If you fill a water bottle right up to the top, put its cap back on, and then shake it, do you feel any water move? No.
If you fill a water bottle up only half-way, put the cap back on, and then shake it, do you feel any water move? This time, definitely yes!
This concept applies to the water and gas tanks on your boat. As tanks gradually empty due to consumption, the liquids will slosh around more, even though the tanks probably have baffles. This sloshing also changes your centers of gravity and buoyancy.
But are there other weights on your vessel? Think about it!
Hidden factors aboard
Every boat has two other factors that affect its ability to right itself, but they are easy to overlook.
What are they? They are people and bilge water.
People tend to move around the vessel, both with the movements of the vessel and of their own accord. As they move, sometimes unpredictably, they make changes in the righting arm.
Bilge water moves more predictably than people, but unless you are constantly monitoring and manually operating your bilge pump, you’re not quite sure how much bilge water is down there. Again, both these factors change your ability to right the vessel.
While we don’t want to jump the gun on the investigation and findings of the National Transportation Safety Board (NTSB), the newspapers have reported that many of the passengers on the Ethan Allen were, just before it capsized, on one side of the vessel.
External factors
As you read about weight distribution and the centers of gravity and buoyancy, I bet you assumed that the vessel was in flat water. Those of us who boat on most lakes assume that the water is essentially flat, with maybe ripples of a wake caused by the occasional passing boat. But waves, too, change the centers of gravity and buoyancy.
Did you also consider wind? If your boat is floating free in the water, not under power, and with a moderate wind, you’ll find the boat moving. If your boat's superstructure is high enough, it acts as a sail, making your boat heel. This is one of the reasons for a keel in a sailboat, to change the righting moment equation, so that the sailboat can accept more list before it capsizes.
When you factor wind, waves, and weight placement together, the picture becomes more complicated. While no single item may have caused the Ethan Allen, or any other vessel for that matter, to capsize, the combination may have done so.
What you can do
We’ll know better about the Ethan Allen after the NTSB investigation, but the Coast Guard and Coast Guard Auxiliary want you to be aware of these factors. To boat more safely, please keep some tips in mind:
- Load your boat evenly and, when possible, secure things so they do not shift.
- Remind your passengers to keep themselves more or less evenly distributed on the vessel, and to avoid sudden movements.
- Keep an eye out for bow wakes, wind shifts, and other things that may affect your boat's balance.
Safe boating courses are offered all over the country by the Coast Guard Auxiliary as well as other organizations. Safety starts with education, and taking an approved course is a good way to start boating more safely.
For more information about safe boating courses, please contact the United States Coast Guard Auxiliary at www.cgaux.org or call 1-877-875-6296.
