A good anemometer is designed to have very low friction (none, for all practical purposes). So the density of the wind will not affect it's steady reading.
What it might affect is the variability of the reading. This would be because the measuring cups or blades have some mass and would accelerate faster in denser air to overcome the small amount of mass/momentum the spinning parts have.
The sailor feels more force with denser wind because, unlike the anemometer, the sailboard has a LOT of resistance to moving. The denser air provides more force to overcome that resistance.
Light wind for me is under whatever wind it takes for me to sail my 87L slalom board with my 6.4m cam race sail. Thats around 14-15 knots on really flat water with steady wind, and a couple more knots on choppy water. There is a difference because the resistance to motion is much lower on really flat water (Like Lake George or Albany/Lilacs) so one can build speed and run more on the apparent wind with a higher board speed to wind speed ratio. We commonly hit over 30 knots in 15-16 knots of wind at LG. In this situation, you don't go faster with a bigger board and sail as there is more drag.
Of course. I am blessed to live in a area where it is very common to have steady winds over 15 knots, so I am spoiled, and generally, very seldom use my 100L+ boards or 7m and larger sails. For the last few seasons, my most used combo is 5.7m cambered sail on IS80 20-28Knots). next would be 5.2m sail on speed board (25-35Kts), and last would be 6.4m on IS87. I rarely bother with IS97 on 7m, but use this if the wind is more variable and holey, and still have not used my IS117 with 7.7m sail this year! I'm actually wondering why I even have that gear!? 
A few days a year, in the middle of summer I will take an old Formula Board for a cruise with a No cam 8.4m sail in 8-12 knots. I didnt do it last summer as I spent the whole time at LG and sailed average 4-5 out of 7 days in over 15-20 knots winds. Often I could have sailed the other two days on that 'light wind' gear, but ya gotta rest sometime. 
Did I mention that I am LOVING retirement!
Select to expand quotedecrepit said..
This is an incorrect assumption for a friction less device, the cup will spin at the speed of the object hitting it regardless of the objects density. It will measure a feather travelling at 10km/hr the same as your brick.
If thats the case i understand now, thanks :)
Sorry for messing up the main subject.
Select to expand quotedecrepit said..Ben1973 said..
All I wanted to know was what people define light, med and strong wind as and what they would use in those conditions.
Well that's what happens on this forum, one question leads to a whole pile more interesting ones.
Just like a family discussion, you have to keep butting in to get it back on topic.
But there's very few off topic police here.
And to prove it here's another very rare but related wind strength subject.
Lamina wind, is more effective on a sail than turbulent.
I've experienced this at Lake George, in light wind. Couldn't get planning where there were small ripples on the water, but just flowed onto the plane when we hit the glassy smooth, then dropped off the plane when we hit the small ripples. A really weird experience, totally opposite to what you'd expect.
The only explanation I can come up with, is where there's ripples, even small ones, there's turbulence, where it's glassy smooth there isn't. I think this means that effective wind is over the whole sail in laminar flow, where as in turbulent flow the bottom of the sail doesn't work as well.
... am I missing something? why isn't it just what we would expect? That is, a smooth surface is less disruptive of motion than a rough one? It would seem to be the case at pretty much any speed. (I cannot cross 32-33 knots because of the water surface around here.). Unless of course you can use gravity to help getting on a plane, from the peak of a, well, big ripple, and then there is enough power to stay on a plane ...
Oh ... right ... definition of light wind. For me it is when it is time to take out my 7.5, or pathetically try to foil again, and failing. So there. Definition! The wind is light when I cannot fly my foil 
(others, of course, can do very happily in the same conditions).
So what we really need to something to measure wind force not speed. Just a long pole with some strain gauges would do it.
Select to expand quoteBen1973 said..
So what we really need to something to measure wind force not speed. Just a long pole with some strain gauges would do it.
yes an old fashioned spring balance, attached to a wind sock would do it. But it would only have a limited wind range, you may need a couple of them to measure a wide wind range.
Select to expand quoteSea Lotus said..
If thats the case i understand now, thanks :)
Sorry for messing up the main subject.
As Sailquick has pointed out, I missed the inertial affect. the brick will sping the cups up faster than the feather, because there is an initial inertial resistance. But the final speed will still be the same, as long as there is enough feathers continuously hitting the cups to do that.
Of course if the cups were also mass-less there would be no difference at all
So we can work out wind force, from that we can work out how much power a certain sail will produce. Still leaves us needing to know how much force is needed to plane so we're back to strain gages on the boom, mast base and board
Select to expand quoteBen1973 said..
So we can work out wind force, from that we can work out how much power a certain sail will produce. Still leaves us needing to know how much force is needed to plane so we're back to strain gages on the boom, mast base and board
They had to have done this at some point with scale models or wind tunnels/flowing water tests back in the day but maybe not. I'd like to know how much power a good pumper puts into it and gets over the planing hump.
Select to expand quoteaeroegnr said..Ben1973 said..
So we can work out wind force, from that we can work out how much power a certain sail will produce. Still leaves us needing to know how much force is needed to plane so we're back to strain gages on the boom, mast base and board
They had to have done this at some point with scale models or wind tunnels/flowing water tests back in the day but maybe not. I'd like to know how much power a good pumper puts into it and gets over the planing hump.
Read the link I posted earlier, it's about 260watts
i think windsurfing was more trial and error than design.
Select to expand quoteBen1973 said..
So we can work out wind force, from that we can work out how much power a certain sail will produce. Still leaves us needing to know how much force is needed to plane so we're back to strain gages on the boom, mast base and board
It still comes down to suck it and see. (and personal knowledge from prior experience). Because every combo of sail, board, fin and sailor will be different. There is no such general thing as 'how much wind/force is needed to plane?'. Thats akin to 'how long is a piece of string'? It all depends on the specific equipment you have. ie: for the same sailor, planing threshold on a Formula v's slalom, v's wave board will be very different for the same wind speed/force. Any 'answer' is very personally specific.
Select to expand quoteAwalkspoiled said..
Light wind is defined as people who are skilled are planing, but I'm not.
Light wind, and non planing conditions are defined by you for what you have and what you can do. It's as much to do with the combination of all the components of your equipment, and your local conditions as by your skill, probably more.
Face into wind, unzip and pee:
Feet dry - light wind
Shins damp - medium wind
knees wet - strong wind
crutch soaked - gale force, go home
^^^^
Perfect
However.......
It depends if it's a light yellow wee , or , the first draught horse pee after downing 6 beers . Then go down one sail size .
Would never drink and sail , that would be wrong .
Never have I ever had a few beers at Sandy Point thinking the wind won't come in ......then it did . It was gloriously sunny and only 15 kts and fabulous.
I was young .
Dont judge me.
Im older and wiser now , strictly no more than two beers between sessions . I hang out with more responsible people now .
You would need to measure the flow to calibrate, also the persons height would affect results.
This pee test is good for reflecting wind power - colder air will naturally adjust hose length and nozzle pressure.
It's fascinating to come late to a thread like this, and to read the responses.
I guess the answers reflect what we do, or what we want, and that in turn depends on what our local conditions are usually like.
In my area 'light wind' is where you can't plane - but in our case that also means we can't plane on short boards or wave kit.
So, light wind is defined not by the Beaufort scale but by basic 20mph or 20knot thresholds.
Different gear planes at a different wind strength, but the bigger difference is the sailor driving that gear.
If it's a 'light wind day' here then my personal definition is I can't plane on my 5.2m rig on a 100 litre freestyle board.
And so 'light wind' then means we look at SUPs, kites or foiling gear. We don't actually measure the wind, we just look at the water and decide whether it's worth bothering or not with the limited gear we have.
In 'proper wind', for me that's when the waves come. In light wind - and we've had a lot of that this year - we go foiling and winging nowadays.
Foiling has slowly taken over from 'dinghy conditions' or 'longboard weather' and indeed from 'kiting' . Slalom racing and light wind big sail blasting have also taken a hit here. Who actually likes a 9m windsurfing rig nowadays?
My SUP has an attachment point for a windsurf rig, so I could still do non-planing windsurfing - but I doubt I will.
But it's not actually the wind meter reading that defines your fun. I spent my earlier decades racing around a lake in a slow sailing dinghy.
Each to his own, right?
Select to expand quoteBasher said..
It's fascinating to come late to a thread like this, and to read the responses.
I guess the answers reflect what we do, or what we want, and that in turn depends on what our local conditions are usually like.
In my area 'light wind' is where you can't plane - but in our case that also means we can't plane on short boards or wave kit.
So, light wind is defined not by the Beaufort scale but by basic 20mph or 20knot thresholds.
Different gear planes at a different wind strength, but the bigger difference is the sailor driving that gear.
If it's a 'light wind day' here then my personal definition is I can't plane on my 5.2m rig on a 100 litre freestyle board.
And so 'light wind' then means we look at SUPs, kites or foiling gear. We don't actually measure the wind, we just look at the water and decide whether it's worth bothering or not with the limited gear we have.
In 'proper wind', for me that's when the waves come. In light wind - and we've had a lot of that this year - we go foiling and winging nowadays.
Foiling has slowly taken over from 'dinghy conditions' or 'longboard weather' and indeed from 'kiting' . Slalom racing and light wind big sail blasting have also taken a hit here. Who actually likes a 9m windsurfing rig nowadays?
My SUP has an attachment point for a windsurf rig, so I could still do non-planing windsurfing - but I doubt I will.
But it's not actually the wind meter reading that defines your fun. I spent my earlier decades racing around a lake in a slow sailing dinghy.
Each to his own, right?
You might be surprised how much fun a windSUP in waves can be. If it's +6kts I'll take it over paddling any day and if under 20kts I'll probably take it over my waveboard since we have horrendous side-shore currents that the SUP tackles without drama.
If no waves then I wing the same conditions. Might try the wing in waves one day once I have a much higher level of competency.
Select to expand quoteGrantmac said..Basher said..
It's fascinating to come late to a thread like this, and to read the responses.
I guess the answers reflect what we do, or what we want, and that in turn depends on what our local conditions are usually like.
In my area 'light wind' is where you can't plane - but in our case that also means we can't plane on short boards or wave kit.
So, light wind is defined not by the Beaufort scale but by basic 20mph or 20knot thresholds.
Different gear planes at a different wind strength, but the bigger difference is the sailor driving that gear.
If it's a 'light wind day' here then my personal definition is I can't plane on my 5.2m rig on a 100 litre freestyle board.
And so 'light wind' then means we look at SUPs, kites or foiling gear. We don't actually measure the wind, we just look at the water and decide whether it's worth bothering or not with the limited gear we have.
In 'proper wind', for me that's when the waves come. In light wind - and we've had a lot of that this year - we go foiling and winging nowadays.
Foiling has slowly taken over from 'dinghy conditions' or 'longboard weather' and indeed from 'kiting' . Slalom racing and light wind big sail blasting have also taken a hit here. Who actually likes a 9m windsurfing rig nowadays?
My SUP has an attachment point for a windsurf rig, so I could still do non-planing windsurfing - but I doubt I will.
But it's not actually the wind meter reading that defines your fun. I spent my earlier decades racing around a lake in a slow sailing dinghy.
Each to his own, right?
You might be surprised how much fun a windSUP in waves can be. If it's +6kts I'll take it over paddling any day and if under 20kts I'll probably take it over my waveboard since we have horrendous side-shore currents that the SUP tackles without drama.
If no waves then I wing the same conditions. Might try the wing in waves one day once I have a much higher level of competency.
If it's under 10knts, what sail size do you go out with?
They call it something like slog and ride don't they?
I prefer windsurfing to SUP but if it's under 20knts then I will usually SUP around, but my largest wave/free ride sail is 4.7.
Very interested to hear what gear you decide to go out on.
Thank you in advance.
Select to expand quoteHenners said..Grantmac said..Basher said..
It's fascinating to come late to a thread like this, and to read the responses.
I guess the answers reflect what we do, or what we want, and that in turn depends on what our local conditions are usually like.
In my area 'light wind' is where you can't plane - but in our case that also means we can't plane on short boards or wave kit.
So, light wind is defined not by the Beaufort scale but by basic 20mph or 20knot thresholds.
Different gear planes at a different wind strength, but the bigger difference is the sailor driving that gear.
If it's a 'light wind day' here then my personal definition is I can't plane on my 5.2m rig on a 100 litre freestyle board.
And so 'light wind' then means we look at SUPs, kites or foiling gear. We don't actually measure the wind, we just look at the water and decide whether it's worth bothering or not with the limited gear we have.
In 'proper wind', for me that's when the waves come. In light wind - and we've had a lot of that this year - we go foiling and winging nowadays.
Foiling has slowly taken over from 'dinghy conditions' or 'longboard weather' and indeed from 'kiting' . Slalom racing and light wind big sail blasting have also taken a hit here. Who actually likes a 9m windsurfing rig nowadays?
My SUP has an attachment point for a windsurf rig, so I could still do non-planing windsurfing - but I doubt I will.
But it's not actually the wind meter reading that defines your fun. I spent my earlier decades racing around a lake in a slow sailing dinghy.
Each to his own, right?
You might be surprised how much fun a windSUP in waves can be. If it's +6kts I'll take it over paddling any day and if under 20kts I'll probably take it over my waveboard since we have horrendous side-shore currents that the SUP tackles without drama.
If no waves then I wing the same conditions. Might try the wing in waves one day once I have a much higher level of competency.
If it's under 10knts, what sail size do you go out with?
They call it something like slog and ride don't they?
I prefer windsurfing to SUP but if it's under 20knts then I will usually SUP around, but my largest wave/free ride sail is 4.7.
Very interested to hear what gear you decide to go out on.
Thank you in advance.
5.3 4 batten wave sail. Also enjoy the 6.3 Fringe 3 batten but you do notice the weight of the longer mast. My SUP is marginal volume however with a board having more volume I believe the 6.3 would work well.
I'm +95kg in gear however.
Select to expand quoteGrantmac said..Henners said..Grantmac said..Basher said..
It's fascinating to come late to a thread like this, and to read the responses.
I guess the answers reflect what we do, or what we want, and that in turn depends on what our local conditions are usually like.
In my area 'light wind' is where you can't plane - but in our case that also means we can't plane on short boards or wave kit.
So, light wind is defined not by the Beaufort scale but by basic 20mph or 20knot thresholds.
Different gear planes at a different wind strength, but the bigger difference is the sailor driving that gear.
If it's a 'light wind day' here then my personal definition is I can't plane on my 5.2m rig on a 100 litre freestyle board.
And so 'light wind' then means we look at SUPs, kites or foiling gear. We don't actually measure the wind, we just look at the water and decide whether it's worth bothering or not with the limited gear we have.
In 'proper wind', for me that's when the waves come. In light wind - and we've had a lot of that this year - we go foiling and winging nowadays.
Foiling has slowly taken over from 'dinghy conditions' or 'longboard weather' and indeed from 'kiting' . Slalom racing and light wind big sail blasting have also taken a hit here. Who actually likes a 9m windsurfing rig nowadays?
My SUP has an attachment point for a windsurf rig, so I could still do non-planing windsurfing - but I doubt I will.
But it's not actually the wind meter reading that defines your fun. I spent my earlier decades racing around a lake in a slow sailing dinghy.
Each to his own, right?
You might be surprised how much fun a windSUP in waves can be. If it's +6kts I'll take it over paddling any day and if under 20kts I'll probably take it over my waveboard since we have horrendous side-shore currents that the SUP tackles without drama.
If no waves then I wing the same conditions. Might try the wing in waves one day once I have a much higher level of competency.
If it's under 10knts, what sail size do you go out with?
They call it something like slog and ride don't they?
I prefer windsurfing to SUP but if it's under 20knts then I will usually SUP around, but my largest wave/free ride sail is 4.7.
Very interested to hear what gear you decide to go out on.
Thank you in advance.
5.3 4 batten wave sail. Also enjoy the 6.3 Fringe 3 batten but you do notice the weight of the longer mast. My SUP is marginal volume however with a board having more volume I believe the 6.3 would work well.
I'm +95kg in gear however.
Are you taking out that hypermut 7"4'? I eventually got the limited edition version. It has been a little bit of a learning curve for me. Started with flat water SUP, did some small wave riding last week. Also took it out in 25knts with a 4.7. Found that it had a very big wet area and so it just decelerated very quickly in the lulls. The wet area is Infront of the front straps.
Saying that in the first 5 minutes I thought there is no way this thing is going to plane. But I got it going, so maybe more time on the water and I will get a better body position to get less wet area.
I'm 88kg without gear, summer here so maybe 89kg all up.
Yes it's the HN 7'4"
It definitely isn't made for planing, with enough wind to plane the HN I can probably be on a waveboard.
It's for digging the rail and grinding upwind then riding waves, slog and ride.
Select to expand quoteBen1973 said..
All I wanted to know was what people define light, med and strong wind as and what they would use in those conditions.
In light winds I use a large sail. In medium winds I use a medium sail. In strong winds I use a small sail
More specifically in the harbour:
sail board vol min avg max avg
8.5 Lion 125 10 15
7.5 Lion 110 14 19
6.5 Lion 110 16 21
6 Cheetah 94 17 22
5.2 Tiger 94 20 25 (different on the sea in waves)
4.5 Panther 94 23 28 "
One of our local anemometers (Parkstone) records historically every 10 minutes, so the min & max average is over a 10 minute period. The max/min gust is also recorded.
The other one (Poole) just has a graph.
As both are around 6-8m above the water, I take off 10% for a more realistic reading. They are 2.2 km/1.3 miles apart.
Yesterday I was foiling in a WSW/SW, and the 2 gave different readings and directions. On the Google Earth, yellow is Poole, blue is Parkstone.
As I'm still learning, I stayed close to the land. Where I sailed, there is a small wind shadow from the hill upwind. Normally on a fin, we sail out to the line of yachts where the wind picks up as its cleaner wind, and head out further into the harbour. Its about 1-2 knots difference.
Where I sailed yesterday, just downwind of the yachts the wind dropped as the 20-30 yachts cause wind shadow. Enough to drop off the foil. The Poole meter is dead downwind of the yachts. I guess where I was sailing it was averaging 11 gusting 14.
You cant take any weather station as granted, unless you sail next right to it.
Parkstone
Poole
Google Earth
Light wind is also relative to gear size. Light winds for a 75L board is different than for a 145L. Same goes with sail sizes.
Equipment, and skill are the determining factors.
For me. light wind is sub planing wind. So, 10 knots is where I can plane on my formula board and a 9.2 race sail. My next board down is a 111 slalom board and an 8.4. Planing wind for this board is about 12-13 knots. And so on.....
With the option to foil. Most of us up here consider light winds higher F2-4(5-16kts).
Select to expand quoteOldGuy3 said..
With the option to foil. Most of us up here consider light winds higher F2-4(5-16kts).
5 knots? What are you doing in 5 knots?
Select to expand quotesheddweller said..OldGuy3 said..
With the option to foil. Most of us up here consider light winds higher F2-4(5-16kts).
5 knots? What are you doing in 5 knots?
Probably 7-8 knots per hour
The definition of light wind is relative to the sailor and gear he is using. At 90kgs for windsurfing light wind is 13 kts, for windfoiling it's 10kts. This is the lightest wind I can get going on my current gear.
