Thomas C. Gillmer, a noted naval architect and ship historian who designed both Prides of Baltimore, the schooner Lady Maryland and other period replica vessels, died of complications from dementia Dec. 16 at the Hospice of the Chesapeake's Mandarin House in Harwood. He was 98.

Mr. Gillmer was born and raised in Warren, Ohio, not far from Lake Erie, where as a youngster he fell in love with boats and the water.

"I first made model boats when I was a kid. I had a friend, an older fellow, who was from Down East, somewhere in Nova Scotia. He was a good model builder and helped me with them," he explained some years ago in a profile in Good Old Boat Magazine, which described him as "one of America's most respected cruising boat designers."

"Later, he built me a 14-foot sailboat, a nice little lapstrake sloop. I learned to sail that by myself on Lake Erie when my family went to our cottage on the lake every summer," Mr. Gillmer said in the interview.

After graduating from Warren High School, he attended the Naval Academy, from which he graduated in 1935.

Mr. Gillmer recalled in the interview that during the 1930s when he was a student at the Naval Academy, the Annapolis harbor was filled during the winter months with skipjacks. He would watch them sail out in the early morning light for a day of oystering.

"It was a beautiful sight. That sight alone probably had as much impact as anything else in my interest in boats," he said.

After graduation, he served on the cruisers USS Raleigh and Savannah in the Pacific and Mediterranean during the late 1930s.

In 1941, he left active sea duty and established the department of naval architecture and marine engineering at the academy, where he was professor of naval architecture for the next 27 years.

During his years at the academy, Mr. Gillmer, in addition to teaching, confined his design efforts to large ships. He also wrote "Modern Ship Design," which is still used at the academy as a standard textbook.

After retiring in 1969, he established Thomas Gillmer, Naval Architect Inc., in Annapolis.

He realized the potential of such then-new construction materials as fiberglass and adapted them in his marine designs. One of his first acclaimed designs, the Seawind ketch, became the first fiberglass boat to circumnavigate the world; eventually more than 200 of the vessels were built.

Other successful designs included the 32-foot Southern Cross and the Blue Moon, a 24-foot English Channel cutter.

"There's a certain amount of art in naval architecture," he told The Baltimore Sun in a 1986 profile. "And I enjoy the historic aspect, having to deal with a different building media, a wooden ship. There are more pieces. It's just more interesting."

In the early 1970s, Mr. Gillmer changed course and started concentrating on designing and building seagoing reproductions of historic vessels.

In 1975, Baltimore officials finally were able to approve a budget of $365,000 to build a replica of an 1812-era Baltimore clipper as a floating goodwill ambassador for the city.

They approved the plans of Melbourne Smith, an Annapolis artist-sailor, who had teamed with Mr. Gillmer to design the vessel, the Pride of Baltimore. It was built at an improvised shipyard along Light Street in the Inner Harbor.

"Smith had the vision, but Gillmer had the credentials to do the actual design," Tom Waldron wrote in a 2004 article in The Baltimore Sun. Mr. Waldron later wrote "Pride of the Sea," which recounted the birth and death of the ship.

The finished Pride was launched in 1977.

"I worked with him for many years and hired him as the architect for Pride I and Pride II. He brought great research to the work and was the best naval architect in the field that I knew," Mr. Smith recalled recently.

Fred Hecklinger, an Annapolis marine surveyor, was a friend and professional acquaintance.

"Tom was a very competent and respected architect and marine engineer," said Mr. Hecklinger.

The Pride sank in 1986 in a storm off Puerto Rico that resulted in the loss of four crew members.

"It was a micro-burst that suddenly came and laid her down," Mr. Hecklinger said.

Pete Lesher, a noted Chesapeake Bay maritime and boat-building historian and curator of the Chesapeake Bay Maritime Museum in St. Michaels, where Mr. Gillmer was a member of its board of governors, said, "He rigorously defended his work and his reputation, which was publicly challenged in the investigation of the sinking of the Pride of Baltimore in 1986.

"There was a very thorough Coast Guard investigation, and the outcome was that the sinking was not blamed on any design flaws or crew inexperience. The sinking was the result of an extraordinary weather event," he said. "In the end, both he and the sailors on the Pride were exonerated."

Mr. Gillmer designed Pride II, which was launched in 1988 as an oceangoing vessel, to exacting Coast Guard licensing requirements.

When asked about Pride II's subsequent worldwide voyages, Mr. Gillmer told Good Old Boat Magazine that "she has been most successful."

Mr. Gillmer went on to design the Living Classroom Foundation's Lady Maryland, a replica of a Chesapeake Bay pungy schooner.

He was also hired by the Navy to evaluate the condition of the USS Constitution - "Old Ironsides" - which was restored in time for its 200th birthday in 1997.

One of Mr. Gillmer's last projects was the design and construction in 1998 of the replica tall ship Kalmar Nyckel, which sailed from Sweden to Delaware in 1638 with settlers who landed in present-day Wilmington.

The Chesapeake Bay Maritime Museum will become the repository of Mr. Gillmer's design drawings, Mr. Lesher said.

"I found Tom to be both gentle and soft-spoken in my interactions with him, but I recall that he could have a sharp pen when he saw work that did not measure up to his standards," Mr. Lesher said.

"Above all else, he was a very generous man who saw potential in our museum and helped it become a more professional organization," he said.

Mr. Gillmer was also the author of "Sailing with Pride" (1990); "Old Ironsides: The Rise, Decline and Resurrection of the USS Constitution" (1993); and "A History of Working Watercraft of the Western World" (1994).

His hobbies included walking around boatyards, making pottery and carving, said his son, Charles Gillmer of Reedville, Va.

Mr. Gillmer, who lived in an Annapolis house he designed and built in 1947, was married for 62 years to the former Anna Derge, who died in 1999.

A memorial service will be held at 10:30 a.m. Jan. 15 at St. Andrews Chapel at the Naval Academy in Annapolis.

Also surviving are his wife of 10 years, the former Ruth Newsome; a daughter, Christina G. Erdmann of Denver; two stepsons, Albert Williams of Cary, N.C., and Alvin Williams of Fort Myers, Fla.; four grandchildren; two step-grandsons; and five great-grandchildren.