Wind instrument siting...

tonybarebones

tonybarebones

Well-Known Member
Joined
20 Sep 2006
Messages
622
Location
Dinas Powis, Vale of Glamorgan.
Visit site
Why do we site our wind instruments at the masthead?

Ostensibly to ensure the instruments are in clear air...

The downside is they are in the most inaccessible place on any craft...

I'd submit if they were sited on a staff mounted midships on the push-pit...

With a following wind they would be in clear air...

With a beam wind they would be in clear air...

With the wind ahead they would still be in clear air...

A conventionally rigged craft sails at 45 degrees to the true wind 30 degrees apparent...

In effect in any wind direction they would still be in clear wind except when motoring ahead of course.

Perhaps I'm missing something here and I'm sure there are plenty of people out there who will be swift enough to correct me.

Anyway I'm going to re site mine if only for the joy of the convenience of being able to access them easily.

Tony

"Barebones"
 
tonybarebones said:
I'd submit if they were sited on a staff mounted midships on the push-pit...

With a following wind they would be in clear air...

With a beam wind they would be in clear air...

With the wind ahead they would still be in clear air...

A conventionally rigged craft sails at 45 degrees to the true wind 30 degrees apparent...

In effect in any wind direction they would still be in clear wind except when motoring ahead of course.

Perhaps I'm missing something here and I'm sure there are plenty of people out there who will be swift enough to correct me.
Click to expand...

If you look at any decent book covering yacht aerodynamics you'll see that the sails significantly effect the air flow around the boat. To the extent that leebowing is a racing tactic which disadvantages the windward boat.

So the idea is to get the instruments above that affected airflow in order to get the most reliable (or least unreliable) measurements.

I agree though that it's an awkward place for instrumentation.
 
To be sited amidships presumably you'd need one each side with all the wiring / software embuggerance, but on the plus side they'd make wonderful if unintentional cleats for springs etc when alongside walls ! :)

After trying a few, I have found the ideal position for windspeed / direction kit; left on the chandler's shelf.

Just use a windex at the masthead ( they're even refective underneath so show up at night via the masthead light, or one can get dedicated lights ) and wool telltales on the shrouds are in line of sight, like a fighter aircrafts' Head Up Display - can't go wrong via u/v or settling seagulls / Cormorants knackering anemometer cups or electrical failure - I don't need a guage to tell if I'm frightened, the windex works when in deep locks and the rest of the time the shroud telltales are the best calibrated sensor displays one will ever get.
 
I tried two of those Clipper things - presents from well meaning if misguided relatives & friends - and they are indeed the worst, in fact one area where we can still be proud of British products still being world leaders at something - but other more expensive kit seemed to have the same results, just took a bit longer to get there. :)
 
I have a Raymarine sensor at the masthead on a conventional mounting. As it is, it can be shielded from a wind from dead astern by the light. It will give a decent wind angle but can be reading 5kn when it should be showing 20. I have learned to live with it but it catches me out occasionally.
 
5 kt instead of 20 I could live with, but many cats don't tell you there's too much wind on a run until it all goes horribly wrong, so you need to know when the wind reaches, say 15 knots to put the first reef in and 20 for the next step, whatever that is.

Not a problem for me as Jissel keeps me up to date with how she feels about the wind anyway, so I don't have an anemometer, but I do remember leaving Newtown Creek for Ryde under full genny once and watching the wind increase as a gentle bimble became a good sail then became exhilarating, then a bit scary, though not quite enough to reduce sail. All the same, I was VERY glad that the genny rolled away obediently when we got there
 
One season I tried my masthead unit intentionally facing the other way, on a prong facing aft ( I used to be part of BAe Dunsfold Instrument Calibration Dept ) - I already knew the thing was useless in normal pointing ahead mode so thought this might be interesting.

It fell apart like an exploding Slinkie Spring on the Simpsons before I could really tell, but as far as I got, as one would imagine it was a tiny bit better in following winds and correspondingly worse in headwinds, though the terms ' better and worse ' are relevant to NASA Clipper kit only and in no way bear any relation to reality - in the name of all that's holy, and this applies to all yot wind ' instruments '- just get a Windex and a couple of bits of wool; make them red and green if it may help ' what tack am I on ? ' under pressure.

A huge amount of expense and effort goes into aircraft instrument design and calibration, for good reason; people who think a yot whirlie thing for a £ thousand is expensive and state of the art are kidding themselves, an aircraft instrument designer would barely use such things to power a little model bloke chopping logs.

Do keep to wool telltales, or if you already have the faux electronic kit, have the wool on the shrouds as well and see which you find yourself referring to...:)
 
Last edited:
Stemar said:
5 kt instead of 20 I could live with, but many cats don't tell you there's too much wind on a run until it all goes horribly wrong, so you need to know when the wind reaches, say 15 knots to put the first reef in and 20 for the next step, whatever that is.

Not a problem for me as Jissel keeps me up to date with how she feels about the wind anyway, so I don't have an anemometer, but I do remember leaving Newtown Creek for Ryde under full genny once and watching the wind increase as a gentle bimble became a good sail then became exhilarating, then a bit scary, though not quite enough to reduce sail. All the same, I was VERY glad that the genny rolled away obediently when we got there
Click to expand...

And you didn't need a guage - or even a dipstick ! :) to tell you how you and the boat were feeling...
 
Stemar said:
Seems to me that the main use for an anemometer on a monohull is bragging rights. I have a story that begins, it was a bit breezy, but I don't know how much 'cos the windex gave up at 55 knots...
Click to expand...

I have noticed that all the skippers who tell me tales of F10 or above do not have a wind instrument... but it is true, you do not need one to sail in a safe and informed manner - unless perhaps on a multi, where reefing by numbers is appropriate. On a mono my experience says if you think you need a reef you almost certainly do and you will probably go faster when you put one in.

W
 
Agreed, on a multihull ( only one I've owned was a Dart 18 ) it's less intuitive and instruments make more sense.

My bragging tale of 55 knot squalls is via the instruments and rather experienced skipper of TS Royalist...

But if Stemars' WINDEX had blown away that does sound like pretty serious stuff ! :)
 
Seajet said:
Angus,

what make please, any other treatment like ( if the mast is lowered ) a winter cover ?
Click to expand...

Raymarine ST60 with standard MHU. It's so old it was actually made by Raytheon before Raymarine existed. The cover for the MHU in winter is my house, I take it right off when the mast is down. I fit an old broken MHU stub (which I was given for nowt) in at the top of the mast and the plug at the bottom of the mast into a dummy deck connector socket to protect all the electrical connections from the weather, with plenty of vaseline slathered about.

The stepper motor driving the needle in the display head failed 3 years ago in one quadrant. I was about to set off on a 4 month trip so I bought a new display head to get going. Subsequently a work colleague identified the motor for me & I fixed it , so I have it as a spare.

My first boat had Nasa kit, & it failed in the first gale. Nasa made me pay for new cups even though it was only a few weeks old. Vowed never to buy anything Nasa ever again.
 
Angus,

ta - exactly how I've always felt; NASA refused to honour their 12 month guarantee when my first, gift Clipper Wind MHU failed, then when a well meaning aunt got me a replacement ( if only she'd asked there were a million things I'd rather have had, even an STD would at least have been more fun to install ) :) - that lasted a few months too - I gave up, never wanted the things in the first place.

That was a long time ago and they say NASA customer services are red hot now, well surely they must be more practiced and more experienced at their jobs than the SAS can ever dream of. :)
 
Last edited:
But if Stemars' WINDEX had blown away that does sound like pretty serious stuff ! :)

It was. It didn't actually blow away, it just stopped working, but we didn't need it to tell us it was far to windy to be out there. our 40 footer was doing 2 knots flat out into the wind

The usual story of a rented boat that's due back today, one that's killed far too many sailors. From that point of view, I was lucky - I spent the evening in A&E with "only" a badly bruised rib
 
' Got To Be Back At The Office On Monday ' syndrome - I'm sure that's more of a killer than any torpedo or Kamikaze, top tip if the weather is too bad, throwing in a holiday or sick day or even stuffing the job is better than risking one's crew ( or just getting frightened fartless ) - guess how I know ? Never again ! :)
 
You must log in or register to reply here.

Share this page

Top