Chart Symbols 2 2 the Fix 3 the Course Line 12 Dead
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CHART SYMBOLS 2 exercises 2 THE FIX 3 Labelling Positions 3 Line of Position 4 Landmarks 4 Taking a Fix 5 Three Bearing Fix 5 Two Angle Fix 7 Running Fix 8 Distance Off 9 Transits 9 exercises 10 solutions to Chart Symbols and The Fix 11 THE COURSE LINE 12 Labelling 12 60D=ST 14 exercises 15 solutions 16 DEAD RECKONING 17 exercises & solutions 19 CURRENTS & LEEWAY 20 exercises & solutions 24 DEVIATION TABLE 25 You Should have from us: • Unit 2 text. • Sample deviation card. • Training chart 2235, Cape Hurd to Lonely Island. • Chart 1. • Parallel rulers. • Dividers. Other tools you'll need: Pencil, eraser, and calculator. How to use this Navpak: • Read carefully if you come across anything you do not understand make sure to figure it out either through your own research or by asking either of the Captains. • Follow along any examples given, do each step and make sure you understand it. • Do the exercises and then correct them. Redo any questions you got wrong and try and figure out what went wrong. • Make sure to bring the Navpak with you for training days. 1 CHART SYMBOLS It is important to be able to understand what is on the chart. This is where Chart 1 comes in. It shows you all the symbols used on charts. Before you continue with this NavPack I would like you to pull out the copy of Chart 1 you have and read the introduction and look at explanation of the layout, they are both at the front of the book. Also take a look at the table of contents, note that it is both at the front as with any book and on the back cover with pictures of some of the symbols. Remember that American charts have some differences in symbols. If you are using an American chart you must use an American Chart 1. Exercises: 1: What is this? 2: What type of land is to the south of Wingfield Basin (on Cabot head)? 3: What would the characteristics of the light on Cove island be? 4: What type of buoy is outside the entrance to South Baymouth? Is it lit? What is its number? 5: What chart would you use you the west of the training chart? 6: What is the water depth at 45° 35' N 81° 45' W? 7: Find a symbol on the chart that you do not know and look it up. 8: As you go through exercises in the NavPack look up any symbols that you come across that you are unsure of. 2 THE FIX Labelling Positions: It is important to mark what you do on the chart and to do so with consistent symbols. This is so you can keep better track of you work and so others can understand what has been put on the chart. The following are our standard plotting symbols for positions: Electronic fix Standard fix Estimated Position Dead Reckoning position • All positions should be labelled with the time in 24 hour format. eg. 0000 = midnight, 0920 = 9:20 AM, 1700 = 5:00 PM • Running fixes should have an R put beside them. • We will discuss course lines later. • All marks you put on the chart should be drawn clearly in pencil. Do not press too hard as this will leave permanent marks. Erase everything on a chart when you put it away. At change of watch you should also clean up your chart so the on coming officer can understand what is going on. Leave fixes until the chart is done with so as to have a record of the ship recent movements. Where are you? The most obvious part of navigation is figuring out where to put those marks. There are a variety of ways of determining your position. When the vessel is very close to a landmark (like a dock, buoy or bridge) then the position can simply be estimated by looking at the landmark. With a known starting point your position can be deduced from the path the ship has travelled (more on that later). Most often you find your position with a fix. There are lots of types of fix. We are going to deal with a few basic fix types in this NavPack and a few others in the next, you will learn others on the ship after mastering the more basic types. 3 Line of Position, LOP: LOPs are the building blocks of any fix (even those where you may not see the LOP, like a GPS fix). The concept is very simple. They are lines which you know you are on. They can be straight lines (like a bearing), Circles (like a distance off), or other shapes (parabola from Loran, irregular from a depth contour). LOPs are not just to make fixes with. Other uses include: • Helping make quick estimated positions. • Keeping track of progress along a course. example: We need to turn after the light house comes abeam. • Keeping out of danger zones. example: As long as that buoy does not bear less the 020 we are in deep water. • Keeping on course. example: Range lights. Landmarks: The choice of what to take fixes off matter. They need to be easy to identify and marked on the chart. It s also important to make sure you can identify the part of the land mark you are looking at, ie if it is the edge on an island make sure you are looking at the shoreline that is marked on the chart. Also things need to stay still. Buoys for instance move around on the anchor chains and can drag their anchors. Buoys should be avoided when taking fixes when ever possible. Some very good things to use include: • Fixed aids to navigation like lighthouses • Any tower or other distinct building that is clearly marked on the chart • The shoreline when it is very steep Some poor choices include: • Buoys • Gently sloping shorelines • Buildings that are hard to identify • Anything that looks like there is construction around Where the landmarks are in relation to you and each-other also matter, such as: • Bearings that are too close to each other or too close to a reciprocal are prone to error. • The further away things are the more an error in the bearing will effect your end results. 4 • For a running fix to work you will need to make sure the object will be visible at both times you plan on taking bearings. Taking a Fix: Needless to say teaching you how to take a fix without a ship to take it from is difficult, the emphasis in the following will be on the plotting side of the operation. Plotting fixes is one of the tasks that will take up a lot of you time when navigating. It is very important that it not take up too much of that time. There are a lot of things a watch officer needs to do and spending too much time in the deckhouse plotting makes it hard to keep up with other responsibilities. The key is striking a balance - and practice! Fixes should be taken: • Every half hour (unless the Captain or XO have established a different frequency) • Whenever needed to unsure safety of the ship • When a particularly easy fix presents itself • After manoeuvring, departure, or a course change • If in the middle of something, such as a manoeuvre, delay the fix as long as there is no doubt as to the ship's present course. • In any emergency (usually using the GPS as it is quick and accurate). Three Bearing Fix: This is the most commonly used fix on our boats. Compass bearings are taken to three charted objects and then plotted on the chart. If you use two bearings you will get a fix that can be used, but it gives no indication of how accurate your bearings are. As you will see, the size of the cocked hat generated by a three bearing fix signifies the accuracy of your bearings. More then three bearings can also be used and will increase accuracy, but not generally by enough to be worth the extra time taken. 1: Choose which objects to take a bearing off, keeping in mind the points made above. 2: Take you bearings. The two primary methods we use are right off the compass and with the pelorus, if using the latter you will be converting relative bearing to compass. It is important to take the bearings in quick secession and the make accurate note of the numbers, not forgetting the ships head and the time taken (that will be the time of the fix not the time you plot it). Using someone to take those notes can speed the process up. 3: Plot each bearing on the chart. Make sure not to reverse your bearings (i.e. use the 5 reciprocal). 4: Your three lines should intersect at some point. If they all cross at the exact same point then congratulate yourself because you just aced that fix, more likely you will have a triangle, called a “cocked hat”. As long as the cocked hat is not too large then use the centre of it as your fix, if it is close to a danger use the side of it closest to that danger. Example: After applying TVMDC you have the following three true bearings: 279 to the light on North Otter island 199 to the light on North point 142 to the east side of Middle island Note: in this example you are given true bearings, in practice you will have to convert compass bearings to true before plotting.