Vincent Colombo, Dynamic Positioning, June 15, 2015


NOAA Teacher at Sea
Vincent Colombo
Aboard NOAA Ship Oscar Dyson
June 11 – 30, 2015

Mission: Annual Pollock Survey
Geographical Area of Cruise: The Gulf of Alaska
Date: June 15, 2015

Weather Data from the Bridge:

  • Wind Speed: 4.52 knots
  • Sea Temperature: 8.5 degrees C
  • Air Temperature: 6.4 degrees C
  • Air Pressure: 1034.33 mb
A United States Coast Guard Sikorsky MH-60 Jayhawk flying over the Oscar Dyson

A United States Coast Guard Sikorsky MH-60 Jayhawk flying over the deck of the Oscar Dyson

Science and Technology Log:

Are you a morning person? How about a night owl? Well if you said yes to the first question, then Alaska during the summer is your place to be. Currently where we are right now, the sun officially rises at 5:08 and sets at 23:12 (that’s 11:12 pm for those of you not used to 24 hour format). But, do not think that it means it turns dark by any means. Sunrise and Sunset are when the sun is officially seen, or disappears on the horizon respectively. So far in my time spent here in Alaska, I have only seen it dark for about one hour.

The 23.5 degree tilt of the Earth exaggerates the effect of the sun during the time around a solstice

The 23.5 degree tilt of the Earth exaggerates the effect of the sun during the time around a solstice

The reason why is easily explained, seasons. Students in Delaware learn about seasons in 8th grade, and again if they take Physics or Astronomy in high school. The tilt of the earth causes the northern hemisphere to be more exposed to the sun for longer periods of time. Thus the concept of day and night is greatly changed.

In order to fully grasp this concept, you must also understand why it never gets dark either. The term we use is twilight, or the time between darkness and sunrise in the morning,  and sunset and complete darkness in the evening. Twilight is also defined as when there is light outside, but the sun is below the horizon.

There are 3 types of twilight: civil, nautical, and astronomical.

  • Civil twilight occurs when the Sun is between 0 degrees and 6 degrees below the horizon. In the morning, civil twilight begins when the Sun is 6 degrees below the horizon and ends at sunrise. In the evening, it begins at sunset and ends when the Sun reaches 6 degrees below the horizon. Typically civil twilight begins and ends one half hour before or after sunrise or sunset. Most outdoorsmen know this as the 1/2 hour before and after rule. If you’re a deer hunter, civil twilight signifies legal shooting time has begun or ended.
  • Nautical twilight occurs when the geometrical center of the Sun is between 6 degrees and 12 degrees below the horizon. Nautical twilight is usually an hour before and after sunset. This twilight period is less bright than civil twilight and artificial light is generally required for activities.The term, nautical twilight, dates back to the time when sailors used the stars to navigate the seas. During this time, observers on Earth can easily see most stars. Although not completely dark outside, one could safely get around.
  • Last is Astronomical twilight, and this occurs when the Sun is between 12 degrees and 18 degrees below the horizon. In the morning, the sky is completely dark before the onset of the astronomical twilight, and in the evening, the sky becomes completely dark at the end of astronomical twilight. This is typically an hour and a half before or after sunrise or sunset respectively.
  • During the summer months, especially around the Summer Solstice, the North and South Poles experience several days with no complete darkness at all. Currently our civil, nautical, and astronomical twilights are exaggerated, only leaving about an hour of actual darkness.

My next scientific topic I would like to discuss is the system the vessel Oscar Dyson uses called Dynamic Positioning. When we were calibrating the acoustic equipment in my last post, the ship did not move more than 0.3 meters in any direction.

Dynamic positioning diagram

Dynamic positioning diagram

The ship uses GPS systems to hold it in one single place for a period of time. Using a minimum of three satellites and triangulation, the ship’s position is able to be maintained. The ship uses its main engines as well as bow thrusters to keep it steady in one position.  I was also introduced to some new vocabulary:

  • surge: moving the ship forward or back (astern)
  • sway: moving the ship starboard (right) or left (port)
  • heave: moving the ship up or down
  • roll: the rotation about surge axis
  • pitch: the rotation about sway axis
  • yaw: the rotation about heave axis
How a ship is able to maintain it's position

How a ship is able to maintain its position

Not only can the ship stay in one position, I also learned that it can stay in one position over a column of water, which is vital for a research ship like the Oscar Dyson when conducting research one specific area of the ocean.

A view of the dynamic positioning monitor from the bridge

A view of the dynamic positioning monitor from the bridge

A view of the current state of the rudder of the ship. It changes as the dynamic positioning controls the ship

A view of the current state of the rudder of the ship. It changes as the dynamic positioning controls the ship

The bow thruster control on the bridge of the ship

The bow thruster control on the bridge of the ship

Personal Log:

It took us almost three days to reach where the scientific study was to begin. For those of you who know me, it is hard for me to stay in one place for an extended period of time. Luckily the ship has an abundance of DVDs to watch, Direct TV and a fantastic galley (aka kitchen) to make it feel more like home. I can honestly say the food is some of the best I have ever eaten.

Luckily (knocking on wood), our ship has not hit any rough seas. It has taken a day or so to get used to the rocking, just make sure you have a free hand to grab hold of something when moving about.

Underway, I got to deploy the first An Expendable Bathy Thermograph or XBT for short. You can find out more by going to this NOAA website: XBT uses

Getting briefed on use of the sensor

Getting briefed on use of the sensor. Notice I am harnessed in.

Deploying the sensor

Deploying the sensor

According to our Executive Officer, LT Carl Rhodes, we will be seeing some AMAZING Alaskan geography including volcanoes. Check back for some awesome photos.

Did You Know?

Most modern oil rigs are not fixed to the sea floor! They also use dynamic positioning. Learn more about dynamic positioning here.

 

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