TWL: Compasses
-----Original Message-----
From: Thataway@aol.com [mailto:Thataway@aol.com]
Sent: Thursday, April 12, 2001 12:24 PM
To: trawler-world-list@samurai.com
Subject: TWL: Compasses
Bob Austin wrote
Actually you can purchase several compasses compensated for both north and
south hemispheres, but why bother, since the GPS gives a very accurate
compass heading--as long as you are moving.
Arild writes.
Pardon me for contradicting you Bob, but the GPS will show a direction of
movement; NOT a heading.
A compass will show an actual heading because the lubber line is aligned
with the keel.
The GPS direction of movement does not show if the vessel is pointing in a
direction other than the dierction of movement.
Usually referred to as making leeway.
A boat towed stern first will show a GPS " heading" 180 degrees different
from the compass heading.
Cheers
arild
Soooo... Everytime I navigate a boat I general care about the direction of
movement. If hand steering I generally set the magnetic heading by using
the GPS to center on the direction of movement. I often set autopilots based
on the GPS direction. I don't like to tie directly - I prefer to run the
systems independently and watch for anomalies.
I also think the conventional magnetic compass has had its day. It will be
a life boat thing in 10 years and gone in 25.
Jim - Runnig for the hurricane shelter.
-----Original Message-----
From: owner-trawler-world-list@samurai.com
[mailto:owner-trawler-world-list@samurai.com]On Behalf Of Arild Jensen
Sent: Thursday, April 12, 2001 2:05 PM
To: trawler-world-list@samurai.com
Subject: TWL: Compasses
Arild writes.
Pardon me for contradicting you Bob, but the GPS will show a direction of
movement; NOT a heading.
A compass will show an actual heading because the lubber line is aligned
with the keel.
The April issue of NW Yachting contains an article by the
Ranne Hemingway and Don Douglass with a sidebar discussing their
autopilot problems. Appearntly they had traveled far enough North
(Glacier Bay ~50N) so that their flux gate compass didn't work
correctly. They resolved the problem by switching to a diffearnt type
of electronic compass (but not a gyro). Does anybody know more about
the limitations of a flux gate compass?
Ross Fleming rossflem@serv.net
Seattle, WA
The April issue of NW Yachting contains an article by the
Ranne Hemingway and Don Douglass with a sidebar discussing their
autopilot problems. Appearntly they had traveled far enough North
(Glacier Bay ~50N) so that their flux gate compass didn't work
correctly. They resolved the problem by switching to a diffearnt type
of electronic compass (but not a gyro). Does anybody know more about
the limitations of a flux gate compass?
Ross Fleming rossflem@serv.net
S/V Renown Gulfstar 39
Seattle, Washington
=
=I also think the conventional magnetic compass has had its day. It will be
=a life boat thing in 10 years and gone in 25.
Let us know how you feel about this after a lightning strike fries all your
electronics.
Rick
Rick the Mouseherder - nh2f
Westsail 32 Xapic, Hull #438
Annapolis, MD
A small boat and a suitcase full of money
beats a 40 footer tied to the Bank.
Creative graphic solutions in vinyl for your boat lettering & designs
http://www.mouseherder.com
Visit our Westsail 32 Xapic
http://www.mouseherder.com/xapic
The Westsail Owners Assn. Homepage
http://www.westsail.org
At 02:42 PM 4/12/01 -0700, you wrote:
Soooo... Everytime I navigate a boat I general care about the direction of
movement. If hand steering I generally set the magnetic heading by using
the GPS to center on the direction of movement. I often set autopilots based
on the GPS direction. I don't like to tie directly - I prefer to run the
systems independently and watch for anomalies.
I also think the conventional magnetic compass has had its day. It will be
a life boat thing in 10 years and gone in 25.
---======================
Jim what do you use when the GPS goes out-----The sun and stars, and how
about cloudy days----fog etc.
.
Captain Al Pilvinis
"M/V Driftwood"--Prairie 47
2630 N.E. 41st Street
Lighthouse Point, Fl 33064-8064
Voice 954-941-2556 Fax 954 788-2666
Email yourcaptain@earthlink.net
Website http://home.earthlink.net/~yourcaptain
That's all great, Jim, but the discussion was about compass direction, not
about course made good or course over the ground (COG). Two entirely
different things, as you know! I, too, set the autopilot (manually) based
on what the GPS is telling me, but that's totally different than using the
compass, although it could be done via the compass if I wanted to
graphically compute set and drift based on fixes and all the other
available info, then dial it into the auto pilot or steer the magnetic
course based on the set and drift computation.
There is a big difference between magnetic direction and COG! The boater
who doesn't understand the difference, and take it into consideration when
setting a course to steer, will eventually find life very exciting.
Undoubtedly something will replace the magnetic compass, and it already has
to some extent - it's called the gyrocompass! Again, just a vital part of
the navigation equation!
At 02:42 PM 04/12/2001 -0700, Jim Donohue wrote:
Soooo... Everytime I navigate a boat I general care about the direction of
movement. If hand steering I generally set the magnetic heading by using
the GPS to center on the direction of movement. I often set autopilots based
on the GPS direction. <little snip>
I also think the conventional magnetic compass has had its day. It will be
a life boat thing in 10 years and gone in 25.
<><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><>
M/V Sanderling Email: rmcleran@ix.netcom.com
Hampton 35 Trawler
Currently docked: Pt. Patience Marina, Solomons, MD
Not nearly as bad as you will feel after it fries your electronics, your
compass, and blows a hole in your boat.
Same thing as asteroids - it almost never happens - but when it does a real
pain in the ass.
Jim
=
Let us know how you feel about this after a lightning strike
fries all your
electronics.
Rick
I have two laptops, individual GPS units for them, and separate power
supplies as well as a hand held GPS. Lightning would have to strike
twice to get me! In the context of risk management, I'll accept this
one...
I'll bet many of you remember the "whistler RADAR" and the old modular
RDF's? "Boatiques!"
Regards....
Phil Rosch
M/V "Curmudgeon"
Currently Moored in Wickford RI.
=I also think the conventional magnetic compass has had its day. It
will be
=a life boat thing in 10 years and gone in 25.
Let us know how you feel about this after a lightning strike fries all
your
electronics.
Rick
We used to have a Raytheon autopilot that would let you input your latitude
so that it could correct a tendency of the fluxgate compass to wander on
N-S headings. Our current CommNav autopilot has a separate black box that
compensates for that same tendency in high northern latitudes. We've had no
problem using either autopilot in and around Glacier Bay. I'm surprised
that the Douglasses found something else other than a gyro compass to use
as I thought that was the only other alternative.
Mike & Lily O'Reilly
Voyageur, GB-42-1311
Portland, OR
: The April issue of NW Yachting contains an article by the
:Ranne Hemingway and Don Douglass with a sidebar discussing their
:autopilot problems. Appearntly they had traveled far enough North
:(Glacier Bay ~50N) so that their flux gate compass didn't work
:correctly. They resolved the problem by switching to a diffearnt type
:of electronic compass (but not a gyro). Does anybody know more about
:the limitations of a flux gate compass?