Deviation

[pennycar9]

I cannot believe that someone would come out with such a stupid statement. "The compass is only a backup" get real.It is one of the most important pieces of kit on any boat and should be adjusted as a matter of course. A compass adjuster can produce an accurate deviation card in less time and more reliability than you can do it your self. Adjusters are to be found in most ports and are reasonably priced I have ours adjusted at least every 2 years,and would never be without and accurate steering compass.

 

[Solitaire]

[ QUOTE ]
Solitaire,

You either have to accept that new deviation values or twiddle the B&C adjustment screws beneath the compass and swing again to reduce these errors.

Alternatively move the compass away from these rev counters. This would be the preferred action as the errors caused by the new equipment seem to be rather high - too much to be adjusted out.

[/ QUOTE ]

When we had the rib's compass swung, the error was greater than is the case with the siting of the new rev counters - he was able to sort that out with no problems at all.

 

[Tugw]

I have to admit that i thought when i first posted the question that most would not have bothered with deviation and swinging the compass,I have to say im pleasently suprised,IMHO when your bobbing about with no electrical power its good to know that your on the right course and you have a good chance of getting home.you cant do that with a GPS and no power.

 

[nonitoo]

I subscribe to the notion that one of the few bits on the boat that will work whatever is the magnetic compass and so it is worth keeping an eye on it.

While I would never question the skills and abilities of the professional adjuster it is worth doing a swing yourself to establish what the deviation is.

If I was then concerned I would not hesitate to bring in a professional (even though I was trained 40years ago in the use of the deviascope and pelorus) and use their more up to date skills.

As with most things parctise makes perfect.

 

[billskip]

Maybe one day somebody will make a GPS that runs on its own batteries...They could call it ..Handheld!

 

[Gludy]

Having seen the way a pro does the swing and the equipment used, IMHO it is a job for the pro. In fact the main aim is to adjust the compass to get rid of the deviation.

I consider the compass a prime piece of equipment.

 

[trev]

Its impossible to get an 'acurate' magnetic steering compass - especially if it is sited off the centre line ( you get what's known as a permanent coefficient 'A' - lop sided deviation)).
A lot of compass 'adjusters' talk a load of nonsenes to justify a far from exact science - Its best just to get to know your compass as it sits in your boat (IMHO)

 

[trev]

How can he possibly adjust a small boat compass to within one degree ? especially if it is off the centre line - Beware of 'black magic '!!

 

[RogerRat]

[ QUOTE ]
He is - based in Hamble 02380453533, called Robinson, Farther and daughter operation.

[/ QUOTE ]

Do you mean Farther, Further or Father? /forums/images/graemlins/grin.gif

I have Dev.' card on my boat and a Fairline label that was attached to the compass saying, " Do not use comass for navigation purposes untill it has been swung and a Dev.' card produced."

Helpful eh?

 

[Gludy]

Disagree Trev.
My compass was over 30 degrees out in some directions and totally unusable. After swinging it was a usuable compass that did not need the deviationm card.

The same chap swings the compasses on very large ships.

I really do consider the compass a prime bit of safety equipment and it should always be usable.

 

[Solitaire]

[ QUOTE ]

Do you mean Farther, Further or Father? /forums/images/graemlins/grin.gif



[/ QUOTE ]

I'll let you into a little secret, but don't tell anybody. I was teaching VHF yesterday and it was lunch time - Julie came in on her way down to prep a student for his YM exam. She said I was a slow typer and she would type it, so I dictated (there are times when it's best not to argue with a woman on a mission) - I didn't have me specs on so did not check her spelling. I did get her to take off the phrase "nice peeps" as I said I would never use such a term. Just goes to show you can't get the staff /forums/images/graemlins/laugh.gif /forums/images/graemlins/laugh.gif

Of course it should have been Father! /forums/images/graemlins/grin.gif

 

[Solitaire]

I'm with you on this one. The school rib's compass was way out, after he had finished it was spot on. He was scheduled to swing Jez's compass when it needed doing, he postponed with an apology that he had to swing two RN ships in a hurry - he is very good! A misreading compass is no good at all and is particularly bad when we are teaching students. Much of the work is done without using electronic aids so it's important that we have a compass that says where the boat is heading. Particularly during blind nav exercises, rather unfair on the student who is on a YM exam and trying to blind nav with a compass that gives him wrong headings.

OK, so electronics are getting more reliable, but they still go AWOL. Ask Sir Robin who in the end had to nav most of his round the world trip using the old ways. We do delivery trips where the electronic stuff goes down - so total reliance on electronics is a bad thing.

 

[Gludy]

Yes - we both agree on this -I have been in a situation where I had to rely on a compass with the elctronic awol. Also the compass and electronics should agree - when they do not there is something to investigate.

Many compasses are so far out that a deviation curve has no meaning - I do not see the point in having a compass that is not usable.

My compass was over 30 degrees out - on a 60 mile journey I could be over 30 miles adrft!! In fact there would be no guarantee that i was not heading out of the Bristol Channel heading right towardsd the USA rather then Padstow!

 

[mjf]

Absolutely! Essential to have a mag compass and an accurate deviation card.

 

[Andrew_Fanner]

New boat has no mag compass beyond the Iris I took off the old boat. There is a flashy electronic one but I plan to stick a mag one in when I rebuild the dash.

Some folk say compass should be on the boat's C/L, others in front of the helm. I'll go for the helm option.

 

[trev]

Absolutely agree with you in that case - over thirty degs is unusable - but the adjuster is merely correcting it as best he can with permanent magnets opposing the boats own field - a trick quite within your capabilities. I could teach you to do a full swing in less than an hour.
The magnetic compass is a complex bit of kit regarding the forces acting on it - but the solutions are very limited.

 

[Gludy]

Trev
He simply adjusted the built in compass magnets by swinging them. He also used the kit in the pictures shown above in this thread.

I am not saying that the process could not be learned, I am sure it could but I rather like tthe idea of someone doing ti who can get within one degree /forums/images/graemlins/smile.gif

 

[grumpy_o_g]

Don't forget that swinging the compass merely calculates the deviation. The skill lies in correcting the deviation so that it is minimal and as consistent as possible on all points. Also the built-in compass correctors are just part of the story - aside from soft-iron correctors you can end up changing or moving equipment and all sorts of things.

I've done hundreds of swings and corrections on aircraft of all sizes and often removed more than 30 degrees of error, sometimes as much as 60 degrees. Aircraft are a lot simpler than doing a boat properly though - I was fascinated by my Dad's description of how it was done pre-GPS, etc in the RN.

As for whether or not they're still a useful piece of kit - I don't care if Sir Robin himself tells me I don't need one (I rather suspect he wouldn't though /forums/images/graemlins/smile.gif) I wouldn't be happy without one in an aircraft or a boat.

 

[oceanfroggie]

Nor I without a sextant if I was living in the 19th century /forums/images/graemlins/laugh.gif With modern marine electronics which includes both a fluxgate compass and GPS headings, the aould ancient thing bobbing around in the glass full of fluid is a mere backup - end of story! Anyway have the HBC as the ultimate backup, but there's also a battery powered handheld GPS in the grab bag!

 

[gandy]

Isn't the fluxgate compass subject to the same magnetic errors that would affect a conventional one? Or do they have an electronic swinging and adjusting process?