AV Training Presentation 8 Taking and reporting a Fix to a Government Agency. In order to develop a meaningful estimate of the depth, we need to project credibility to the agency. The action goes well beyond reporting a reading from an echo sounder. The reading on this exhibit indicates 54.6 feet.. Some echo sounders show whole numbers only—no decimal feet. These instruments have a built-in error of half to a full foot. Below 0.5 feet, they will round down the lower full integer. Above 0.5 feet, they will round up to the higher full integer.

Elements of a Fix Report 1. Charted Fix – check taken from the NOAA Chart as a comparison. 2. Accuracy – Horizontal Datum 3. Read out format from the GPS in degrees, minutes and seconds. 4. Quality – EPE – Estimated Position Error or HDOP – Horizontal Dilution of Position. 5. Date and time taken. Chart No. 1 contains everything that is used on a nautical chart. This is a document that should be reviewed and studied by every AV. Also, keep a copy in your Navigation Kit for reference while underway. Always compare your on-scene observations of an aid to the symbols and abbreviations that identify that aid on the NOAA chart. Also, verify that the observations, the symbols and abbreviations shown on the chart and the narrative printed in the Light List all match.

Initial set up requirements 1. List the manufacturer’s name and model number of the GPS on your NS-PN04 Private Aid to Navigation Report. The General Information Block on a NOAA chart contains some important data bits. The chart’s name is contained here which reflects the name of the local waterway covered by the chart. From a depth point of view, the vertical datum shown on the NOAA chart should also be the depth unit of measure that is set on your echo sounder – either feet, meters or fathoms. Be sure that your echo sounder is reading the same vertical depth datum as is used on the NOAA ffchart. A fathom represents six feet of water depth. Depths are usually identified as MLW-Mean Low Water or MLLW – Mean Lower Low Water. Daily, there are two highs and two lows tides in our AOR. MLLW is the average of the lower reading and is a more conservative expression. MLW is the average of both low readings. Depths are shown on a NOAA chart as numbers, dotted lines, color variations, etc. Depths reported by AVs should always be considered as best estimates and , when reported, must always be corrected to the charted datum. Or, add this information to your “Accuracy Statement” for use on the Web-Based PATON System.

Sample “Accuracy Statement” GPS 76 by GARMIN with WAAS enabled in 3D Differential was used for fix. GPS was pre-checked at the dock with another GPS set. On-scene EPE was 6.7 feet. Wide 100 echo sounder by Hummingbird that was pre- checked at the dock with a lead line. Substation used was Neponset River. Correction for transducer was 0.9 ft. White = Data normally stays the same while you are on your own OPFAC. Yellow = As you move around, this data will change for each verification. Keep a standard “Accuracy Statement” on your Desktop. Copy it onto the ‘Comments” section of the Web-Based PATON System. Change the items in “yellow” to reflect the data collected for the Fix and the Depth while on-scene at the PATON. This statement adds to your credibility for accuracy. While depth is not always a big issue, it may be important evidence for proving that an aid is stranded at certain times of the tide.

Perform a pre-underway check of the GPS. Confirm that the horizontal datum on the GPS matches the horizontal datum used on the NOAA chart. 2. Insure that the GPS is operating accurately by checking it against: a. A known location. b. Another GPS or by c. A fixed object on a NOAA chart.. Establish the “EPE” is reading under 20 feet in 3D Differential. 4. Update your “Accuracy Statement” This page of Chart No. 1 shows the various abbreviations and symbols used to identify buoys and beacons on NOAA Chart.

Taking a FIX for a PATON 1. Take the FIX while close aboard the PATON while in the channel. 2. Record the FIX from the GPS. 3. Record the date and time when the depth was taken. 4. Record the EPE or HDOP from the almanac screen on your GPS. 5. Plot the FIX on your NOAA chart. 6. Record the Fix for the PATON. This Chart No. 1 page shows the abbreviations used to identify the depth of the water on a NOAA chart.

Correcting the depth to charted datum Your recorded depth: 25.3 feet PLUS Correction for transducer: 0.9 feet MINUS HOT- Height of Tide: 2.5 feet EQUALS Estimated Depth at Datum 23.7 feet Compare Estimated Depth at Datum to Charted Depth. Make a statement in the Comments Section, if needed. This Chart No. 1 page shows the abbreviations used to identify the depth of the water on a NOAA chart.

Update the observed sounding data to the “NS-PN04 Private Aid to Navigation Report.” Accuracy Statement Update for the “Web-based PATON System” Wide 100 echo sounder by Hummingbird was pre-checked at the dock with a lead line. Substation used is Neponset River. Correction for transducer is 0.9 ft.

AV Task Enter the depth data on the your NS-PN04 Private Aid to Navigation Report. Sounding - 23.5 feet. Transducer correction – 0.9 feet. Height of tide - 2.5 feet. Charted depth – 24 feet. Calculate Estimated Depth at Datum. Calculate Depth Difference (Estimated Depth at Datum versus Charted Depth.)