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Old December 1st 05, 01:36 AM posted to rec.boats.electronics
b393capt
 
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Default True "true wind" & the Raymarine ST60, or other

I am just about to buy a bunch of Raymaine instruments for my new B
393, and just found out that the ST60 is limited to using SOW, and
won't use GPS SOG & COG, to calculate true wind.

After looking thru this forum, I see some references to this issue, but
don't see either
(1) A way to get true wind on any of the Raymarine instruments, does it
work on the Tri data ??

(2) Another vendor who does not have this limitation mentioned.

Can anyone help me ?


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Old December 1st 05, 02:12 AM posted to rec.boats.electronics
krj
 
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Default True "true wind" & the Raymarine ST60, or other

The Raymarine ST60 wind instrument uses the masthead windvane and
anamometer for apparent wind. It uses the SOW from the Tridata paddle
wheel and the COG from the autopilot to compute true wind.
No gps input needed.
krj

b393capt wrote:
I am just about to buy a bunch of Raymaine instruments for my new B
393, and just found out that the ST60 is limited to using SOW, and
won't use GPS SOG & COG, to calculate true wind.

After looking thru this forum, I see some references to this issue, but
don't see either
(1) A way to get true wind on any of the Raymarine instruments, does it
work on the Tri data ??

(2) Another vendor who does not have this limitation mentioned.

Can anyone help me ?

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Old December 1st 05, 02:32 AM posted to rec.boats.electronics
Glenn Ashmore
 
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Default True "true wind" & the Raymarine ST60, or other

"krj" wrote in message
.. .
The Raymarine ST60 wind instrument uses the masthead windvane and
anamometer for apparent wind. It uses the SOW from the Tridata paddle
wheel and the COG from the autopilot to compute true wind.
No gps input needed.
krj


That will not account for set and drift. It will give you true wind
relative to the boat but not true wind. relative to the mark you are trying
to get to.

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com


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Old December 1st 05, 03:04 AM posted to rec.boats.electronics
krj
 
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Default True "true wind" & the Raymarine ST60, or other

Glenn Ashmore wrote:
"krj" wrote in message
.. .

The Raymarine ST60 wind instrument uses the masthead windvane and
anamometer for apparent wind. It uses the SOW from the Tridata paddle
wheel and the COG from the autopilot to compute true wind.
No gps input needed.
krj



That will not account for set and drift. It will give you true wind
relative to the boat but not true wind. relative to the mark you are trying
to get to.

Works OK for me since I use waypoints 20 to 50 miles apart instead of marks.
krj
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Old December 1st 05, 03:48 AM posted to rec.boats.electronics
Garland Gray II
 
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Default True "true wind" & the Raymarine ST60, or other

I see what you are trying to do, but not sure why you need to be that
precise about wind direction and speed relative to the bottom as opposed to
the water. I mean, my boat isn't a weather buoy !
I use the instrument to help in optimizing performance thru the water, and
then use a separate instrument (GPS) for navigating to a point, if
necessary.

"b393capt" wrote in message
oups.com...
I am just about to buy a bunch of Raymaine instruments for my new B
393, and just found out that the ST60 is limited to using SOW, and
won't use GPS SOG & COG, to calculate true wind.

After looking thru this forum, I see some references to this issue, but
don't see either
(1) A way to get true wind on any of the Raymarine instruments, does it
work on the Tri data ??

(2) Another vendor who does not have this limitation mentioned.

Can anyone help me ?





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Old December 1st 05, 11:14 AM posted to rec.boats.electronics
b393capt
 
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Default True "true wind" & the Raymarine ST60, or other

I use true wind in combination with the GPS to navigate. Being on a
Swan 48 with B&G instruments that using the SOG from the GPS, all you
need to do is to convert between north and magnetic (if your navigating
by magnetic). On a boat with an ST60, I also have to compensate for
inaccuracies in the paddle wheel (I use a measured mile) and compensate
for current (i get a vague idea comparing paddle wheel with GPS SOG)
.... which is a lot of work, and then at that not possible 1/2 the time,
as half the boats I have sailed recently report zero (0) on the
Paddlewheel when the actual speed over water is under 3 knots (light
winds) (the owners tell me they use the GPS, and are not motivated to
maintain paddlewheels).

I figure on my own boat, I would like to get a real true wind, without
any hassel's. I was thinking that I could get the ST60 to use the SOG
from the GPS, but that isn't an option, and Raymarine isn't yet
motivated to make changes. The way they compute it, as stated in this
post, can be off my more than 60 degrees (as published "Establishing
more truth in true winds", 13 October 1997, Shawn R. Smith, Mark A.
Bourassa, and Ryan J. Sharp in )

Dan

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Old December 1st 05, 02:50 PM posted to rec.boats.electronics
Glenn Ashmore
 
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Default True "true wind" & the Raymarine ST60, or other

A waypoint is the same as a mark. It does not move with the current.
Using only the speed through the water a cross set with a couple of knot
drift in light wind can create a huge error.

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

"krj" wrote

Works OK for me since I use waypoints 20 to 50 miles apart instead of
marks.
krj



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Old December 2nd 05, 04:06 AM posted to rec.boats.electronics
Garland Gray II
 
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Default True "true wind" & the Raymarine ST60, or other

I'm not sure how you use wind direction/speed to navigate. I can understand
how an inaccurate knot meter will mess up true wind determination, butI'd
say, fix the knotmeter.
To me, sailing is utilising the movement of air relative to water to provide
forward motion thru the water (ultimately aparent wind), and this is
irrespective of the ground underneath. The ground underneath is vital to me
only for navigation.
I'm not meaning to dispute what you are seeking, only puzzled. Maybe I just
haven't been exposed to what you are used to.

"b393capt" wrote in message
oups.com...
I use true wind in combination with the GPS to navigate. Being on a
Swan 48 with B&G instruments that using the SOG from the GPS, all you
need to do is to convert between north and magnetic (if your navigating
by magnetic). On a boat with an ST60, I also have to compensate for
inaccuracies in the paddle wheel (I use a measured mile) and compensate
for current (i get a vague idea comparing paddle wheel with GPS SOG)
... which is a lot of work, and then at that not possible 1/2 the time,
as half the boats I have sailed recently report zero (0) on the
Paddlewheel when the actual speed over water is under 3 knots (light
winds) (the owners tell me they use the GPS, and are not motivated to
maintain paddlewheels).

I figure on my own boat, I would like to get a real true wind, without
any hassel's. I was thinking that I could get the ST60 to use the SOG
from the GPS, but that isn't an option, and Raymarine isn't yet
motivated to make changes. The way they compute it, as stated in this
post, can be off my more than 60 degrees (as published "Establishing
more truth in true winds", 13 October 1997, Shawn R. Smith, Mark A.
Bourassa, and Ryan J. Sharp in )

Dan



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Old December 6th 05, 06:53 PM posted to rec.boats.electronics
b393capt
 
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Default True "true wind" & the Raymarine ST60, or other

All,

On the Beneteau site we had a discussion about the ST60, true wind, and
why it might be reasonable to approach Raymarine to get a true wind
even though they are a mid--range product.

Some excerpts:


"Ok Raymarine don't as yet provide this feature today on the ST60
system but for sure soon they probably will as they add more and more
knobs bells and whistles to the mid range ST60 system." - I agree,
kind of looking to speed this process up.


"Of course the ST60 pretends to calculate TWA and TWS but the results
are unreliable total lies most of the time and totally flawed. " -
Ain't this the truth


"TWA and TWS are calculated parameters based on removing the velocity
of the vessel thru the water " - Yes, got to get rid of the vessel
thru water component.


"I've been following this thread as a lurker for a while and am
amazed at the level of invective this seemingly academic issue can
raise. Everyone is right of course. We all have to trim our sails to
apparent wind, there can be no doubt about that. But we all need to
know true wind, and I don't see how anyone can question that either."
- Right on Ted


"Even on short sails I determine when and where to tack based on
where I expect the wind to be, and I predict the apparent wind on the
next tack by knowing the true wind and my anticipated course. If I
don't have an estimated true wind, I have no idea what will happen when

I turn 90 degrees. And I suspect those who don't think they use true
wind do a rough estimate of it in their heads, consciously or
unconsciously. " - Yes, yes, and written very clearly and with
style


"As a matter of terminology I have never heard anyone use True Wind
Speed to be in reference to the moving water, as opposed to a fixed
geographic point. While it is true that in a zero wind and a current
there will be a wind past the boat, I think that is apparent wind, not
true. I don't think that the fact that the wind and water are fluid
media moving in different directions makes the wind relative to the
water a true wind. I always assumed (and I refuse to do research to
back this up) that true wind is the wind that exists at a point if the
boat wasn't there. you need a new, even more confusing acronym for
that, such as WRTW (wind relevant to water)." -- Yes, right on, WRTW
(wind relevant to water) is a great description of the results the ST60

provides, Raymarine should advertise it that way, not as true wind ...
and anyone who navigates with WRTW should be consider NWORTL
(navigating with out regard to land)


"Still leaves room for B&G,
Ockam, and other high-end systems to differentiate with their
refinements (e.g. correction via rate sensors, leeway, heeling angle,
etc.) that can take the last 10 degrees of inaccuracy out of things."


Perhaps someone on this site can offer a contact name or email address
of someone inside Raymarine you
were impressed with, etc?


Thank you,
Dan

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Old December 6th 05, 07:36 PM posted to rec.boats.electronics
Timothy.Rulon
 
Posts: n/a
Default True "true wind" & the Raymarine ST60, or other

b393capt wrote:
I am just about to buy a bunch of Raymaine instruments for my new B
393, and just found out that the ST60 is limited to using SOW, and
won't use GPS SOG & COG, to calculate true wind.

After looking thru this forum, I see some references to this issue, but
don't see either
(1) A way to get true wind on any of the Raymarine instruments, does it
work on the Tri data ??

(2) Another vendor who does not have this limitation mentioned.

Can anyone help me ?


To calculate true wind you also need true heading. SOW, SOG and COG
alone won't work as set/drift begin to effect your vessel which will
occur as you slow down. At zero speed, a GPS is likely to report
anything for COG unless it has a built in aid like a magnetic flux gate
compass. There are some expensive GPS receivers which provide true
heading by using 2 antennas and lower cost LORAN-C sensor units being
developed which does something similar. Should also work great as an
input to an autopilot rather than magnetic sensors which can get tricked
by magnetic anomolies.

I'm not aware of a recreation-priced system which performs all the above
but would very much like to hear about it for a government application.

For marine weather information, please visit
http://www.nws.noaa.gov/om/marine/home.htm



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