Why anemometers

Joe

Joe

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Jun 1, 2004
8,195
Catalina 27 Mission Bay, San Diego
The question was why one needs wind speed data from the mast head. Not wind direction, not hand held wind data in the cockpit. Not tell tales or windex's. Not instruments to convert apparent speed and direction data to true.
No... what is the advantage of wind speed data from the mast head?
 
Joe

Joe

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Jun 1, 2004
8,195
Catalina 27 Mission Bay, San Diego
jwing said:
How does a masthead anemometer determine true windspeed and direction and what good is that knowledge to me at the helm?
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The masthead sensor doesn't do that calculation. It sends its "apparent" data to the instrument in the cockpit. That instrument needs boat speed data to finish the true wind calculations.
We use true wind data to make navigational decisions. We use apparent wind data to trim our sails.
The first thing we do when we start sailing is to check which way the wind is blowing.... that's true wind direction... we decide whether to leave the beach or dock on port or starboard tack based on that simple observation. Once we get the boat moving... our senses read apparent wind.. our sails feel apparent wind. However, the course the boat sails relies on the true wind direction.
 
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Skipper

Skipper

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Oct 9, 2008
1,742
Bristol 29.9 Dana Point
Joe said:
The question was why one needs wind speed data from the mast head. Not wind direction, not hand held wind data in the cockpit. Not tell tales or windex's. Not instruments to convert apparent speed and direction data to true.
No... what is the advantage of wind speed data from the mast head?
Click to expand
I'm fairly sure I answered that: correlation.
It doesn't matter where the sensor resides, as long as the data is consistent. Since you can't have a sensor at every 3 feet of the mast, you have to put it somewhere. The mast head is a good spot because its view of the wind is unobstructed.
If I know the speed at the masthead, I can make assisted calculations as to sail area and trim, etc. even if the speed on deck is different. Because, where I sail the speed at the masthead and on deck correlate, at least in enough of a range to be usable.
Of course, my answer is specific to my sailing, so really it's only one use. And the reality is I don't really need it. It just helps. Like other gear.
 
JamesG161

JamesG161

SBO Weather and Forecasting Forum Jim & John
Feb 14, 2014
7,769
Hunter 430 Waveland, MS
woodster said:
that storm of yesterday has pushed a lot of water into the bay here making unusual high tides even with the wind coming out of the north west totally adverse to what it should be
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Us too! I am not kidding about the near scam of 40 mph (named storm) causing my business building deductible to go $20k. Since I build, I could replace that roof for about $9k so what good it the insurance? Plus my bank won't let me drop that worthless insurance.

Luckily my boat is covered for all winds.

Like @captnron said...
We don't need no stinkin' APPs!

Wet your finger and point toward the Apparent Wind.
Jim...
 
rgranger

rgranger

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Jan 19, 2010
12,563
Hobie 16 & Rhodes 22 Skeeter Charleston
druid said:
About all the windspeed indicator is good for is bragging rights: "I was out in 35-40 last weekend", "I can carry full sails in 15 knots...", and so on.

druid
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But if you don't have one.... You can just make it up
 
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Bill Roosa

Bill Roosa

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Jun 6, 2006
6,990
currently boatless wishing Harrington Harbor North, MD
I use wind speed to keep an eye on how gusty it is. If you keep an eye on it you may even notice the speed leads the direction change (apparent wind does this by definition) so you get a little bit of warning of a direction shift.
 
justsomeguy

justsomeguy

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Feb 20, 2011
8,060
Island Packet 35 Tucson, AZ/San Carlos, MX
Skipper said:
where I sail the speed at the masthead and on deck correlate, at least in enough of a range to be usable.
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I have read of the phenomenon of the masthead readings preceding the readings felt at cockpit level.
FWIW.
 
L

LloydB

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Jan 15, 2006
927
Macgregor 22 Silverton
Because wind speed and direction are more affected by the surface, general velocity and direction can be determined better by measurement taken from above 20 feet.
 
J

jwing

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Jun 5, 2014
503
ODay Mariner Guntersville
Thanks to all who contributed. Here are my main take-aways from this thread, so far:
1) The tendency toward conflating 'anemometer' with 'wind vane' confused me until I did a little research and found that most masthead anemometers are also wind vanes.
2) True wind data can be ascertained by using the apparent wind data gathered at the masthead and the boat's velocity (I'm guessing this is determined by GPS). I'm still unclear what one does with this knowledge and why it's better than what I can discern by my natural senses and knowledge of apparent wind vs. true wind. I'll file that under 'Still to Learn - probably when I get serious about navigation.'
3) All the other uses that have been mentioned remind me of my clumsy sailing of 40+ footers in the pre-GPS and other electronics days, and why I own and so much enjoy sailing a small boat. The power of the sails goes through my hands and feet; the feedback from my actions is instantaneous.
 
Gene Neill

Gene Neill

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Sep 30, 2013
3,595
1988 Catalina 22 North Florida
JamesG161 said:
Us too! I am not kidding about the near scam of 40 mph (named storm) causing my business building deductible to go $20k. Since I build, I could replace that roof for about $9k so what good it the insurance? Plus my bank won't let me drop that worthless insurance.
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Don't get me started. Insurance is the only SCAM by which we are all REQUIRED BY LAW to be victimized. :mad:

On topic: I have a little hand-held anemometer, left over from my days in competitive rifle shooting. It's a learning tool, and it's fun to use. I can't imagine not wanting to know what the wind speed is, especially when it's blowing hard.

Then, next time the forecast is calling for x knots/mph, I have a clear mental picture of what x knots/mph was like last week, or whenever, when I measured the wind at that same speed. Or a little less, or a little more, or whatever.

Again, it's a learning tool. I find it very helpful. It would be much handier on the masthead though.
 
Joe

Joe

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Jun 1, 2004
8,195
Catalina 27 Mission Bay, San Diego
jwing said:
2) True wind data can be ascertained by using the apparent wind data gathered at the masthead and the boat's velocity (I'm guessing this is determined by GPS). I'm still unclear what one does with this knowledge and why it's better than what I can discern by my natural senses and knowledge of apparent wind vs. true wind. I'll file that under 'Still to Learn - probably when I get serious about navigation.'
Click to expand
Instruments speed up the calculations... and remove the guess work. You don't need instruments to determine true wind direction.... it's just easier and more accurate.

I'm not sure what your contention is..... but I will tell you that no matter how you gather it... you use true wind info all the time. In sailing.. it is fundamental to know which way the wind is blowing. As far as "getting serious about navigation" ... that can be as simple as when to turn the boat to get back to the marina.

You can easily determine true wind direction by watching your boat compass (the course you are steering).. compare the course on starboard close hauled with that on port close hauled... an average of those two numbers would be your true wind direction. Not once do you have to look at your windex or tell tales to make this assessment.

After 5 or 10 seconds on the new tack a course change can be attributed to true wind direction change.... i.e. lifts and headers. If you've raced small boats that don't allow certain electronics, using the boat compass for tactics becomes second nature.... and this is, no doubt, how you've become adept at sensing things rather than relying on an electronic wind instrument.
 
J

jwing

.
Jun 5, 2014
503
ODay Mariner Guntersville
Joe said:
...I'm not sure what your contention is...
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That's understandable - I have no contention. I'm trying to learn, so it would be stupid of me to be contentious. While I was reading the rest of your post, I was thinking to myself, "I have no wind instruments on my boat, yet at any given moment, I can instantly say where the true wind is coming from. Isn't that an absolutely basic thing for sailors?" Then I read this:

Joe said:
After 5 or 10 seconds on the new tack a course change can be attributed to true wind direction change.... i.e. lifts and headers. If you've raced small boats that don't allow certain electronics, using the boat compass for tactics becomes second nature.... and this is, no doubt, how you've become adept at sensing things rather than relying on an electronic wind instrument.
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The truth is, I've never considered using the compass for that purpose. So I thinks to meself, "I've been sailing on a lake for the past few years, and I can always see land on all sides of me. In fact, I see the same land all the time, so I'm familiar with all the land features from all different angles. That must certainly help me to understand how the changes in wind direction affect by boat. Maybe if I got out where I can see only water an sky more often, then I'd start understanding the utility of wind instruments as Joe and the other fine sailboatowner guys are describing."

Does that sound right?
 
J

jwing

.
Jun 5, 2014
503
ODay Mariner Guntersville
shemandr said:
Since the insurance companies have instituted the rule that deductibles go up for a named storm it's amazing how many named storms there are.
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I was wondering why weather dudes started naming winter storms until I learned about the insurance scam regarding named storms. Truly deplorable. Now I am being contentious!
 
Justin_NSA

Justin_NSA

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Jul 7, 2004
8,492
Hunter 30T Cheney, KS
topcat0399 said:
Perhaps it would be a good thing if more people hoisted their smart phones to the masthead....
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LOL! Seriousness aside, the sailor across from me gets his mast top information on his cell phone (in the cockpit). Not sure who makes the system.
 
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