{Stus-List} Instruments - wind calculations, etc.

Dennis C. captbuy at yahoo.com
Thu Jun 18 17:22:45 EDT 2009


Well, perhaps.  See if my logic holds on this one.  Read it carefully.  I've been wrong before.

First, some terms:
	* True wind - wind observed if you were standing still.
	* Apparent wind - angle and speed you feel on the boat relative to the centerline of the boat looking forward. This is what's observed by the masthead unit.
	* True wind angle - the difference between the course of the boat and the direction of the true wind.  For instance if boat course was 060 and true wind direction was 140, the true wind angle would be 80 starboard (I think).
	* VMG (wind relative) - velocity made good directly upwind or downwind.  
	* WCV (waypoint closure velocity) - the speed at which you are closing directly toward the GPS waypoint (some GPS units label this as VMG)
Given that, if your system has boat speed, course from compass and wind velocity, it could calculate true wind and true wind angle.  It would be inaccurate by the set and drift.

It could also calculate VMG (wind relative).

Now, if you had a GPS connected, it could use SOG (speed over ground) and COG (course over ground) from the GPS to better calculate true wind and true wind angle relative to the ground.  It could also calculate set and drift.

Instrument makers probably choose one way or the other.  I'm not 100% sure but I think, in the Nexus system, you can set which instrument, GPS or Nexus system with its compass, is navigating.  Thus, if you don't have a GPS connected, you could still determine true wind (kinda).

I'll be on boat this weekend and will see what I get with GPS off and GPS on.  I'll ask the admiral to remind me.

Dennis C.
Touche' 35-1 #83
Mandeville, LA




________________________________
From: Gary Russell <captngaryr at gmail.com>
To: bob.mclaughlin at alumni.duke.edu; cnc-list at cnc-list.com
Sent: Thursday, June 18, 2009 4:00:27 PM
Subject: Re: {Stus-List} Instruments

That actually makes some sense.  Without a GPS input, your instrument can only give you the wind with respect to the water (which is moving).  With a GPS input it can give you the wind with respect to the ground. 

Gary
S/V Expresso


On Thu, Jun 18, 2009 at 4:50 PM, Robert Mclaughlin <rmclaughlin2 at earthlink.net> wrote:

I was assured it would not, unless you have GPS input.  They label it "Ground Wind" for reasons they couldn't explain.  Works great with a GPS input.
>
>Bob
>
>bob.mclaughlin at alumni.duke.edu
>
>
>
>----- Original Message ----- 
>>From: Roger Ware 
>>To: cnc-list at cnc-list.com
>>Sent: 6/18/2009 6:21:24 AM 
>>Subject: Re: {Stus-List} Instruments
>>
>>Does anyone know why a Raymarine ST60+ system won’t display a digital (true) wind direction? It has the information, so why won’t it give it to you? Or perhaps it will and I just haven’t figured it out.
>> 
>>Thanks, Roger Ware, Kingston, ON
>> 
>>From:cnc-list-bounces at cnc-list.com [mailto:cnc-list-bounces at cnc-list.com] On Behalf Of Gary Russell
>>Sent: Wednesday, June 17, 2009 12:49 PM
>>To: cnc-list at cnc-list.com
>>Subject: Re: {Stus-List} Instruments
>> 
>>I'm an NX2 fan.  Won't put Raymarine on my boat ever again.  I've heard of a lot of sailors having all sorts of reliability problems with TackTic and especially Navman.  My dock neighbor had to replace all of his Navman instruments last week.  They were only 2 years old.  ALL the displays had failed.  My NX2s are about 8 years old and the only problem I've had was 1 failed speed transducer ($120.00).  I haven't heard anything bad about B&G except the price.
>> 
>>Gary
>>S/V Expresso
>>'75 C&C 35 M k II
>>On Wed, Jun 17, 2009 at 11:49 AM, Pete Shelquist <Pete.Shelquist at comcast.net> wrote:
>>Bill – 
>>FWIW, about 5 yrs ago I did a number of distance races on a boat with Tacktic.  Every time a storm rolled by all displays would go blank.  The owner is a pretty serious racer and the instruments were gone the next season.  The boat now has B&G.   
>> 
>>I’m in the same spot you are in looking for instruments and the timing to purchase.  Keep us informed on what you’re finding.  The more research I do, the more I like Garmin (wind VMG, barometer, tru/apparent wind/boat speed, Per Panbo: decent graphics/trends and bright displays, also nmea 2000).  It’d be nice to know someone that has actually used it.
>> 
>> 
>>From:cnc-list-bounces at cnc-list.com [mailto:cnc-list-bounces at cnc-list.com] On Behalf Of Dennis C.
>>Sent: Monday, June 15, 2009 1:48 PM
>>To: billbina at sbcglobal.net; cnc-list at cnc-list.com
>>Subject: Re: {Stus-List} Instruments
>> 
>>I installed a Nexus 2000 (now Comnav NX2) system on Touche' in 1999.  Replaced the depth transducer (lightning strike?) and the masthead wind unit.  Other than that, the instruments have performed well.  The multidisplay provides more info than most casual sailors need.  One thing the Nexus system provides is wind relative VMG.  That is, velocity made good directly upwind or directly downwind.  This differs from "VMG" according to a GPS which is really WCV, waypoint closure velocity.  I find VMG very valuable for racing.  I'd consider NX2 again if I was replacing.
>> 
>>I'd also consider NKE instruments.  Have heard good things about them.  Mauripro Sailing sells both the NX2 and the NKE systems.  A full wind/speed/depth system will run you about $2300 for NX2 and about $2500 for NKE.
>> 
>>I've been on several boats with Raymarine instruments.  Other than the bad experience with their wheelpilots, I haven't heard much negative on their instruments.
>> 
>>I've installed B&G instruments on a couple boats and they're still working.
>>Dennis C.
>>Touche' 35-1 #83
>>Mandeville, LA
>>
________________________________

>>From:Bill Bina <billbina at sbcglobal.net>
>>To: cnc-list at cnc-list.com
>>Sent: Monday, June 15, 2009 1:24:10 PM
>>Subject: {Stus-List} Instruments
>>
>>Well, I think it really is getting to be time to replace all of my instruments. The little annoyances are starting to accumulate. I'll most likely do it after the season is over, so I've got time to shop and compare. I would be replacing wind, depth and speed. Since instruments don't get replaced very often, I'd like to try and get this right. The setups I seem to see more than most is the Raymarine ST60 stuff. One brand that looks interesting, and very different in their approach is Maretron, but I haven't heard much of anything about them. They aren't exactly budget priced. I'm strictly a cruiser, but I sail in pretty much anything other than hurricanes, so I need good, simple, tough, equipment. I do like the idea of using combined data to get things such as apparent wind direction and apparent wind speed. I'm not crazy about having everything on one screen, either. I'd like the wind on a separate display from the speed and depth. With Maretron, that
 gets pretty expensive.
>>
>>I'm shying away from Garmin, only because they haven't been doing this for very long. I've had great luck with their GPS/Plotters. I'm not sure how I feel about Tacktick.
>>
>>Any thoughts?
>>
>>Bill Bina
>>
>>
>>
>>_______________________________________________
>>This List is provided by the C&C Photo Album
>>http://www.cncphotoalbum.com
>>CnC-List at cnc-list.com
>> 
>>
>>_______________________________________________
>>This List is provided by the C&C Photo Album
>>http://www.cncphotoalbum.com
>>CnC-List at cnc-list.com
>>
>>
>>
>>
>>-- 
>>~~~~~~~_/)~~~~~~
>>
>>
>_______________________________________________
>This List is provided by the C&C Photo Album
>http://www.cncphotoalbum.com
>CnC-List at cnc-list.com
>
>


-- 
~~~~~~~_/)~~~~~~


      
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://cnc-list.com/pipermail/cnc-list_cnc-list.com/attachments/20090618/c1a2578f/attachment-0001.html>


More information about the CnC-List mailing list