Wot no wind?

[Peter Taylor]

I slept in Seatern last night and woke to find the wind whistling in the rigging and the Nasa Meteoman indicating 0 kts. Whether or not as a result of storm Doris (which was not that bad down here in the south), the Nasa anemometer is now a 2 cup version. I have now ordered a replacement from Nasa for £14.50 plus postage - you can't fault the price of their spares!

Peter

[Andy Dingle]

Went to check mine after reading your post Peter - Equinox is at Rutland Water for the winter and Doris's breath hit there at approx 74 mph apparently. (RAF Wittering, just east of RW).
My cups seem to be ok, but several trees were down and I saw at least one dismasted boat.
I wonder what effect that sort of wind has on the bearings and electronics of the NASA wind - and other more expensive makes for that matter?
For that price I think I will order a spare set as well and change it when I get the mast down. I hope NASA have a lot of spare cups in stock, there could be a bit of a run on them!

Incidentally I recorded (at my house - where I also had a tree down) 970 hpa...  Is that pretty low do you think?

Regards Andy

[Peter Taylor]

Hi Andy, to put it in context, Seatern is afloat all year so the anemometer which failed had been exposed to the elements and working almost continuously since the start of 2014. In that time it's had significantly stronger winds than we had in Southampton this last week.

However, in my experience, it is unusual but not unknown for anemometer cups to fail. On a Canadian research ship I was on, the ship's anemometer lost all three cups during storms with sustained winds of 60 kts (gusts would be higher). That was over the Grand Banks in November.  In fact the gustiness of winds in a city like Southampton probably puts more stress on the sensor than the stronger but less gusty winds when at sea. The other question with regard to my anemometer is whether the bearings have failed which really would put stress on the cups; I haven't lowered the mast yet to look.

Nasa use magnetic sensing of the anemometer rotations which should be more reliable than some other types (like the more expensive Davis weather stations) which use a mechanical reed switch. I don't think cheaper is necessarily worse.

970mb is low but by no means extreme. I usually reckon 940mb as around "the lowest it might get" although I believe sea level pressures of around 930mb have been recorded in the UK. Remember that it is the pressure gradient which determines the wind strength, not the absolute value. 

Where the absolute value does matter is for coastal flooding. 970mb will add about 0.4m to the height of high tide and large scale wind effects might increase that significantly. You can view the latest storm surge forecasts for different sites around the coast at
http://www.ntslf.org/storm-surges/surge-forecast

Peter

ps anyone looking at the storm surge residuals (departures from astronomical tide) on the NTSLF site will see the high tide times marked by circles. Residual peaks away from the high tide time indicate the tide coming in earlier or staying in longer. For flooding its the value at high tide which normally matters!

[Andy Dingle]

Thanks Peter, very interesting as always, thanks for the explanations.

On a previous boat, the NASA cups failed completely with all three cups blown off. I don't know what the wind speeds were that actually did the damage but when I lowered the mast there was plenty of evidence of UV damage - cracked and brittle plastics. There is quite a lot of discussion on the internet about the NASA cups - I agree that I suspect more expensive equipment can and will fail just as easily, so for less than twenty quid NASA gives good value I personally think.

Being on the east coast I'm particularly interested in storm surges and thanks for the link.
Lessons were learned in 2013 when the predicted surge hit us at unpredicted heights, unfortunately a lot of boats were on the hard and quite literally floated off their cradles, our members were wading chest deep desperately holding onto them to ensure they settled back safely as the tide eventually went out. Millions of pounds of damage was caused that night.
Contrasting with the recent surge warnings (14 Jan) when huge preperations were made (the lads were in their waders at 4 am, ropes in hand!), and the predicted surge didn't materialise. But that's Mother Nature for you..

The relationship between pressure and tide heights - and, times and length of HW is also very relevant where I sail too where it's really good to know how much water you can expect over a sand or mud bar  - clearly still a very inexact science!

[Peter Taylor]

Having received the Nasa replacement cups I'm reminded that the "bearing" is simply a couple of washers. It seems unlikely that that jammed and I suspect when I lower the mast I'll find that that UV damage is the culprit. Makes me wonder about painting the cups to protect against UV.

The primitive bearing is probably the reason that the anemometer has never been accurate - it under reads compared to my Davis weather station which is situated on the jetty where Seatern is moored. The Nasa direction works OK which is all I'm really bothered about.

The relationship between pressure and tide heights - and, times and length of HW .....  clearly still a very inexact science!

I feel I have to defend my oceanographic colleagues on that one but will start a new thread!

Peter

[Tony]

Not being blessed ( or is it cursed?) with on-board electrics on my Cardigan Bay Lugger I don’t have a mast-head anemometer and only use my hand held Windtronic infrequently. When I’m trying to reassure myself that I will certainly die if I’m foolish enough to launch today would be a typical instance. Otherwise, I basically operate on a tripartite wind speed scale: “Not enough!”, “This is great!!” and “Too much!!!”
 It’s apparent from reading this thread that others take a more scientific approach and need a digital readout. Why, then, are we still using 19th century sensors? These 3-cup rotors are too delicate for the environment they are used in. None will survive a knockdown or even a perching seagull. The Windtronic has a vertical axis rotor in a cage which might be more robust – but why have any moving parts at all? Ocean buoys are fitted with ultrasonic sensors which record wind speed and direction, do not need servicing and are not destroyed by high winds, waves or sea birds in transit. I presume there must be a reason why they are not the default sensor on small boats?
Industrial versions cost £1000 and more.... but have a look at this:

http://www.johnlewis.com/netatmo-wind-gauge-for-netatmo-weather-station/p2726100?sku=236090520&s_kwcid=2dx92700016581949876&tmad=c&tmcampid=2&gclid=Cj0KEQiA9P7FBRCtoO33_LGUtPQBEiQAU_tBgBQqeNfFKDfst9h68liQDdM4SU4OLBjakkvpzURpU0saAvB58P8HAQ&gclsrc=aw.ds

Ninty quid, and it links to your smartphone.
 I don't think you could glue this particular model to your mast - but the technology exists and at a reasonable cost. Anyone seen a marinised version?

[Graham W]

In defence of 19th century anemometers, my Tacktick wireless masthead model is fairly robust.  I've only destroyed it once, I think by backing it into a wall with the mast down. It's survived a turtling and near gales but as far as I know has never been molested by birds.

The replacement spare parts cost about £70. I'm fairly sure that it runs on proper ball bearings, the bedding for which was also partly destroyed in the wall incident.  Cups alone would have been about £20.

[Tony]

Nothing wrong with any technology, 19th century or otherwise, when it works  and when it's fit for the job. By which I mean a bamboo 'depth sounder' is fine on my boat but not on a BayCruiser 26 !
BR 20s can certainly benefit from high tech gear if it's robust enough for trailing. The tougher the better!

[Peter Taylor]

Why, then, are we still using 19th century sensors? These 3-cup rotors are too delicate for the environment they are used in.

Actually cup anemometers are rather more sophisticated than they might appear. The cups allow the sensor to maintain calibration better when the sensor is tilted (as it tends to be on a yacht) compared to some other designs .

I was interested in Tony's Netatmo ultrasonic anemometer and was tempted to get one but then read reports of the weather station (which it connects to) not being weather proof! Most "cheap" ultrasonic anemometers are around the £700 to £1000 mark at present, so one for £90 does sound rather too good to be true.

I was involved with testing at sea one of the new generation of sonic anemometers back in the early 1990's. At that time they cost about £14000 which was around half the cost of the previous generation. Admittedly these were scientific instruments which measure all three components of wind speed some 80 times each second - which is a bit of overkill on a BC20 like Seatern. The modern two axis "domestic" version nowadays costs around £700 (e.g. http://www.r-p-r.co.uk/windsystems/windsonic.php ).

In the early days we collaborated with the firm in Lymington that makes them - Gill Instruments. They started with a device for fitting inside motorbike engines, then it evolved to domestic gas meters and anemometers. But I digress!

Designing an ultrasonic anemometer that works is not simple because you need to measure the time sound takes to travel each way between different pairs of transducers to very high accuracy. Water, dirt, bird droppings, spiders - can all interfere with the desired accuracy - as does tilting the sensor!

From a yachting point of view I can see an ultrasonic anemometer having value when put on top of the sort of mast that is erected using a crane in the boat yard. Then their extra reliability is an obvious advantage, even if you might not gain in accuracy. However for us Swallow Yachties who can easily lower the mast (and frequently do) a cup anemometer and wind vane still seems a sensible choice of wind sensor.

Peter

[Peter Taylor]

I thought people might be interested to see what you do when you really want to know about the wind!

The attached photo was an experiment we did on a Canadian research ship over the Grand Banks in November. The wind is around 60 knots (average, not gusts!). The inset shows the instruments at the top of the mast. There are sonic anemometers at each end of the cross-trees (the £14000 variety), in the centre is a fast response propeller-vane anemometer. Other instruments are measuring temperature and humidity and all 6 components of the motion of the sensor array. Corrections for the effect of the ship on the wind flow were calculated using a computer model of the ship and of the airflow at different angles.

The weather conditions were exactly what we were hoping for!
Peter

[Andy Dingle]

Hello Peter.

I'm interested if you have now replaced your spinny cups on your NASA Wind?
I've been having problems with mine now as well- just working basically when it feels like it and then I question the accuracy (?!).
Having just moved my boat I've got the mast down and the cups looked a bit like they had been with you out in the Grand Banks! -Tho they are only three years old.
How did you change them and is there any other bits inside that could do with some maintenance - I noticed I've got dirty grease on the central hub - not sure if that is meant to be there?

Anyway, as I was feeling reckless I've decided to change the lot for a the NASA wireless system - It arrived yesterday and I'm fitting it today - initially, the mast head unit seems better made and with better plastics than the hard wired version?
Also (importantly) the whole mast head unit is now more easily detached for towing, with far less risk of damage.
The receiver unit will also transmit a nmea sentence. The wireless version doesn't come with the standard NASA clipper wind display, but the NASA 'wind repeater' that works from the nmea sentence sent by the receiver unit, so I can now also feed that to my 'home made' chartplotter. It does offer the option of using the display - or you can buy the unit without a display to 'feed' other systems you may have.

The 'home made' chart plotter is a Raspberry Pi3. running open cpn with CM93 ENC charts ('obtained' off the internet). Usb puck gps. Depth and now wind, via serial to usb connectors.
Raspberry pi standard 7 ins touch screen. Fraction of the cost of a commercial one and I can use it as a normal laptop system on the boat - the pi has wifi and bluetooth built in too and with very low power consumption.


I'll keep the wiring in up the top of the mast and use it for a separate Meteoman at some stage in future - or revert back if (when!) the wireless system packs up!

Regards

Andy

[david]

Interesting thread, and I must admit a little over my head! I know Raspberry's are like Blackberries, in that I can pick and eat them rather than the electrical ones! You lost me a Pi3 Andy 

The 'home made' chart plotter is a Raspberry Pi3. running open cpn with CM93 ENC charts ('obtained' off the internet). Usb puck gps. Depth and now wind, via serial to usb connectors.
Raspberry pi standard 7 ins touch screen. Fraction of the cost of a commercial one and I can use it as a normal laptop system on the boat - the pi has wifi and bluetooth built in too and with very low power consumption.


I'll keep the wiring in up the top of the mast and use it for a separate Meteoman at some stage in future - or revert back if (when!) the wireless system packs up!

Regards

Andy

[Andy Dingle]

David.
 
No black magic stuff involved, and, as anyone who knows me can confirm I am a complete computer numpty! This is all not much more than 'plug and play' I assure you!

I just like playing when I'm not sailing. It all runs off free linux (debian) operating system which I use on a daily basis as I refused to pay for Windows stuff at their exorbitant prices. When all this is freely downloadable  - a trend developing there!
It's all stuff I picked up off the internet - there is loads on't web about the pi 3 - which is basically a tiny little hobby computer and very cheap - about £30 (USD 40) which is very powerful and ideal for these little projects. Chart plotters, AIS, Navtex loads ..  all dead cheap.

 https://thepihut.com/collections/raspberry-pi/products/raspberry-pi-3-model-b

Open Cpn is a charting and nav program. Open source and free. It is really quite excellent and I've been using it for years - I would say it is better than my C-map stuff I use on my expensive Standard Horizon chart plotter.

https://opencpn.org

The charts I use are admittedly old ones (2011)- but are free off the internet. Open Cpn will also run up to date NOAA charts (free to download) and loads of other electronic charts eg

http://www.openseamap.org/index.php?id=openseamap&no_cache=1&L=1

Open CPN also comes with a free tides and current 'plugin' as well as loads of others (grib files) radar - even an electronic 'log book' which is actually quite useful.


Here in the uk we have to pay for Admiralty charts. (Don't get me going on that one!).
But I do use up to date paper charts (as well as the c-map stuff). But for general use the CM93 charts work well. Open cpn also comes with a free tides and current 'plugin' as well as loads of others (grib files) radar - even an electronic 'log book' which is actually quite useful.


The gps receiver is off ebay

http://www.ebay.co.uk/itm/USB-GPS-Receiver-VK-162-2-Metre-Cable-Magnetic-Ublox-GPS-RasPi-Win-7-8-10-Linux-/182201032583

as are the serial to usb connectors ..  as the pi only has usb inputs, It has bluetooth and wifi so a very cheap bluetooth keyboard works very well...

Keeps me out of mischief anyway...

[Ray S]

Thanks for all that info!  By coincidence just joined a new RPi group down here in Dorset and I thought of the GPS project too. I was thinking of a GPS HAT and didn't realise there were all these GPS UPS dongles which seem much more convenient.  Can you give any pointers to the data stream from the puck - did you use Python to decode?

How about a BRRPi group or thread? or is is BR2Pi?

Ray S
BRe 047 'Whimbrel'




 

[Peter Taylor]

I'm interested if you have now replaced your spinny cups on your NASA Wind?

Hi Andy, yes I replaced the cups - the old ones looked a bit crazed but not that bad, however when I wiggled one of the two remaining cups it came off easily. Theres a photo in my Seatern blog under March 14th but it simply looks like a NASA cup unit with only one cup left! Replacing the cups is "easy" - they are just held in place on the (greased) spindle by either a tiny nut (as in my case) or a grippy sort of washer. For me it was not so easy since the nut is very small and Seatern was floating with the mast lowered but responding to waves and I was standing on the jetty and not responding to the waves - but that's my cack-handed way of working on the mast! 

The only thing that can go wrong with the unit apart from the cups breaking off is that the magnet could rust - but mine was coated white and also greased so looked fine.

I use the wired NASA NMEA sensor at the mast head not the NASA Clipper sensor.  The NMEA sensor feeds wind and temperature sentences to a Meteoman unit in the cabin and to NASA Clipper Wind Repeaters in the cockpit. I think this is much better than using the NASA Clipper wind system. Unfortunately the NMEA sentence is not that required by my Raymarine Tiller Pilot - otherwise I could program a track into the Garmin Echomap and send Seatern off for a sail by itself while I did other things!

I imagine your wireless system would feed into a Meteoman if you wanted it to, but I'd check with the guy at NASA to make sure! When playing with NMEA I found this web site (or a clone of it) invaluable... http://catb.org/gpsd/NMEA.html - it defines all the NMEA 0183 sentences.  Actisense also produced a good guide to connecting an NMEA feed to a computer in such a way as to avoid possibly wrecking the computer due to power spikes on the NMEA wiring. I can't find it on their web site now - they probably want you to buy one of their products (I have their multiplexer). Send me a PM if you are interested in the wiring guide! But it may well be that the RPi protects itself being designed for use in schools!

Peter