Deviation Table with GPS

[meirriba]

Originally Posted by psneeld

I dont beleive all, especially older APs/flux gates have this capability.

It is possible that older equipment cannot do this.
This is the reason that I was specific with the model of our MFD (it is about 6 year of age and already obsolete...).

[estarzinger]

To the OP, the correct way to do this is locate fixed points (like significant nav marks), position yourself some distance North/south/east/west of those marks using your gps and point the boat at mark.
If you pick a mark which is either totally fixed like a lighthouse or church spire or measured mile marks; or floating but on a small scope so its location does not vary much; and you set up some couple hundred meters from the mark (to minimize the effect of gps error on the positions) this method is dead accurate

You can use the gps cog, but it is viewed as a somewhat less accurate method, and the above correct way is not hard at all.

Originally Posted by meirriba

Basically - during calibration procesd the inner computer, using connected GPS, builds deviation table for the flux compass.

hmmm . . . . I am aware of the details of several fluxgate autocalibration routines, and I am not aware of anyone that uses gps - all the ones I am aware of in fact will autocalibrate even without any gps connected. They mostly look for 'lumps' in the turn rate as you drive around in circles. Not to say that there is not some model out there which I am unaware of which uses gps input for this, but it is sure not the normal standard.

[unbusted67]

Originally Posted by billknny

Not at all. With all traditional methods of compass swinging you point the bow of boat at something. Thats a heading, not a COG.

Here is a long list of ways to do it...
How to swing a compass - Practical Boat Owner

My personnel choice is to use a hand bearing compass. Easy, quick to check, and more than accurate enough for small boat work.

I thought you might catch me on that. I am referring to the method in Chapman's where they have you drop a buoy and line the boat up with that mark and a fixed spot on land. This method is subject to current, wind, and the boat's wake which has me totally thrown off.

[El Pinguino]

Originally Posted by unbusted67

I thought you might catch me on that. I am referring to the method in Chapman's where they have you drop a buoy and line the boat up with that mark and a fixed spot on land. This method is subject to current, wind, and the boat's wake which has me totally thrown off.

No need to drop a buoy, either - as just suggested - put a GPS possy on the chart and use that , or park close to a pre-existing buoy and then 'point ship' at distant marks. So you are 50 metres from the buoy? That is of no consequence if your distant mark is indeed 'distant'.

But what if you can see no suitable marks anywhere to the west ? No probs..... just wait until, a few days later , you do have distant marks to the west. Complete your card then.

[missourisailor]

There is also a way to create a deviation table using the sun.

Maryland School of Sailing has a You-Tube video that shows how to do it.

https://www.youtube.com/watch?v=iIRLTyp8vhg

I've done it this way several times. All with good results.
I've even did the No-No by using GPS time as the boat did not have SSB for WWV time.

[unbusted67]

Originally Posted by missourisailor

There is also a way to create a deviation table using the sun.

Maryland School of Sailing has a You-Tube video that shows how to do it.

I've done it this way several times. All with good results.
I've even did the No-No by using GPS time as the boat did not have SSB for WWV time.

Man this is fantastic. I watched the whole damn thing! Does a cell phone not put out accurate time?

[missourisailor]

Originally Posted by unbusted67

Does a cell phone not put out accurate time?

Several things.
The time stamp is how the DoD degrades the accuracy of GPS. They can and will mess with it however and whenever they want.

But more importantly to us is the way the GPS display takes care of leap seconds.

Here is a condensed white paper on it.

How accurate is the TIME DISPLAY on my GPS?