[C38] Autohelm-Chart Plotter Interface

[les]

On Mon, 2011-01-31 at 11:33 -0800, Jay Sorensen wrote:
> Good Day All,
> 
>  
> 
> Broad Reach got an Autohelm autopilot installed over the weekend and
> we are interested in having some type of chart plotter on board to tie
> in to the autopilot.  We are considering having one of our laptop
> computers on board for our cruises and are wondering if anyone has
> experience connecting an Autohelm autopilot to Offshore Navigator or
> another similar program via laptop computer.  
> 
>  
> 
> For a stand alone chart plotter it’s very easy to connect but I’m much
> less sure about using a computer interface.  We would really like to
> have our laptop do everything!
> 
>  
> 
> Experiences, suggestions??  Thanks!
> 
>  
> 
> Jay & Dorothy Sorensen
> 
> C-38 #31, Broad Reach
> 
> San Diego, CA 
> 
> 
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I never saw any replies to this, but I kept it in my inbox so I wouldn't
forget about it.

The autohelm book should guide you through the connect process, and for
most autopilots, there are drivers for Offshore Navigator.  

	I don't know about the Autohelm, but I have a wheelpilot.  I connected
it to my GPS plotter, and it works OK, but and this is a big caveat, on
my system, any course change the boat remains on the original course
until it hits the off course error limit, which is about 0.1 or 0.5
miles by default.  So you are going merrily along, and you hear the
waypoint alarm, then about 5-10 minutes later the course changes to the
new course.  Of course it corrects down to the correct line, but there
is a nice wide triangle formed by a line of the original course to the
off course error limit and then about a 5 degree hypotenuse back to the
desired new course.  For open ocean this may not be too bad, but for
coastal navigation, it is a really nerve wracking business.  

	I don't know if the issue is one of the GPS or the Wheelpilot, but I do
know that I pay lots of attention at waypoints.  Also if the autopilot
is not calibrated correctly you will find that it will as a "safety
measure" go to the course limit and then back when first switched on.
So if I am to the left of the course, it will go left to the error
limit, then back and viceversa.  The wheelpilot calibration procedure
requires calm water and sailing in circles while it figures out the
compass correction.  Fun fun, fun... People often look at us weirdly on
that first cruise of the season as we do corkscrews trying to get
compensation working.

	I know that a computer in the link, running the autopilot in servo mode
could do a better job, but I haven't looked into that as our cruising
kitty won't support a separate laptop for the boat right now.

Regards,
Les H