I've been using an SC50 SAT Compass for the last three years on my
N55. It has performed flawlessly anyplace that it can get a good 3D
fix. I have a fluxgate built into the Simrad autopilot as a backup.

Nice thing about the SC50 is that its provides TRUE heading data
without reference to variance, local magnetic anomalies or any
calibration or deviation issues on the boat since the data is decoded
from the satellites. I run everything on the boat in True mode as a
result.

The one issue with the SC50 is in narrow fjords where the view of the
GPS constellation is restricted enough that the compass can't resolve
heading, or sometimes even position. It then alarms, but continues to
provide heading for a few minutes based on the solid-state rate gyros
and then after a timeout it drops heading outputs altogether. When
underway, the rate gyros are usually adequate to maintain continuity
of heading updates until the terrain blocking shifts enough to lock
back on, but its more troublesome at anchor because it can take tens
of minutes to a half hour for the constellation to shift enough to
regain a 3D fix when the boat is static.

This has been an issue about half a dozen times in Alaska and Northern
BC, and mostly bothersome at anchor because I use the SC50 as my
primary GPS as well, and my anchor alarm goes off out at those times.
That said, my other GPS is also reporting nonsensical position
information at those moments.

I can only recall one time where I lost heading when underway and the
"black out" exceeded the rate gyro timeouts, and that was when I was
very close in to a mile high cliff at the end of Princess Louisa Inlet.

One nice thing is that the rate gyros also give you real time pitch
and roll data. Not terribly useful data, but interesting sometimes.

John Marshall
N55-20 Serendipity

On Sep 18, 2009, at 9:22 PM, Philip Eslinger wrote:

Dear Philip,

My company manufactures GPS receivers and compasses.  In fact, we
pioneered the concept and today are the largest producer of them,
although we do not manufacture Furuno's which is also a nice product.
In the early days, we had to have antenna separation of at least one
meter to get the accuracy required with the technology we had then.
On many installations, we used discrete antennas and placed them bow/
stern or athwartship on the wheel house.  The accuracy with that much
separation was high despite the early technology.  Most of the units
we sold then were at a high price and were purchased primarily for
working vessels, that is commercial shipping, fishing, dredging,
marine surveying and the like.  The initial value was seen with
vessels moving at extremely low speeds or not moving at all, but were
required to control orientation precisely.  Then captains discovered
how well they worked with virtually any autopilot.  Sail racing
captains came to appreciate heading accuracy regardless of boat
orientation or movement.

There have been numerous (too many to count) advancements since then.
The speed and accuracy of the receivers, the antenna technology, noise
and multi-path mitigation and fusion with inertial sensors to name a
few.  This brings us high performance in a smaller and less expensive
package while maintaining incredible reliability.  Focus over the last
few years has been on products designed specifically for the leisure
marine markets and for applications outside marine such as agriculture
and construction.  Keep in mind that if you have one of these mounted
on any machine, you now have a location address for every bolt on that
machine in real time.  This capability ushers in unprecedented
opportunities for automated machine control far more accurately than a
human operator.  In agriculture, for example, automatic steering for
tractors virtually eliminates overlap which significantly reduces
diesel fuel consumption, seed, fertilizer or any other treatment being
applied.

It is my opinion that a boat captain today can rely on his GPS compass
with a high degree of confidence for primary heading, but like with
all other mission critical elements, redundancy is good.  Assuming one
GPS compass on board is not working, the second one may not be working
and maybe not even a single antenna GPS which would at least give you
course data underway.  So a non GPS backup is a good choice.

For more information, you might visit our company web site http://www.hemispheregps.com/
.  You won't recognize Hemisphere GPS as a brand because our marine
products are integrated into other OEM branded products.  I was the
founder and ran it for awhile before retiring.  I now serve as vice
chairman on the board.

All the best to you...

Rick Heiniger
N7617 Eliana

On Sep 18, 2009, at 11:22 PM, Philip Eslinger wrote:

----- Original Message -----
From: "Heiniger Rick" >

REPLY
Quite true, but the above statement  is based on an assumption that the
electrical power supply is  constant and  100%  reliable at all times.  Is
that  a valid assumption for recreational boats.

This list  represents  a wide range of boat owners and just as many  boat
brands.  Some new and some not so new. Unfortunately, some boats have less
reliable  electrical systems  than others.  Otherwise why are marine
electricians in demand?

My comment were addressed to those who  have not  yet rebuilt  their system
to the level required  by  Lloyds with dual, independent  power supplies to
all critical equipment  like navigation, steering gear ( autopilot ) and
what have you.

regards
Arild

Aw come on Arlid, give the guy a break.

He not only said "redundancy is good" but thinks a "non GPS backup is a good
choice" which could certainly include a real compass for us old steam
gauge/wet compass guys.

What more could we ask from a guy that develops and makes them?

Jon
Outbound
Hatteras 58 LRC

----- Original Message -----
From: "Heiniger Rick" >

REPLY
Quite true, but the above statement  is based on an assumption that the
electrical power supply is  constant and  100%  reliable at all times.  Is
that  a valid assumption for recreational boats.

This list  represents  a wide range of boat owners and just as many  boat
brands.  Some new and some not so new. Unfortunately, some boats have less
reliable  electrical systems  than others.  Otherwise why are marine
electricians in demand?

My comment were addressed to those who  have not  yet rebuilt  their system
to the level required  by  Lloyds with dual, independent  power supplies to
all critical equipment  like navigation, steering gear ( autopilot ) and
what have you.

regards
Arild

No offense taken.  Arlid makes a good point and I agree.

R

On Sep 20, 2009, at 4:58 PM, Jon Hill wrote: