smaller gear, smaller fin.
Becomes very difficult at the extremes with formula gear, but that's why you push out into depth and up haul formula gear most times.
Still, why are we sailing in no wind? Sometimes there is no wind on the inside when launching. Sometimes it's also very gusty on the beach launch.

Select to expand quote

Francone said..

In my condition, I need learning B.S. and possibly W.S. much more urgently than you need getting into the straps. I have to nail B.S. ! I cannot afford not to, because I risk serious problem with my back, possibly fractures, if I continue uphauling as wildly (and , often, as wrongly )as I have been doing so far.

Francone

In that case put the textbooks away, and approach this empirically. Ideally find a thoughtful instructor, and explain your situation.

Alternatively you may get good advice here.

For starters, place some sensible limits on your windsurfing, I would say restrict yourself to 5.3 sail (or similar depending on what you have) unless there is sufficient wind to water start larger sails, say 15knots. IMHO For someone like yourself learning to water start first before moving onto the beach start would be more helpful.

A simple formula might be a 5.3 for 0 to 15knots, slightly bigger sails from 15 knots up 20knots and 5.3 and down from 20knots and above, or something like that.

Select to expand quote

Sparky said..

Subsonic said..

Sparky said..
Beach starting in 0 knots doesn't take superhuman skills. It's doable by nearly anyone who can beach start. As long as the board is floaty enough.

So how much water under the board are we talking about here? And sailor height?

300/400mm of water no worries...

A bit more difficult if your fin is over 40cm, but yes, average fin depth. Easy, no worries, as you say. Sailor height is all proportional, smaller sailor, smaller gear, smaller fin.
Becomes very difficult at the extremes with formula gear, but that's why you push out into depth and up haul formula gear most times.
Still, why are we sailing in no wind? Sometimes there is no wind on the inside when launching. Sometimes it's also very gusty on the beach launch.

Yes, that's about it. I can put back the Dolphin fin on the Windsup . It is only 10 " deep . I can practice B.S. on shallow water with that, then I 'll reinstall the regular ( longer) weed fin for deeper water when I am more comfortable.

Now I am doing mock B.S. and W.S. at home.
For the B.S., I practice it by hopping on a 20" high chair with one leg ( back leg first) and by extending my arms upward and forward just as if I had the boom in my hands.
Since I can do it very easily at home, without wind, I imagine it will be even easier with some wind and only a ft of water..
The only tricky thing I can foresee on the water is that the board moves around a bit when positioning the back foot..

For the W.S. I am practicing with a rope hanging about 3 ft from the floor from a cross bar on a door. ( I figure 3 ft is just about the distance of the boom from the water when I initially raise it with the arms while lying almost flat on the water, on my back.)

First, I reach for the hanging rope by raising my back from the floor (= lifting the boom from the water ) and leaning on the back leg bent at the knee ( about 90 degr) .
Even without wind, I am perfectly able to raise myself up completely, but it takes a bit more of an effort than B.S. ( probably 4 or 5, on a 5-10 scale).
It is well within my physical capabilities and I don't feel any strain on the back. I tried both with the lumbar brace and without. The brace helps a lot, but even without, it is not too much of a strain. Definitely, a lot less strain than uphauling.

Another thing I intend to work on is rig recovery and turning the board around while standing in the water or swimming.
Since the rig was always floating on the lee side after a fall and I always uphauled, I never felt the need for rig recovery or turning the board around..Now that uphauling is in back burner, I have to learn all this.
I found many instructional sites. The technique is simple, but it is like ..Columbus' egg!

It somewhat odd that it should be my condition that now forces me to re-learn ( or learn) windsurfing properly, in spite of the fact that I have been doing it my..own way for more than 20 years and with a lot of fun, too.

Francone

Select to expand quote

kato said..
And the water start relies on you using your legs and moving your body closer to the board to get up. Not the sail using its lift to pull you out. At 85 kg with an 8.5 sail I can water start in 6/8kts. As just a maths exercise it would be just vectors and moments with a distribution load

Kato, if you weigh 85 kg and you can push yourself up on only one leg ( assumedly the back leg, which is the first one engaged) with only a 6/8 knts wind, you must have bionic legs, unless you are on a 250 lt board, almost as unyielding as hard land !

An 8.5 sail is 91 sqft . If you feed this sail size into the P=v^2x.0053 formula ( P=lbs/sqft pressure, V= windspeed in knts, see below) and assuming the wind is blowing full front into the sail, it means that the wind will relieve you of only 8 kg, while the bulk of the remaining weight ( approx 80 kg) is still borne by only one leg and one knee! Even less wind relief if the sail presents a more downwind angle of attack)

When you are waterstarting, not only are you half floating almost horizontally on the water, with only one leg partially resting on the board, but, more importantly, you are rising on an almost 45 degr( or less!) bent back leg (!) , which forces the knee joint to undergo the high mechanical stress of raising 80 kg and straightening the leg from 45 degr into vertical position.
Once this is done, the knee and the bones ( tibia and femur) can certainly support the whole body weight, but until then not only does your knee ( one!) have to support 80 kg, but there are additional stresses on the tendons and cartilages, on different axial directions, which means tears and snaps.

Perhaps you should double check your wind speed, because it doesn't sound right that you can waterstart 85 kg in 6 knts!

One final note: the above P=v^2x.0053 formula is from forum.woodenboat.com/showthread.php?69064-Wind-pressure-on-sails

It is used to determine the wind pressure( lbs/sqft ) on a given sail saize , for a given windspeed. It is basically a reliable formula, especially, as somebody jokingly said, if you want to know what windspeed will take down your ..garage door during a hurricane..
It doesn't of course take into account the aerodynamic variables of sailing, ( angle of attack, boat speed, drag, etc) but it is adequate in the waterstarting scenario. A mechanical engineer has commented on it and he seems to agree.

Francone

You are trying to make science of what is an art. Not easy!
Many, many variables.
What about the front leg that is kicking in the water and propelling you upwards?
The buoyancy effect of being half submerged?
And the twenty other things not yet considered?
Anyway, most people can do quite a deep one legged squat.

This will be a very approximate number, there are soo many contributing factors.
Sailors ability, sail shape and where the max draft is in comparison to the boards most efficient position and fin type.

These things actually effect the sails max pull.......if the sails max pull is say 60kg, that could then only have say 50% of its power put into the board as the board and fin are not as efficient.....Then theres the twit holding onto it.......thats a whole other story...

Select to expand quote

Sparky said..
You are trying to make science of what is an art. Not easy!
Many, many variables.
What about the front leg that is kicking in the water and propelling you upwards?
The buoyancy effect of being half submerged?
And the twenty other things not yet considered?
Anyway, most people can do quite a deep one legged squat.

Yes, I am sure, the buoyancy effect and the kicking in the water may help ( even more with ..fins) . How much, though? I think only marginally, if you consider that, with only 6/8 knts winds, there would still remain a hefty 80 kg ( in our case) to be ...lifted off the water on a.... one legged squat.
I can do, too, one legged squats on land , (not as deep, though, as Ukrainian folk dancers, starting with the butt almost on the floor..). but I doubt that it is possible to do them for waterstarting, with an 85 kg weight, without adequate wind support ( most people say at least 12-15 knts) because neither the water ( especially fresh water, a far cry from saltwater, buoyancy wise !) nor the board offer the same support as the land : on the water, the energy expended in pushing down on the board in order to rise gets considerably absorbed ( and wasted) by the sinking board, however marginally it may sink and, of course, the problem, I believe, should get worse with 160 or 145 LT shortboards..

It is almost the same as when you tread on fresh snow without skis or snow-shoes : the more vigorously you tramp on fresh snow, the more you sink. Try doing a one legged squat on the snow and you'll see what I mean! Of course water is not quite the same because of the hydro-static force, but it is still a sinky element, for all the flotation devices you may wear..
From this perspective I think I have an advantage, because my board is an 11 footer, 230 lt Windsup, hard to sink!

May be if I knew what the other twenty variables are I'd be more convinced. Theory can indeed be at times proven wrong empirically , but until I see it for myself on the water, I have some reserves about waterstarting in 6 knts winds!

Francone

In this one respect, the single legged strength to get onto the board, the reverse of what you are saying is true. It is easier on your leg to climb onto a sinking board than a very floaty board. Maybe more wobbly etc, but when the board sinks down to meet you under the water it is easier to get on.

Select to expand quote

Sparky said..
In this one respect, the single legged strength to get onto the board, the reverse of what you are saying is true. It is easier on your leg to climb onto a sinking board than a very floaty board. Maybe more wobbly etc, but when the board sinks down to meet you under the water it is easier to get on.

Good point, Sparky.
I agree, theoretically, that a sinking board somehow eases up the windstarting process ( assumedly because it makes the leg squat less deep, therefore not as hard on the knee, the tendons and the muscles of the leg.

Perhaps, though, the truth is, as it often is, somewhat in the middle.. It all depends on how much the board sinks.

Certainly, if it sank ..one foot, you would be absolutely right ( from the ergonomic standpoint of the leg movement), because the leg would be only slightly bent, so that there would be little strain and effort involved in in rising up on it .

Realistically, however, unless you sail on a 90 lt sinker, most mid-volume shortboards only sink a few inches( very few, I surmise) and the gain of this is likely to be offset by the reduction of the full upward momentum predicted by Newton's 3rd law: as you press with the leg on a sinking board, a part of the energy is transferred not into pushing you up, but into pushing the board down .

With a very low wind, this loss of upward momentum , however marginal, may make the difference between being able to complete the W.S. or not.
Of course, the sailor's experience, his( her) strength and stamina are a contributing factor, but I can hardly envisage a 100 kg sailor , no matter how fit he ( or she ) is, waterstarting on 6 knts winds with an 8.5. Maybe a larger sail , yes, but then there would be other problems.. With a 85 kg it may be possible, but we have probably reached a limit which is within reach of only few of us...This is why I am always a bit skeptical when somebody claims ( in all good faith!) to windstart in 6 knts winds. Wind speed perception is subjective. ON one occasion, I was convinced that I was sailing in something like 18 knts winds, until somebody lent me an anemometer and I found they were only 13 knts...

Interesting debate, though ( maybe not for all!)


Thanks for the input

Francone

Select to expand quote

Francone said..

Sparky said..
In this one respect, the single legged strength to get onto the board, the reverse of what you are saying is true. It is easier on your leg to climb onto a sinking board than a very floaty board. Maybe more wobbly etc, but when the board sinks down to meet you under the water it is easier to get on.

Good point, Sparky.
I agree, theoretically, that a sinking board somehow eases up the windstarting process ( assumedly because it makes the leg squat less deep, therefore not as hard on the knee, the tendons and the muscles of the leg.

Perhaps, though, the truth is, as it often is, somewhat in the middle.. It all depends on how much the board sinks.

Certainly, if it sank ..one foot, you would be absolutely right ( from the ergonomic standpoint of the leg movement), because the leg would be only slightly bent, so that there would be little strain and effort involved in in rising up on it .

Realistically, however, unless you sail on a 90 lt sinker, most mid-volume shortboards only sink a few inches( very few, I surmise) and the gain of this is likely to be offset by the reduction of the full upward momentum predicted by Newton's 3rd law: as you press with the leg on a sinking board, a part of the energy is transferred not into pushing you up, but into pushing the board down .

With a very low wind, this loss of upward momentum , however marginal, may make the difference between being able to complete the W.S. or not.
Of course, the sailor's experience, his( her) strength and stamina are a contributing factor, but I can hardly envisage a 100 kg sailor , no matter how fit he ( or she ) is, waterstarting on 6 knts winds with an 8.5. Maybe a larger sail , yes, but then there would be other problems.. With a 85 kg it may be possible, but we have probably reached a limit which is within reach of only few of us...This is why I am always a bit skeptical when somebody claims ( in all good faith!) to windstart in 6 knts winds. Wind speed perception is subjective. ON one occasion, I was convinced that I was sailing in something like 18 knts winds, until somebody lent me an anemometer and I found they were only 13 knts...

Interesting debate, though ( maybe not for all!)


Thanks for the input

Francone

I am not talking "theoretically", but instead what I find in practice. I am convinced it is easier to pull up onto a semi sinking board than a big voluminous board.

My current example is 15-20 knots, 5.8 wave sail, 94 litre starboard kode, I'm 95kg.

It is all well and good to hypothesise on a subject but it's the practical experimentation that brings the truth. The theory needs testing.

Select to expand quote

joe windsurf said..

Yes Joewindsurf, the Beaufort scale is very useful here. I don't think we are going to be waterstarting in less than a force 4. We need to see some consistent white caps. Once going, we need to be in planing or very near planing conditions. A large sail can be hard to even lift off the water if there is no breeze to get under the leading edge and provide the initial lift.

I do admire Francone's quest for knowledge. However, I don't really give much thought to such an academic complexity as when I am on a windsurfer, I will be too busy worrying about the maths of it all. On the other hand, when I was marooned some distance away from the beach, and the wind has gone, and there I was sitting atop my board pontificating about life in general, then I did give such a topic a bit of going over. Then just when I nearly had the answer, the wind arrived...And I forgot what I was pontificating about !

Naval,navel gazing