Re: [Paddlewise] GPS Errors Summary

PeterO wrote:
> 
> Michael Neverdosky wrote:
> >Using normal gear on a sailboat I was more than
> >happy if my 'triangle'was only 2 miles across.
> 
> Michael Daly replied:
> >That's a little more like it :-).
> 
> G'Day,
> 
> Well if thats what is achievable with a $1000 sextant it makes our student
> efforts with deck compass, thumbs or sticks and string look quite cost
> effective. (900m error over a 10km distance). But I'm guessing the two
> Mike's error estimates were for navigation rather than pilotage, i.e not
> using landmarks by Mike's earlier explanation. Would that be the case? In
> fact I would have thought a kayaker more experienced in pilotage would have
> made less than half the error we did.

If you want to compare using a GPS to using compass bearings on
landmarks
then you need to use a DGPS.
Try using your compass, thumbs and sticks and string to fix your
position
on a large sheet of ice with no identifiable features.

The big reason for pilotage when along a coast is because it references
to
the LAND and that is what you care about. When you are out of sight of
land
you use celestial nav because you need to. In celestial you have to be 
concerned about the position error of the charts because you are fixing
your 
position relative to the sun and stars. In coastal pilotage you have
removed
the chart position error because your reference is to features on land
that
are shown on the chart.


> 
> By the way has anyone actually tried to use a sextant in a kayak? I tried
> once with a very cheap plastic sextant. My friends refused to paddle with me
> until I put it away. They made a number of extremely impolite remarks:~)
> 

There are a number of problems with using a sextant on a kayak. First is 
staying upright while taking the sight. Second is the height of eye, as
it
is very low and keeps changing. Third is the difficulty of plotting the
LOPs found onto your chart.

The smallest boat that I *used* celestial nav on was a 24 foot monohull 
sailboat and it was not very easy.
Doing celestial on my 28 foot trimaran was downright easy because of the
stability.

The GPS is always more accurate and easier than celestial as long as
long as it is working. OTOH celestial only requires your tables and
watch with a sextant. 

michael
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