Swinging the compass against the GPS?

[grumpy_o_g]

Just a point - spend a bit of time with a chart finding somewhere where you have good transits before you get under way and then check and double-check the variation in that area and work out when slack water is. Don't forget to make sure the boat is fettled in sailing trim - worth checking with engine on and off and even 'fridge, etc. on and off if that's anywhere near the compass or flux-gate. And while your doing it it's a chance to check your hand-bearing compasses too.

 

[rob2]

The whole business of noting two variables whilst navigating to make a deviation table makes me shudder! It would require a very quiet day, let alone dead calm weather for you to be able to take the readings and make the notes without tee-boning a passing vessel. I would still suggest the best way is to borrow a couple of spare anchors so you can put out three and thereby rotate the boat on the spot using a pelorus to set up each reading. A favourite spot used to be in Poole harbour where you could anchor on the transit of the two chimneys, now demolished. On a recent course, we anchored outside Cowes and took a three point fix using Calshot power station chimney, the Spinnaker Tower and a cardinal buoy - all a good distance away. I've never had a fix which showed no cocked hat error before! It might just be the perfect spot to swing the compass.

Rob.

P.S. The GPS would then be ideal for establishing the True bearing to your reference.

 

[lw395]

The whole business of noting two variables whilst navigating to make a deviation table makes me shudder! It would require a very quiet day, let alone dead calm weather for you to be able to take the readings and make the notes without tee-boning a passing vessel. I would still suggest the best way is to borrow a couple of spare anchors so you can put out three and thereby rotate the boat on the spot using a pelorus to set up each reading. A favourite spot used to be in Poole harbour where you could anchor on the transit of the two chimneys, now demolished. On a recent course, we anchored outside Cowes and took a three point fix using Calshot power station chimney, the Spinnaker Tower and a cardinal buoy - all a good distance away. I've never had a fix which showed no cocked hat error before! It might just be the perfect spot to swing the compass.

Rob.

P.S. The GPS would then be ideal for establishing the True bearing to your reference.

Fair comment, but if you go east of the Solent on a weekday, using the Nab Tower and one of the forts, you can normally do the job reasonably easily on a light day.
It's also something you can do underway, check the deviation on whatever heading you are on, it's another datapoint on the graph.
I would think if you were actually adjusting the compass, you'd want the boat still though.

I agree it's worth looking for changes in deviation with electrical systems, fast charging the batteries can make a difference!

 

[PhillM]

I was thinking about this again today, while sailing in the eastern Solent.

The point about Day Skipper is valid, albiet because GPS is NOT covered.

It did teach me to do chart work and it ensured I knew the difference between heading and course.

But there is nothing (that I covered - and as I say 2 years ago I passed practicle) that explains what GPS is all about.

Bearing in mind just how useful GPS is (and also how careful you need to be with it) I wonder if there is a case for teaching its use and limitations in RYA Day skipper?

 

[SvenglishTommy]

I had the GPS and compass out by over 90 degrees whilst messing about in the straits of Gibralatar, just to show how much they can differ.

Surprised no one has mentioned the Sun yet for checking the
On a side note.
Our main ships compass is a Silva 150T binnacle mounted compass circa 1989.
Silva in Sweden have stopped making spares.
At the last count there were only 3 sets of adjusting bars/magnets left in Sweden. (The adjustment magnets that sit under the compass.) AllSpars in Plymouth are the agents if you need a new set. Ours are all corroded so have just ordered a set. Hence only probably 2 sets left now in existance.

To add to the side note, I also just had to replace a whitlock(silva) binnacle compass recenty and they are getting very hard to find. There dont seem to be any alternatives to the silva models, so if you have one that isn't 100% then it's probably a good time to replace it while they're still available.

 

[ex-Gladys]

I was thinking about this again today, while sailing in the eastern Solent.

The point about Day Skipper is valid, albiet because GPS is NOT covered.

It did teach me to do chart work and it ensured I knew the difference between heading and course.

But there is nothing (that I covered - and as I say 2 years ago I passed practicle) that explains what GPS is all about.

Bearing in mind just how useful GPS is (and also how careful you need to be with it) I wonder if there is a case for teaching its use and limitations in RYA Day skipper?

I'm sorry you are in error. GPS and its usage IS covered in DS... Of course the vast majority is chart work based, but the use and shortfalls (i.e heading vs COG) are most definitely covered... We even have to teach a session with the poxy RYA Training plotter which bears no relationship to any real life product...

 

[John Barry]

Although GPS will give good true (or magnetic) bearings of known objects you will still need to use something like a pelorus to calculate the offset from your heading - which is why the recommendation for most small boats is to use a hand bearing compass from a suitably magnetic neutral position.

If you're going to swing to create a deviation card make sure you do the adjustments to the N/S and E/W correction magnets first - otherwise you may have a lot of error to correct for in your regular chartwork.