Boston — As the summer heats up, boating enthusiasts are taking to the water in near-record numbers. So are boat thieves.
Across the country, boat owners, insurance companies, and law enforcement agencies are increasingly concerned about the growing number of boat thefts.
The FBI received 12,710 reports of boat theft in 1981 - an increase of nearly 40 percent over the two preceding years. But this statistic doesn't tell the whole story. David MacGillis, chief investigator of the Florida Marine Patrol, says there is a significant gap in the reporting of boat thefts to the FBI's computer system - perhaps as much as 75 percent. Florida, the state where the most thefts occur, records fewer than 50 percent of theft cases. Consequently no one knows exactly how many boats are stolen each year.
Another problem is insurance fraud, owners sinking their boats to collect insurance money.
Both the battle to prevent boat thefts and the recording of such thefts are hindered by the lack of a permanent means of identifying boats, as well as the lack of titling laws.
A 1972 federal law requires boat manufacturers to affix identification numbers to their boats. Many manufacturers have complied. However, Mr. MacGillis estimates that only 100 out of more than 6,500 manufacturers permanently affix ID numbers similar to those found on all automobiles. The law has not been enforced.
Only 13 states have boat-titling requirements. One of them, Florida, finds that because there are so many manufacturers and types of boats, including many home-made boats, registering them can be complicated.
Without standardized identification numbers and registration requirements, Mr. MacGillis says, recovering a stolen boat is very difficult. Tracing a boat from one state to another is all but impossible. Indeed, fewer than 20 percent of boats reported stolen are recovered (compared to 60 percent for cars).
However, both law-enforcement agencies and insurance companies are working on various measures to combat the problem, including the following:
* Many insurance companies now offer their policy-holders suggestions on how to protect their boats, including information on available alarm systems, where best to dock, and how to protect it while in storage.
* Aetna Insurance Company of Hartford, Conn., has started the ''Stolen Hull Intercept Program'' (SHIP) to help recover boats valued at $25,000 or more. They distribute eye-catching, full-color posters of stolen boats, and offer substantial rewards for information leading to recovery.
Since SHIP began, the company recovery rate has jumped to 30 percent, saving more than $300,000. The company says SHIP is a deterrent; claims are down this year.
* The National Automobile Theft Bureau, supported by many of the country's major insurance companies, is pushing for better record keeping in the insurance industry and for more cooperation between insurance firms and law-enforcement agencies.