NAUTICAL CHARTS Can anyone explain the purpose of a Nautical Chart?
(let them answer) A chart onboard allows you to compare what you are seeing with what you should be seeing and can help you keep your bearings. I. Purpose of Nautical Charts
Nautical charts are different from maps in that they specifically depict water areas, while maps concentrate on land area, roads, landmarks, etc. Land areas and features on charts are sketchy and are noted only for their interest to the boater. Unlike maps, the nautical chart conveys much information specifically designed to assist in safely navigating the area that the chart covers Nautical charts are different from maps in that they specifically depict water areas. Land areas and features on charts are sketchy, meaning that there is not much detail/it is just a rough outline, and are noted only for their interest to the boater Nautical charts are specifically designed to assist in safely navigating the area II. How to use a nautical chart for a boating trip
Study your chart thoroughly. Look at the position from which you will start and visually follow along the course you wish to take. Look for "notes" - water depths, obstructions (especially under water), bridges, power lines or any other unusual items that may be a hazard to your progress. Look for visual objects featured on your chart that you should be able to observe and identify to confirm your position. When utilizing a Nautical Chart, even for reference you want to: Study the area that your chart covers or the area you intend to be at What are some of the things you should look for? Yes you want to pay attention to notes, water depths, obstructions or any other items that my be a hazard Look for visual objects on your chat that you should be able to observe and identify to confirm your position. III. Reading a Nautical Chart
A.Look for the chart title at the top right of the chart. Now to use a Nautical Chart you have to understand some basic features: a. Every chart has a title. It will be larger than the rest of the print and can also be found by the chart number in the margin III. Reading a Nautical Chart
B.CHART ORIENTATION TRUE NORTH is at the top of the chart. EAST is at the right-hand side of the chart. WEST is at the left-hand side of the chart. SOUTH is at the bottom of the chart. Charts are always oriented with True North at the top, East on the right hand side of the chart, West on the left hand side of the chart and South at the bottom of the chart. III. Reading a Nautical Chart
THE COMPASS ROSE MAGNETIC NORTH TRUE NORTH Magnetic North moves over time.For the SF Bay, it is currently about 15 East of North. True North is the point around which the earth rotates. Every Chart has a compass rose. The compass rose is used to get bearings from landmarks, or buoys The star on the Compass Rose points to True North. Where the North pole actually is The inner circle projects Magnetic North. Which shows the pull from earths magnetic field III. Reading a Nautical Chart
C.SOUNDINGS Soundings are in meters, feet, or fathoms (6 feet per 1 fathom) Sounding Numbers reflect the depth of the water Map Colors - shallow water is tinted a darker blue and deeper water is a lighter blue and white. 1. All chart measure the depth of the water in meters, feet, or fathoms.A fathom is a measurement that 1 fathom equals 6 feet and is only used in water depths. 2. Each chart will show the unit of measurement in the margin 3. No chart will have more than one unit of measurement for soundings Soundings As you can see here the white area depicts an area with deeper water depth (point out a couple water depths feet) Then the blue shows the area that is not as deep and could pose a hazard to normal boating traffic. (point out a couple water depthsfeet) You can see a channel that the larger vessels have to follow. NAUTICAL CHARTS SOUNDINGS CONT.
Depths of water are the mean depth for that area. Water depth can be affected by the storms, the moon, wrecks, and shoaling (sandbanks), and winds It is important to know that soundings are only the average depth for that area, which means that depths can be higher or lower than the printed depth What are some factors that would cause the water depth to change? (if they get stuck here is a hint, think about tides!) 2. The reason they are only an average depth if because water depth can be affected by storms, wrecks, shoaling, or general daily tides. Note: For any particular location, the height and fluctuation of tides depends to varying degrees on the location of the Sun and the Moon, and to the details of the shape of the beach, coastline, coastline depth and prevailing ocean currents D.Other Symbols There are 39 different types of bottom for the ocean floor. If an areas bottom is knownit will be displayed on the chart M = Mud The type of ocean floor is important information for fisherman, wade fishers, marine biologist, and vessels anchoring in that area There are 39 different types of ocean floors. Harbor charts will annotate what type of ocean floor was observed In this example the M means that the ocean floor is made up of mud. Does anyone know what type of bottom comprises a good part of San Francisco Bay?(mud and silt) LIGHTS AND AIDS TO NAVIGATION (ATON)
D.Other Symbols LIGHTS AND AIDS TO NAVIGATION (ATON) There are numerous different types and configurations of aids to navigations (ATONs). In fact way too many and way to complicated to go over. Can anyone tell me what this is and what it is for? (buoys can be used to mark channels, bays, wrecks and sometimes have horns or whistles which aid mariners in navigating during foggy conditions.) E.Latitude & Longitude Points of latitude and longitude are plotted like X, Y coordinates Latitude = X coordinate Longitude = Y coordinate (Latitude, Longitude) Latitude and Longitude are measured in degrees. One degree is broken into 60 minutes Here is a graph that everyone is familiar with right? And The graph is made up 4 quadrants just as the earth is split up into 4 quadrants. E. Latitude & Longitude = 1 Minute = 1 Minute LARGE SCALE SMALL SCALE
As you can see with the small scale chart each block is 1 minute But with the Large scale chart each minute is broken down to seconds. LARGE SCALE SMALL SCALE Can you find the coordinates for the red X?
Latitude = 39 57 min N Longitude = 24 53 E Now looking at Latitude and Longitude- Charts are in Degrees, minutes, and seconds. Each charts will be labeled with a number and a degree symbol indicating the degrees lat or long. As shown here (point) with 40 degrees North Thenit will be further broken down, between each degree, with numbers and a minute symbol. As shown here (point) with 55 minutes North. Note that there are 60 minutes in 1 degree. It is further broken down to seconds, which there are 60 seconds in a minute Coordinates: (39 57 min N, 24 53 min E) Fishing vessel northern belle
Emergencies Nautical Charts are not only used for navigation, but for emergency situations as well.Knowing your location allows responders to get to you quicker.In fact, one of the first things the Coast Guard does is plot the position to get a visual reference of the person in distress, then they dispatch resources to that location to search. The video linked from below is an example of a rescue operation that started with a distress call in which the boat captain provides his position as a lat & long coordinate. (after audio) This is an example of a Search and Rescue case, something the Coast Guard does daily.This shows that Nautical Charts are not only used for navigation, but for emergency situations as well.Knowing your location allows responders to get to you quicker.In fact, one of the first things we do is plot the position to get a visual reference of the person in distress, then we immediately dispatch resources to that location to search. Does anyone know what the numbers were that the Captain called out? Fishing vessel northern belle