Heather O’Connell: Using a Sextant, Distilling Glacial Water and Kayaking to Icebergs, June 18, 2018


NOAA Teacher at Sea

Heather O’Connell

NOAA Ship Rainier

June 7 – 22, 2018

Mission: Hydrographic Survey

Geographic Area of Cruise: Seattle, Washington to Southeast, Alaska

Date: 6/18/18

Weather Data from the Bridge

Latitude and Longitude: 57°55’ N, 133 °33’ W, Sky Condition: Broken, Visibility: 10+ nautical miles, Wind Speed: 10 knots, Sea Level Pressure: 1023.5 millibars, Sea Water Temperature: 3.9°C, Air Temperature: Dry bulb: 15.0°C, Wet bulb: 12.0°C

Science and Technology Log

Using a Sextant

Greg Gahlinger, H.S.S.T., hydrographic senior survey technician, shared his knowledge of using a horizon sextant. He traveled to Hawaii from San Diego and back using this technology when he was in the navy. Utilizing his Cassens and Plath horizon sextant when there was an atypically sunny day in Tracy Arm allowed me to experience this celestial navigation tool. While the sextant is easy to use, the calculations for placement can be more involved.

A sextant is used for celestial navigation by finding the angle of a celestial body above the horizon. Originally, the graduated mark only measured sixty degrees, thus the derivation of the name. The angle between two points is determined with the help of two mirrors. One mirror is half silvered which allows light to pass through and this is the one used to focus on the horizon. The other mirror attached to the movable arm reflects the light of the object, such as the sun, and can be moved so that the light reflects off of the first mirror. A representation of the object, or sun, superimposed on the horizon is seen and the angle between the two objects is recorded. Angles can be measured to the nearest ten seconds using the Vernier adjustment and it is this precision that makes the sextant such a useful tool.  One degree is divided into sixty minutes or sixty nautical miles. Each degree is divided into sixty seconds.

Horizon Sextant

Horizon Sextant

To use a horizon sextant, you hold onto the arm piece and look for the reflection of the sun from the mirror and through a horizon reflection onto the scope or the eyepiece. There are several different filters that make it safe to view the reflection of the sun. After you adjust the index, the rotating part on the bottom of the sextant, you align the reflection of the disk of the sun onto the horizon. If there is no actual horizon, as was the case when we were in the fjord, then you can align the image of the sun onto a false horizon. Once the reflected sun is sitting on the horizon, you can swing the frame back and forth until the sun lies tangent to the horizon. From here, record the angular measurement and use a table to determine your position of latitude. If you have an accurate time, you can also determine longitude using another set of charts.

Taking a sight of the sun at local apparent noon with a Sextant

Taking a sight of the sun at local apparent noon with a Sextant

Salt Water Distillation

While in transit to our survey location, First Assistant Engineer Mike Riley shared the engine room with me. There is a control panel for all of the different components of the ship along with the electrical circuit board. Amongst all of the parts that contribute to making the ship function, I was interested in the two evaporators.

The two evaporators change saltwater into potable water in a desalination process. These two stage evaporators are filled with seawater that comes into the vessel via suction into sea chests. If the ship is going at full speed, 12.4 knots, which varies depending on currents and tides, the distillers will make about 500 gallons of freshwater an hour, or 3,000 gallons a day. Engine heat is used to boil the sea water for the evaporation. The water goes through a booster heater to make it even hotter before coming into the tanks. The distilled water comes from the tank next to the current generator in use.

Two Stage Evaporator

Two Stage Evaporator

The two stage distillers have a demister screen in the middle. There are about twenty metal plates with grooves between them located on both hemispheres of the spheroid shaped distiller. The plates are sealed and the metal groove space, or gaskets, between them is open. Jacket water, a mixture of coolant, or propylene glycol, and water, that is already at about one hundred and seventy degrees comes in and fills the metal plates. The jacket water is heated from the exhaust from the generator. It is further heated from going through a vacuum and turns into steam. Salt water from the salt chest comes into the space between the metal plates over the grooves.

Metal plates and gasket inside of evaporator

Metal plates and gasket inside of evaporator

The porous demister screen keeps salt water droplets from going above and the brine water collects at the bottom and goes out the ejector pump. Once the steam from the lower part of the tank heats the water and it enters the upper part of the tank, the water is cleansed and condenses on the plates. From here it goes to a tank where it is heated before being stored in another tank and then being allocated to the appropriate area. This water is used to cool the engine, flush the toilets and provided distilled drinking water while in transit.

So, currently, all on Rainier are consuming filtered artesian drinking water and showering in distilled glacier water. Ship Rainier has been consistently surpassing all expectations.

Sources

http://www.pbs.org/wgbh/nova/shackleton/navigate/escapeworks.html

https://oceanservice.noaa.gov/education/kits/geodesy/geo03_figure.html

Personal Log

After dinner I decided to tag along with Able Seaman, or A.B., Dorian Curry, to kayak up close to some icebergs. Leaving the safety of the ship  docked by Point Asley, we headed towards Wood Spit Island. After about twenty minutes of paddling, I saw three distinctive spouts followed by some black dorsal fins surfacing to the northeast towards Sumdum Glacier. Orca whales were off in the distance. Soon these orca whales appeared closer and they were now about two hundred yards away. While the whales made the majestic sound of blowing bubbles in the water, I feared that they would approach the kayak. Putting the boats together in the hopes that these massive mammals would not think of us as prey seemed to be the logical thing to do.  It appeared that there was a mother and two juvenile killer whales.

Video Credit: Dorian Curry

This incredible opportunity to be so close to these creatures along with the terrifying reality that they may mistake me for a seal, proved to be an invigorating experience. The whales dove under and then once again appeared behind at a distance that was slightly too close for comfort in a kayak. At this point, I thought paddling away from these carnivorous predators would be the best approach. I paddled towards the smaller island south of Harbor Island and Round Islet, the place where the base station was set up just a few days earlier. After docking on the island shortly, I was grateful to be on shore post such a stimulating and intimidating experience.

Blue Iceberg

Blue Iceberg

Walking the kayaks over the beach and watching the channel where the Endicott Arm and Tracy Arm channels converged, proved to be a good strategy before paddling onward. A strong, circular current resulted from the two channels merging but was relatively safe due to the fact that it was ebb tide. After paddling strongly for a few minutes, smooth waters followed and I approached one of the most spectacular blue icebergs I have ever seen. The definition from all of the layers of different snowfalls that created this still existing piece of ice was truly amazing. Observing it from different angles overwhelmed me with the brilliance of this natural phenomenon. Next, I found myself paddling towards an iceberg with an eagle perched on it towards Sumdum Glacier.  Again, the different vantage points displayed various concentric circles and patterns of frozen ice accumulating over thousands of years. With only about an hour before sunset, the return journey to Rainier began and choosing to go to the west of Harbor Island to avoid the difficult channel of the now incoming tide made the return safe.

Iceberg

Iceberg

After almost four hours of paddling over a distance of about 8.4 nautical miles, or 9.6 miles, I found it difficult to use my upper body strength to ascend the ladder. Thanks to Airlie Pickett I safely stepped onto the Rainier and began to process this magnificent adventure that I had just embarked upon.

Did You Know?

Wind direction can be calculated by using a wind plotting board calculator. This dial allows you to rotate until the line matches up with the coarse bearing, then mark the wind speed on the clear dial with a grease marker, and then match this up with the angular measurement of the wind and mark this. Then, line up your two marks on a vertical line and this will provide the true wind direction.

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