ROCKPORT – To a casual observer, it looked like grown men in uniform playing with toy boats in a tank.

In reality, Coast Guard officers were demonstrating life-and-death facts at their booth at the Maine Fishermen’s Forum trade show Saturday afternoon.

The Coast Guard officers had three sheet-metal scale models of lobster boats in the tank, each with slight but important differences.

One of the models had a hull with no cross-partitions. When the model was placed in the tank, water steadily glug-glugged through a hole that had been drilled through the rear, bottom of the boat. A Plexiglas deck allowed a clear view of the progression.

As the water entered the below-decks area, it flowed to the bow, causing the 18-inch-long boat to pitch forward. After about 90 seconds, the boat went quickly and dramatically to the bottom.

When two metal rods are placed on the deck – representing the weight of a load of lobster traps – the boat sinks in a mere 27 seconds.

A second boat features partitions running from one side of the hull to the other. But because small holes have been drilled through the center of the partitions, this boat also sinks quickly.

The third boat has partitions – subdivisions, the Coast Guard officers call them – which create watertight compartments. This kind of boat can take the filling of two of four compartments, and still float.

The Coast Guard’s Bob Moschetti explained that fishermen often modify their boats when replacing a drive shaft or steering rods to open the passage between the compartments, rendering the boats much more susceptible to sinking. Some fishermen drill holes through the compartments, because they don’t want water to sit in the bilge; a mistake, Coast Guard officials believe.

Meanwhile, on the proactive side, Moschetti used a representation of a boat’s deck to show how easily fishermen can improve their plight when a boat springs a leak. A 2-inch hole three inches below the waterline can bring 300 gallons of water per minute into the boat.

If the bilge pump is throwing 280 gallons of water back out, a simple “bucket brigade” to deal with the remaining 20 gallons per minute is not enough, Moschetti said.

Displaying a half-dozen scraps of wood, a few small sheets of rubber of varying thickness, and a hatchet and small hand saw, he showed how a crack in the hull could be kept from sinking a boat.

With the saw and hatchet, he trimmed the wood scraps and hammered them into the crack. The rubber sheeting and-or duct tape wrapped around finishes off the repair.

On another crack, Moschetti first jammed in a “favorite old Patriots sweat shirt,” followed by a wedge of wood. If the rubber is not available, a raincoat will do to wrap the patch.