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#359590 - 11/19/07 12:46 PM Compass: Your Classification?  
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F14bombcat Offline
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How do you classify a compass? Is it an instrument or a navigation tool?

Instrument or Navigation tool?
single choice
Votes accepted starting: 11/19/07 12:45 PM
You must vote before you can view the results of this poll.

1995 Formula 303 SR-1, 454 MAGs
2015 Chevrolet Silverado 1500
#359602 - 11/19/07 01:10 PM Re: Compass: Your Classification? [Re: F14bombcat]  
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nyminute Offline
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OK, I will bite, what do I Win??


Its a matter of degrees from being up on your luck to down on your knees
#359612 - 11/19/07 01:29 PM Re: Compass: Your Classification? [Re: nyminute]  
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Opus Offline
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Why can't it be both? It is an instrument that is used as a navigation tool.


"If a man is to be obsessed by something, I suppose a boat is as good as anything, perhaps a bit better than most".
#359615 - 11/19/07 01:34 PM Re: Compass: Your Classification? [Re: Opus]  
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Al Offline
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I would classify it as both as well.

Since you did not have an answer for that option, I answered #3.


President and CEO - Napmoor and Doolittle.


2004 Mercury 270 Dinghy.
2016 Grand Design Reflection 29RS 5th Wheel
2016 GMC Sierra 2500HD SLT 6.6L Diesel

previous boats:
1995 Carver 325
1999 Four Winns 268
1999 Four Winns 225
1996 Rinker 180
#359633 - 11/19/07 01:56 PM Re: Compass: Your Classification? [Re: Al]  
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GoFirstClass Offline
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Pasco, WA
I chose #3 because it can do double duty. I almost never use the compass on my boat. I have the GPS/Plotter but seldom hook that up unless I'm headed out of town with the boat.

It's pretty hard to get lost on the river so a compass is not a real necessity here.


"Beachcomber" 1995 Sea Ray 550 Sedan Bridge


Anchor's down......Bottoms Up!
#359643 - 11/19/07 02:09 PM Re: Compass: Your Classification? [Re: GoFirstClass]  
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Al Offline
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I upgraded to a digital compass so that I can transmit heading data into the Chartplotter - supposed to make MARPA more accurate, but I have not yet verified it.

Compasses are supposedly still more accurate for heading than GPS.


President and CEO - Napmoor and Doolittle.


2004 Mercury 270 Dinghy.
2016 Grand Design Reflection 29RS 5th Wheel
2016 GMC Sierra 2500HD SLT 6.6L Diesel

previous boats:
1995 Carver 325
1999 Four Winns 268
1999 Four Winns 225
1996 Rinker 180
#359650 - 11/19/07 02:29 PM Re: Compass: Your Classification? [Re: Al]  
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F14bombcat Offline
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I always thought of it as both too. I was just looking to see where the majority stood, hence no both option. Although some seemed to make their own.


1995 Formula 303 SR-1, 454 MAGs
2015 Chevrolet Silverado 1500
#359658 - 11/19/07 02:34 PM Re: Compass: Your Classification? [Re: Al]  
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GoFirstClass Offline
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Al, it's my understanding that a GPS by itself will not give a compass heading on a stationary boat. An example of that is on boat that is just drifting with no movement and the boat was pointed North, the GPS wouldn't know what direction it was pointed. If the boat were pointed North and drifting East with a current, the GPS would think the boat was actually pointed East because that's the direction of movement.

I had a flux gate compass (sounds like something from Back To The Future!) installed when I put my system on the boat to correct for that. Now, whenever the system is turned on I get a digital readout from the flux gate compass. It always seems to be within a degree of the Ritchie compass.


"Beachcomber" 1995 Sea Ray 550 Sedan Bridge


Anchor's down......Bottoms Up!
#359683 - 11/19/07 03:24 PM Re: Compass: Your Classification? [Re: GoFirstClass]  
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Al Offline
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Yes, that is my assessment GFC. But when under way, the GPS does also calculate heading. But its typically +/- 5%, and is greatly influenced by boat speed. As you said, when the boat is hardly moving forward, its hard to get a good bearing.

I am using a KVH Azmuith 1000 digital fluxgate compass which has a spec of +/- 0.5%. So it is basically a combo flux compass with NMEA0183 output and dedicated display.

The NMEA0183 output goes into the RayMarine C80 and it supplies heading information rather than the GPS receiver.



President and CEO - Napmoor and Doolittle.


2004 Mercury 270 Dinghy.
2016 Grand Design Reflection 29RS 5th Wheel
2016 GMC Sierra 2500HD SLT 6.6L Diesel

previous boats:
1995 Carver 325
1999 Four Winns 268
1999 Four Winns 225
1996 Rinker 180
#359792 - 11/19/07 10:41 PM Re: Compass: Your Classification? [Re: Al]  
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ESC Key Offline
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Western Lake Erie
Not having been a boater all that long, I thought my GPS was messed up when we were anchored out one day and I knew land was to the North but the GPS said it was the other way. Obviously I learned that yes you need to be moving to get an accurate reading. It taught me a lesson to never rely only on the GPS, verify your compass and use it. I was taught to keep an eye on my compass heading and kind of frquently take a mental note of it and not just rely on the GPS to tell me where to go. Come to think about it my GPS and my wife have something in common....they both tell me where to go.

#359811 - 11/20/07 12:20 AM Re: Compass: Your Classification? [Re: ESC Key]  
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 Originally Posted By: ESC Key
GPS ....I learned that yes you need to be moving to get an accurate reading [of the compass function from the GPS].


Not necessarily. Some GPS' have an 'electronic' Compass that will function while stationary. (They still need to be calibrated though)

Last edited by kenhdog; 11/20/07 12:52 AM. Reason: clarity

2002 Rinker 212 Captiva
Merc 5.7 EFI Alpha
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1999 GMC 'Burb
#359818 - 11/20/07 12:36 AM Re: Compass: Your Classification? [Re: kenhdog]  
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GoFirstClass Offline
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Ken, that's what I was referring to in my post. Without that compass input, the GPS knows where a boat is, but if it's not moving it doesn't know which direction the boat is pointed.


"Beachcomber" 1995 Sea Ray 550 Sedan Bridge


Anchor's down......Bottoms Up!
#359820 - 11/20/07 12:42 AM Re: Compass: Your Classification? [Re: GoFirstClass]  
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kenhdog Offline
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GFC, my comment was in response to ESC Key.

He mentioned that his GPS compass function only works when he (it) is in motion. I was just telling him that some GPS' (like my 76CSx handheld) have electronic Compass' that will function when the unit is not moving.


2002 Rinker 212 Captiva
Merc 5.7 EFI Alpha
Trail-Rite Trailer
1999 GMC 'Burb
#359821 - 11/20/07 12:50 AM Re: Compass: Your Classification? [Re: kenhdog]  
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Opus Offline
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 Originally Posted By: kenhdog
He mentioned that his GPS compass only works when he (it) is in motion. I was just telling him that some GPS' (like my 76CSx handheld) have electronic Compass' that will function when the unit is not moving.


Yes, some units will function when not in motion. I have a 76s handheld. It has a compass and barometer. The "s" stands for "sensors". The unit has a compass and barometer built in, and does NOT rely on data from the satelites to provide directional information or barometric pressure (= altitude).


"If a man is to be obsessed by something, I suppose a boat is as good as anything, perhaps a bit better than most".
#359822 - 11/20/07 12:57 AM Re: Compass: Your Classification? [Re: Opus]  
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kenhdog Offline
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 Originally Posted By: Opus
The "s" stands for "sensors".


I thought the 's' stood for the more sensitive SiRF receiver configured unit.


2002 Rinker 212 Captiva
Merc 5.7 EFI Alpha
Trail-Rite Trailer
1999 GMC 'Burb
#359825 - 11/20/07 01:16 AM Re: Compass: Your Classification? [Re: kenhdog]  
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Opus Offline
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 Originally Posted By: kenhdog
 Originally Posted By: Opus
The "s" stands for "sensors".


I thought the 's' stood for the more sensitive SiRF receiver configured unit.


I'm not sure what SiRF is. But, I'm pretty sure my 76s doesn't have it.


"If a man is to be obsessed by something, I suppose a boat is as good as anything, perhaps a bit better than most".
#359827 - 11/20/07 01:19 AM Re: Compass: Your Classification? [Re: Opus]  
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Opus Offline
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One limitation to the electronic compass is that the unit must be held horizontally to get an accurate reading. Neither the mount on my boat, nor the mount on my four wheeler, hold the unit horizontally. It would be difficult to read the display while operating either of those vehicles if the mount where horizontal. So, the electronic compass is not necessarily a big benefit to me.


"If a man is to be obsessed by something, I suppose a boat is as good as anything, perhaps a bit better than most".
#359828 - 11/20/07 01:24 AM Re: Compass: Your Classification? [Re: Opus]  
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kenhdog Offline
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 Originally Posted By: Opus


 Originally Posted By: kenhdog
 Originally Posted By: Opus
The "s" stands for "sensors".


I thought the 's' stood for the more sensitive SiRF receiver configured unit.


I'm not sure what SiRF is. But, I'm pretty sure my 76s doesn't have it.


hmmm, quick google....I guess the 's' is sensors. (like you said!)


2002 Rinker 212 Captiva
Merc 5.7 EFI Alpha
Trail-Rite Trailer
1999 GMC 'Burb
#359838 - 11/20/07 07:28 AM Re: Compass: Your Classification? [Re: Opus]  
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Al Offline
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Ken, its my understanding that the GPS unit you have includes an electronic compass, so that its actually the internal compass, not the GPS tracking that is providing the heading when not moving, right?

That is an interesting feature, and I did not know they existed.

I am basically doing something equivalent by using an external flux-gate compass to feed heading; of course, for a few-times more cost.

But notwithstanding those little helpers, the GPS technology itself (i.e. receiving signals and triangulating speed and direction) is not very good at heading unless you are moving.

Here is a pretty good white paper from KVH on compass technology, probably more than you want to know. I'll admit, it lost me about half way through.

Compass Technology

I think one reason that the Multi-Function Displays may not include an intrinsic compass built into the GPS receiver is that there is provision to hook up an autopilot, which already has a flux-gate compass. For those that don't need an autopilot, then you can add a flux-gate via NMEA0183/2000.


President and CEO - Napmoor and Doolittle.


2004 Mercury 270 Dinghy.
2016 Grand Design Reflection 29RS 5th Wheel
2016 GMC Sierra 2500HD SLT 6.6L Diesel

previous boats:
1995 Carver 325
1999 Four Winns 268
1999 Four Winns 225
1996 Rinker 180
#359869 - 11/20/07 11:22 AM Re: Compass: Your Classification? [Re: Al]  
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Opus Offline
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NW Arkansas
 Originally Posted By: Al
Ken, its my understanding that the GPS unit you have includes an electronic compass, so that its actually the internal compass, not the GPS tracking that is providing the heading when not moving, right?

That is an interesting feature, and I did not know they existed.


Al, that is correct. The Garmin 76s that I have, and the Garmin 76CSx that Ken has, both have an electronic compass. Additionally they have a barometric altimeter. So, they can provide compass direction and altitude information without data from the satellites. The 'S' in the model number indicates 'sensors' (compass and barometer), the 'C' indicates a color display. I'm not sure what the 'x' in Ken's model indicates.

And, yes, the GPS technology is not much good if you are not moving. But, you don't have to be moving very fast. Walking is sufficient to provide reasonable accurate data.

I think the Multi-Function Displays, and associated devices you are talking about are a completely different class of equipment. The devices Ken and I have are handheld, battery powered units (with an optional 12-volt 'lighter style' adapter). For my purposes, it is much more useful than a fixed-mount device. For a couple hundred bucks I have a GPS on my boat, in any car/truck I drive, on my four wheeler, and when hunting, hiking, etc.

I wish my was color like Ken's (denoted by the 'C' in the model number). But that was another hundred bucks that just wasn't in the budget at the time. \:\)


"If a man is to be obsessed by something, I suppose a boat is as good as anything, perhaps a bit better than most".
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