All inboard and outboard boats under 20 feet in length must have a maximum capacity, listed in both persons and pounds, stamped or printed on a clearly visible plaque. In addition, there must be a maximum horsepower shown for the engine on outboard boats. But there are likely to hold several surprises for boat owners and buyers.

Most boaters (myself included) believed that a maximum capacity, such as " Four Persons or 530 pounds", is the point beyond which a boat is likely to become unstable or will capsize. It seems obvious that the maximum horsepower rating is to keep us from speeding out of control with an oversized engine and, since these ratings are mandated by the U.S. Coast Guard, it's a logical assumption that these capacities are the result of their testing.

Wrong on all counts.

First, the maximum capacity is actually the number of people (or their total weight) that the boat will safely support if it is swamped.

Second, the horsepower rating has nothing to do with speed. "Horsepower has only to do with weight," says Philip Cappel of the Coast Guard. "We're not so much concerned about the speed but that the boat will float upright if swamped so that people can hold on to it until rescued. That's the whole reason for the flotation standard and why we say how many people can be on board. Horsepower only has to do with engine weight. If you put too big an engine on a boat, you throw the flotation off."

Last, the manufacturers set the Coast Guard capacity maximum, which they reach using an accepted formula, and they also determine the horsepower since they know how much engine weight will still allow their boat to float level.

It should be noted that the NMMA is much tougher on calculating weight maximums, as well as increasing the size of boats requiring flotation from the Federal standard of 20 feet up to 26 feet. The NMMA also has a test where the driver must crank the wheel 180 degrees in a split second. If the boat is not capable of such a turn through 90 degrees at full throttle without the driver losing control, then the NMMA requires a "Maneuvering Speed" placard be posted warning that sudden turns may cause a loss of control above a certain speed.