(Editors note>: Wayne Spivak provides information for us from time to time regarding safe boating. In this article he describes what we can do to prevent another tragedy.)
By Wayne Spivak National Press Corps United States Coast Guard Auxiliary
Weight shift likely caused Ethan Allen to capsize
Vessels capsizing are a major cause of both accidents and deaths. In 2004, 393 vessels were reported capsized (as the primary casualty event), with 229 injuries and 184 fatalities, according to the United States Coast Guard Office of Boating Safety's 2004 Boating Statistics. Unfortunately, the trend of these statistics over the last five years has been less than encouraging.
Boaters can easily reduce their risk, though, so let's take a closer look at capsizing and how to prevent it.
Weight Distribution
Recreational boaters can reduce the possibility of capsizing by understanding some basic laws of physics.
The laws of balance discussed here have four components: the center of gravity, the center of buoyancy, the righting arm, and the righting moment.
When a vessel is riding evenly in the water, the center of gravity is directly over the center of buoyancy. As weight is placed on one side of the vessel, the center of gravity moves toward that side, and the boat lists. This listing causes the center of buoyancy to move, so that now the center of buoyancy is no longer directly under the center of gravity.
The distance between the centers of gravity and of buoyancy is called the righting arm. As the righting arm increases, the ability of the vessel to right itself (bring the center points back in line) decreases. This is intuitively obvious: the more unbalanced the vessel, the more unevenly it rides in the water, and the more likely it is to capsize.
The righting moment is related to the ability of a vessel to right itself. When the righting moment is positive, the vessel will return to a stable position in the water if it is rocked. When the boat is rocked too far, though, the righting moment becomes negative, and the boat will "lose its balance," keep going over, and capsize.
So what does all this physics mean to the typical recreational boater? Put simply, the more uneven the weight distribution on a boat, the more likely the vessel is to capsize.
Weight distribution is not always obvious
What changes the weight distribution on your boat?
If we remember our science lessons from school, we recall that matter normally exists in one of three forms: solid, liquid, and gaseous. On our boats, we may find all three, but most of us can discount gaseous matter, since the weights are negligible. Let's look at solids and liquids. Solids are easy to think of: the fire extinguisher, the tackle box, or the cooler, for example. Liquids are also easy: the contents of the water tanks and fuel tanks.
Solids
Of the solids aboard your vessel, there are two types, static and dynamic. A static solid stays in one place. For example, if you securely mount your fire extinguisher to the starboard side of the boat, that solid is now fixed in place, and its weight will stay on that side of the boat. The same holds true of anything that is permanently attached to the superstructure of the vessel. It has a weight that is fixed in place.
But what about that cooler you placed on board, and put in the corner of the deck? It too has a weight, but unlike the fire extinguisher in our previous example, that cooler can move if the vessel rolls or pitches. The cooler can slide across the deck, forward or sideways or diagonally, so it counts as a dynamic (moving) solid.
As the cooler moves, your vessel's weight distribution changes. This change then moves the center of buoyancy and center of gravity apart, creating a righting arm. If we remember the physics we just went over, the larger the increase in the righting arm, the more difficult it is for the vessel to move back to the neutral position (where the centers of gravity and buoyancy are in line).
We'll get back to this concept shortly.
By Wayne Spivak National Press Corps United States Coast Guard Auxiliary
Weight shift likely caused Ethan Allen to capsize
LAKE GEORGE, N.Y. - The passengers aboard a tour boat that capsized on Lake George, killing 20 people, were sitting on long benches and slid sharply to one side of the vessel just before it flipped over, authorities said Monday. [Oct 4, 2005 Times Argus - www.timesargus.com]
Vessels capsizing are a major cause of both accidents and deaths. In 2004, 393 vessels were reported capsized (as the primary casualty event), with 229 injuries and 184 fatalities, according to the United States Coast Guard Office of Boating Safety's 2004 Boating Statistics. Unfortunately, the trend of these statistics over the last five years has been less than encouraging.
Boaters can easily reduce their risk, though, so let's take a closer look at capsizing and how to prevent it.
Weight Distribution
Recreational boaters can reduce the possibility of capsizing by understanding some basic laws of physics.
The laws of balance discussed here have four components: the center of gravity, the center of buoyancy, the righting arm, and the righting moment.
When a vessel is riding evenly in the water, the center of gravity is directly over the center of buoyancy. As weight is placed on one side of the vessel, the center of gravity moves toward that side, and the boat lists. This listing causes the center of buoyancy to move, so that now the center of buoyancy is no longer directly under the center of gravity.
The distance between the centers of gravity and of buoyancy is called the righting arm. As the righting arm increases, the ability of the vessel to right itself (bring the center points back in line) decreases. This is intuitively obvious: the more unbalanced the vessel, the more unevenly it rides in the water, and the more likely it is to capsize.
The righting moment is related to the ability of a vessel to right itself. When the righting moment is positive, the vessel will return to a stable position in the water if it is rocked. When the boat is rocked too far, though, the righting moment becomes negative, and the boat will "lose its balance," keep going over, and capsize.
So what does all this physics mean to the typical recreational boater? Put simply, the more uneven the weight distribution on a boat, the more likely the vessel is to capsize.
Weight distribution is not always obvious
What changes the weight distribution on your boat?
If we remember our science lessons from school, we recall that matter normally exists in one of three forms: solid, liquid, and gaseous. On our boats, we may find all three, but most of us can discount gaseous matter, since the weights are negligible. Let's look at solids and liquids. Solids are easy to think of: the fire extinguisher, the tackle box, or the cooler, for example. Liquids are also easy: the contents of the water tanks and fuel tanks.
Solids
Of the solids aboard your vessel, there are two types, static and dynamic. A static solid stays in one place. For example, if you securely mount your fire extinguisher to the starboard side of the boat, that solid is now fixed in place, and its weight will stay on that side of the boat. The same holds true of anything that is permanently attached to the superstructure of the vessel. It has a weight that is fixed in place.
But what about that cooler you placed on board, and put in the corner of the deck? It too has a weight, but unlike the fire extinguisher in our previous example, that cooler can move if the vessel rolls or pitches. The cooler can slide across the deck, forward or sideways or diagonally, so it counts as a dynamic (moving) solid.
As the cooler moves, your vessel's weight distribution changes. This change then moves the center of buoyancy and center of gravity apart, creating a righting arm. If we remember the physics we just went over, the larger the increase in the righting arm, the more difficult it is for the vessel to move back to the neutral position (where the centers of gravity and buoyancy are in line).
We'll get back to this concept shortly.
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