Wednesday, July 22. 2020 JAY JACOBSON EXPLAINS THE WATERWAYS

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WEDNESDAY, JULY 22nd, 2020 

OUR 111th ISSUE
OF 
FROM THE ARCHIVES

NAVIGATING THE WATER
 AROUND

ROOSEVELT ISLAND

JAY JACOBSON

Of Course We’re Surrounded by Water! We’re an Island!

On land, we use a map. On the water, we use charts. Nautical charts. Published by the National Oceanic and Atmospheric Administration. Everyone calls it NOAA. A nautical chart is like a map, if your’re traveling on the water. It will tell you how deep the water is — around Roosevelt Island, the deepest point is just north of the Queensborough Bridge, where the chart tells us that the water is 99 feet deep when the tide is at what’s called “mean low water”.

The nautical chart tells us also that the clearance between the East River at “mean low water” and the Queensborough Bridge is 133 feet. If you’re the captain of a vessel planning to travel in the East River and the highest point on your vessel is more than 133 feet above the water, you had better find a different route because you’ll hit the bottom of the big Bridge. The Roosevelt Island Bridge, when it is in its “closed” condition, is 40 feet above the east channel of the East River. Occasionally, a careless, casual, recreational captain has been caught under the RI Bridge because, among other things, a vessel’s mast is more than forty feet above the water and the navigator has failed to consult the charts.

Both the east and west channels of the East River have plenty of depth for the usual traffic near Roosevelt Island. Nautical charts show the navigator where the buoys, beacons and lights — reliable old friends to people who ply the inland waters — are located. These aids to navigation in the United States are established and maintained by the U.S. Coast Guard.

Around Roosevelt Island, we have a green daybeacon sitting on Belmont Rock (a/k/a U Thant Rock) just south of the FDR Memorial; lights on the underside of the Queensborough Bridge, and then, north of Roosevelt Island, lights on Mill Rock. Many aids to navigation have light or sound-producing patterns that are noted on the nautical chart. The aids enable the navigator to be sure of the boat’s position. On foggy days, we hear vessels traveling the west channel sounding a fog horn. The mournful sound warns users of the channel that a boat (or, more often, a hard-to-maneuver boat with a barge) has limited visibility and limited ability to change course in the channel and needs to have other vessels take careful action. Most often, in dense fog conditions, captains will communicate using radio frequencies reserved for nautical messag to be sure that there is no confusion about which vessel is going to do what.

Even NOAA is wrong. Their nautical chart covering the area between Port Morris in the Bronx and the Queensboro Bridge is entitled “East River”. But, of course, despite the name, the East River is not a “river”. It is a salt water tidal estuary. It connects Long Island Sound with New York Harbor and, ultimately, the Atlantic Ocean. But, it is not a river. It has no source from which fresh water flows to to the sea.

About those tides. The body of water that circumscribes our island has an important feature: tides cause the body of water to rise and to fall. Twice a day, every day, a tidal flow from the Atlantic Ocean passes the Battery at the southern tip of Manhattan, and travels up the “East River”, past the tower at our northern tip, through “Hell Gate”, out under the Whitestone and Throgs Neck Bridges, and out into Long Island Sound. And twice a day, the flow reverses. Water from Long Island Sound comes under the bridges, though the “Hell Gate”, divides into the east and west channels, flows along our flanks through the BMW bridge system into New York Harbor and there mingles with water from the Hudson (a real river!) and out into the Atlantic Ocean.

Among its most important publications, NOAA publishes Tidal Current Charts. Tides are caused (a) by the gravitational attraction between the moon, the sun and the earth, and (b) by centrifugal force generated by the rotation of the earth and moon around their center of gravity. As the earth rotates once every 24 hours, there is a high tide at any point each time that point passes under the moon. But the opposite side of the earth also experiences a high tide as centrifugal force flings outward the water on the side of the planet away from the moon. So, there are two high tides, and two low tides at each point on the planet each day. (It’s OK to reread this paragraph; I have done it several times, and I think I’ve got it right.)

Each month, when the moon is new and when it is full, we have what are called “spring” tides. These “spring” tides are higher and lower than at other times during the month. At these times, the sun and the moon line up, so the sun’s weaker gravitational effect is added to that of the moon. The Tidal Current Charts for New York Harbor (including the area around Roosevelt Island) are very interesting. The daily rise and fall of the tides are seen as water flows in both the east and west channels. The speed at which the water flows is known as the “tidal current”. The tidal current for spring tides flows around Roosevelt Island at a rate of 4.6 knots going north, and 5.2 knots going south. While nowhere near the speed of the tidal current in the Bay of Fundy in Canada, or in some of the nearby Maine bays, the Roosevelt Island tidal currents are very swift. When you see a small boat appearing to make no progress as it tries to move up or down the East River, the reason it is having so much difficulty is the tidal current pushing it in a direction at a rate that the boat is unable to overcome.

SWAN SONG FOR A FLOATIE IN EAST CHANNEL

Sometimes you see the FDNY rescue people from the river. Today, July 19th 4 people fell in the river when their SWAN was overcome by the currents.

To safely travel the East River current charts are available on-line.

WEDNESDAY’S PHOTO OF THE DAY

What is this and where is it located?
E-mail rooseveltislandhistory@gmail.com
 Win a trinket from Kiosk

TUESDAY’S PHOTO OF THE DAY

The structure of the new elevator
at the Manhattan Tram Station
NINA LUBLIN AND VICKI FEINMEL ARE THE WINNERS

EDITORIAL

Knowing very little about rivers, estuaries, tidal flow, currents I asked Jay Jaboson who is very knowledgeable to write today’s article on river currents.

Thanks for your enlightening words about the waterway around us.

JUDITH BERDY

WE ARE WATCHING A TRAGEDY IN THE MAKING. THE CONSTANT ROAR OF OUT-OF-CONTROL JET SKIES IN THE RIVER. LAST WEEKEND THERE WERE TWO KAYAKS PADDLING ALONG AND JET SKIES SPEEDING PAST.  WHAT NEXT?

Text by Judith Berdy
Thanks to Bobbie Slonevsky for her dedication to Blackwell’s Almanac and the RIHS
Thanks to Deborah Dorff for maintaining our website
Edited by Melanie Colter  and Deborah Dorff

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Roosevelt Island Historical Society
unless otherwise indicated
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