Simple Hydrodynamics

Physics make it happen.

Hydrodynamics is the science of liquids in motion. In simple terms, it describes the properties of liquid flow such as we see in water. Hydrodynamics can be used in a wide variety of applications such determining the flow rate in a petroleum pipeline, determining the thrust of a propeller and predicting weather patterns. There are applications all around us.

One of the principles of hydrodynamics is Bernoulli's principle. Bernoulli's principle states that for non-viscous flow, an increase in the speed of the fluid occurs simultaneously with a decrease in pressure. How does that apply to restricted channel maneuvering situations such as bank suction?

In towboat operation, you deal with hydrodynamics and Bernoulli's principle all the time. Let's look your operation and see how it is affected by these principles:

Bank Suction:

Bank Suction

Bank suction starts when a vessel strays too close to a bank, restricting the water flow on its bank side. Assume two gallon of water start at the head of the tow at the same time; one goes to the port and one goes to starboard.  To keep equilibrium, the water rushing down the bank side of the tow needs to reach the stern at the same time as water flowing down the open side of the tow.  Because there is less space on the bank side, that gallon of water has to speed up in the restricted space to reach the stern at that same time as the open side water.  This increase in speed, as described in Bernoulli's principle, causes a decrease in pressure.  That decrease in pressure will cause the vessel to slide toward the bank.  If the tow gets too close to the bank, it can be forced sideways into it.  The same effect occurs between two vessels passing close to one other.

The bank suction will increase as speed increases. Therefore, in shallow water and narrow channels, wheelmen may need to decrease speed to minimize these effects.  But what if circumstances make it impractical to bring the vessel to a slow crawl or abrupt halt?  In those cases the idea is to keep the bow pointed slightly away from the near bank to overcome the bank suction, while at the same time maintaining a few degrees of rudder toward the bank to compensate for bank effect. This is a tricky and delicate balance of forces so be sure that you stay alert and expect the unexpected.

A skilled wheelman can use these effects to his advantage in particular situations, but the best choice is to slow speed and to pay careful attention to piloting.

Sucked off the bank:

How often has this happened to you?  Your tow is pushed into the bank and a passing tow causes it to break loose and float free.  What is happening here in terms of hydrodynamics? 

Sucked off of the bank.

As the passing tow nears your tow that is pushed into the bank, the initial bow wave causes your tow to lift up as the water rises.  As the passing tow continues, the bank suction effect takes hold and pulls your tow toward the passing vessel.

In anticipation of the lift and pull from the bank, have the main engines engaged ahead with the rudders hard to starboard.

The Squat Effect:

Squat is caused by the interaction of the hull of the towboat, the bottom, and the water between.  As the boat moves through shallow water, some of the water it displaces rushes under the vessel to raise up again at the stern.  This causes a Bernoulli Effect, decreasing upward pressure on the hull.  Squat makes the boat sink deeper in the water than normal and slows the vessel.  The faster the towboat moves through shallow water, the greater is this effect.  When navigating in shallow water, the Wheelman must reduce speed to avoid squat.

Wave Action:

In incompressible liquids such as water, a bow wake is created when a vessel is underway; as the water cannot be compressed, it must be displaced instead, resulting in a wave. As with all wave forms, it spreads outward from the source until its energy is overcome or lost, usually by friction or dispersion.

In Conclusion....

Understanding the hydrodynamic forces that are working on your vessel is necessary to anticipate and counter problems in narrow channels and shallow water.

Hydration

Hot, hot, hot....

The heat is upon us!  During the hot summer months it is important to keep properly hydrated.  There are various calculations on how much you should intake, but these numbers all depend on how healthy you are, your environment, and how much exercise you are getting. 

When you are sweating in the sun your body requires more fluids to keep properly hydrated. You can generally determine if you are properly hydrated when you will rarely feel thirsty and produce 6.3 cups of colorless to light yellow urine a day.

There are also many sources of hydration. On average your food counts for about 20% of your daily water intake. Beverages such as milk and juice are mostly water. Sodas and caffeinated drinks (tea and coffee) provide little hydration. Water is still your best source of hydration; it is calorie free, inexpensive and readily available.

2012 Higman Leadership and Management Courses
Scheduling Change

MOB Follow Through

Crews practicing MOB techniques. 

Life Ring

Capt. David Jones of the M/V ROCKFISH recently had a MOB drill on board. During his drill, he had each crewmember throw the life rings to ensure that all understood the technique and had practice in geting them to the victim.

 

Here is a message from Capt. David Jones to Port Capt. David Devall:

 

"I returned to the boat on JUN 5 and read the messages on a recent MOB and such. I had a safety meeting again with the crew on JUN 8 to discuss MOB situations.

 

Last month I had the crew out on the stern of the M/V ROCKFISH, throwing life rings and heaving lines. It was a lot of fun but the crew realized that it is a rough and tough job to get those life rings out where needed. The new plastic life rings are hard to get any distance on and they take practice. They are hard to get a good grip on when throwing.

 

It was a good wakeup call for all of us knowing that you might be in the water a good while before a response is made, especially if half the crew was asleep. Practice, practice, practice!"......Capt. David Jones 

 

What has your crew been doing to be prepared for a MOB situation?.  Send your MOB practice ideas and pictures to to Jay. 

Electric Deck Scaler Maintenance

Nav Zone

Rose Point Navigation System

Stern Shots

M/V PORT NECHES in service June 8, 2012.

Capt Arnold Argullin in the wheelhouse of the  M/V PORT NECHES.

M/V PORT NECHES galley.

A sea of green at Channelview.

The M/V SABINE PASS spots a tree climbing goat on the TennTom.

Galveston Daily News, SEP 1, 1918

The ICWW had it roots early in the history of Texas. Below is an excerpt from the Galveston Daily News from September 1, 1918 talking about the opening of the canal from Galveston to Corpus Christi on May 29, 1918:

"Finished on May 29....

The Intercoastal Canal between Galveston and Corpus Christi was a reality on May 29, when the last few feet that remained to be dug was finished. In the presence of Lieutenant Colonel C. S. Rilche of Galveston, head of the United States engineering department for this district, and several invited guests of local prominence, the last barrier crumbled away and the waters of two rivers the San Bernard and Brazos, combined for the one general purpose; that of giving the Texas coast one of the most useful waterways to be found coast wise. The canal runs from Matagorda Bay to Galveston, a distance of 200 miles along its main line, with branches aggregating a total of over 800 miles. It was built at a cost of about $664,000 and its estimated maintenance is $50,000 per annum.

Suderman and Dolson Tug used in Galveston, Texas circa early 1910s.

The Intercoastal Canal is navigable for vessels drawing close to five feet of water and not too great a beam. It is especially adapted for the use of barges of light draft with large cargo-carrying capacities. A limit of seven to eight miles per hour is placed by the engineering department using the canal.

Started Before the War.

The Texas coast canal movement had its beginning many years ago. The old Galveston and Brazos Canal was constructed in 1856. No figures are available as to what the cost was at the time, but it is believed to have been in excess of the $30,000 which the old corporation received for the waterway from the federal government. The ruling depth of the canal at that time was eighteen inches. Since it has been taken over by the federal authorities it has been reopened and re-dug to a depth of five feet at mean low tide; and a width of about thirty-five feet."

The Galveston waterfront, as depicted in a London periodical in 1841. This is one of the earliest authentic images of the city to depict a Western Rivers steamboat (left).