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Hello I have a question about magnetic declination as it pertains to its use with compass navigation. I currently live in Albuquerque, New Mexico which has a Magnetic declination of 7.98°E currently. Let’s say that I am trying to get to a location that is straight ahead (000°) from where I am currently located.
I align myself and compass so that I am pointing due North(Put Fred in the Shed all that stuff). How would I get to my actual location? Would I walk 8 ° East or West? Greg Kuhn, Albuquerque
Greg, thanks for your question. It is a slightly unusual one for us as New Mexico does not have any coastline, nevertheless, the principles of navigation are the same on land and at sea.
Magnetic Declination is another name for Magnetic Variation. As we use the term “variation” on our courses I will use it here.
Variation is the difference between True North (i.e. the top of a globe where all the meridians of longitude converge and Magnetic North (i.e. where the Earth’s Magnetic fields have placed the Magnetic North Pole. A magnetic compass will point to the Magnetic North Pole, which is currently over Ellesmere Island in Northern Canada, (some 500 miles from the True North Pole). The Magnetic pole is constantly moving and it would be impractical for cartographers to keep re drawing the world’s map every year so they use True North and us navigators allow for the error.
The 500 mile difference at the pole translates to an angular distance which will be different in different locations.
You have told us the variation in Albuquerque is 7.99° East. I consulted the GC Map website, and discovered that was the case in 2020, the same website told me the annual change is -0.1° per year. At the time of writing (2023) the variation has decreased by 0.3°, therefore it is currently 7.69°. Having calculated the current variation is it now acceptable to round to the nearest whole degree so we end up at 8° E, which in this example would have been the same if we had rounded the 2021 figure but will sometimes produce a slightly different result.
Now to the original question. How does the navigator apply this correction. If you start with a true bearing (i.e. from a chart) of 000° and you want to use a magnetic compass then we need to apply the variation. We add westerly variation and we subtract Easterly variation. So 000° (aka 360°) minus 8° gives me a magnetic bearing of 352°. You would then align your compass (using “Put Red Fred in the shed” if you want) to 352° and follow that heading.
If however you had followed a compass bearing of 352° and you wanted to plot that onto a chart you would do the opposite sum, i.e . Magnetic to Compass you add Easterly variation to get back to 000°.
COURSE TO STEER WITH A TSS
“I’m planning my course to steer for a channel crossing but it crosses a Traffic Separation Scheme, how do I allow and plan for this?” Toby, Hamble
You can plan a single course to steer for the entire time you are not actually crossing the TSS. If you follow these step by step instructions, you should make it!
- Draw a line for your ideal ground track from your Departure point to Destination… and beyond.
- Estimate the time required for the entire journey at an assumed average boat speed.
- Draw tidal vectors for each hour of the journey from the Departure point.
- The clever bit now…Draw a vector for the distance across the TSS at right angles to the TSS from the end of your tidal vectors.
- Estimate the time required to cross the TSS and subtract it from the overall journey time.
- Estimate the distance you will travel in this new journey time at your chosen boat speed.
- Use this distance as the vector for your Water track starting from the end of the combined Tide/TSS vectors to where it crosses the ideal ground track.
- This is the Course to Steer at all times except when you are crossing the TSS.
Don’t forget that combining this Course to Steer with intelligent use of your GPS/Chart plotter will allow you to make the quickest crossing!
SAILING IN FOG
“What should I do if I get caught in fog when I’m out in my sail yacht?” Piers, Eastbourne
If you are caught out in fog, there are a number of things you should and could do. These include ensuring you are keeping a lookout by all available means (including visual, hearing, radar, VHF, AIS etc), as well as making the appropriate sound signals.
Carefully and expeditiously navigating to an area known to have less traffic will lessen the risk of collisions. A popular move is to head for an area of shallower water (obviously deep enough that you remain safe) to guarantee there will be no larger vessels around. Crew should be alerted to the possibility of an unexpected and sudden collision. They should be on deck and wearing a lifejacket, with safety equipment and a liferaft, if carried, readied for rapid deployment. Speed should be reduced to a minimum required to stay manoeuvrable.
As this is a hypothetical situation (on paper!), remember that prevention is always better than cure. Fog is not an ideal situation to be caught out in at sea and should be avoided; better to delay departure than take the risk. Common sense and seamanship should prevail if you find yourself at sea in fog, but it must be stressed that prevention is better than cure, so a safe harbour (perhaps with a good pub!) is a much more favourable location.
“I’ve seen many apps that will give me all the tide and weather information instead of having to search for it myself but I’ve been told I shouldn’t use them, why is this?” Martin, North Hampshire
Hi Martin, that’s a good question. Many people are very skeptical of new technology, often rightly so, but in this case it looks like the important message isn’t completely clear. As with all things, it comes down to the validity of the information you are getting and whether or not it is from a verifiable source. In the case of weather information, most boaters will take one or more sources of forecast and combine them with their own local knowledge and MK 1 eyeball skills. If the forecast is published by the Met Office on behalf of the MCA, then this is a good sign that it’s been considered from the perspective of a boater. If the forecast is on an App made by a developer in a different country for a global market, using an autonomous computer model then the information is likely to be a bit broad brush.
One of the advantages of Apps is that you can download more than one – for example the Aycaramba app aggregates the Shipping Forecast (as published by the Met Office, so you know where it’s from!) and displays it with no frills for later reading. Combine this with the Windguru App, which attempts to give a more granular breakdown, look out of the hatch, maybe grab a surface pressure chart from the marina office or Met Office website (accessed via a bookmark on your phone’s home screen for speed) and you will start to get a fairly robust feel for what’s happening. The BBC Weather App can give useful information for an afternoon of dinghy sailing at the local reservoir, but is sadly a bit lacking in the Ocean weather trends department. PredictWind can be combined with a paid for subscription, and is considered among the best by many racers. Different Apps, different users. I favour XC Weather, it covers UK and half of Europe, however it delivers the same information as many other apps that source their data from GFS (A US met model). Once you have the choice of two apps that use the same data it comes down to personal preference as to layout/display.
So, the answer is that Apps, as with all things, should be used with an understanding of who their target market is, and where their information comes from. They can be a valuable and user friendly resource, should always be combined with ‘official’ forecasts where relevant and that all-important visual interpretation. Don’t avoid them out of fear, rather, use them in conjunction with other sources and understand the sources and relevance of what they’re showing you.
“On our boat the engine battery switch has 3 positions – 1, 2 and both. We have been using “both” all of the time and are unsure when we should use “1″ or “2″. Does “2″ mean 2 batteries or is it battery number 2?” Jo, Sheffield
Hi Jo, there are actually four positions, the fourth one being “off.” You have not said if you are on a sailing or a motor boat but the principles are similar. Let me start by explaining the system. I expect you have two banks of batteries; number 1 and number 2. One should be considered your engine start battery and one should be considered you domestic (used for lights, stereo, 12V charger, nav instruments, fridge etc.). Certain batteries are more suited to engine starting (a cranking battery) and some are more suited to domestic use (often known as deep cycle or leisure batteries). On some boats there may be a single battery on each switch (1 or 2), on some boats there are actually two leisure/domestic batteries in a bank and they are connected together so to all intents and purposes can be considered as 1 battery. Once you have established whether “1” is connected to the engine start or domestic battery label it “engine” or “domestic as appropriate. Do the opposite with “2” so that we then think of the 4 options on the switch as:
- Engine start battery
- Domestic battery
- Both Batteries
Before you start the engines select, “Engine”. This means the engine battery is doing the hard work of starting the engine. Once the engine is running select “Both”. This will ensure the engine alternator is charging both batteries (or battery banks) all of the time it is running. If later in the day you turn off the engine(s) (as your sailing or anchored etc.) you should now select “Domestic.” This ensures that you cannot drain your engine starting battery while you have no means of charging. If the domestic battery is drained while you are at anchor then the engine battery is full and available for engine starting. When you later select “engine” to start the engines, you can then re select ”Both” so that both batteries are again being charged from the engine alternator while the engine(s) are running.
Forgetting to select “Domestic” when not charging can lead to you draining both batteries and being unable to start the engine(s) later. When the boat is not being used you should turn the batteries “off” unless you specifically need power for something such as an automatic bilge pump, in which case you would select “domestic.”
In motor boats with twin engines there is likly to be seperate batteries for each engine, therefore the above switch may be duplicated so each battery (bank) can be isolated
“I want to mark my anchor chain on my Dufour 37. Ive been told to use day glow paint, I’ve also been told not to use paint as it will damage the galvanised metal of the chain, is there a particular sort of paint I should use?” Paul, Reading
Paul, marking your chain is a good idea. Depending on your cruising ground will depend how frequently you mark it (i.e. every 3m, 5m or 10m etc.). There are a number of marking systems people use. Some colour code, some mark with more stripes, I’ve heard of one skipper who used the snooker ball system, (so 5m was red stripe, 10m was yellow stripe, 15m was green stripe and so on). Personally I think a decent stripe (about 30-40cm worth of chain) every 5m is plenty. If they are all the same colour there is no need to remember a complicated system, you simply count the stripes out as you pay the anchor out (5, 10, 15 and so on…). In terms of what to you use I advocate a hammerite (or similar) day-glow paint or perhaps aerosol. You can however use an anti foul that is designed for your propellor/P bracket. The advantage of hammerite is you can buy it in bright visible colours. Depending on how often you anchor, you may need to top this up every winter or two as your windlass (and a sandy or rocky seabed) will wear the paint away.
Don’t worry paint will not de-galvanise your chain, in fact completely the opposite. If you ever take the chain to be re-galvanised you will find the galvaniser will charge you considerably more to remove the paint first. If your chain is starting to look a bit rusty it would be worth getting it re-galvanised before marking it. There are of course other options. Some people use cable ties, however they can get “eaten” by the windlass and sometimes you won’t spot they are missing This is of course a simple and cheap system. You can also buy dedicated chain markers. These are small plastic inserts that clip into your chain, they are available in various colours from many chandleries. I’ve heard of people marking their chain with short bits of rope or even leather. Personally I like something bright that can be seen easily by day or night and I am sure won’t come off. Day-glow Hammerite therefore works for me.
“How do you remember whether to add or subtract your magnetic variation?” Tom, Bristol
When you take a true bearing from the chart you walk up the companionway to steer it. As you go up, add your westerly variation. Alternatively if you want to plot a magnetic bearing onto the chart, as you go down the companionway subtract your westerly variation. This works anywhere in the world that has Westerly variation.
EXTERNAL VARNISHING QUESTION
“Every year I end up rubbing down and re varnishing my washboards. Is it normal for the varnish to peel of so quickly and for water stains to start appearing?” Andrew, Reading
It sounds like you may need more coats of varnish or better materials. There are several techniques for a good waterproof, UV-proof long lasting finish. Like most jobs preparation is key. Option 1 is to go for a good quality marine varnish. Rub the boards down to bare wood, clean with acetone to remove any oils from the surface of the teak and paint 6 coats of varnish on. Give each coat at least 12 hours to go off and a light wet and dry between each coat.
Option 2 is to rub down to bare wood, clean with acetone again and paint with a good quality epoxy system. You will need 3 or 4 coats of epoxy and this can be done in a day. Then 3 coats of varnish to protect from UV. After that you should only need to lightly sand the varnish every couple of years and apply a new top coat. Both options really need to be in a heated workshop or garage.
The third option is to again rub down and clean with acetone before applying a generous coat of universal primer. Follow it up with 5 coats of varnish, again in a warm garage with 12 hours and a quick wet and dry between coats.
“Dear Team Chieftain. I have a problem with my roller furling genoa. I struggle to furl the sail after sailing. I’ve checked the furling gear with no sail up and its fine. How can I solve this?” Alison, Chichester
Well, without knowing a bit more its hard to say but we we think it could be one of several problems.
- The halyard may be to tight, thus stopping the sail furling round the head of the foil. This is because of the extra pressure put on the furling drum and swivel.
- The halyard may be too loose so that it doesn’t stop the top swivel from turning.
- The angle between the halyard exit and the top swivel may be too close to parallel. You could try fitting a halyard deflector.
OUTBOARD FUEL CAN PROBLEM
“I recently bough a new fuel can for my RIB, it’s a red plastic 20l can and has the name of a well known company on the top. Shortly after fitting the new can my engine stopped working. After realising it was suffering from fuel starvation I opened up the fuel filter to find several lumps of small plastic the same shade of red as the can. A friend has suggested that the can is really for diesel and the petrol has broken down the plastic. Is this possible or is the can just faulty?” Tony, Isle of Wight
A far more likely cause is that the manufacturers of the can left some swarf in it during the moulding/machining process. It is these small bits of red plastic that have made it down the fuel hose to the filter and quickly blocked it. When you buy a new can you need to clean it out first. I use a small amount of petrol to do this. This clears swarf, dust and any other debris that should not be there. I very much doubt the can is breaking down due to the petrol.
“I recently passed my CEVNI Test with you. Can you tell me if the CEVNI regulations apply on the UK inland waterways?” James, Surrey
As you are probably aware from your studying you do not need any form of ICC to operate a pleasure craft in the UK. The actual CEVNI regulations themselves do not apply in the UK (although a few individual rules are present). CEVNI regulations are used throughout the interconnected inland waterways on the continent. It is worth bearing in mind that some of mainland Europe’s inland waterways are massive canals transited by supertankers and huge freight ships, compared to our much smaller canals that are mostly populated with slow leisure barges. The need for a set of navigation regulations for the continental waterways is far greater than here.
– DOUG INNES, Instructor
RULES OF THE ROAD QUESTION
“If I am hove-to on Starboard tack what are my rights and responsibilities?” Peter, Surrey
As a sailing boat you are still underway, so normal sailing and steering rules therefore apply between yourself and another sailing boat or a power vessel. If another yacht was on port tack then you would stand on (however be ready to give way if he does not). If another yacht was on starboard tack then the windward rule would apply. Being hove to does not effect the way we apply the rules. It is for this reason it is preferable to hove-to on starboard tack instead of port.
CHANNEL CROSSING QUESTION
“I have been told by an RYA Instructor that when I cross the English Channel from the Solent to France that I should calculate one massive course to steer allowing for 10 hours of tide. Surely it would be more efficient to use the chart plotter to follow the rum line route? Would this not mean I sail a much shorter distance?” Tricia, Southampton
Tricia, this is a good question. We will for the minute ignore the fact that you may not be able to sail on all headings and we will assume that you are reaching the whole way. If we look at distance travelled over the ground then, yes the rum line is in fact the shortest route and would therefore appear to be quicker. However what we are more interested in, is the distance we actually sail or motor through the water as this will effectively be our total distance travelled. To make things easy lets assume the rum line route runs due South and that the Channel tides run East/West.
So lets also assume that the boat travels at 5 knots. Picture now a boat that adjusts its heading every hour to allow for the changing tide and to ensure he stays on the rum line. During the strongest hours of tide he will be pointing almost straight into the tide, expending a considerable amount of power to stay on the rum line without actually making much headway towards his destination.
Another boat however that has calculated a ten hour course to steer will always be making headway South and not wasting power to fight into the east or Westerly tide he will of course sail a shorter distance through the water although his track over the ground will have been all over the place as he was pushed down tide one way and then back the other.
In summary I would calculate a Course to Steer for the whole passage based on your assumed speed. About three quarters of the way across I would calculate a new course to steer, as it would be likely that I would have travelled slightly faster or slower than originally predicted. I may also re calculate a final course to steer when I am about an hour away from destination to tidy up any other errors that have occurred and based on a new eyeball fix.