Which Barometer Reading

[Gary Fox]

Not being funny, but what is the point of setting a yacht's baro so precisely?
I totally get it for aviation collision avoidance; but to us, the exact number of bars/pascals/inches of mercury is no more essential than knowing the wave height to the nearest inch.
It's the change over time which matters, in my opinion.

 

[Gary Fox]

Here are the frequencies of the Volmet for the main, (international), airports in Ireland:
18.60 MHz

Frequencies

Airport	Tower	ICAO
Dublin	118.60 MHz	EIDW
Cork	119.30 MHz	EICK
Shannon	118.70 MHz	EINN
Knock (Ireland West)	130.70 MHz	EIKN

They are all available on an FM radio which is enabled for the Airband frequencies, which are just above the normal broadcast frequencies, between 108Mhz and 137Mhz. It's also possible to listen to all of the ATC frequencies. It's very easy to find out the frequencies used by your nearest airport, online.

I used to have London Volmet South permanently playing in the background, the soothing repetition of the calm lady's voice induced the relaxed, trance-like state which some ignorant landlubbers claim from listening to the Radio 4 Shipping Forecast

 

[RobbieW]

... The atm pressure readings used by aircraft are actually reduced to Mean Sea Level.

It depends what they are doing (remembering stuff I learned as an apprentice 50 years ago!) Cruise altitude (Flight Level) is established using QNE, a mean sea level standard of 1013.25, so all fly using the same height reference. When operating around the airfield you want to know the baro at the airfield, QFE, to establish actual height above ground at that location. This all assumes suck/blow instruments are still prevalent !

 

[Gary Fox]

It depends what they are doing (remembering stuff I learned as an apprentice 50 years ago!) Cruise altitude (Flight Level) is established using QNE, a mean sea level standard of 1013.25, so all fly using the same height reference. When operating around the airfield you want to know the baro at the airfield, QFE, to establish actual height above ground at that location. This all assumes suck/blow instruments are still prevalent !

I avidly devoured all that stuff in the 70's as a air cadet, and those Q-codes still exist in daily use.

 

[tjbrace]

I found the adjusting screw?. The Barigo is now aligned to the Garmin at todays reading of 1016.
Thanks all.

 

[Roberto]

Hello, a couple of cases where I found it useful:
1. To have an idea what is actual vs forecast: if a low is forecast to cross your area with a 1000hPa minimum pressure at say noon, if at 0800 you are already reading 995 on your barometer and the wind has not even begun to veer... o-ho
2. When trying to climb the western side of a high pressure (namely on a west to east transat) and avoid the central area, charts can sometimes indicate a preferred specific isobar corridor along which it can be preferable to remain, say 1030 to 1032. Example once were south of a sequence of highs moving westward from mid-US coast, we kept port tack and chose 1030hPa to tack north (there was some more "bumps" and gradient), we could then follow it for a number of hours to get north of the moving highs without engine at all.
Ok, a correct reading is not absolutely essential, but it can help to play a little bit

Not being funny, but what is the point of setting a yacht's baro so precisely?
I totally get it for aviation collision avoidance; but to us, the exact number of bars/pascals/inches of mercury is no more essential than knowing the wave height to the nearest inch.
It's the change over time which matters, in my opinion.

 

[Gary Fox]

Hello, a couple of cases where I found it useful:
1. To have an idea what is actual vs forecast: if a low is forecast to cross your area with a 1000hPa minimum pressure at say noon, if at 0800 you are already reading 995 on your barometer and the wind has not even begun to veer... o-ho
2. When trying to climb the western side of a high pressure (namely on a west to east transat) and avoid the central area, charts can sometimes indicate a preferred specific isobar corridor along which it can be preferable to remain, say 1030 to 1032. Example once were south of a sequence of highs moving westward from mid-US coast, we kept port tack and chose 1030hPa to tack north (there was some more "bumps" and gradient), we could then follow it for a number of hours to get north of the moving highs without engine at all.
Ok, a correct reading is not absolutely essential, but it can help to play a little bit

Ok thanks that is very interesting

 

[emnick]

I use an app (iPhone) called "barometer" its free and I check it against the local (nearest) airport. Its been so accurate ! I have a small Oregon weather station and the barometer is reset and still out next time I check.... its worth a look IMHO nearest airport now is Wattisham showing 1011, app showing 1011.6

 

[ronsurf]

It sounds like you've sorted it, but all barometers on boats should be corrected for sea level. Pressure decreases with elevation (I seem to remember 1mB with every 10m?), so a pressure reading at an airport for instance needs to be corrected for it's elevation if your barometer is at sea level.

 

[VicS]

It sounds like you've sorted it, but all barometers on boats should be corrected for sea level. Pressure decreases with elevation (I seem to remember 1mB with every 10m?), so a pressure reading at an airport for instance needs to be corrected for it's elevation if your barometer is at sea level.

Only if the reported pressure is not already corrected to sea level pressure

SEE my post at #20 .... All the pressures reported by XC weather , many if not most of which come from airports and airfields are sea level pressures

 

[Spirit (of Glenans)]

It sounds like you've sorted it, but all barometers on boats should be corrected for sea level. Pressure decreases with elevation (I seem to remember 1mB with every 10m?), so a pressure reading at an airport for instance needs to be corrected for it's elevation if your barometer is at sea level.

As stated above, pressures reported at airports are corrected to MSL.
I live at an elevation of 80 metres and when I compare the pressure reported at Dublin Airport (of which the control tower is in sight of my house) to the reading on the baro on my (Lidl) sports watch, I find that it reads 9 mb lower. When I get to my boat in Malahide, which is in earshot of the Airport) the reading matches the one reported there.

 

[oldmanofthehills]

It sounds like you've sorted it, but all barometers on boats should be corrected for sea level. Pressure decreases with elevation (I seem to remember 1mB with every 10m?), so a pressure reading at an airport for instance needs to be corrected for it's elevation if your barometer is at sea level.

True, but your boat is not a reporting weather station, so provided your boat barometer is set moderately correct all you need to know at sea is rising or falling, high or low. That will tell you what weather is to be expected and if a low is tracking over you.

Bellows type barometers on boats are often quite hard to set precisely as the set screws are usually behind them thus they cannot set while mounted, and the act of mounting will risk disturbing the setting by frame distortion.

 

[Spirit (of Glenans)]

Not being funny, but what is the point of setting a yacht's baro so precisely?
I totally get it for aviation collision avoidance; but to us, the exact number of bars/pascals/inches of mercury is no more essential than knowing the wave height to the nearest inch.
It's the change over time which matters, in my opinion.

You are quite right, it does not have to be absolutely accurate. All that we require at sea is a trend; how much the pressure falls or rises in a given time period, but many of us feel more secure if the instrument is actually giving a reading similar to those given out by the Met Office etc.

 

[colind3782]

It depends what they are doing (remembering stuff I learned as an apprentice 50 years ago!) Cruise altitude (Flight Level) is established using QNE, a mean sea level standard of 1013.25, so all fly using the same height reference. When operating around the airfield you want to know the baro at the airfield, QFE, to establish actual height above ground at that location. This all assumes suck/blow instruments are still prevalent !

And the "NH" in QNH stands for "Newlyn Height" the Mean Sea Level for the UK, set in Newlyn as the datum about a hundred years ago.

 

[Gary Fox]

And the "NH" in QNH stands for "Newlyn Height" the Mean Sea Level for the UK, set in Newlyn as the datum about a hundred years ago.

I never knew that.. here's a guess, QFE means Field Elevation?

 

[colind3782]

I never knew that.. here's a guess, QFE means Field Elevation?

Correct!

 

[RobbieW]

And the "NH" in QNH stands for "Newlyn Height" the Mean Sea Level for the UK, set in Newlyn as the datum about a hundred years ago.

I'm sure I learned it as Nautical Height, but thats aviation for you

edit: Thinking about it, it makes more sense for NE to be Newlyn Elevation as it refers to a mean sea level pressure

 

[colind3782]

I'm sure I learned it as Nautical Height, but thats aviation for you

I admit that I didn't know until I was taking my aviation radio licence exam many years ago and the examiner told me. Interesting stories about it if you Google it.

 

[PeterBoater]

It depends what they are doing (remembering stuff I learned as an apprentice 50 years ago!) Cruise altitude (Flight Level) is established using QNE, a mean sea level standard of 1013.25, so all fly using the same height reference. When operating around the airfield you want to know the baro at the airfield, QFE, to establish actual height above ground at that location. This all assumes suck/blow instruments are still prevalent !

QNE is not a pressure setting at all and is not 1013.2 hPa. It is the elevation of the landing threshold on an altimeter set to 1013.2 and is a setting passed by Air Traffic Control to aircraft that cannot set an abnormally high or low pressure on their altimeters (not very common now).

 

[Gary Fox]

These pilots have nearly as many ways to talk about heights, as sailors do about the tides!