Wooden "shiplap" on the water

Why "Edge-rabbeting of bottom planking" called in New World "shiplap"? (sub-arch Underwater Archaeology forum) The "shiplap" I know was used in a church in Centereach/Lake Grove, NY now a Town of Brookhaven Landmark, near the "Good Steer" restaurant. Once known as "New Village" it was settled by shipbuilders et al of nearby Setauket, NY. The floors are "shiplap" constructed, and some of the wallpaper removal revealed some of the early carpenter's pencil markings. In Setauket about 25,000 tons of wooden ships were made and in the adjoining harbor, Port Jefferson (once also known as "Drowned Meadow") about 45,000 tons were made as the focus shifted apparently in the 19th century. Liverpool mail "packets" (sailing ships mostly started and run by Quakers there and in New York City) put in there every two weeks in the 19th century and the port of New York. The "infamous" luxury yacht "Wanderer" was built there, bought by a Louisiana cotton merchant, and conducted slave trade between Africa and Jekyll Island, Georgia after being thought harmless by British blockaders of Africa for slavery (1858 Wikipedia). The National Parks Service (?) plaque at Jekyll Island was placed around 1963, next to a large iron pot, where the survivors were first fed. A written argument went on about its place of building, wrongly attributed to Port Jefferson at first, actually bult by Captain Brewster Hawkins in Setauket, and a historic site I've partly investigated archaeologically (written correspondence available in the collections of the Emma Clark Library, Setauket, NY). An ascendant (or indirect descendant) proved it to the historians. The confusion was over the construction and concealment of large water tanks placed behind the luxury accommodations in Port Jefferson, NY by metalworkers there. Maybe it was used in old church construction first? Often churches look like inverted ships. George Myers "I have yet to see any problem, however complicated, which, when looked at in the right way, did not become still more complicated." Poul Anderson