Deviation Diagram

[tartansailor]

Just out of curiosity, how many members here have gone to the trouble of
swinging the boat and constructing a Deviation Diagram?

[Paul D.]

We did when we first purchased the boat. Used 1st Ave W in Grand Marais, MN as a north/south range! Good times.

[BernieA]

After I rebuilt my Gemini compass I swung the boat and corrected the compass to within 1-2 degrees on all points. I didn't create a deviation table since we are rarely out of sight of land and know the area pretty well. We normally sail with the chart plotter, but write down our lat/lon hourly when we are in the Strait of Juan de Fuca. That's because conditions can change pretty quickly even when not forecast, and fog can develop leaving us out of sight of land. We will probably never go offshore in the north Pacific. I like to steer by compass even with the chart plotter running because its more responsive to course changes than the plotter, and its good practice.

[sgbernd]

When I installed the replacement compass some years ago, I swung it. It isn't too hard, just takes some time and patience. I use paper charts which have the rose printed in magnetic, so I just use that for navigation and ignore the year to year drift which is small here in So Cal. I also use GPS and if they disagree by more than a couple of degrees, there is a problem that needs to be resolved. So far, I'd say the GPS errors (fat finger, transposing digits, mis-entering waypoints, etc.) and paper chart errors occur with about equal frequency, that is rarely, but both have happened.

Steve Bernd

[tartansailor]

Way back in the late 50s' (no GPS then) I just completed the Navigator course in the Northern New Jerset Power Squadron. My dad had a 55' Trumpy. I offered to construct a deviation diagram, but my Dad (who also downgraded everything I ever attempted to do) said while flipping the ash from his humongous stogie :"I know my boat"! Ha! well that following weekend he ran aground inside Barnagate.
He called the Coast Guard and they towed his boat free. He said thanks and goodbye, but the Coast Guard said No no, you come with us.
He did not know the coordinates of his home port! The Coast Guard fined him $200.00 which was a lot of money in those days.
He didn't talk to me for over a month.
Dick

[BernieA]

That reminds me of the time , as a high school kid, I got in trouble with my dad because a friend and me took a canoe out through the surf on the Oregon coast. after we paddled back and surfed into shore, we got a pretty good chewing out by dad, the former Marine officer. Think Great Santini level of chewing out. About 10 years later, Dad and a buddy decided to take an inflatable raft out over the surf. You probably guessed already. They did it with an outgoing tide and winds parallel to the shore. After drifting south for at least an hour and more than a mile, the Coast Guard picked them up and took them to the nearest Station. You'd have loved his glare at me when I commented, "Wow, that was smart."

[Tom Keevil]

Generally I am fairly sloppy, and first get the boat headed in the right direction using visual clues (easy to do in the PNW with all of our hills and mountains), and then note the compass heading to follow. With no visual clues I do the same thing using radar or Navionics. I do understand why this is not best practice, but it is convenient, and I don’t have to work out compass deviations. Yes we have swung our compass, and have a table and a graph at hand, mostly as a deposit to our black box (a la John Vigor).

[John Stone]

I rely on my compass quite a bit. I swung it after launch and made up a diagram. Will need to do so again after launch now that I installed an engine. I rely on a hand bearing compass and charts even though I do have inavx on a iPad mini which I run sometimes—usually just to check SOG. I like traditional skills. It keeps my head outside the boat and in general I think I have better situational awareness that way. Offshore I rely more and more on celestial so having an accurate compass is very important.

[tartansailor]

I rely on my compass quite a bit. I swung it after launch and made up a diagram. Will need to do so again after launch now that I installed an engine. I rely on a hand bearing compass and charts even though I do have inavx on a iPad mini which I run sometimes—usually just to check SOG. I like traditional skills. It keeps my head outside the boat and in general I think I have better situational awareness that way. Offshore I rely more and more on celestial so having an accurate compass is very important.

Traditional methods are the way to go all right.
I vividly remember being a few miles off shore when our gps stopped functioning.
I later learned that it was deliberately shut down for maintenance.
Dick