The iron and steel bottom of the three-masted 1877 Elissa is nearly rusted through in places, prompting the U.S. Coast Guard to declare that the vessel is not seaworthy.

Officials at the Texas Seaport Museum in Galveston where the Elissa is berthed were astonished when a Coast Guard inspection earlier this year revealed the rotten hull.

The tall ship is inspected twice every five years, said John Schaumburg, museum assistant director. The latest inspection uncovered the worst rot since the tall ship was rebuilt in 1982, he said.

Very little corrosion was discovered during the previous dry dock in 2008, prompting surprise that the bottom could have deteriorated so quickly, Schaumburg said.

"Everyone's jaw just dropped," said Ed Green, one of about 100 volunteer crew members from Houston. About half of the volunteers are from Houston, as are most of the ship's visitors, Schaumburg said.

No one knows for sure what caused the rapid deterioration, but officials suspect that Hurricane Ike might be the culprit. Elissa rode out the September 2008 storm at a special mooring designed for violent storms, losing a sail, a spar and suffering some other minor damage.

The worst damage was unseen, Schaumburg said. Sea water eats into any metal, so 15 zinc "anodes" are fastened to the hull to draw off the corrosion. Naturally occurring electrical currents draw the corrosion to the anodes, Schaumburg explained.

Officials believe that an electric current, possibly caused by an electric line dislodge by the storm, may have caused the rapid erosion, he said.

The series of inspections were conducted at the Bollinger Texas City LP ship yard. Enough repair was done to allow the Elissa to sail back to Galveston, where it will remain until it celebrates the 30th anniversary of its reconstruction at a Greek shipyard.

By then the museum hopes to have raised $3 million to replace the hull as well as do a long overdue replacement of the fir deck and deck furniture, such as the companionway and skylight.

Schaumburg said officials won't know until refitting begins whether the entire hull below water will need replacement or only the 54 corroded steel plates, each 4 feet by 10-12 feet. If all goes according to plan, the Elissa will be sailing again in 2012, he said.

The museum is negotiating with a professional fundraiser and has established a system that allows $10 donations to be made by texting "ELISSA" to 50555.

Green, a 7-year volunteer, said it is vital that the Elissa keep sailing.

"The Elissa is indicative of the types of ships that brought commerce to Galveston and to Texas," Green said. "I think it's important to keep that part of history for everyone to see it."

harvey.rice@chron.com