Skipper’s Tips #17 – Magnetic or True

plotter-picture

I’m sure most boaters or walkers or anyone who navigates their way around using charts or maps will have come across the situation where their compass is pointing one way and their maps or charts are pointing in a slightly different direction.

The reason for this, in simple terms, is that the molten core of the earth, which is constantly moving, is what compasses point at.  However, when you look at the globe from a human perspective, it has been drawn with the North Pole at the top and the South Pole at the bottom, a slightly skewed axis and to add insult to injury, the beautifully drawn land masses are not quite in the position that our trusty new GPS gadgetry now correctly indicates.   Here’s an interesting observation to chew on; if you went out into space and looked at the world, how would you know which way is up? Is the North Pole actually at the top?

I digress…

Obviously, if we are to sail around without bumping into things we need to work out how to work on the same page as the compasses we are utilising.  What we do, is allow for the difference in opinion (Variation) and once applied to the (True) or unadjusted heading, we end up with a (Magnetic) heading figure.  The story doesn’t end there though.  Stick a compass on a boat and all the electronic and magnetic forces on the boat will have a further effect on the compass, confusing the ‘poor dear’ even more, this we call (Deviation).  Making an allowance for the Deviation inaccuracy of the compass gives us the most accurate heading and is called a (Compass) heading.

Do not despair. When you buy a new boat, a compass adjuster will get on board and eradicate as much of the Deviation as possible.  The bit that’s left will be listed on a compass Deviation card so you can allow for it when navigating.  Beware though.  If you change any electronic equipment, or bring items onto your boat that have any electronic or magnetic properties, they will have an effect on the compass and it will have to be ‘swung’ again!

By now you must be starting to wonder how you’ve managed to navigate safely between ports without bumping into rocks and chunks of unexpected land. The answer, of course, is that we all readily use the chart-plotter/GPS equipment that’s become almost as intrinsic as the hull!  The chance of this equipment failing is remote and I have touched on this in another tip but if it were to fail or cease to operate correctly we will have to deal with Variation and Deviation before we can start to steer a course by the boat’s compass.

So, how do we work with Variation and Deviation?  Importantly, you must remember to make these ‘allowances’ in a specific order.  Allow for Variation first and then Deviation. You will also need to decide how you apply the correction.  When dealing with Variation this correction is essentially adding or subtracting the appropriate amount of degrees difference between what the compass is indicating and what the local Variation is shown to be on your chart as either degrees (West) or degrees (East)

Doc 3 Sep 2017, 12-37This is an example of a compass rose on a chart.  The Magnetic Variation shown is 2 degrees, 45 minutes West, correct in 2006.  Each year, this ‘error’ is decreasing by 8 minutes.  There are 60 minutes in a degree, so for 2017 – 11 years on – that’s a reduction of 1 degree and 28 minutes.  Therefore the Magnetic Variation in 2017 is 1 degree and 17 minutes West. Yes, there will come a point when the error disappears completely and then starts to become an East Magnetic Variation.  When I first started teaching, the Variation in parts of the Med was just under 2 degrees West and the last I saw it was almost zero – Point & Go!

N.B. Please remember, Magnetic Variation is nothing to do with whether you are going in a Westerly or Easterly direction, it is actually about your position on the globe relative to that molten core of the Earth which we spoke about earlier.

The question now is, how do we know whether to add or subtract these degrees of Variation or Deviation?  I don’t doubt that there are many different ‘aide memoirs’ but the one I favour, naturally, is the one I made up myself.  If you are calculating from True (shown on the chart) to Compass (the heading you are going to steer to by the ship’s compass) then any Variation or Deviation you allow for that is West must be added.  In other words True To Compass Add West – TTCAW.  It therefore follows, that any Variation or Deviation that you encounter when going from True to Compass that is East must be subtracted; the opposite, see?

Furthermore, when you are calculating from Compass to True, as you might when taking a Magnetic bearing with a hand-bearing compass, you would add East and subtract West. Clear as mud isn’t it?  Have a look at the table below, which has some examples.

Just to reiterate, don’t fall into the trap of thinking the direction you are pointing your boat in determines whether the Variation or Deviation is West or East.  The Variation figure comes from the compass rose on your chart and the Deviation figure from your boat’s deviation card.

True    Variation        Magnetic       Deviation      Compass

231        6 W                  237                  2 W                  239                             add West

079        3 E                   076                    0                     076                             subtract East

147       4 W                  151                   1 E                   150

013       2 E                    011                   2 W                 013

348       2 W                   350                  1 E                   349

To remember the order try,  ‘True Virgins Make Dull Companions’.  Alternatively, if that’s too racy for you, remember the reverse order with,  ‘Cadbury’s Dairy Milk Very Tasty’.

This has been another Captain Corbett’s Adventure.  If I’m not on Jersey teaching a private tuition Day Skipper theory or Yachtmaster theory course, then I’m either spending time with someone on their boat, giving them the confidence to take their boat out with their family and friends on board or I’m off somewhere exotic delivering a boat. Either way, I’ll write it up and put it on the Blog for you all to see, so keep popping back to see my most recent adventures.

 

 

Rock hopping for lunch!

IMGP1898hi res

So, picture the scene. It’s 06:30, the sun’s been up for a couple of hours and there’s not a breath of wind.  We’ve untied the lines and we’re motoring out of the harbour at the start of our day out to îles Chausey.  I was simply bursting with excitement! There was just one little problem; this time I’m on a 37 foot sailing yacht and no wind means we’re going to end up motoring the whole way.  It’s been an awfully long time since a day at sea with no wind hasn’t put a smile on my face.

Never mind.  We are on a boat, the sun is out and our destination is a collection of tiny little islands just off the coast of Normandy and lunch is booked for 12:30, French time; does it get better than this, I ask myself? Definitely not!

IMGP1818hi res

I can’t remember the last time I was out on a yacht but it was most certainly a while back.  I’d forgotten how serene it can be.  We ghosted along at a sedate 6 knots through the water and the tide added a couple more to help us on our way.  Slicing through the waves instead of feeling every little bump made a lovely change. We chatted and drank coffee and chatted some more and watched the Condor ferry come past at 9 million knots as it made ready to swallow the yacht in its path…

IMGP1826hi res

Then we rounded the first of our waypoints and started the second leg of the route. Once we’d passed the NE Minquiers cardinal we headed south to pass west of Chausey before turning east along the bottom of the islands.

IMGP1830hi resLooking back towards Jersey with NE Minquiers in the foreground

Gradually, we got closer and Chausey started to become more defined through the high- pressure haze.  I guess it should have come as no surprise that it looked to me just like the Minquiers and the Ecrihous but I was still superbly excited nevertheless.  There is something magical about sailing to a group of rocks barely clear of the surrounding sea, with a few houses, a restaurant, a couple of shops and precious little else.

IMGP1849hi res

The last leg along the south of the main island, Grande îletook no time at all but before we reached the bay where we’d decided to anchor, we got a distant glimpse of the house built by the Renault family many years ago.

IMGP1856hi res

Finally, nearly 4 hours after we left the marina in Jersey, we pulled up and started choosing a suitable spot to anchor.  In short- order the pick was down, the dinghy inflated and a serpentine row later we were on the shore with soft white sand underfoot.

IMGP1867hi res

We had surely arrived at paradise. I know the weather plays a huge part in making places that ordinarily seem average, look like they’ve been crafted by planet manufacturers to appear flawless but I reckon this little island would be special even in the pouring rain. On the other hand, it might just be that I’m so excited…

Lunch was over an hour away, so we set off on a tour of the island.  I’m not going to describe what you can see for yourselves, I’m simply going to put some shots up.

Enjoy!

It really isn’t a huge island and it wasn’t long before we’d done the tour and were sitting at a table with a view in the restaurant/hotel (Hotel du Fort et des Iles).  You’d imagine a business with little or no competition might rest on its laurels but the food was excellent if mostly fish dishes.  Incidentally, the desserts were to die for!

Soon after lunch, we headed back to the boat.

IMGP1885hi res

By now the wind had picked up and we knew we were in for a proper sail on the way back – this day just kept getting better and better.

IMGP1907hi res

What a wonderful way to spend a sunny summer’s Saturday!  If you keep your boat in the Channel Islands and you’ve never been to Îles Chausey then it’s about time you remedied that.  If you normally do your boating somewhere further afield then a visit to the Channel Island has to be on your wish list for this summer and whilst you’re so close, get yourselves down to Îles Chausey.

This has been another Captain Corbett’s Adventure.  If I’m not on Jersey teaching a private tuition Day Skipper theory or Yachtmaster theory course, then I’m either spending time with someone on their boat, giving them the confidence to take their boat out with their family and friends on board or I’m off somewhere exotic delivering a boat. Either way, I’ll write it up and put it on the Blog for you all to see, so keep popping back to see my most recent adventures.

Here we go again…

IMG_1253hi res

Just before Christmas 2013, Lynn, my chief number one crew and I headed off to a small island off the Brittany coast. We were going to tackle the obviously impossible task of moving a boat up the Bay of Biscay in a tiny gap in the disastrous weather we’d been suffering for weeks. When I wrote about the trip I entitled it, ‘What price a life?’ as it made me think very seriously about the merits of going out to sea when it is rough.  Well, would you believe it, here I am again to tell you about the same route, the same model of boat but much, much better weather?

One of the things I learned about this trip the last time I made it, was that accessibility to this section of the French coast line is not easy using public transport. I don’t think I’ve ever used so many coaches and trains getting back and forth from a boat.  Fortunately, this time it was quite straight forward but still, more involved than just getting into a car and driving to the marina. I set off on Friday evening, on the ferry to St Malo.  Staying overnight in a hotel opposite the station made it easy to stroll across the road the next morning and virtually walk straight onto the waiting train without so much as adjusting the speed of my step. Less than an hour later and I was in Rennes. The next train got me to Nantes and then a coach took me the rest of the way to Noirmoutier.  Not bad really but when you consider I started travelling on Friday evening at 18:30 and it was now 16:30 the following day, it does seem like a long journey for such a short distance across the globe, especially when we keep getting told how small the world is these days.

So, Bill, the owner of the new Swift Trawler 50, was waiting to greet me when I arrived. As we walked to the boat, we discussed the plan and the weather and came to an amicable agreement that we would go ‘balls out’, given the favourable weather conditions, to get to Guernsey on the second day to collect Bill’s wife.  Jane was planning to come across on the ferry from Poole and complete the last leg with us.  Personally, given the distances involved, I would have preferred to have split the trip into three legs, allowing a day for each but Bill was on a mission and as long as it’s not dangerous, I’m happy to help.

The following morning, at 06:20 sharp, we left the marina on the first leg of our trip.  It was supposed to be 06:00 sharp but neither of us had had much sleep – new boats don’t come with bedding and pillows and rolling clothes up to make a pillow is only slightly successful. It started off fairly flat but as we got a couple of miles off we encountered the standard swell from the SW that plagues Atlantic facing shores and what was left of the previous few days wind blowing at a slight angle across the top of the swell.  This made it slightly lumpy but the semi-displacement keel on the Swift Trawler kept it comfortable.  Our target was Roscoff and if we could keep up a steady 12-15 knots this was going to take us about 12 hours – long day, especially after a night of very little sleep.  As it happened, we had patches of extremely smooth water and made the Raz de Sein just after 13:30.

IMG_1243hi res

Lighthouse & West Cardinal marker at the Raz de Sein

Skimming across the water at 18 knots and over the ground at 15 knots was a little disappointing but we’d had a good run so far and it was inevitable we’d hit some foul tide at some stage. Nevertheless, it wasn’t long before we’d passed in front of Brest and made our way around the westerly tip of Finistère. We were now on the home run into Roscoff.  By the time we got in, the sea was like a mill pond and what wind there had been, had subsided. At this time of year, this really should have been a clue…

A tip for any motor yachts thinking of staying over in Roscoff – the diesel pump will only dispense €300 worth of diesel in one go.  We had to go through the process for refuelling eight times before we had filled the boat up!

IMG_1259hi res

Sat on the fuel berth after our lengthy filling up session

Roscoff seemed to be a sleepy little marina – quite clean and contemporary looking but nobody about.  The restaurant stopped serving early so we had no choice but to stroll into town.  In fairness, it was only the 20 minutes the restaurant owner said it was.

Over the hill and down towards the town centre is a lovely and clearly affluent street of houses, punctuated by something I’ve not seen growing in such neatly aligned rows and in such quantities before – a field of Artichokes!

IMG_1260hi res

Past the artichokes and a little further towards the ‘centre ville’ and the vista opens up to reveal the old port (drying) and the town tucked behind it. Here’s a couple of shots of the entrance to the old port.

IMG_1262hi res

IMG_1264hi res

The next day we woke up to pea-soup fog! Advection Fog is common at this time of year. The warm, moist winds coming across the Atlantic are chilled as they encounter the waters around northern France and the UK which are still cold from the winter.  (Water takes a long time to change temperature and is at it’s coldest in the early months of the year, not warming up properly until September, October).

In busy commercial waters I would be very hesitant about setting sail in thick fog but this was a week day now and the only craft we were likely to meet were the local fishermen.  We had radar, AIS and two huge plotters to view it all on – off we jolly well went.  I reckon we were the only boat blowing it’s horn out there but it made us feel righteous. After an hour, we drove out of the fog and left it hanging in the air behind us. We had popped out into a sunny day of cloudless blue skies and flat calm waters; how lovely, Guernsey here we come.

Sadly, Jane couldn’t make it in the end, which was probably just as well as it got really lumpy going around the Les Casquets . The tide would have been against us going through the Alderney Race and with a slight wind over tide effect it would have been pretty rough there too, so we chose the Casquets route but honestly, it was rough enough to slow us down to 7 knots at one point and I seriously wonder if the Race might have been a better option.

Once we’d crossed the shipping lanes and made it to half way across the Channel it smoothed off enough for us to get back up to 18 knots.  From there on in it was pretty uneventful and so, just after 16:30 we arrived in Poole. A successful , speedy, slightly foggy crossing and one very happy owner!

This has been another Captain Corbett’s Adventure.  If I’m not on Jersey teaching a private tuition Day Skipper theory or Yachtmaster theory course, then I’m either spending time with someone on their boat, giving them the confidence to take their boat out with their family and friends on board or I’m off somewhere exotic delivering a boat. Either way, I’ll write it up and put it on the Blog for you all to see, so keep popping back to see my most recent adventures.

 

Skipper’s Tips #7 – Chart Plotter Rules, OK?

Hello all!

Please excuse my prolonged absence, I’ve been rather preoccupied with work lately and everything else has had to take a back seat.  However, I have finally managed to find the time to sit down and post a new Skipper’s Tip.

I do hope you enjoy this tip and also that you find it informative.  If you have any questions or are at all confused by what I write, then please contact me and I will try to explain.  

This tip is all about paper charts and the tool we use to extract navigational heading information from them. Electronic chart plotters are amazing pieces of technology these days and they hardly ever go wrong.  Nevertheless, we must not forget that as good as these pieces of equipment have become, they are still no substitute for knowing how to navigate ‘manually’.  You should always plan on a paper chart and always keep a paper chart with you when you are on your passage and you should make a regular note on the paper chart of your position.

The single best tip I can give you regarding navigation, is to know exactly where you are, at all times!

The Chart Plotter

When you first see a paper chart and start looking carefully at the detail, it can be a little awe-inspiring. Imagine all the work that went into collating that information.  Especially impressive, is the fact that charts have changed very little since the world was first mapped.  I have a mental image of a couple of men in naval uniform in a small boat with a long piece of string and a heavy weight, a big pad of paper and infinite patience.  Today, we take for granted the effort that must have gone into making the world’s seas and coastlines appear in 2D, so that we can safely navigate in our boats. However, if it weren’t for the efforts of these determined explorers we wouldn’t stray very far from home would we.

To use a chart effectively you need to understand a few basic rules.

  • Always measure distances from the side of the chart nearest to where you are planning to sail
  • Look at the compass rose shown on your chart to determine what the allowance for variation must be
  • All the numbers peppered across the chart are ‘charted depths’ or ‘drying heights’ and as such make no allowance for tidal height
  • These depths or drying heights could be in feet, fathoms or metres and you need to look at the key for the chart to know what you are dealing with
  • Make sure the chart is designed to be used with GPS, if that is how you intend to navigate
  • The squiggles, lights, lines, abbreviations, etc. are all explained in the Admiralty publication ’Chart 5011’
  • The tide stream data will be referred to one specific port and will be listed as ‘true’
  • In fact, everything shown on the chart is ‘true’ not ‘magnetic’
  • Pay particular attention to the scale of the chart

In order to work out which way to point the boat or indeed, to describe a line on the chart to show where we have been, we will need to employ an accurate process.

Enter the ‘chart plotter’.

There are many incarnations of the modern chart plotter, a great improvement I have to say on the ‘parallel rules’ of the past. Essentially, the one I am going to describe using in this example looks like a very large and wide rule with, in the centre, a dial that you can swivel.

There are two key things to remember with ’chart plotters’. Firstly that whenever you place the plotter on your chart, the centre dial, which spins, must always have ’N’ (North) pointing to and aligned accurately with, true North on your chart.  The second rule is that the big arrow at one end of the plotter will always indicate the direction or heading of the bearing.

If you are trying to draw a line in an easterly direction, i.e. 090 degrees and yet the arrow on the plotter is pointing west (270 degrees), then you have it upside down…  It will be really helpful if you try to think of these numbers as directions, rather than just random numbers.  000/360 is North, 090 is East, 180 is South and 270 is West.

So, the way it works, is that you lie the plotter on the chart, parallel to a line which you want to know the bearing of, spin the dial until the ‘N’ at the top aligns with North on your chart and then read the bearing figure from the dial, which lines up with the large arrow at the end of the plotter.  This will tell you the ‘true’ bearing of that line or indeed, the bearing between two points on your chart.  The next thing you will need to do, of course, is to convert this ‘true’ bearing to a ‘magnetic’ or even ‘compass’ bearing, so that you can use it with the ship’s fixed compass to navigate your course.

If you are using the chart plotter to show your course travelled on the chart, in the way you might if you were showing your passage as part of your log, then you will need to do all this is reverse. Firstly, assuming you know the direction you have been travelling in, convert that direction from compass or magnetic back to true. Then align this number with the chart plotter dial and the large direction arrow.  Lastly, place the chart plotter on the chart, being careful not to turn the dial and align the whole plotter with true North (use the N on the dial for alignment; DON’T TURN THE DIAL, TURN THE WHOLE PLOTTER) and then draw a line down the length of the plotter to show your track.

I have to say, trying to describe this process in words is not easy.  It is much easier to actual show someone this but if you sit down with my explanation, your chart plotter and a chart you will soon get the idea I’m sure.

I think my next Skipper’s Tip had better be about True, Magnetic and Compass bearings!

This has been another Captain Corbett’s Adventure.  If I’m not on Jersey teaching a private tuition Day Skipper theory or Yachtmaster theory course, then I’m either spending time with someone on their boat, giving them the confidence to take their boat out with their family and friends on board or I’m off somewhere exotic delivering a boat. Either way, I’ll write it up and put it on the Blog for you all to see, so keep popping back to see my most recent adventures.