Re: T&T: NAV Mode and Autopilots
After all the posts on AUTO vs NAV and reconsiling my own operation,
I feel I have to make the following somewhat counter opinion to the
trend of the discussion.
The trend I think I am reading is
Bad - NAV mode -- which on my AP means follow the course and
crosstrack error (XTE), from the chart plotter or other GPS device
Good - Auto mode -- on my AP means follow a specific heading
Best - manually steer
This means:
Auto mode, any current or wind effect will cause the boat to run off
course without intervention and when you get to a course change
point, it will continue on the heading until you notice.
NAV mode, the AP will correct the steering to keep to a very small
XTE without intervention and when you get to a course change point,
it will continue on the heading until you notice, while beeping like
crazy to tell you to notice.
NAV is simply an XTE corrected and end of course alarmed AUTO, so if
AUTO is okay, NAV is essentially a more accurate attempt at the same
goal. So do we need to always hand steer?
Perhaps the real subject here is about the responsibility of standing
watch and running the boat. The feeling appears to be that, if I use
my AP, then I must not be paying attention. My counter opinion is, I
can create plenty of work for the helmsman to do, to make sure they
stay busy at their post. However, I believe that having the helmsman
free to watch the movement of other boats, look for lobster pots,
verify depth sounder matches the chart, verify chart position via GPS
and surrounding visuals, check buoy positions against the chart,
compare charts and sightings to the radar, etc. is more constructive
than trying to focus on handling the rudder every 10 seconds while underway.
I use NAV when possible. This requires that I have a course in my
plotter. This regimen means that before heading out for the day, I
must enter my route into the plotter. When doing this, I closely
review and adjust the entire route at close scale and insure I have
plenty of margin around all obstacles. I put in additional waypoints
at the closest obstacle passes to help me identify them when
underway. I make notes of any areas of specific caution.
By manual steering or AUTO steering, I could just wing it on the
planning. Basically, I could point the boat and let it go. So if my
only objective was to use tools that force good practices, NAV mode
does that. But, I believe the procedures should be followed because
they work, not because a tool or lack of it forces a particular
operating behavior.
Bottom line, I use my NAV mode extensively. My helmsman stands a
good watch. I follow a well planned course accurately and with
care. I don't agree with those who insist that using the good tools
available to us makes us sloppy captains. To me, the key is have
good, well thought through procedures and duties, then follow them
and constantly improve them.
-Wray
M/V Anjumal
-----Original Message-----
From: Wray West
I feel I have to make the following somewhat counter opinion to the
trend of the discussion.
Perhaps the real subject here is about the responsibility of standing
watch and running the boat.
Bottom line, I follow a well planned course accurately and with
care.
-Wray
M/V Anjumal
REPLY
Excellent points Wray!! Your argument rest on the premise that ALL boat
owners do in fact know and practice careful route planning and meticulously
plot their intended route, using the most detailed charts available.
However, it has been my observation that many boat owners do not practice
what you advocate.
Instead they often use the "GOTO" function of the GPS system. Or else take
similar short cuts.
In other words at the point of departure they simply pick the next waypoint
and instruct the GPS based system to "GOTO" this next waypoint. This
differs from actually planning a route with multiple waypoints.
GOTO means the autopilot simply continues to point the boat towards the
destination waypoint.
Set and drift does not enter into the calculations.
A route by comparison, involves several waypoints which allows the
calculation of cross-track error.
Unfortunately navigation systems are dumb and cannot distinguish a bad route
from a good route or foresee the consequences of a poor choice in
instructions to the navigation system.
I quite agree that your approach will keep you out of trouble but many
people do not practice navigation in that manner.
They have unrealistic expectations of the capability of the system. This is
no doubt a result of listening too closely to the sales hype.
regards
Arild
After all the posts on AUTO vs NAV and reconsiling my own operation, > I
feel I have to make the following somewhat counter opinion to the > trend of
the discussion.> > NAV is simply an XTE corrected and end of course alarmed
AUTO, so if > AUTO is okay, NAV is essentially a more accurate attempt at the
same > goal. So do we need to always hand steer?
I'd suggest that NAV mode is inherently safer than AUTO. However many skippers
punch in waypoints at points where course changes should be made and at the
destination point. If these points are far apart, Xtrak error (in degrees) can
lead to problems. You can have a Xtrak error of 1 mile, that is still only 2
degrees if the next waypoint is 30 miles off. Breaking the route into smaller
chunks of 1/2 hour segments, even if that means 20 waypoints on a straight
line course for a day's cruising, will keep a tighter course if set, drift and
wind will play a factor.
Peter
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Dear List,
I use auto steering when "close" to land, or on a lake, or in a
river, with a VERY close eye on the bow of the boat and the chart
while going slow (displacement speeds) and in all cases, where there
is NOT a lot of traffic around.
I pay PARTICULAR attention when going under bridges, and if in doubt,
I had steer.
I have never had a problem with an unexpected swing, but could one day.
I use Nav when going across the ocean where way points are selected
based on the planned great circle route.
I hand steer all other times
My friends that have sailboats probably do not know what Nav mode is.
They use auto, or hand steer.
Lee
However, it has been my observation that many boat owners do
not practice what you advocate. Instead they often use
the "GOTO" function of the GPS system.
I've always wondered about this every since I was in a meeting with some
people at Maptech. Their head of technical support told me that only 10% of
their customers actually use routes. I thought this was odd because I use
them 90% of the time. Even if I'm just going out for the day to another
island or town, I usually pop in a route to keep me out of trouble. I've
done this on my trawler and other smaller boats.
Is it normal to run without a route planned? Are there that many people out
there just winging it?
Even on the ICW, I like to make sure there is a "magenta line" or other such
capability showing to make it obvious when turns come up. Is this so
unusual?
---=
Jeffrey Siegel
M/V aCappella
DeFever 53PH
W1ACA/WDB4350
Castine, Maine
www.activecaptain.com
Content, Communications, Community
On 11/27/07, Jeffrey Siegel jeff@activecaptain.com wrote:
Are there that many people out
there just winging it?
Yup. I think perhaps you've become a bit spoiled by this list,
Jeffrey, where a large number of operators exhibit a large degree of
professionalism, at least to the degree that they think about things.
My experience with land, sea, and air vehicles is that the great
preponderance of humanity invests only enough care and attention to
approach bare adequacy.
JG
Awesome post, Wray. That couldn't be any more perfectly said. It is all about managing the resources you have the best you can to provide the safest most efficient outcome. Kudos!!!
Trawler on,
John
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Arild wrote:
<<GOTO means the autopilot simply continues to point the boat towards the destination waypoint. Set and drift does not enter into the calculations.>>
This is NOT true. The GPS does not direct the AP to "home" towards the GOTO point. When you punch the GOTO button, that point in space is marked and a "route" from that point to the GOTO point is built. The GPS will "maintain" that route and instruct the AP to do so if it is in the NAV mode. Based on the above points, SET and DRIFT will be corrected for as the GPS/AP will be maintaining a specific Course Over Ground.
Trawler on,
John
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-----Original Message-----
From: John Baker
Arild wrote:
<<GOTO means the autopilot simply continues to point the boat
towards the destination waypoint.
Set and drift does not enter into the calculations.>>
This is NOT true. The GPS does not direct the AP to "home"
towards the GOTO point. When you punch the GOTO button, that
point in space is marked and a "route" from that point to the
GOTO point is built. The GPS will "maintain" that route and
instruct the AP to do so if it is in the NAV mode. Based on the
above points, SET and DRIFT will be corrected for as the GPS/AP
will be maintaining a specific Course Over Ground.
REPLY
So I have just been told in a few off-list emails.
My source for this information was a book by Kevin Monahan and Don Douglass.
Admittedly this book was published several years back 2000 - 2001.
I packed the book away for our recent move and do not have it ready at hand
for me to find the page reference.
Point being, such books and instructions are still widely circulated long
after their technical content is made obsolete by newer technology. If I was
led astray by such a book; so could other people who would not know the
latest technology has drastically altered how things work.
No doubt my (2004) copy of the RADAR Book by the same author and published
by Fine Edge Publishing is now also obsolete and no longer relevant for
learning how to use a radar.
My apologies to the list for mis-leading you all.
And technology marches on
Arild
I have routes set up for damm near everywhere I go in Nobeltec. Also, my
autopilot is an old manual one, and only holds a course. I like it that way.
Keith
"Good judgment comes from experience, and a lot of
that comes from bad judgment." - Will Rogers
----- Original Message -----
From: "Jeffrey Siegel" jeff@activecaptain.com
I've always wondered about this every since I was in a meeting with some
people at Maptech. Their head of technical support told me that only 10%
of
their customers actually use routes. I thought this was odd because I use
them 90% of the time. Even if I'm just going out for the day to another
island or town, I usually pop in a route to keep me out of trouble. I've
done this on my trawler and other smaller boats.
Is it normal to run without a route planned? Are there that many people
out
there just winging it?