Introduction to GPS L2 American Sailing Institute Prepared by Sherri Gregory Most illustrations copied from Garmin Owners Manuals and Reference Guides GPSMAP 76Cx GPSMAP 182C Ver 1 2017

What is GPS GPS (Global Positioning System) was developed by the U.S. Department of Defense then made available to the public Allows you to know to a high degree of accuracy where you are Provides exact local time Presents location to your GPS receiver in terms of latitude and longitude.

GPS Components Space – Satellite Constellation At least 24 active satellites plus spares Each satellite contains atomic clocks and signals to determine position of itself and other satellites Operational – Ground based Monitors Ensures accurate positioning information User – GPS unit Contains antenna, amplifier, signal decoding, computer, display screen with controls No direct communication to satellites

How GPS (Global Positioning System) works The GPS receiver receives and compares signals from 3 or 4 orbiting satellites that are in the line of sight of the receiver. Each satellite transmits its exact location along with a time signal. The GPS receiver uses this data to determine its distance from each of the satellites. Once the position and distance of each satellite is known, the GPS receiver calculates it’s current location which is the position where all these LOPs cross. Diagram from Ben Levitan and Lawrence Harte: Introduction to Satellite systems

BASIC GPS Features Satellite tracking (shows positions and signal quality) Presents detailed system status Displays latitude and longitude Displays exact time Shows where you’ve been (track) and speed Projects required direction, speed and time to a destination Shows distance and direction to a desired route (Cross track error) Optionally contains nautical charts

GPS is used to answer these questions* Where am I now? What is my course from here to destination? How far is my destinations? How fast am I going? How long will it take to get there? Am I still on course? If not, what correction is needed? Are we there yet? *From Power Squadron Introduction to GPS Manual

GPS Operation

Cleaning the Screen The device is coated with a special anti-reflective coating which is very sensitive to skin oils, waxes, and abrasive cleaners. Cleaners containing ammonia, alcohol, abrasives, or anti-grease detergents will harm the anti-reflective coating.  Apply an eyeglass lens cleaner specified as safe for anti- reflective coatings to the cloth. Gently wipe the screen with a soft, clean, lint-free cloth.

Activating a Garmin GPS Press the On button to turn on the unit Often requires agreeing to warning message These messages differ depending on unit Note: This button usually also controls backlight intensity. (For the GPSMAP 76Cx, press and release quickly to control backlight.)

Buttons 76Cx Quit – Return to Previous menu/page ON/Off/backlight Find/MOB – Press to open search menu. Hold to store current location as a waypoint and begin navigation to it. Zoom In, Zoom Out Page – Scroll through main pages Menu – Open menu for current page, press twice for main menu Enter/Mark – Press to select options. Hold to save current location as waypoint Rocker – selects menu options and moves cursor

GPSMAP 182 Keyboard

Main Menu – Can get to everything from here usually by pressing “Menu” key twice GPSMAP 182C GPSMAP 76Cx

Commonly accessed GPS Pages Map Satellites Compass or Pointer Highway screen Various Setup screens Trip Computer or Gauges or Numbers Route and Waypoint lists and detail information Route and Waypoints edit screens Active Route Track list Note: In some units some of these can be scrolled using the Page button. In some units you can customize the Page button to just show your favorites.

Pages Both 182C and 76Cx units have a “Page” button to scroll through the most popular pages. Some have a fixed set of pages while in other units you can select what to show. The example below is from the GPSMAP 76Cx. Pages can be added or deleted and order can be changed.

Pages The example below is from the GPSMAP 182C. The pages are fixed.

MAP PAGE Shows current location of the GPS unit graphically. Contains chart* and optional data fields Use in preparation for your trip: Change contents and sometimes number of data fields Determine appearance Determine which charts to use Create Waypoints and Routes if not imported * Not all GPS units are sold with nautical charts.

MAP PAGE Uses while underway: View waypoints and routes Measure distances to objects Know your location on a chart and see your relationship to landmarks and depth ranges Create “Goto” routes Follow tracks Zoom in and Out

Compass – May be electronic (true compass) or GPS controlled (sometimes called Pointer) Example: GPSMAP 76Cx GPS controlled; It only works when you are moving. Your track is shown at the top of the ring. The pointer is the bearing or course to your destination. If the arrow points up you are moving toward your destination. To use for navigation, travel in the direction of the arrow.

Highway Page Example from Garmin GPS 76Cx This page shows a 3D view of your course, with the waypoint to which you are currently navigating ahead of you. It also includes user selectable data fields (number and size of fields can also be changed)

Trip Computer, Trip Gauge or Numbers Page A similar page can be found on most GPS Units. In the GPS 76Cx (seen here) these fields can be customized for the number of items and which data items to show.

Check or Change: Basic Settings Simulator mode on/off (simulator mode is also called GPS off or Demo Mode in some units) North Reference: Magnetic or True Distance: Nautical Miles or Statute Miles Depth: Feet, fathoms or meters Data fields (numbers): How many fields and contents to display on any applicable screen

Check or Change: Basic Settings GPSMAP 76Cx Simulator on/GPS off: Main Menu=>Setup=>System=>GPS=>GPS Off North Reference: Main Menu=>Setup=>Heading=>North Reference Distance: Nautical Miles or Statute Miles: Main Menu=>Setup=>Units=>Distance/Speed Depth: Feet, fathoms or meters: Main Menu=>Setup=>Units=>Depth Data fields (numbers): Press Menu from applicable page=>Data Fields (to change number) or Change Data Fields (to change contents)

Useful Map Options GPSMAP 76Cx Change orientation: Main Menu=>Setup=>Map=>General=> Orientation=> Track or North Up View and select/deselect Charts: Main Menu=>Setup=>Map=>Information Display Bearing Line or Course Line: Main Menu=>Setup=>Map => Tracks => Go To Line

Check or Change – Alarms Instructions for GPSMAP 76Cx Anchor Drag: Sets an alarm to sound when you exceed a specified drift distance while anchored. (Main Menu=>Setup=>Marine) Off Course: Sets an alarm to sound when you are off course by a specified distance (also called cross track error)

Examples of Selectable Data Fields or Numbers Accuracy Bearing (direction)* Course (direction)* Depth Dist to Destination Dist to Next ETA at Destination ETA at Next Location (lat/long) Max Speed Moving Avg Speed Off Course (distance) Pointer Speed Time of Day Time to Destination Time to next To Course (direction)* Total Avg Speed Total Trip Timer Track (direction)* Trip Odometer

Chart Latitude and Longitude display Caution: In most GPS units the only way to see your current position is to have it displayed as an optional data item or number. The lat/lon that appear on the map screen is generally the lat/lon of the position of the pointer or cursor. Boat position (optional) Pointer (cursor) position

Useful (but sometimes confusing) data fields used for navigation Bearing – Compass direction from your current location to a destination point Track – Course the boat has been sailing over ground or COG. Course – Desired path of travel from the point navigation is initiated to your destination waypoint (also referred to as rhumb line) Heading – There is no GPS readout for your heading which is the compass course you are steering. GPS doesn’t know or care where your boat is pointed – only where it is actually going. Robert Sweet, the Weekend Navigator pg 101

A course has been established from start to destination (compass directions are for illustration only). North is up. Destination Bearing = 275 To Course = 210 Track = 350 Course = 320 Start

Waypoints Waypoints are specific locations that you will use on your journey. They can indicate points along a route as well as your destination. They can also indicate an obstruction or other danger point. GPS units have two ways to set up waypoints: directly from a waypoint page, and using the map page to point to the desired location of a waypoint Most units can also import waypoints from other sources via data chip, direct computer transfer, Wi-Fi etc.

Creating a Waypoint The easiest way to create a waypoint using a GPS unit is by using the cursor to locate a position on the Map page. In the GPSMAP 182C and 76Cx press “Enter/Mark” to create a waypoint at that position. You can also create a new waypoint by editing an existing one. The original waypoint will not be retained.

Waypoint Names When you create a new waypoint it’s automatically given a name (often a sequential number) by the GPS unit. It is recommended that you change the name to reflect something meaningful about the location or route.

Man Overboard All units have a quick way to mark the spot where you are currently and navigate to it. On the GPSMAP 76Cx press and hold the FIND/MOB key. You will be asked if you want to begin navigation. Caution: Make sure you know where MOB is on the GPS you are using

Proximity Waypoint/Proximity Alarm Lets you define an alarm circle around a waypoint Useful for identifying obstructions GPSMAP 76Cx: Main Menu=>Proximity=> Select the item and the radius of the circle. Example from GPSMAP 182C

GPS Text Editor Can be cumbersome but necessary for some actions such as editing waypoints: Waypoint Name Waypoint Symbol Latitude and Longitude

GPS Text Editors Each GPS has its own method for text editing. Two common methods: For each character scroll through the entire set of letter, numbers and symbols to find the character you want (GPSMAP 182C) The Edit page displays a keyboard and you use the cursor to select the character you want (GPSMAP 76Cx)

Navigation

Routes A route is a path that you want to navigate It’s made up of two or more connected waypoints. You can create waypoints first then connect them to create a route or You can establish the beginning and end waypoints first then fill in the “turns” or waypoints afterward.

Three methods of establishing a route Create a fixed route to follow Use for planning or if your route contains multiple waypoints Use if there are obstacles you need to avoid between your current location and destination. Use “Go To” Use when your current location is the starting point and the course is straight to your destination with no obstacles nearby Easy to use Follow an existing track Note: Your map page may show your initial course or current bearing to your destination. Check your settings.

“Go To” Cautions Stay on your initial course if obstacles are in the area If necessary set the Proximity alarm on obstacles Know your position and track by plotting fixes on your paper chart at regular intervals. If your bearing (direction to your destination) changes check your chart to make sure that your current bearing will take you safely to your destination.

Creating a Fixed Route Fixed Routes can be established in a number of ways Directly from a Route Page by selecting existing waypoints that make up the route. Using the map page to draw a route Most units can also import routes from other sources via data chip, direct computer transfer, Wi-Fi etc.)

Activating a Route If you want to use “Go To”, it’s easiest to just select a destination location on the map screen. Follow the instructions to navigate to that point. If a stored route or waypoint is desired, use the Find Key to select the route or waypoint.

Transferring data from an external source It is time consuming and cumbersome to set up routes and waypoints directly on handheld GPS units because of size and editing limitations. You may want to quickly load your own waypoints and routes on your personal handheld GPS. (You will not be able to do this with the L2 units.) Most units have a way to import and export data from another source such as a computer, tablet or another GPS unit.

Practical uses of GPS Lets you know “exactly” where you are Allows you to determine if you are too close to a marked danger zone Allows you to know the distance to your destination What else?

Practical uses of GPS How can these waypoints assist in navigation? (“North Buoy” is Fl(2+1)G6S; “South Buoy” is “1”,Fl G4S)

Why use GPS with a Paper Chart? Using GPS with Paper Charts Why use GPS with a Paper Chart?

Some reasons to Use a Paper Chart with GPS The GPS unit doesn’t have charts Battery/power source unavailable Overlapping charts, missing expected charts Other GPS unit malfunction GPS signal interruption Paper chart provides the big view and detail at the same time. You could have programmed your GPS incorrectly You could misinterpret your GPS data.

Planning – GPS and Paper Charts Establish waypoints (and routes) including danger points and enter them on your GPS. (If using your own GPS, it’s easiest to enter them on your computer and then download) Use short meaningful names Make a list of waypoints with name, lat, long and description of location Draw your route on your paper chart including hourly projected DR plots based on your estimated speed and time of departure. Indicate your waypoints on your paper chart as shown below. X Waypoint symbol/name used on paper chart (USPS) (Symbol is omitted if waypoint is also a nav aid) SC01

Underway – GPS and Paper Charts Each hour use your GPS to determine your location and plot this fix on your paper chart (see plotting conventions below). Occasionally take compass bearings and GPS fixes simultaneously to test your ability to take compass bearings and check your GPS if you suspect a problem. 2045 GPS - GPS fix plotted on a paper chart (USPS) X SC01 - GPS fix plotted on a waypoint 2045 GPS

Waypoint Exercise Create waypoints for these four locations in Lake St Clair. Use short meaningful names for each: Jefferson Beach Marina N 42 28.042 W 82 52.503 North Buoy N 42 28.503 W 82 51.510 South Buoy N 42 27.709 W 82 51.719 St. Clair Light N 42 27.915 W 82 45.250

Exercise result (from map page) Jefferson Beach Marina N 42 28.042 W 82 52.503 North Buoy N 42 28.503 W 82 51.510 South Buoy N 42 27.709 W 82 51.719 St. Clair Light N 42 27.915 W 82 45.250

Garmin Marine Handheld GPS units (April 2017)