Compass adjuster

[stelican]

I have been advised I should have my boats compass swung,Can anyone put me in touch with such a person. The boat is on a trailer is it possible to swing compass whilst ashore and how much can I expect job to cost. The boat is in Fareham Hants

 

[Talbot]

Must be done afloat - check your magazine for appropriate adverts.

 

[gonfishing]

Seems a bit radical to me, unless of course you intend going blue water cruising or do Atlantic crossings!!! If you have any mates out on the water next time your out, get together say 2 or 3 of you and point boats in same direction and compare compass readings obviously there will be come discrepancy but for your average inshore cruising not a problem however if yours is reading way out compared to the others change the compass for a new one. Far cheaper than trying to get the compass swung!!!

IMHO

Julian

 

[Deleted User YDKXO]

Whats the point in that then? The whole reason to get a compass swung is to take account of deviations caused by the boat itself so changing the compass will just give the same wrong bearings again /forums/images/graemlins/smile.gif

 

[Deleted User YDKXO]

Get a local chart, find 3 or 4 transits (2 solid objects in a line like lighthouses, headlands, shore marks, piles - not floating buoys - they can move) and measure the bearings of the transits. Take your boat out on the water, line it up as accurately as you can with the various transits, record the compass readings and compare with the measured transit bearings you've got from the chart not forgetting to add/deduct local magnetic variation. If the compass readings are more than 1-2degs different in any direction, get the compass professionally swung

 

[mjf]

I agree with Deleted User, you can take bearings of transits around the 360 degrees and make a deviation chart yourself.

If the bearing are out by more than say 5/10 degrees then you ought to recosider your options again.

How do you use the compass, for steering or for navigation or for both?

As a thought - I have a compass on my 'boat' watch and it is amazingly accurate

 

[jhr]

[ QUOTE ]
As a thought - I have a compass on my 'boat' watch and it is amazingly accurate

[/ QUOTE ]

By the same token, could you not use the compass function on your gps?

Just a thought.

 

[hlb]

A compass on a trailable boat is about as much good as a chocolate teapot anyway. Not many folk use them much these days anyway. Just get a GPS and maybe a chart plotter. Then take a note of the compass reading on each heading. Mines about right on some headings but miles out going east. Keep the notes and if ever the GPS goes down, at least you have something. I've been promising to do it for about the last ten years! /forums/images/graemlins/shocked.gif

 

[miket]

I always have my compass swung whenever I change boats.

As a club we get half a dozen boats together and a super chap called Roger Muir from Eastliegh area comes up and charges about £50 a boat.

To my mind it's not worth buggering arounf doing it yourself for that kind of money.

 

[hlb]

Yep. But in my experience a compass on a little boat swings about all over the place and is only any good if you already know where you are.

 

[David_J]

My compass is way out on some headings. Like way out, both of them so its not just what they are mounted near. I have put up with it so far and used the GPS but if I was to rely on the compass, well a bit scary. One day I will make a deviation chart comparing from the GPS. Cant afford swingy thing for two compass's

 

[hlb]

Even the royal navys compasses are out. Your supossed to have a card with about twelve different headings and deviation. Once that is done it dont matter if compass is out. Get a GPS anyway.

 

[Wiggo]

Easy enough to do - we swung our upstairs one in November against the fluxgate/gyro thingy. It was at worst 10* out, but at least we know now. I have to say, overall, if the leccies did fritz completely, I'd be happy enough to find the coast and then coast hop home. So a 10 degree error from mid channel would still land me on a recognisable stretch of coast. Doing it in the dark might be another matter, I suppose, but yer man here has a trail boat, so unless he's as daft as Brendan, he won't be out in the dark...

 

[stelican]

Thankyou for your opinion. I am planning to do several channel crossings this season and I am cautious of fog and dont want to rely on electronics.I am surprised at the Hap-hazard way you suggest to check the compass.I take safety at sea seriously ,Do you realise how off course you can be after a 60nm passage with a 10 degree compass error.
I have just got a quote to swing compass £130+vat boat will have to be launched job will take about 20 minutes. seems a bit expensive but chap tells me he usually does supertankers and mentioned 5 year apprenticeship to qualify.

 

[Wiggo]

ah well. Fog's another matter, IMO. It's very easy to get completely disoriented in fog, and given the way a mag compass swings about underway, they can be useless. We got caught in awful fog in Lyme bay, and the combination of my corrections and the steering compass was so useless that I almost had to stop at times. GPS is no better, as it computes a heading based on last position, so it only updates every few seconds, and radar only updates every rotation.

Between the lot of them, at times there could be 100* disagreement! So I bought a fluxgate/rate gyro.

Anyway, fog in the channel rarely extends from one side to the other, so I doubt you'd be going 60 miles at 10* out.

A bit more detail on the boat in your bio might give people a better idea of the sort of answers you're looking for.

 

[mjf]

Bollox!

Its part of the exams for Masters' FG or Class 1 Cof C these days....


Yes, you should take these matters seriously as all the above people have done.


The point is that in a smallish boat you will not be able to steer to 10 degrees accuracy - period. So as long as you know your deviation for an arc of the compass , apply it and steer the resultant to obtain an average CMG of roughly what you need. I assume too that you will have computed the tide affects for the passages - this will throw you much more that a bad compass - more than the 10 degree issue unless of course the thing is a basket case but you will know that from comparisons with GPS/other compasses and indeed other boats.

 

[BrendanS]

[ QUOTE ]
but yer man here has a trail boat, so unless he's as daft as Brendan, he won't be out in the dark..

[/ QUOTE ]

You didn't see Jan PBO article on Pathfinder Powerboat Club then?

loads of trailer boats out in the dark /forums/images/graemlins/grin.gif

 

[stelican]

Thankyou Wiggo but my reply was not addressed to you but to Gonefishin ,I take it he uses a net but thats another matter.
However I have a very large compass that is extremely well damped and as my boat is quite small I only go out in calm weather s oit is relatively easy to hold a heading

 

[stelican]

Hello mjf
I dont know what you do or did for a profession but your first para reads like gobbledegook.
I obviously take tides into consideration when heading in any direction apart from east or west.
I do make use of my plotter gps and autopilot but I am cautious these could fail.

 

[hlb]

Think you need to hang about a bit before you rubbish every ones oppinion on here. There must be a few hundred thousand sea miles between us!! Against good electronics a compass is next to useless, ok if all else fails, but mine never has.