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Old 07-10-2011, 18:29   #46
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Re: Replace Compass at Helm with GPS

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Originally Posted by bewitched View Post
Yeah, that was my point. The electronic data is likely to be more accurate than looking at the binacle compass, because although a few sailors do keep an updated deviation card, the vast majority don't. So going by the binacle compass alone is a bit of a lottery (without the deviation card).
But that is not how most sailors make use of it today. I think more people use compass for course changes etc. while ale route planing etc is done via chart plotter or similar. Things get cross checked, deviation gets found and is most of the time insignificant.

I have not used the deviation card NOT ONCE in 8 years... Not to say I do not check for it now and then.

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Old 08-10-2011, 03:20   #47
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Re: Replace Compass at Helm with GPS

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Originally Posted by barnakiel View Post
But that is not how most sailors make use of it today. I think more people use compass for course changes etc. while ale route planing etc is done via chart plotter or similar.
I agree with you. I use the compass for sighting gybes and nothing else.

What I was trying to get across (and obviously failed) was those who do the old school...in other words...... work it out on the chart below, accounting for variation and a bit of drift and leeway and then use the deviation card to take the magnetic course to a course to steer are few and far between.

Those that do something less than that are far more common.

And to that I'd add that those who do the whole thing electronically are far more common still.
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Old 08-10-2011, 03:33   #48
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Re: Replace Compass at Helm with GPS

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Originally Posted by Jim Cate View Post
While I agree about the paucity of folks who make and update a deviation table for their magnetic compass, how many with fluxgates routinely re-do the deviation correction routine? Just as much a chance of the deviation changing for the fluxgate as a magnetic compass...

Cheers,

Jim
I think there is a difference Jim. Once an fluxgate compass has been swung, the reading it gives is correct, but a magnetic compass typically has errors on certain points of sail and so simply reading the compass is not sufficient (if absolute accuracy is required)

But I do take your point about the need to keep it calibrated.
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Old 08-10-2011, 04:25   #49
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Re: Replace Compass at Helm with GPS

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Originally Posted by hoppy View Post
My thought is really just to move my two compasses from the primary "navigation position" and either placing one centrally on the table or using two smaller compasses set closer to the rail.
The OP clarified compasses will still be mounted. As long as compasses are accurate and readable from the helm, I see few problems. We just have to make sure crew do not get lost in the virtual reality of plotters, and are not totally reliant on electronic data.

I rely on my mag compass, especially on passages in heavier seas and on longer passages traveling across strong currents. So my usual preference is usually to give precedence to reading compasses. That said, I still want to get the plotter's feedback on COG calculations, to test VMG, and most importantly to have real time position information about tracks and hazards (esp. at night). Both compass and plotter are bulkhead mounted. Both get looked at quite regularly.

How often each is used depends on what I am doing, what I can see, and local knowledge.
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Old 08-10-2011, 05:06   #50
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Re: Replace Compass at Helm with GPS

Actually if you check the CFRs; You are required by law to have a magnetic compass on board your vessel. After that if you want a Gyro compass or a GPS compass or a fluxgate compass you can.

Why is the Magnetic compass is required? 1. It does not require any power supply... 2. The chances of it going belly up on you is nil. 3. If you need it lite for night operations, you can use a candle, oil lamp or a battery powered blub.
All other Compasses are complex in design and the more complicated the design, the easier for it to screwup.
By doing compass checks between the magnetic compass and your favorite expensive electronic compass, you can tell when that big buckwise compass has gone belly up.

From personal experience; I've seen Gyros and fluxgate go bellyup and all we had to steer by is a magnetic compass. About four times in my sea going career.
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Old 08-10-2011, 05:34   #51
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Re: Replace Compass at Helm with GPS

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Originally Posted by boasun View Post
Actually if you check the CFRs; You are required by law to have a magnetic compass on board your vessel. After that if you want a Gyro compass or a GPS compass or a fluxgate compass you can.

Why is the Magnetic compass is required? 1. It does not require any power supply... 2. The chances of it going belly up on you is nil. 3. If you need it lite for night operations, you can use a candle, oil lamp or a battery powered blub.
All other Compasses are complex in design and the more complicated the design, the easier for it to screwup.
By doing compass checks between the magnetic compass and your favorite expensive electronic compass, you can tell when that big buckwise compass has gone belly up.

From personal experience; I've seen Gyros and fluxgate go bellyup and all we had to steer by is a magnetic compass. About four times in my sea going career.
Strictly speaking, fluxgate compasses and consumer grade solid state compasses are also magnetic, as they sense earth's magnetic field. Gyrocompasses and GPS compasses (using two or more gps antennas to determine heading) are non-magnetic.

My main objection to relying solely on a gps chartplotter is that it does not provide heading information. Whether relying solely on electronics for heading information is sufficiently reliable is a different question entirely.
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Old 08-10-2011, 08:16   #52
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Re: Replace Compass at Helm with GPS

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Originally Posted by bewitched View Post
I think there is a difference Jim. Once an fluxgate compass has been swung, the reading it gives is correct, but a magnetic compass typically has errors on certain points of sail and so simply reading the compass is not sufficient (if absolute accuracy is required)

But I do take your point about the need to keep it calibrated.
G'Day Bewitched,

I'd have to disagree about the stability of the fluxgate... your statement assumes that there is no change in the static magnetic field associated with the boat. In real life, it is quite possible that there are changes that would change the deviation. Things like changing wiring near the fluxgate, storing something ferrous or even magnetized near the fluxgate, electronic changes within the circuitry and so on.

We've had various bits of kit that had fluxgates associated with them over the years, and have had to re-do the "circles in the bay" routine more than once due to such changes. YMMV, but I kinda doubt it!

Cheers,

Jim
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Old 08-10-2011, 08:33   #53
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Originally Posted by ADMPRTR
I think when this "type" of question comes up to do something the old way or go with the new we have to ask if we are doing it the old way just because of tradition or because it is dependable.

The new technologies add a lot of features and ease of use but with that convenience comes increased complexity, steeper learning curves and arguably greater potential for equipment failure. Conversely, the old technologies typically are simpler to use but in some ways require more knowledge and effort by the user. Each technology has it's good and bad points and when working together can often fill-in the shortcomings of the other.

A common thread in this discussion is keeping redundant systems that can work when others fail. I think the key to success with redundant systems is that we need to also maintain the skills to use those systems. So steering a bearing on a compass course is just as important as steering by a plotter display.

Where I sail, there are places where magnetic disturbances makes a compass unreliable but I have also seen the GPS lose satellite locks for no apparent reason.

On a personal note, I force myself to maintain a paper log and chart in addition to setting routes on the plotter. It takes a lot more time but I can often find something on paper that isn't in the software or visa versa.
Probably the most sensible reply on this topic.
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