Hadenough
Well-Known Member
I still think of wind in Beaufort and get fed up with referring to a table to convert back from knots, mph and kph when I look at a forecast. Does any one know a simple mental arithmetic conversion formula to apply?
Wind speed
- Thread starter Hadenough
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Long John Silver
Well-Known Member
To convert knots to Beaufort add 5 to the windspeed in knots, then divide by 5.
To convert mph to Beaufort add 6 and divide by 6.
To convert mph to Beaufort add 6 and divide by 6.
prv
Well-Known Member
Find a forecast in Beaufort in the first place 
I use a combination of Windguru and the official Inshore Waters - the latter is naturally in Beaufort, the former can be set to it.
Pete
I use a combination of Windguru and the official Inshore Waters - the latter is naturally in Beaufort, the former can be set to it.
Pete
Wandering Star
Well-Known Member
Hadenough
Well-Known Member
Perfect, many thanks
Hadenough
Well-Known Member
Find a forecast in Beaufort in the first place
I use a combination of Windguru and the official Inshore Waters - the latter is naturally in Beaufort, the former can be set to it.
Pete
Where is that on wind guru I have looked but couldn't find?
Ex-SolentBoy
Well-Known Member
Thats why Beaufort is such a rubbish scale IMHO. The bands are just too broad to be meaningful.
On this basis 11 knots is a Force 3 (11+5)/5 = 3.2
Actually 11 knots is a 4
maby
Well-Known Member
It's a pragmatic scale based on effect rather than linear measurement. It is useful to sailors because it is easy to communicate and you can quickly associate the wind speed in Beaufort units with the likely effect on sailing conditions for your boat. If the forecast says Force 2, I know I'm in for a slow, boring drift down river, if it says 7, I know I'm going to be hanging on for dear life!
sarabande
Well-Known Member
agreed, Beaufort is an empirical scale. The science of anemometrics was not in existence to help Beaufort when he drew up his scale.
My pic plots Beaufort scale against wind pressure in N/Msq. I think the Admiral would have been pleased to see the resolution of a smooth curve against his ordinal list.
My pic plots Beaufort scale against wind pressure in N/Msq. I think the Admiral would have been pleased to see the resolution of a smooth curve against his ordinal list
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snowleopard
Well-Known Member
I put the formula in a spreadsheet and compared it to the 'official' numbers. It is accurate to within 2 knots at all speeds up to F9. Not bad.
The modern scale is based on calculation of the force of the wind so is not a linear scale. The formula used is
v = 0.836 B^3/2
where v is the wind velocity in m/sec and B is the Beaufort number.
Almost any scale will do the job, it's just a question of what you are used to. I have used Beaufort all my life but I was able to adjust easily enough to hearing forecasts in knots on the other side of the Atlantic.
Ex-SolentBoy
Well-Known Member
Not sure what you mean by accurate. What about my example. I tell you it's blowing 11 knots. You think it's a low three, actually it's a four.
I agree that it's what you are used to though. I learnt wind speed flying. Cross wind limits are very important and a few knots can be lethal. Beaufort would just not cut it in the aviation world.
maby
Well-Known Member
Not sure what you mean by accurate. What about my example. I tell you it's blowing 11 knots. You think it's a low three, actually it's a four.
I agree that it's what you are used to though. I learnt wind speed flying. Cross wind limits are very important and a few knots can be lethal. Beaufort would just not cut it in the aviation world.
Exactly - it's horses for courses - Beaufort was defined in terms of effect on ships and their environment, the numeric wind speeds were added in later and don't fit perfectly.
wotayottie
Well-Known Member
Its on the borderline isnt it, and thats why you chose it. 10.999knots would of course be a 3 whilst your 11.00001 knots is a 4. But in real world sailing the difference between the bottom of a 3 and the top of a 3 doesnt matter.
Thats not what Beaufort is about. Its based on sea state and the beauty of it is that you can look at the sea and tell what the wind is "out there". Particularly useful if like me you are a bit cautious and dont leave harbour in a 6 which corresponds to whitecaps
RobbieW
Well-Known Member
Knots, MPH & Beaufort I can cope with - its m/s that does my head in
Ex-SolentBoy
Well-Known Member
Ex-SolentBoy
Well-Known Member
Of course thats why I chose it. I was just being a smart ass proving that the "add five divide 5" thing doesnt work.
The sea state thing doesnt work either as that is vastly influenced by fetch. I happily sail in 30 knots of wind if the sea is flattish, but would be unhappy in open water. To make a sailing decision I like to know the speed in knots and the sea state.
Beaufort was invented for old fashioned sailing and IMHO it should be in a museum and nowhere else.
FWB
N/A
Well as an ex aviator I find that thought rather amusing "Speedbird 123 you are cleared to land, the wind is Southwesterly force 4"
I like Beaufort, my Raymarine Graphic display gives me exactly that, so i dont need the 5's example...which I think is rather good.
It's horses for courses.
maby
Well-Known Member
Interestingly, out Tacktick instruments refused to calculate a Beaufort figure till I got the compass heading plumbed into the NMEA2000 data bus - I could never work out the logic behind that...
FWB
N/A
It needs heading so it can work out the wind direction from the wind angle.
The Raymarine Graphic will also display ground wind so I think it uses that to get the correct Beaufort direction.
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maby
Well-Known Member
Hmmm, I'm not aware of it displaying wind direction - I'll have to look again.