Tag: compass

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Elli Simonen:  Survey Launches, July 24, 2023

NOAA Teacher at Sea

Elli Simonen (she/her)

Aboard NOAA Ship Fairweather

July 10, 2023 – July 28, 2023

Mission:  Hydrographic Survey of the Pribilof Islands 

Geographic Area of Cruise: Pribilof Islands, Alaska

Date: July 24, 2023

Weather Data

Location:  56°36.8259’N,169°32.2224’W

Outside temperature: 11°C

Water temperature: 10°C

True Winds: 16kn, 185.4°

Skies: Foggy with Drizzy Rain

Visibility: 5nmSea

Wave: 1-2 ft

Swell Wave: 1 ft

Science and Technology Log

We are currently at anchor off the north shore of Saint George Island and the survey launches are going out daily to survey a portion of the surrounding waters.  I have been on the survey launches twice, each time surveying a different area.

Survey Launch July 22, 2023

The Pribilof Islands are the breeding grounds for more than two thirds of the world’s fur seal population and their numbers peak in July.  Our surveying operations do their best not to disturb the Fur Seals.  I was on a launch that was assigned the harbor.  However, upon entering, we saw a colony of Fur Seals and had to turn back around.  We then went onto survey another area in open water.  Later that morning, the winds increased and all survey launches returned to the ship out of caution for the weather.

view over the edge of a survey launch vessel of the harbor on a small island. it's a cloudy day, and the sky, trees, and water are all shades of blue-gray. the only color comes from the bright orange life ring mounted on the vessel.

Entering the harbor at Saint George

view at a distance of fur seals swimming near the shore of St George island. the fur seals appear as small dark shapes poking out from the water. the land is covered in large gray boulders.

Fur Seals in the Saint George harbor

Survey Launch July 23, 2023

We went out to survey an area closer to shore and were out all day – a good weather day.  We surveyed using set lines; this is where survey lines are parallel and evenly spaced apart. During post survey data processing, these lines of coverage will be used to update soundings on the chart. Set lines are used in areas of shallow water where there is not much bathymetric data, such as the Pribilof Islands.  This process allows the survey team to complete a larger survey area in less time.  

Our surveying boundary close to shore is defined by the navigational area limit line (NALL), which is the distance from shore that vessels can reasonably navigate.  The other boundaries are mapped out by the survey team ensuring coverage of the entire area.  During surveying in addition to depth data, any information about features that can impact navigation need to be noted.  This can include an outcrop of rocks, shipwrecks or a kelp forest.  We did see a kelp forest close to the shoreline during this survey, and indicated that in our data.  Kelp forests can increase or decrease in size depending on the year and water temperature, but generally stay in the same place.

The swath is the width of the survey lines.  During surveying the swath gets larger as the depth increases.  In this survey, as you move away from shore the depth becomes deeper, so the width of the swath increases as well.  This is due to the fact that the MBES angle is fixed and the depth is related to the swath by the tangent function.

photo of a computer screen showing, in a large window, a map of the survey area. black lines surrounded by swaths of bright red, green, or yellow bands of color snake up and down the map, representing the transects surveyed.

Screen showing the set line spacing and data taken near the shore.

cliffs along the shore of St George, as seen from a survey launch. the water is turquoise-colored in the foreground and brownish closer to shore. tall cliffs of black, brown, and gray colors, with some green growth at higher points, rise out of the photo. there are white specks - the seabirds - all over the cliffs.

Close to the shoreline of Saint George.  The color change of the water indicates a kelp forest.  Thousands of sea birds are on the cliffs.

calculations on a whiteboard. at top is a simple depiction of a boat, labeled 'launch.' a triangle extends down from the bottom of the launch toward the seafloor. the top angle (between the lines extending from the launch) is labeled 130 degrees. arrows show the direction of the echosounder pings (labeled MBES) toward the seafloor. The height of the triangle is labeled "depth" and the base "width of the swath." Below this image is a drawing of a right-angle triangle, one half of the above. The top angle is labeled 65 degrees (half of 130 degrees), the height is labeled "Depth" and the base is labeled "1/2 swath."  written calculations read: tan (theta) = opposite side length / adjacent side length. tan 65 degrees = (1/2 swath)/depth. (depth)(tan 65 degrees) = 1/2 swath. 2 (depth)(tan 65 degrees) = swath. 2(depth)(~2.1) = swath, ~4.2 (depth) = swath.

How the width of the swath can be calculated.

headshot of Elli on a survey launch vessel. she's wearing a heavy jacket and a Teacher at Sea beanie. we can see St George's island in the background.

TAS Elli Simonen on a survey launch close to shore of Saint George, one of the Pribilof Islands

At the Helm of the Survey Launches

Coxswains are responsible for steering and navigating the survey launches.  They use a variety of instruments and sensors to maintain safety and guide the survey launches over the planned survey lines. The heading is the direction the bow of the ship is pointing, expressed as a degree measurement from 0° to 360°. We were mainly surveying lines that were running north-south and the heading measurement was 0° when we went north and 180° south.

a small black instrument panel showing the heading, currently 002.0 (close to 0).

Heading indicator showing the direction of the survey launch and allows for autopilot.

a compass mounted to a surface on the survey launch. it reads close to 0 N.

Magnetic Compass showing heading on the survey launches.

photo of a computer screen showing a map of the survey area

Screen for coxswains on survey launches showing depth, the water column and survey lines.

two people at the helm of the survey launch vessel. Elli grips the helm while Ashley looks on. we can see gray ocean surface out the windows. the compass is mounted to the dashboard above the helm.

TAS Elli Simonen attempting to steer the Survey Launch with NOAA Corps member ENS Ashley Howell.  It is much harder than it looks!

Personal Log

Day to Day

Most of my days have been spent on the ship or lately, on survey launches.  If I’m on the ship, I usually spend most of the day in the survey room with the survey technicians.  Breakfast is served from 7-8 am, lunch is from 11-12 pm and dinner is 5-6 pm.  Sometimes a movie is shown in the lounge in the evenings, but the other day we streamed the Women’s World Cup to see the USA win their opening game! 

Some of the common areas of the ship

view of the survey room. a large island in the center contains cabinets and a map table. computer desks line the walls. four people sit working at computers, while a fifth stands reading something.

The survey room where all the survey technicians have their work stations.

view of the galley, or kitchen, from the service bar on the outside.

The galley with lunch available

tables and chairs in the dining area. the legs of the chairs have been capped with cut open tennis balls to slow sliding during rough conditions.

The mess, where we all eat meals.

three washing machines and two dryers in the laundry room of NOAA Ship Fairweather.

Washers, dryers and soap are provided for everyone’s use.

Did You Know?

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Heather O’Connell: Misty Eyed for Misty Fjords, June 12, 2018

 

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: 6/12/18

Weather Data from the Bridge

Latitude and Longitude: 55°33.1’ N, 133 °16.1’ W
Sky Condition: Overcast
Visibility: 10+ nautical miles
Wind Speed: 23 knots
Sea Level Pressure: 1008 millibars
Sea Wave Height: 2 feet
Sea Water Temperature: 8.9°C
Air Temperature: Dry bulb: 12.8°C, Wet bulb: 9.6°C

Science and Technology Log

After discussing geology with resident expert Amanda Finn, I developed the following understanding of the geology of Alaska. Alaska accreted, or merged with the larger continent, from the Pacific Plate colliding with the North American plate. These shifting tectonic plates created catastrophic earthquakes and many of the rock formations that you see in Alaska today. The three thousand foot metamorphic rock mountains in Misty Fjords were most likely formed from these collisions. Initially, there were sedimentary rocks that were changed from heat and pressure into metamorphic rocks. Because the sedimentary rocks were altered, the original age of these rock structures cannot be determined.

While tectonic plates created the landmass, glaciers contributed to the structure of the mountains in Southeast Alaska, creating fjords. A fjord is a narrow inlet of the sea created by a glacial valley with steep cliffs. Seventeen thousand years ago, Misty Fjord was covered in ice. As the ice melted, long narrow inlets were created that filled with ocean water. Mineral springs and volcanic activity still exist around these areas where they are closer to fault lines. It was determined by NOAA scientists in 2013 that Misty Fjord has a sunken cinder cone volcano that must have formed after the glaciers created the fjords thirteen thousand years ago. As Amanda explains, “The disappearance of all the pressure from the overlying ice caused Earth’s crust to bounce back in the area, uplifting rock and carrying magma chambers closer to the surface, causing the volcano to form. This added traces of igneous rocks to the metamorphosed sedimentary rock in the form of quartz deposits. As more ice melted and the water level rose, the cinder cone was eventually submerged underwater.”

 

Sources 

Alaska Geology

Connor, Cathy. Roadside Geology of Alaska.

Adjusting a Compass

I met a compass adjuster who was picked up in a launch from San Juan islands who learned his skill from an apprentice. He carried a wooden box with his equipment and seemed like he arrived from another time period. I was fortunate to witness this annual ritual that compares the direction of the ship according to the magnetic compass with true magnetic North in a process known as swinging the compass  A compass adjuster observes the difference between the ship’s compass and the four cardinal and four intercardinal directions to determine the difference. Since North and South were only one degree off, the magnets on the compass did not need to be adjusted. If there were a larger discrepancy between the two values, then magnets would be moved around until the directions came into alignment.

Captain Keith Sternberg swinging the compass from the flying bridge
Captain Keith Sternberg swinging the compass from the flying bridge

A compass functions based on the Earth’s inner molten iron core which generates a magnetic field around the Earth. The needle in a compass points towards the magnetic pole, which is not necessarily the same as the geographic pole. This difference between magnetic North and true North is known as magnetic variation. In addition to magnetic variation, each ship has a magnetic fingerprint that alters the magnetic compass slightly. If welding were done with metal, especially iron, this would change the magnetic signature of the ship. The combination of compass deviation and magnetic variation alters the true bearing of the ship and must be considered when viewing the bearing of the compass.

Since a magnetic compass differs from a true bearing, NOAA Ship Rainier has two gyrocompassses that are actually used for navigation. Each of these have a wheel spinning a gyroscope which is parallel to the Earth’s center of rotation, and do not rely on magnetism but depend on the Earth’s rotation and gravity. The spinning gyroscope, based on inertia, will always maintain its plane of rotation. Since these gyrocompasses are not altered by the magnetic signature of the ship and provide a true North reading, they are utilized in navigation. The NOAA Corps navigator plans the track lines of the course of the ship based on the true North reading of the gyroscope compass and is the bearing that is observed from the bridge of Rainier. The magnetic compass acts as a backup if the vessel were to lose power.

Gyrocompass
Gyrocompass on Rainier

Sources

http://www.skysailtraining.co.uk/compass_variation_deviation.htm

https://www.marineinsight.com/marine-navigation/gyro-compass-on-ships-construction-working-and-usage/

Personal Log

As I was relaxing in the lounge about to watch Black Panther yesterday evening, a call came in requesting my presence on the Bridge. When I entered the fresh air, granite mountains with ridges full of melting snow waterfalls and a breathtaking view welcomed me. To say I was awe inspired would be an understatement. We were in Misty Fjords within the Tongass National Forest, part of the nation’s largest forest about 22 miles west of Ketchikan. Observing a sliver of this almost 17 million acre temperate rainforest with evergreen trees amongst misty clouds for a brief period of time includes a moment that I will treasure. I was happy to share this experience with other crew, survey technicians and NOAA Corps members who weren’t currently on shift. While appreciating  this beauty, I thought of a Japanese saying, “Iche-go Ich-e,” which means this moment only happens now. Observing the still glassy water reflecting the cloudy sky against green islands and three thousand foot mountains touched my soul. The enormity of the steep granite humbled me as I appreciated it in its untouched state. This pristine environment existed from a landscape formed ten thousand years ago by a massive glacier that created this geological phenomenon. Luckily, this Tongass National Forest was claimed to be a protected zone in 1978 by the president. I’m grateful for this natural beauty that invites a tranquil, peaceful feeling. When a blow spout of a whale appeared off the port side of the vessel, my elation couldn’t be contained and I was overwhelmed with gratitude.

Observing Misty Fjords in the Inner Passage
Misty Fjords in the Inner Passage

 

Did You Know?

Lookouts use a coordinate plane-like reference for directions. If you are standing at the center of the Bridge, similar to the origin of a coordinate plane, then the y-axis would be dead ahead. The x-axis, or 90 degrees to the right would be beam starboard, while to the left would be beam port. To the right forty five degrees would be broad off starboard, while to the left forty degrees would be broad port. If you count the three equidistant points leading up to forty five degrees on the right hand side of the ship, you would command one off, two off or three off starboard respectively.