Why document your boat with the Coast Guard? After all, it costs at least $133 (and could include other small fees) and adds more than a little paperwork to your life.

The answer will depend on what you plan to do with your vessel. Documentation, which is required for many commercial vessels, is optional for recreational boaters and most people choose to simply register in their own state. There were more than 17.7 million recreational boats in use in the United States last year, according to the National Marine Manufacturers Association. Only about 245,000 were documented.

But documentation does have advantages, most of which apply when vessels change hands. It can help owners obtain preferred financing -- many lenders now require documentation -- and make sales easier by establishing ownership. For those traveling offshore, documentation also insures that your vessel is recognized as hailing from the United States.

"A certificate of documentation is conclusive evidence of nationality for international purposes," said Thomas Willis, director of the Coast Guard's National Vessel Documentation Center (NVDC). "There are some countries where it's a lot easier to get a cruising permit, so you don't have to clear Customs every time you turn around."

Financial concerns also play a role. If the owner is in debt and the boat is sold, documentation gives the bank priority status, insuring that they will receive their money before other creditors such as boat yards and mechanics, Willis said.

"The reason most people document recreational vessels is that their banks insist on it," he said, adding that, "If it's documented and the mortgage is recorded, then the yard's going to have to wait behind the bank. For the banks, this is an important issue."

If your boat is not documented with the Coast Guard, it must be registered with the state in which it is docked in order to avoid penalties. Even if it is documented, some states still require registration. To document a boat, you must be an American citizen and be able to demonstrate ownership. Forms and instructions are available on the National Vessel Documentation Center website (see link below). The process can take less than a week for new boats and as long as a month for used vessels, Willis said.

There are four types of documentation, including a recreational category, a fishing category, a registry endorsement for vessels conducting foreign trade, and a coastwise registration for vessels that transport cargo or passengers. Commercial boats may also have additional regulatory requirements. While a commercial boat may be used for recreation, recreational boats cannot be used for commercial purposes, and the fine for doing so can run as high as $10,000 a day.

Sound complicated? Companies specialize in jumping through the hoops for you, for a fee.

"It's a lot less painful to hire a documentation service," said Kathi Krencik, president of the American Vessel Documentation Association and manager of The Mary Conlin Company, a vessel documentation firm. "If you don't fill out everything exactly, they can kick it back and keep the fees if you don't resubmit in a timely manner."

Willis disagrees that the process is difficult.

"If you look at our forms, there's the application for documentation," he said. "That's the only form you have to fill out. If you know your name, your social security number and what you're going to call the boat, you ought to be able to go ahead and fill out the paperwork."

The process was more complicated prior to 1994, Willis said, when it took many more forms to get a boat documented. "They are aware of all the negative feedback and comments they are getting from mariners," said Nadine Santiago, a Coast Guard spokeswoman.

After registering, you will also have to break out the paint. The number assigned to your vessel must be marked inside the hull in printed block letters at least three inches high. On the stern, the boat's name and hailing port must be marked in letters at least four inches tall. After completing the process, take a deep breath and mark your calendar. Documentations must be renewed yearly, but there are no additional fees if you file on time.