Deviation?

[threesprings]

Does anyone take the trouble to determine deviation on their boats for chart plotting. Sorry if it's a dumb question- first time posting.

[chrisr]

knowing accurate deviation might still be worthwhile on a steel boat as then it could be significant. for other construction : cannot speak for others, but i don't bother about deviation as i do not believe the error is significant

it's impossible to steer a small boat to within 10deg of a heading, and the autopilot is correcting for whatever current / leeway to head to the next waypoint anyway

this current / leeway will include deviation. iow you are steering 175, but tracking 165. who cares if the diff is leeway or deviation ?

rarely does it matter on a a small boat what is your exact heading...it is course made good over the ground that matters, and this handled by the gps

of course somebody is going to bob up and say 'what if gps is taken down...you need to know your exact heading for DR etc etc'. imho this is not the case

nb : there is no such thing as a dumb question...only dumb answers

cheers,

[ChrisJHC]

Deviation is the error in your magnetic compass observed when your boat is heading in different directions. This is usually due to things like your engine, cockpit speakers and other metal things near the compass affecting the compass needle.
This error is normally only a couple of degrees either way and, like Chris R, I usually don’t bother unless I’m doing a Yachtmaster Theory course .
You can check deviation pretty easily by comparing your GPS course with your magnetic compass (allowing for magnetic variation of course) while heading in various directions.
Once you know what it is you can decide whether to include it or not.

[Bowdrie]

Originally Posted by threesprings

Does anyone take the trouble to determine deviation on their boats for chart plotting. Sorry if it's a dumb question- first time posting.

It's NOT a dumb question at all.
Compasses get installed in all sorts of locations, (hopefully in good view of the helm position,) and many times with all sorts of mechanical/electrical devices and contraptions close enough to cause error.
I'll speak my mind; Only a fool takes a boat to sea without an adjusted compass and a deviation card.
And, welcome to the forum, and it IS wise to learn plotting on a real chart.

[Don C L]

That reminds me I need to swing my compass. I am one of those who likes to know how far off my compass is. My boat is small, but I'd sure like to be a lot closer than 10 degrees off! Something else to consider is to be sure not to leave any pliers or knives or metallic objects laying around close to your compass. My compass is on the bulkhead and last summer I was wondering why my heading was so screwed up. Behind the bulkhead, on a shelf, I had left some big pliers. Anyway, count me as one who says yes, swing your compass. But old habits die hard. I grew up with radio direction finders as high tech.

[requiem]

Originally Posted by chrisr

it's impossible to steer a small boat to within 10deg of a heading, and the autopilot is correcting for whatever current / leeway to head to the next waypoint anyway

Not all boats have autopilot. Not all autopilots are immune from failing (nor are plotters). In some places with currents you might not always want the autopilot to correct for them.

Apart from that, some people are simply OCD about having their instruments in good working order. I like to know how much I can trust the number on the compass.

[chrisr]

Originally Posted by Bowdrie

... Only a fool takes a boat to sea without an adjusted compass and a deviation card. ...

be careful who you re calling a fool my friend because you know not to whom you speak

would you care to justify such a sweeping statement - or retract it ?

cheers,

[5BTM]

"What brings you down is what you are not up on"

True both in personal finance and navigation.

[Benz]

While a properly swung compass isn't critical (you can always work with the heading it shows by correcting your course and checking it against a true course on the GPS), I don't see why anyone wouldn't want their compass properly swung. It's kind of nice when you have accurate variation data on the chart, and you navigate according to it, and you arrive where you aimed at.
An un-swung compass makes you more dependent on the GPS, and if non-GPS navigation and piloting is your hobby (mine is), then the compass needs to be in tip-top shape.

[thomm225]

It's also always nice have two compasses for comparison.

Plus if they are handheld you can check the bearing of an approaching ship to see if you can pass ahead safely.

[Kettlewell]

An un-swung compass makes you more dependent on the GPS, and if non-GPS navigation and piloting is your hobby (mine is), then the compass needs to be in tip-top shape.

Today 99% of boaters are steering to the GPS or using the autopilot to steer to the GPS, and everyone who does should have multiple backups just in case. However, on a sailboat under sail I find myself going by the wind, the waves, etc. Coastal sailing one often can see various landmarks and once you know your rough course you just sail to the landmark, or a certain distance off it based on the way the wind and current are pushing you. Offshore a small deviation this way or that is almost irrelevant compared to what the wind and current are doing to push you off course. The GPS will tell you that. An argument can be made that a swung compass is critical in the fog, but again it really isn't safe to not use all available navigation tools when in poor visibility so chances are good you will be traveling via GPS waypoints. When every phone can be a GPS navigation device that is far superior to anything I sailed with for decades before these things I am comfortable saying you should never be without GPS navigation.

[Wotname]

Originally Posted by threesprings

Does anyone take the trouble to determine deviation on their boats for chart plotting. Sorry if it's a dumb question- first time posting.

Some do, many don't.
If you are planning to actually do chart plotting, then it is a good idea. The more accurate the bearings are, the more accurate the resultant plot is. Most simply let the GPS to plot the fix on the screen. Doing it yourself certainly increases your situational awareness and helps you to keep your eyes where they should be - looking around outside the cockpit!

Good to see your first post even if it was delayed .

[capt jgw]

I have to teach compass correction in my OUPV/Master course, but in real life I pretty much don't bother with it. I do a lot of rivers and canals where direction is irrelevant anyway. On open water I usually steer the boat so the GPS says I'm in going the right way then note the compass heading and steer by that. I noted that the compass in my new to me boat has some pretty significant deviation but I haven't gotten around to correcting it, I've mostly been on rivers and don't even look at it. Back when I was sailing open water on the Great Lakes I did have a dev table and corrected all my headings. Some of that was back before GPS or even LORAN C, the compass and dead reckoning were all we had.

[danstanford]

Calculating deviation and incorporating it along with variation to compute an accurate compass heading is great practice every once in a while and it can make you fell much better about your skills. A great element is the fact that your practice can be done with GPS as a safety net!

[Wotname]

Taking bearings, applying deviation and variation, plotting a position, preparing a true course, converting that back into a magnetic heading to steer by etc kind of forces you to properly understand the navigation process which IMO is a good thing but for many, understanding the fundamentals of navigation is simply a bridge too far, it is way easier to look at the screen. I make no judgement of those who are OK with simply taking the easy route.

So it's a redundant skill for 99% of the time, perhaps 99.9%. YMMV.