Conference unifix::sailing

    I adjust my own, using charted landmarks, at slack tide.
    
    Greenwich Bay has a lot of those.  Last time I checked both
    the bouy NE of Goddard St. Park and the one south of Oakland
    where just where the charts say.  Those plus landmarks can
    give you a couple courses in each quadrant.
    
    Its probably more time consuming than with a Peloris, but I can
    do it myself and dont have to buy/correct one.
    
    The results seem to verify nicely with LORAN calculated headings.

    You might have to look around Newport for someone who can make
    a living doing this. (I dont think most bay sailors have any idea 
    what their compass is for, since they are surrounded by landmarks 
    and seldom ever experience heavy fog)   I saw one boat (a Hunter
    31 as I recall) which had mounted a pair of speakers in those
    round binnacle instrument housings, about 8" either side of the
    compass. I bet that solved that pesky distraction of having the
    card rotate ;^)

    Walt

    I plan on having my compass adjusted in the next couple of weeks.
    Sam Lawson, of Lawson Yachts, recommended Henry Rioux.  Henry is
    out of Plymouth.  The price quoted was $100.  The process takes
    about a couple of hours.  Anyone that Sam recommends is always
    excellent.
    
                           John
     

There are a number of accurate and not-so-accurate do-it-yourself
methods for determining the deviation in a compass. One of the 
(potentially) accurate methods uses azimuths of the sun, which sounds 
more difficult that it is.

Beg, borrow, steal, or buy a (cheap) Davis pelorus. Attach it firmly to
the your boat along the centerline (I used a piece of plywood clamped
to the mainsheet traveler) and align it with the centerline. I used
the mainsail groove in the mast and the backstay (which requires some
faith in the care the builder used in building your boat) as the
centerline references. 

Now the hard part. Wait for a calm, sunny day. The sun should be low in 
the sky, which means either early in the morning or late in the 
afternoon. When facing the sun the front sight vane of the pelorus 
casts a shadow on the pelorus scale, giving the relative bearing of the 
sun. 

Making bare steerageway, steer as many compass headings as you have the 
patience for, and note the exact time (to the nearest minute) and 
relative bearing of the sun on each compass heading. 

You now need the azimuth of the sun. The data in the Nautical Almanac or 
Reed's, your geographic location, and the FORTRAN program below give the 
azimuth. (The FORTRAN program is easier than trying to teach celestial 
navigation in a short note.)

Once you know the sun's azimuth, and the magnetic variation, simple 
addition and subtraction will give your actual heading on each of the 
compass headings. 

With standard sight reduction tables (eg HO 249), you don't even need a 
computer, and the method works on any sunny day.

Alan



C
C	 THIS IS A PROGRAM TO FIND THE TRUE AZIMUTH OF THE SUN
C	 AS A FUNCTION OF TIME. THE REQUIRED INPUT DATA IS OBTAINED
C	 FROM THE NAUTICAL ALMANAC AND GEOGRAPHIC LOCATION.
C
C        WRITTEN DECEMBER 1983
C
	REAL MIN,LHA,LAT,LATR,LONG
	TYPE 5
5	FORMAT (1X)
C
C	 ENTER LATITUDE (ASSUMED NORTH) IN DEG, MIN
C
	TYPE 95
95	FORMAT (1X,'LATITUDE      ',$)
	ACCEPT *, DEG, MIN
	LAT=DEG+MIN/60.
C
C	 ENTER LONGITUDE (ASSUMED WEST) IN DEG, MIN
C
	TYPE 90
90	FORMAT (1X,'LONGITUDE     ',$)
	ACCEPT *, DEG, MIN
	LONG=DEG+MIN/60.
C
C	 ENTER MAGNETIC VARIATION (ASSUMED WEST) AT LOCATION IN DEG, MIN
C
	TYPE 10
10	FORMAT (1X,'VARIATION     ',$)
	ACCEPT *, DEG, MIN
	VAR=DEG+MIN/60.
C
C	 ENTER GHA AND DECLINATION DATA IN DEG, MIN
C	 ASSUME 2 HOURS (120 MINUTES) BETWEEN GHA AND DEC DATA
C
	TYPE 20
20	FORMAT (1X,'FIRST GHA     ',$)
	ACCEPT *, DEG, MIN
	GHA1=DEG+MIN/60.
C
	TYPE 100
100	FORMAT (1X,'FIRST DECLINATION     ',$)
	ACCEPT *, DEG, MIN
	DEC1=DEG+MIN/60.
	TYPE 40
40	FORMAT (1X,'SECOND GHA     ',$)
	ACCEPT *, DEG, MIN
	GHA2=DEG+MIN/60.
	TYPE 120
120	FORMAT (1X,'SECOND DECLINATION     ',$)
	ACCEPT *, DEG, MIN
	DEC2=DEG+MIN/60.
	TYPE 5
	TYPE 5
	TYPE *,'   MINUTES     AZIMUTH     MAGNETIC AZIMUTH'
	TYPE 5
C
C
C	 LINEAR INTERPOLATION
C
	IF (GHA2 .LT. GHA1) G=(GHA2+360.-GHA1)/120.
	IF (GHA2 .GT. GHA1) G=(GHA2-GHA1)/120.
	D=(DEC2-DEC1)/120.
C
	I=0
1000	IF (I .GT. 120) STOP
	GHA=GHA1+G*I
	DEC=DEC1+D*I
C
C
C	 NEXT CONVERT TO LOCAL HOUR ANGLE (LHA)
C
	LHA=GHA-LONG
	IF (LHA.GT.360.) LHA=LHA-360.
C
C	 NEXT CONVERT TO MERIDIAN ANGLE (T)
C
	IF (LHA.LE.180.) T=LHA
	IF (LHA.GT.180.) T=360.-LHA
C
C
C	 TYPE VARIOUS COMPUTED INFORMATION
C
C	TYPE *,'MERIDIAN ANGLE     ',T,' DEG'
C	TYPE *,'DECLINATION     ',DEC
C	TYPE *,'GHA             ',GHA
C	TYPE *,'LHA             ',LHA
C
C	 AZIMUTH COMPUTATION 
C
C	 CONVERT DEGREES TO RADIANS
C
	DECR=DEC*3.14159/180.
	LATR=LAT*3.14159/180.
	TR=T*3.14159/180.
C
C	 COMPUTE AZIMUTH USING FORMULA IN H.O. 229
C
	X=COS(DECR)*SIN(TR)
	Y=COS(LATR)*SIN(DECR)-SIN(LATR)*COS(DECR)*COS(TR)
	Z=X/Y
	AZ=ATAN(Z)*180./3.14159
	IF (AZ.LT.0.) AZ=AZ+180.
	TYPE *, I, AZ, AZ+VAR
	I=I+1
	GOTO 1000
	END

    I have just installed a new autopilot.  Installation involved removing
    the binnacle mounted compass, so I will have to swing the compass again
    this season.  It seems to me that Loran is so very accurate that it
    could be used as a fairly easy method of swinging the compass.  
    One of two ways would be possible:
    
    
    1.  Simply find a convenient bouy and sail really close and lock it
    into memory.  Then proceed to sail toward it from the North, then
    South, back and forth a few times, each time correcting half the error
    between the compass and the loran.  The object would be to put enough
    distance between you and your adjustment waypoint to make it a fairly
    accurate reading.  Then proceed to east, then west attacks, adjusting
    again.
    
    2.  The second method would take a little time initially, but would
    probably be faster in the long run.  Find four marks, two roungly north
    and south, and two roughly east/west.  Sail really close by each one of
    them, putting them into memory as you go.  Start out midway between
    your north and south waypoints.  Alternately head toward the north
    mark, then the south mark, taking out half of the error between the
    compass and the loran each time.  Repeat the process east and west.
    
    This seems to me to be a credible way of adjusting my compass.  Any
    thoughts pro or con?
    
     

    What about set and drift? Can you find a place to do this that has no
    currents? I believe there is an instrument called a peloris (sp?) for
    performing that task. Also, the LORAN reports to you the average course
    bearing, which may vary quite a bit from what you can actually steer.
    
    -John
    

    No problem as far as drift or set are concerned.  Remember, you are
    taking an instantaneous look at both the loran and your compass.  
    
    I'm not sure what you're referring to as an average course bearing.  My
    loran gives me an exact magnetic course to steer which seems remarkably
    accurate.

re .4:

I think your first method would work, at least in theory. Your compass 
should be fairly close right now. There may be some interaction between 
the N/S and E/W adjusting magnets, so that adjusting one affects the 
other. This simply means doing a lot of fiddling to get matters right.

If the compass reads correctly N/S and E/W, then it should read 
correctly on every other heading. But, compasses aren't perfect (mine 
isn't anyway). It will probably still have errors on other than cardinal 
headings. Unless your N/S and E/W errors are large, I wouldn't try to 
correct them. What I would do is construct a deviation table. Using your 
loran to determine actual magnetic bearing, head for the buoy and note 
the actual compass reading. Do this in 10 degree increments. The 
difficulty is knowing when you are heading directly for the bouy. You 
may need to set up something akin to gunsights parallel to the 
centerline of the boat.

Alan

When I first started sailing 12 years ago (with Hunter 30, still 
own same boat), I couldn't get my boat to go where I navigated. 
When I sailed with friends on a compass course, we would be 
diverging rather than sailing in parallel. I later found that my 
compass was off by nearly 15 degrees! But-- the error wasn't 
constant, it varied all over the place depending on what 
direction the boat was heading. The method I used to fix the problem 
worked well for me and maybe will work for you. 

I considered and tried some of the methods described earlier but 
one would have to be located on "Golden Pond" in order to make 
them work. My approach was to tie the boat against a dock at 
Wessagussett Yacht Club in Weymouth and aim out about 2 miles to 
Hull Gut with a pointer over the compass. I knew direction from a 
chart so the rest was easy, just had to make the  compass agree 
with the chart (obviously, this doesn't have to be done at 
Wessagussett).

I found that when I removed the screws that secured the compass 
to the binnacle post, I could rotate the compass while it rested 
on the binnacle. By rotating the compass 360 degrees and adjusting 
the compensating magnets as needed to maintain  the correct 
reading to Hull Gut, I took out all of the error. Yes, I know one 
should turn the boat, not the compass but turning the compass 
worked. It would have been impossible to pick a spot in the 
water, take a bearing, adjust the compass, check the bearing and 
so forth in the real world of wind, waves and current. I have had 
no compass problems since I did this 11-12 years ago. Hope this 
idea may work for you.

Joe

    
I forgot to comment on .4 in my last note. I agree that method 
should work but will be a little time consuming moving the boat 
around the mark. In any case, I wish you good luck.

Joe

RE.  Adjusting compasses with loran.

Unless you are really going to be very far from the buoy you're using
for reference, it seems to me that your compass would have to be very
far off to benefit from this.  I mean, your loran could be off in
its idea of where the buoy is by a few boatlengths, plus the location of
the buoy can easily move that much.  If you can see the buoy easily,
you're probably too close to it!  Picture the buoy 100' to the right 
(or left) of where yo see it, and realize that you could easily have that
much error in your system.  How many degrees is that?  Is that close enough
for your purpose?

A daymark may be better (doesn't move), but I'd still rather use 
two fixed objects in line to do this right--forget about Loran.

F.

    
    
         I was finishing some glas work on one of my catamaran hulls
    earlier this morning when I noticed I had forgot to pull one of my
    sailing bags out of the hull. Although the boat is stored in the
    basement for the winter (how many of you can say that?? ;>)  ),
    the boat has been reassembled outside for the past 2 weeks in the cold.
    
         When I opened the bag, I found my $1.98 auto compass (you know,
    the ones with a suction cup on the end) had cracked. I guess they use
    water instead of oil in these lower grade units. this was my backup 
    should the real ones on the hulls be destroyed.
    
         Time to go to K-mart, home of the bass-angler yachtman.
    
    
       john
    
    p.s. I don't intend to do any recaliberation. As long as north and west
    look close, I can still find North America from 10 miles.  ;>)

I am installing a new compass and have never adjusted one before, so I
read all the notes in this conference dealing with compasses.  This note
suggests several great sounding methods for adjusting them.

In each case, however, it seemed that the goal was to make the compass
point at the physical north pole.  It has always been my understanding 
that the compass should point at the magnetic north pole, and the local 
deviation between magnetic north and true north should be applied to a 
compass heading when relating it to a chart.

A compass adjusted to true north not only can't be used outside the local
geographic area, but must be recalibrated periodically to compensate for
drift in magnetic north for that area.  

Would someone help me interpret what I've read so I do it right?

Thanks,
Tom

re .12:

Yes, you are correct in your understanding that a (magnetic) compass 
points to the magnetic north pole. Magnetic variation is the difference
between the direction to the true north pole and the magnetic north
pole. Variation in a particular location changes slowly with time and
variation changes with location. 

Compass deviation is the difference between the compass heading and the
correct heading. Adjusting a compass (magnetic or other) means reducing
its deviation to as nearly zero as possible. 

Compasses are not quite perfect mechanical devices. There is also some 
interplay between the compensating magnets in the compass. 

I have found that extremely small adjustments of the compensating
magnets make large changes in the compass reading and that the factory
adjustments aren't very good. Here's the process I used to improve
matters: 

Make a temporary mount with a straight edge for the compass. Take the
compass somewhere well away from magnetic materials (I used our front
yard) and place it on a wood box or table or something. Have another
parallel straight edge (a strip of wood or aluminum, for example).
Position the compass until it reads exactly north and fix the position
of the parallel straight edge on the box. Now rotate the compass 180
degrees so that the straight edge of its mount is against the other side
of the parallel straight edge fixed to the box or table. It should then
read exactly south, but probably won't.  Adjust the N/S compensating
magnet to remove half the error. Then back to north, adjust magnet, then
back to south, etc, until the compass reads exactly north and south.
Repeat for east/west. Repeat for north/south, etc, until the compass
reads correctly for north/south and east/west. 

After doing this, I used sun azimuths (see previous reply to this note) 
to check the compass on various headings with the compass mounted on the 
boat. The maximum deviation was 3 degrees, which I thought was rather 
nice. Given the large effect of small adjustments to the compensating 
magnets, I'm a little skeptical about trying to adjust the compensating 
magnets with the boat underway.

Alan

    I have always understood the compensating magnets are to handle various
    deviations caused by lumps of iron on the boat- things like engines and
    anchors. So Ive always done compensation with the compass on the boat,
    and all gear on the boat in more or less normal locations.
    
    The drill Ive used is to run a course aproximately north, sighting on
    some shore based fixed object. Check the compass reading. Turn 180
    degrees, and run again based on sighting  ( backward now) the same
    fixed object. The compass should read exactly 180 degrees different. It
    likely wont, so adjust out 1/2 the error, then swing about and re-run
    the test. The goal is to have as close as 180 degrees as possible. Keep
    runing and adjusting one half the error until it is as close as you can
    get it. 
    
    If possible, run a similar exercise on an east-west course.
    
    Exact north-south course is not essential, most important is that the
    runs be exactly 180 degrees different. Ive heard of doing this with
    shore based objects, and various moored objects- race marks, lobster
    pots, whatever is handy to give you a repeatable course.

        I agree with Ron (.14). It is the 'lumps of iron' etc. that can
        be the real problem. Even after all possible adjustments have
        been made to the compass, there can still be deviation.  
        
        Its been several years since I took the Power Squadron's Advanced
        Piloting course, BUT, as I remember things, the deviation tables
        in USPS texts list 24 headings in increments of 15 degrees. If a
        boater plans to be navigating with the boats compass, it would
        seem to me that the creation of such a deviation table and 
	aquiring the knowledge of how to use it would be a wise 
	investment.
        
        I disagree with .8 and turning just the compass. You must
        actually turn the boat not just the compass, so that the 'lumps
        of iron' are moved in relation to the magnetic force of the
        earth. Remember it is these 'lumps of iron' that are the cause of
        deviation with an other wise properly adjusted compass. 
        
        Once the basic N/S and E/W adjustments have been made, you would
        look for the fore mentioned 'golden pond' conditions and 'swing'
        the compass. This swinging of the compass (boat) can best be done
        using two objects that are documented to form a range. When these
        two objects in line, you are on a 'line of position'. You start
        by locating the boat on that 'line of position' with the compass
        reading magnetic north or 0.  Then using the previously mentioned
        pelorus and the boat's center-line, measure the angle off the bow
        of the objects forming the range.  Remembering to apply local
        variation as noted on your chart, note the difference between the
        angle off the bow and the (magnetic) bearing of the objects.
        This difference is the deviation for a 0 degree heading. The boat
        is kept on the line of position and turned in increments of 15 or
        30 degrees and the differences are noted. 
        
        The above is just and overview and if anyone is interested, I
        would be glad to make a copy of the related USPS text and mail it
        to them. Obviously the whole procedure is made much easier when
        several crew members are available to assist.
        
        Another important thing to remember. It is not just the permanent
        parts of your boat or its equipment that can cause deviation.
        There was a story in OFFSHORE's Mishaps in Boating section some
        time ago that talked about the young fellows that were headed out
        to Nantucket.  They were not keeping any DR track to know when
        they should have reached the island or even see it, and missed
        completely.  Luckily they were found after they ran out of fuel,
        with a portable radio wedged between the compass and the
        windshield.  

re lumps of iron:

I wonder how much effect these have. I adjusted our main steering 
compass ashore and then checked it afloat. I couldn't discern any 
influence from our lumps of iron (diesel engine, anchors -- 4 to 6 feet 
from the compass). Of course, one shouldn't put lumps of metal or radios 
anywhere near a compass.

Given the difficulty I've had getting a compass to read correctly 
ashore, I'm skeptical of trying to adjust it afloat. My feeling is that 
it is best to adjust is ashore and then simply do a deviation table 
afloat (by whatever method you choose to use). We keep our deviation 
table inserted in the current page of our logbook. With deviations under 
3 degrees we usually don't bother except on longish passages.

Alan

Re: .13

>>Compass deviation is the difference between the compass heading and the
>>correct heading. Adjusting a compass (magnetic or other) means reducing
>>its deviation to as nearly zero as possible. 

This is exactly what I was referring to in .12.  My point was that the 
previously described methods that use published locations of navigational 
aids or GPS readings all result in forcing your compass to point to true 
north instead of magnetic north.  

Re: .15

>>two objects in line, you are on a 'line of position'. You start
>>by locating the boat on that 'line of position' with the compass
>>reading magnetic north or 0.  Then using the previously mentioned
>>pelorus and the boat's center-line, measure the angle off the bow
>>of the objects forming the range.  Remembering to apply local
>>variation as noted on your chart, note the difference between the
>>angle off the bow and the (magnetic) bearing of the objects.

You finally said what I was looking for!  In my sailing days we wanted 
a properly adjusted compass to point to magnetic north no matter which 
way the boat (and all of the ferrous metal it contains) is pointed. 
If that was impossible, a deviation table was created.  Then no matter
where you were or which way you were going you always knew exactly 
where magnetic north was. 

All headings drawn on a chart were annotated with true directions.  
Adding or subtracting the current local deviation between true north 
and magnetic north produced a compass heading which was written down 
somewhere else.  The compass would then be faithful to that compass 
heading if it was properly adjusted.

Tom

    Does anyone know how close the north star is to the earth's axis?
    Or how much the earth's axis wobbles?  In other words is the north
    star a reliable reference for true north?
     
    I was thinking that you could use a plumb bob to get a straightedge
    aligned with the north star, and use that plus the local magnetic
    deviation to "zero" the compass off the boat.  Then one of the
    half-the-difference methods could be used on the boat to compensate
    for the boat and its contents.
    
    Tom

>    Does anyone know how close the north star is to the earth's axis?
>    Or how much the earth's axis wobbles?  In other words is the north
>    star a reliable reference for true north?
     
It varies. Right now, Polaris is at 359 degrees, 13 minutes (from here in
Colorado, anyway). The nautical almanac will tell you the direction at any
time, although I would be hard pressed to offset the compass the local
variation plus deviation minus 47 minutes.

>    I was thinking that you could use a plumb bob to get a straightedge
>    aligned with the north star, and use that plus the local magnetic
>    deviation to "zero" the compass off the boat.  Then one of the
>    half-the-difference methods could be used on the boat to compensate
>    for the boat and its contents.
    
MIght be kinda hard to keep a plumb bob straight unless you're in really calm
seas. In any case, if you're really interested in getting the compass as
precise as possible, check out Bowditch, volume 1, chapter VII. I would try to
summarize here, but I nearly fell asleep after reading about parameters Q and
R, and coefficients A through J (although one might wonder about the lack of
coefficients higher than J, given the natural tendency of a sailboat under
wind...)

Have fun.

 - Ken :-)

    I used the procedure in Chapmans quite successfully. Similar to what 
    Alan said:
    
    1. Start with the compensators set to "neutral"
    
    2. Go out into the yard away from all magnetic influences. I set a
    sheet of plywood down on the snow.
    
    3. Do the n-s 180 degree adjustment
    4. Using a book or other square, rotate 90 degress and do the e-w
    corrrection.
    
    I ended up with very minor adjuatments of the compensators.
    When I mounted on the boat, I kept the port cockpit bulkhead
    clear of everything else and have been hard pressed to find any
    deviation on the boat. I'm about 7 feet from the permanent magnets
    in the outboard (magneto) and 4 or so feet from the speaker in the 
    VFH, but only if the instrument cluster is mounted in the companionway
    (It slides over / into the l-shaped teak strip that holds the 
    starboard side of the waetherboard.
    
    Bill
    

Catchy title eh?  This ought to get my rearside tanned. :)

Perhaps this will help explain why a compass is compensated, and why a deviation
card is still needed for accurate compass navigation.

Remeber, this is from someone who does NOT maintain a deviation card, and has
NEVER sailed offshore.  This is primarily deduced in an effort to answer the
questions in a manner which made sense to me, for both land and sea navigation.

I am not attempting to discuss how to swing a compass or adjust it.  Chapman's
USPS etc. do so in excruiating detail.  Rather, I am trying to explain why you
even care about this nonsense.

The goal is ultiamtely know where true north (axis of earth's rotation) is, with
a minimal amount of repeated corrections done by hand.  Of course, since my
arithmetic is faultless so this means nothing to me.

Compass compensation is the adjustment to minimize the effects of relatively
constant misalignment of the compass to magnetic north.  These misalignments are
mainly due to local magnetic field distortion caused by such stuff as a large
chenk of ferrous material (engine), pesky magnets (magnetos, speakers), and
wires carrying current.

First step if possible is to locate the compass in a convenient area, physically
remote from these disturbers.  That is, do not coil a wire around the compass,
nor mount it ontop of the engine block, next to the starter, with a boom box
located next to it.  My compass mounts on the mizzen, about 5 feet aft and above
of my Atomic IV engine. 

The compass compensation magnets are then used to "correct" for the inevitable
diffeflections left.  If there were only one compass in the world none of this
would be necessary.  It's sort of like the man without a watch does not know the
time.  A man with one watch knkows the time.  A man with two watches does not
know the time.  Well there was a differnt compass used in making the chart, than
the one on my boat, bummer.

Now for the deviation table.  Why bother if you are compensated.  Well vectors
for the magnetic fields rear their ugly head.  See I can sneak math into almost
anything.  That block of Atomic IV iron is on centerline immediatly foreward of
my compass.  The Atomic IV distorts the magnetic field of the earth.  The effect
is to give my compass a slight bias towards lining up with Holiday II.  No big
deal if I am going basically north and south.  However this becomes a problem as
I head East or West.  Let's say I want to go East.  I line my compass up so it
says I am going East.  Unfortunately, I will end up a trifle north of my desired
end point.  My compass bearing is "pulled" a little bit south by that magnetic
field distorting Atomic IV.  Hence the deviation table.  This table is differnt
for each boat.  It is formed by measuring the actual difference between what the
compensated compass says, and what has been observed for various bearings.

Now of course there is the deviation of magnetic north from true north.  Why not
simply compensate the compass for true north.  Well, I can think of two reasons.
First, convention is to align to magnetic.  You could choose to aling to true
north. Once more your compass will do just fine, for you when you are all alone.
 However, all of your crew from other craft will get confused.  And of course,
you will have troubles on other craft, charts will be a headache, and doing
navigation by a fixed proceedure will be unique for your boat.

Second, think about what happens when you leave your immediate area.  The
difference between magnetic and true north will change.  This makes life more
difficult.  You will need to generate a new deviation table (since the old one
is presumably set for true north).  In the sense of keeping things simple, if
your compass is set up for magnetic north, the deviation table will not change. 
All you do is now add the new difference between magnetic north and true north
to your compass bearings + deviation table.  True north results, from simple
arithmetic. Not so important for my 40 mile trips, but a biggy for world
traveling.  For instance, my memory seems to indicate something like a 60
degree! difference in magnetic deviation between parts of the Sargasso Sea and
the Carribean.
 
Loran, GPS, fluxgate and inertial compasses, sort of make these points moot. 
But my compass always works.  No batteries, selective availability, ground
propogation error etc. to ruin my life.  Would I dump my Garmin 75 GPS? No way!
But since the most valuable piece of safety equipment on my boat is my brain,
the more knowledge I give it, the safer I will be.

Anyone, what to know how to find north using an analog watch, moss on trees,
sticks in the ground, Polaris, blooming flowers.  The old Boy Scount Handbook is
a good place to start.

Doug
dtn 592-4787

    I agree and have used the process in the back yard which Allan
    described. I also have tried the final adjustment using a range as
    described by the Power Squadron. Practically speaking, IMHO, it never seemed
    to work primarily because of the problems of other boats, lobster bouys
    etc. Also, IMHO, if you are within 1 to 3 degrees, that is better than you
    can steer for any distance. Also over a long course there are so many
    things impacting the boat that a small compass error is not a big deal.
    
    What I have found very useful is a sun pin, my name. I get out in the
    middle of Buzzards bay early before the wind is blowing, Turn North on
    my compass note the suns angle, and then turn south. The angle should
    be the same, if not, out with the BRASS screwdriver and take out half
    the error. repeat as in the back yard. 
    
    Brass screwdrivers for adjusting compasses are available for about
    $200.
    
    However, when in the fog, or where it realy matters, I check with a 
    hand bearing compass,and if there is a difference adjust to the side
    of my arrival point where there is the least danger.
    
    BTW - Only kidding about brass screwdrivers, a brass bolt, filed into
    the shape of a screw driver is quite adequate. 
    
                          Bill