NavList:

> Do you remember the days of LORAN C?
>
> Most units had a dampening/averaging factor that was user selectable, i.e. to
> average data and present a display based on the last 10-20-30 seconds, etc.
> Consumer GPSes do not, as far as I know, have any similar option. They simply
> perform internal calculations and, if you are lucky, they present "the latest"
> data once per second on the NMEA output bus and the screen. If a vendor chose
> to
> take longer to average data (like course headings) or used slower cheaper
> hardware that was really using a longer time base to present this information,
> there's no way you would know about it.

Red

Sure do.  I was looking at hand-held units and had gone as far as ordering
the manual for the unit I thought I wanted.  About that time hand-held GPS
(Magellan, $1500) hit the scene and prices began to drop on GPS's so I held
off.

My only hands-on experience was on Catalina 34 the owner bought used.  The
LORAN was a built in unit.  Asked the owner if he ever used it, he said not,
it was a backup for his GPS, and he turned it on once a month to make sure
it worked.

The crew decided to crank it up, mostly out of curiosity I suppose, and it
was 10' off on both lat and lon.  We grabbed the manual and went about
setting it up from scratch.  I read, my buddy tweaked.  Fired it up and same
results.  So my buddy read and I tweaked.  Same results.  My guess, some
sort of antenna problem (short, open).

Well we asked the owner if the lat lon was close when he fired it up.  He
said he never looked at the numbers, just wanted to make it "still worked."
So I guess the definition of "worked" means it lighted up and displayed
numbers.  This is the same skipper that had a good laugh at my first
on-the-water attempt with my cardboard sextant (in rough seas) when I came
up 5 & 7 minutes from our GPS position (not averages, just one shot each).
"What good is that, he laughed."  I noted we were coastal piloting, it would
suffice in the middle of the Atlantic.

As you might imagine it was my turn to laugh and rub it in.  Suggested he
get a cardboard sextant as a GPS backup, it was at least twice as accurate
as his LORAN.  Of course that would not do as it was not waterproof.  How
about a plastic sextant?  Silence.

He still loves to rib me when I pullout the sextant.  Now that I do
reductions and T15 and T16 calculations with my TI-30, his position is that
I need electronics to do it, why not just a GPS?  I point out that there are
tabular methods for all the above, but I don't think I'll ever convert him.
I do sense some hidden interest after I used nothing but a hockey puck
compass and sextant to track us for the first 20nm from Chicago to Michigan
City, including a tack.  Compared to the GPS I was within a quarter mile or
better the entire time.

Now he will go as far as asking me to track freighters to see if we are on a
collision course and estimate their distance, and after passing his 100
ton-offshore masters exams seems to actually care about compass deviation.
And we have the game where he checks the true and apparent wind directions
and velocity, and boat speed on his instruments; and I have to "guess" at
the figures.  Using the number of standing waves or dropping a potato chip
off the bow, and just racing experience in general I come within 5-10% of
wind true and apparent velocity and direction, and boat speed through the
water.

Having won that game so many times, I like to get his goat when at the wheel
by swiveling the GPS toward him so I can't see it, setting an alarm on the
depth meter, and placing a towel over the instruments, claiming I don't need
them and it protects them from UV. <g>

I think I have his attention, but doubt I'll ever see a sextant in hands.

As to user selectable speed updates, I believe my  Garmin GPS 76  (about 5
years old) does have a speed filter under main menu >setup >units >speed
filter >user where I can specify an interval.

I do not believe I can change filter settings for position update, but
suspect there is some averaging going on there.  For example I have
waypoints set up for the trip to my mothers home 100 mile north. (Keeps me
in practice and helps kill the time.)  If I pass through a stoplight at 20
mph it will not nail the waypoint (off by maybe 40-80 ft. If stopped at the
light it will, over a period of 10 seconds or so nail that puppy within 10
feet.  So it is probably not updating raw information by the second.

There is also an undocumented feature that will average out a waypoint
location if you are entering automatically and stationary.  I don't know the
magic to access it, but it has popped up once or twice over the years.

As I've remarked in the past, GPS is an excellent way to fine tune the
traditional skills I feel a prudent boater needs.  Instant feedback, like
looking at the answers to the Silicon Sea questions AFTER you have worked
out your answer.  If one relies on GPS as their primary or only source, that
is similar to reading the answers without ever looking at or understanding
the problems.

After a couple of warnings and cautions the GPS manual clearly states, "Be
safe; remember that while the GPS is very reliable, you should always have a
backup means of navigation."

It still seems odd that the best method to date of checking my skipper's
compass is a hockey-puck compass on the cockpit coaming.

Bill


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