Down the Amazon

Every morning we try to take a walk on the Lower Promenade deck which is exactly one-quarter around once. Early in the morning many moths that were attracted by the ship's lights during the night are sleeping at various places on this deck. I took pictures which are posted on my Picasa site under an album called "Moths of the Amazon". I hope you find them as fascinating as I do.

It is just past 1:00 PM on Thursday and we feel the effect of the incoming tide from the Atlantic - and we are still 250 nautical miles from the ocean!!! This tide is strong enough both to reduce our speed by 2 or 3 knots and to bring salt water up the river during a rising tide. This afternoon we drop off the two pilots and an Immigration Officer at Macapa before proceeding towards the Atlantic.

As we approach the mouth of the Amazon the width increases dramatically. As it widens, the flow rate of the river decreases because a given volume of water is spread over a greater area. As the river current slows, all the silt the river has been carrying for thousands of miles starts to settle to the bottom of the river and forms both the delta area as well as the bar at the entrance to the Amazon.

The Amazon becomes very shallow over the bar and the Captain will time his arrival to coincide with a high tide. Even so, he will need to slow the ship in order to ease over the bar. Over the loudspeaker today the Captain told us at full speed the vessels hunkers down and runs with the hull about 8 feet lower than at rest. I couldn't remember the word he used for "hunkers down" so I asked someone to ask the Bridge for the word. Here is the response the Officer on Duty sent to me:

Squat
When the vessel has a flow of water over its hull, several pressure differentials are formed due to increased flow rates. This increase flow rate causing pressure differentials are similar to the effect an aircraft wing or sail feels. This is called the Bernoulli effect. The resultant is that the ship is drawn downwards towards the sea bed thus increasing its draft. It happens more in shallow water and when the speed of the vessel is high..


So now we know, I think.

We will likely go over the bar at about 1:00 AM Friday morning. Then we contiue our cruise toward Bridgetown, Barbados and are scheduled to arrive about 8:00 AM, October 27.