NOAA Teacher at Sea
Heather O’Connell
NOAA Ship Rainier
June 7 – 21, 2018
Mission: Hydrographic Survey
Geographic Area of Cruise: Seattle, Washington to Southeast, Alaska
Date: 6/9/18
Weather Data from the Bridge:
Latitude and Longitude : 49°49.7’ N, 124 °56.8’ W, Sky Condition: Overcast , Visibility: 10+ nautical miles, Wind Speed: 5 knots, Air Temperature: 12.2°C
Science and Technology Log
Today while in transit through the Inside Passage, I learned to mark the position of the vessel from the pilot house, or Bridge of the ship, using three different methods thanks to Junior Officer Airlie Pickett. Utilizing this triangulation of data ensures accuracy in the placement of the ship on the two dimensional chart located on the port side of the bridge. This process must be completed every fifteen minutes when the ship is in motion close to small landmasses or every thirty minutes when further from land.
The first method involves choosing three different landmarks and recording the angular measurement to the body using alidades. Alidades are located on the port and starboard sides directly outside of the Bridge. When looking at your landmark, it is important to choose the easternmost or westernmost side of the body with a more prominent feature. When viewing the landmass through the alidade, there will be a bearing of the object in relation to the bridge. Once you have the measurements, use the north lines on the map as the zero degree of the protractor and mark a line with the proper angular measurement from the landmass. Repeat this process for the other two locations. Then, draw a circle within the triangle formed from the three intersecting lines along with the time to mark the placement of the ship.
Another way to mark the placement of the vessel visually is to look at the radar for three known landmarks. Record the distance to each landmark. One nautical mile equals one minute of latitude. Longitude cannot be used for distance since these values change as you approach the poles of the Earth. Use a compass to mark the appropriate distance from the scale on the perimeter of the map. Then, draw an arc with the compass from the landmass. Repeat this process for both of the other landmarks. The three arcs intersect at the current location of the vessel and should be marked with a circle and the time.
The two visual methods for marking the placement of the vessel are used in conjunction with an electronic fix. The digital latitude and longitude recording from the G.P.S, or Global Positioning System, provides the third check. This data is recorded and then charted using the latitude and longitude marks on the perimeter of the chart.
Another responsibility of the navigator is to mark on the nautical chart the approximate location of the ship moving forward. This is called D.R, or dead reckon, and it shows where you would be if you were to continue on coarse at the current speed for up to two hours.
Personal Log
As we approached the Inside Passage, a feeling of peace and serenity came over me as I viewed snow capped mountains beyond islands with endless evergreen trees. The feelings of the navigators may be different since this is a treacherous journey to traverse, although it is preferred to the open sea. The Inside Passage proves to be a great learning opportunity for new junior officers without much navigation experience. However, due to the weather issues and narrow passages, the Commanding Officer, Senior Watch Officer and Officer of the Deck have extended experience navigating the Inside Passage.
The strong currents at Seymour Narrows in British Columbia can make this voyage dangerous. This was taken into consideration and we crossed them during slack tide, the time between high and low tide, with a current of only about two knots. Tides can get as high as 15 knots during maximum ebb and flood tides. The visible circular tides, or eddies, are created from the current coming off of Vancouver Island being forced into a narrow channel. As Senior Survey Technician Jackson shared, the Seymour Narrows once had Ripple Rock, a two peak mountain, that caused several shipwrecks and was home to the largest non-nuclear explosion in North America in 1958.
As we entered the Inside Passage, islands covered in Western red cedar, Sitka spruce and Western hemlock provided the beautiful green amongst the spectacular ocean and sky blue. These colors paint the canvas indicative of the Pacific Northwest that make my soul feel at home. The cloud covered sky could be seen in every direction. We saw moon jellyfish floating by from the flying bridge and later a group of porpoises jumping up out of the water. The watch from the deck crew would spot lighthouses and fishing boats with binoculars well before anyone with a naked eye. I observed the approaching sunset from the bow of the ship and felt gratitude for the day.
Did You Know?
There are two different types of radar on the Bridge. S Band radar sends out pulses between 4 and 8 centimeters at 2-4 GHz and can go over longer distances. This is helpful to determine what is happening far from the boat. The X Band radar sends out smaller pulses of 2.5 -4 cm at 8-12 GHertz and can create a clear image of what is occurring close to the boat. Both radar systems provide useful information and must be used in conjunction with one another to have an understanding of what is happening near and far from the ship.
Source – https://www.everythingweather.com/weather-radar/bands.shtml
