DIY Compass swinging
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- čas přidán 7. 09. 2024
- The steering compass should be the most accurate traditional instrument on board, but it can be affected by magnetic influences within the boat herself. Swinging the compass to determine what these are, and so to compensate for them, is a vital part of responsible seafaring that’s often overlooked in today’s electronic world. Using practical time-honoured methods, there’s not a lot to it. In fact, it’s something that any sailor can do. All you need is a good mate, a quiet day, a hand-bearing compass and an hour or so to spare. Here’s how!
#sailing. #yachting. #compass. #TomCunliffe
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![Swinging the Compass on a [Tiny] Containership](http://i.ytimg.com/vi/E43MTWSojsw/mqdefault.jpg)
Got a hand compass. Now all I need is a boat.
Don't lose heart!
Brilliant demonstration. Thanks Tom and Ros.
Excellent Tom Cunliffe!
I also swing my compass from time to time. Your method is easier than mine. Deviation cards are important and builds confidence to trust our compass readings.
In the 1980s, I had NO Loran or GPS and NO sextant. But I only did coastal sailing and used Deduced Reckoning (DR) with hand bearing compass fixes for LOP plotting. It was fun.
Wasn't it just. And real job satisfaction too...
Nice to see her indoors making a show😊
My compass on a steel boat is max 5 degrees out. In practical terms, that is more or less within the accuracy I am able to steer. There are some plus and minus as we sail along. But in sum, on an 8 hour sail, I am more or less spot on. I have been sailing for 60 years. So GPS is a relative new thing to me, first GPS on the boat we have now, less than 15 years ago. I have never had a log, just clock, paper and compass. Of course, today GPS. The point being, I know the copass is out :-)
Good Job, Thank you so much for really caring about us!
Thanks Tom. If you are still in Karlskrona, be sure to pay a visit to the Marine Museeum, you have probably been there or been there before. My grandfather sailed on the Jarramas and later became the captain of the submarine HMS Ulven. You can see the flag hanging in the ceiling in the submarine hall showing the submarine HMS Neptune. Enjoy and thanks for teaching your knowledge, now reading your Yachtmaster 10th edition.
Visited the museum last week. Saw your granddad's flag. Wonderful.
Always learn from you, Captain!! Thanks again!
Very good.
I will do It! 👍👍
Invaluable knowledge. Thank you very much!
Excellent…..time to recalibrate mine! Thanks, Andrew
Brilliantly explained - and I've learned a new word: chunkling :-)
Electronics also has a magnetic field that can deviate a compass too.
Small electrical currents produce small magnetic fields off short range. The mass of the (mostly) iron engine and the starter motor current will have a greater effect.
Too right!
Thanks
Very opportune video! I just reinstalled my compass into the binnacle. Cheers Tom!
Tom, you and Roz are awesome. Great video. Several questions:
1- can you build a deviation card by using a gps to cross reference the main ships compass?
2: would it be wise to do this procedure 3 or 4 times to take into account any changes?
3: would it be wise to confirm that your card is correct by plotting several different routes on charts and confirm your deviation card?
Thank you!
Your method is OK if you have a crew member to run the hand bearing compass, and if it can truly be guaranteed that somewhere on your boat will be free of deviation, and that the hand bearing compass does not suffer from lag due to internal friction.
As a solo sailor I use a combination of known transits (as published or plotted from paper charts) and GPS to satisfy myself that the main steering compass is within 2 or 3 degrees - which is close enough, given the unknown effects of drift etc.
In the narrower reaches of the river where I sometimes sail I have seen external magnetic influences such as ships, tank installations and overhead power lines cause compass errors, and of course the effects of electrical equipment must be considered. If you sail at night there’s no point in swinging the compass by day with internal compass lighting off, but on the other hand if it’s swung with lighting on, the deviation card is only valid for that condition.
All good stuff. We do our best!
Nicely done Tom!
Cheers, Harry
Interesting and I have absolutely no idea want he was talking about. But it was fun watching, its like reading a Stephen Hawking book - I get it until about the third page.😊😊.
Very well explained Tom, thank you
Brilliant. Thanks Tom.
Excellent advise. Thanks
I'm sure that Ross has always kept you on course, whatever the weather ☁️ ☀️ 🧭 👌🏼😅
Get it done❗️
Losing Roz overboard with the only handbaring compass.
I reckon she didn't miss that Tom.
.... And she looks small dark and deadly to me.
thanks Tom~!
Very good thank you Ros and Tom. Any advice on auto pilot and Chartplotter?
Thank you for a nice video again 😊 How you make sure when compearing the compasses that your bearing compass is exactly on bow direction😊
Sort of 'up to you' really. If you line up with the forestay and the stem head you won't go far wrong.
What about writing down minus or plus values instead of E and W? For example if you read 135 on compass and deviation is +3 then corrected heading becomes 135 + 3 = 138.
Good idea. Why did nobody think of that before?
Excellent suggestion! Do all the 'least or best' head scratching beforehand, once and for all.
I spotted you in Nynäshamn a week ago so it must have been just before your recorded this video. You were too busy for me to say hello but I was star struck anyway. I am puzzled as to where you recorded this. I don't recognise the place. Anyhow I will put down a deviation table so you won't complain if we get this close anytime again. 🙂
Sorry we missed you. We were up the fjord to Tyreso. Wonderful place. Totally flat. The opportunity was too good to miss.
You can also check compass is accurate by taking a bearing of the rising sun or setting sun. These values can be obtained from the celestial almanac for any day anywhere in the world
Many's the time I did that in the old days on a long ocean traverse.
On warships we would at least once a year hit the compass course and swing the ships magnetic compass
Hi Tom. It's not clear watching this, that when you actually made up the deviation table, Ros with the HB compass was taking bearings of the heading of the boat. Not of the castle.
The castle bearings serve to find a deviation-free spot for the hb compass. Once you have that, the hb compass is lined up with the ship's heading to see if there's any deviation.
Two of your books just arrived in the mail. This sort of tip is why I bought them. Good old fashioned, hard earned knowledge. Thanks for sharing it with us!
Does AngelNav have a deviation card built-in? Maybe best to have it on paper anyway, but it could help a bit with subtraction/addition (I know, I'm lazy).
Thanks for your kind words. No nav system can have an inbuilt deviation card. Sadly,
it goes with the boat!
@@TomCunliffeYachtsandYarns I was thinking of storing the derived deviations in the app, so that when you take a compass fix it would correct it for you. It would be per boat of course.
But I'm green when it comes to navigation, so I may be misunderstanding things. If so, I apologise!
Tom. Could you please show us your hand bearing compass of choice? What Brand and Model do you recommend?
Thank You!
--Chuck in Jensen Beach Florida.
Hi Chuck
The best is the old Sestrel Major with the wooden handle. Beautiful but very expensive now if you can find one at all. Mine is in my study to remind me of the old days. I use a Suunto on board which is very clear and works well.
Thank You Tom! First Rate. I will search for that Suunto brand that you are using now. Chuck in Florida.
Some would say that I am good at swinging the lead, perhaps I should have been swinging the compass.
I guess my question is why is the HB compass used as the standard? Why can't it be wrong - effected by the same on board magnetic effects as the binnacle? EDIT: OK - I see this has been asked and answered. So if you swing the HB through 360 degress and the "cow" is still at the identical bearing, you're good. I guess.
You've got it!
Stunning! I never thought about it but to my excuse I am not a boater.
Is there no way to calibrate the compass to compensate for the misseeading?
Or is the deviation so inhomogeneous that you cant do a compensation and need the table for every quadrant as it is a diffrent reading?
Thanks for the education, great job to get my brain working on this 😊.
Good luck Mate. There's no way to permanently calibrate it out I fear.
@@TomCunliffeYachtsandYarns Thanks, it will be just a mind exercise as the solution to the problem is not to use a traditional compass and go for modern solutions 🙂
If someone serious tells me "What if....." I tell them that if we lose the GPS sattelites or have a total electric power outage , we have way more serious problems to deal with .
But I like to understand the background problem of these compass deviations and why they even change over time. As I said just a mind exercise
Thanks for the video, Tom. How often should the deviation card be updated?
Whenever you change something with iron in it, on the boat…. In theory 😊
Every year or when you change latitude by 20 degrees. However, we all live with our own consciences.
Thanks for this. I learn a lot from your videos. Do you notice any difference in steering compass reading if your engine (and therefore your alternator) is stopped, or if the electrical system is on or off? Yours is on a binnacle, and I didn’t notice whether any electronic gear is mounted nearby. I was also thinking about bulkhead mounted compasses that might have a VHF radio mounted a foot or two away.
Good point. I don't have any issues, but I once sailed a yacht with two helms on which, when you operated the electric sheet winches, the compass spun round and round!
Tom, it is not evident from the video, which direction to point the HB compass when comparing with boat one. From video it seems to be pointed to castle again, but it doesn´t make a sense of course.
Straight down the fore and aft line so that it lines up with the steering compass. Sorry for ambiguity!
Thank you for quick explanation and all you do for us!
Is this declination? I worked in forests for 10 years pre GPS, and depending on where I was in the west, I had to adjust it. Never considered the difficulty on a boat.
No. Deviation is different and applies only go the individual boat since the compass on board is affected by on-board influences.
If i understand this you only checked the west course. Do you have to find a new bearing of something that is north of the actual boat and then steer north and then find something on each of the bearing you check?(So 8 different points?)Sorry I am a slow learner.
Yes. I think I do explain that you steer the boat on 16 headings and check them as you go.
@@TomCunliffeYachtsandYarns Ok so you need 16 different hand bearing points? Thanks for your explanation.
One bearing to confirm your hand compass is free of deviation. You know the spot is good if the bearing doesn't change while the boat is spun around.
Once you have found a spot that is free of deviation compare the redings of the hand compas to your main in all (8, 16, 32 or whatever it takes to feel comfortable) directions.
How do you know the hand compass is free of deviation? Sorry if I missed the explanation
Hi. Have another look at the video. I explain exactly how I know the HB is free of deviation and how we determine this. Sorry if I wasn't clear enough.
If there is deviation the bearing will change while you go through the 360 turn. If it stays the same you know the spot is good.
Tom you have some advert piggy backing in on your vlog.
Not much I can do about that I'm afraid.
@@TomCunliffeYachtsandYarns just thought I would let you know.
I think your mate should tell you to steer 4 degrees left to head 270.
Port
You're right insofar as they card I just made up is concerned. Thanks for making the point. I'm sorry if the remark creates confusion. I was just talking off the top of my head in general terms. Could have just as well said 'North'. Shame I didn't!
@@TomCunliffeYachtsandYarns Or 'South' 😊
Why bother. Obsolete nowadays
Because you never know when the GPS might fail, and it pays to get where you want to go instead of have your bottom ripped out on the shoal you found because you're miles off from where you think you are.
They don't require power and even modern airliners still have magnetic compasses.