one of the adjusting magnets in my ritchie compass broke in half, i have the new one to put in, but of course the compass will need adjustment - ? anyone has done this themself, e.g. using GPS as recent article in offshore navigation discussed -
len
md.frel@nwh.org
compass adjustment
Moderator: Jim Walsh
-
Ken Coit
Re: compass adjustment
Len,
I have never tried it with a GPS, but that ought to make it easy to find ranges. You need N-S and E-W ranges (or the GPS) so you know how the boat is headed. Set the boat on, for example, a northerly course, check the compass, adjust 1/2 the error out; turn around to a southerly course, check the compass, take 1/2 the error out. Repeat until it doesn't seem worthwhile. Do the same procedure on the E-W range, taking half the error out each time. After that, I'd check the N-S adjustment again and if that needs to be reset, I'd also re-check the E-W range. In your case, I'd probably start with the range related to the broken magnet and assume that the other magnet is close.
Having done all that, then you can create a new deviation card so that when you really need the compass, like when the GPS dies, you will know where the boat is really headed. This is another task greatly simplified with the GPS; just head out on a course, record the course and the compass reading, repeat at some reasonable interval, maybe 15 degrees, all around the card. In addition to making a table, if you plot it out, it will be easy to interpolate between measured courses.
How does that go? Can Dead Men Vote Twice At Elections? Compass, Deviation, Magnetic, Variation, True; Add East (Subtract West).
BTW, I drove the Coasties crazy one day doing this on our Grady White "Joseph Burnham" in front of the Swansboro CG station (Bogue Inlet) on the west end of Emerald Isle. I think they thought I was nuts or up to something interesting. We later went for a short ride from there to Swansboro proper and were boarded before we ever got to the ICW. To their credit, they were polite and thorough. I was delighted only after the boat passed their inspection with flying colors.
Have fun!
Ken
parfait@nc.rr.com
I have never tried it with a GPS, but that ought to make it easy to find ranges. You need N-S and E-W ranges (or the GPS) so you know how the boat is headed. Set the boat on, for example, a northerly course, check the compass, adjust 1/2 the error out; turn around to a southerly course, check the compass, take 1/2 the error out. Repeat until it doesn't seem worthwhile. Do the same procedure on the E-W range, taking half the error out each time. After that, I'd check the N-S adjustment again and if that needs to be reset, I'd also re-check the E-W range. In your case, I'd probably start with the range related to the broken magnet and assume that the other magnet is close.
Having done all that, then you can create a new deviation card so that when you really need the compass, like when the GPS dies, you will know where the boat is really headed. This is another task greatly simplified with the GPS; just head out on a course, record the course and the compass reading, repeat at some reasonable interval, maybe 15 degrees, all around the card. In addition to making a table, if you plot it out, it will be easy to interpolate between measured courses.
How does that go? Can Dead Men Vote Twice At Elections? Compass, Deviation, Magnetic, Variation, True; Add East (Subtract West).
BTW, I drove the Coasties crazy one day doing this on our Grady White "Joseph Burnham" in front of the Swansboro CG station (Bogue Inlet) on the west end of Emerald Isle. I think they thought I was nuts or up to something interesting. We later went for a short ride from there to Swansboro proper and were boarded before we ever got to the ICW. To their credit, they were polite and thorough. I was delighted only after the boat passed their inspection with flying colors.
Have fun!
Ken
parfait@nc.rr.com
-
T.J.
Re: compass adjustment
Just a thought on using GPS for compass deviation comps. GPS doesn't know which way the bow of your boat is pointing, it only measures measures the boat's track over the ground (note at the dock you get no heading info from GPS). That track info includes current, so you might not be getting accurate info for your adjustment.
tjsan@atlantic.net
tjsan@atlantic.net