Finding a home for all our provisions before heading off on a cruise is always a challenge since I tend to overstock on the basis that we will use everything up in the end but running out of something vital in some out of the way place would really inhale. So, as always, there was a last-minute scramble to put everything away before we left last week. And then off we went for our 200-mile overnight.
It quickly became apparent that our fluxgate compass, which runs our autopilot, was off by at least 15 degrees. At first we assumed that it was due to current pushing us off course. However, because we don’t have our autopilot connected to our plotter and we have a magnetic compass on the binnacle that we have swung regularly, it didn’t take us long to realize that the magnetic compass and our course didn’t correspond to the autopilot heading and we were able to compensate for the error without any great difficulty.
Then we started trying to figure out why the compass, which had been working fine 5 weeks ago, should suddenly act so strangely. What had we done in the meantime?
Why, stored a pile of provisions in the locker directly next to where the compass is mounted below. What kind of provisions? Why, tins of peanuts and porridge! Yup, when tested with a magnet, the tins were definitely ferrous. So a big shakeup of provisions ensued and the compass miraculously straightened itself out.
In most circumstances this would be no big deal. However, given the wrong situation:
- plotter dies,
- datum way out on the chart against the GPS,
- intricate navigation;
this could have been a problem.
Keeping our electronics separate (separate radar, separate autopilot) and incorporating redundancy into the system:
- magnetic and fluxgate compasses,
- second stand-alone GPS,
all contributes to maintaining our situation awareness—knowing where we are.
Old-fashioned, maybe, but it could save the day given the right (or wrong) circumstances.
Hi Phyllis,
Sounds like a classic! . I had a similar one two years ago when a ‘helpful’ crew decided to put my sandals into my cabin for me, only problem being that they have magnetic straps, and the fluxgate is under the head of my berth…… .
Redundancy is agreat asset on a boat, in my case the error was obvious because we were heading fo the headland rather than around the end of it, however in other circumstances it might have take a while to notice the 25 degree error.
Paul
Hi Paul,
Magnetic shoes, who knew. The number of ways that one can get messed up in the game never ceases to amaze me.
If you had it integrated with the plotter you would have noticed this as well!
If you would have had a waypoint set in the plotter you would immedeatly seen the difference between the course the plotter say it is to the waypoint and the compass course from the fluxgate. Your system would have been taking you safely to the waypoint even with the wrong course from the fluxgate. But yes I agree redundency is the key. And a reliable magnetic compass is still a must on a boat.
Hi Roland,
You are, of course, right. That is as long as the plotter continued to work. But, like you, we still like to have a well adjusted high quality magnetic compass as the ultimate check. Does not need and electricity either.
Roland—You and I have a religious difference with John and Phyllis: We believe in sometimes letting the chart plotter and auto-pilot steer the boat (while, of course, keeping a careful watch), but they don’t. About 2 decades ago a cruise ship bound from the Caribbean to Boston, Mass., ran aground on Nantucket Shoal. Whatever instrument she was using to navigate was off by 15 miles. The U.S. Coast Guard District Commander was quoted as saying: “Electronic navigation instruments are fine, but you still should look out of the window from time to time.”
Your storage tale reminds me of a delivery where I, as navigator, finally figured out that the substantial compass error was due to a crew member storing flashlight batteries in the binnacle cover.
I trust you strung him up by his thumbs?
Yes, it can be pretty problematic, when we forget how some of the installations in the boat works.
Before the holiday trip to Norway this season, I wanted to carry one more anchor og some more chain. I put it in the locker close to the cockpit … You can image the consequences, bacause the fluxgate compass, was placed just below …
The other day, I removed an “car like” old antenna with a magnetic “foot” … and I just put it on top of my basket … where my wallet happen to be … the consequense? All data om my credit gards, my gasoline cards, insurance card, my personal ID card etc. were erased … I did not learn it until my Visa Card did not work … Oh, what a lesson …
Best regards Flemming Torp
pt. at anchor in Nerdvikvågen – SE of Smøla – Norway on the way to Lofoten …