Mr. Hall explains that this picture is about scraping the bottom of boats, in this case a Block Island Double Ender, at very low tides Seaweed and barnacles slowed work boats. So this stuff needed to be regularly scraped off. Predictable very low tides would leave parts of Old Harbor, on Block Island, above water for 6 to 8 hours a day for several days in a row in the 19th Century heyday of these boats, which were essential for the islanders' fishing and transportation needs.
Double Enders were secured to the dock to wait for the extreme low tides. When they sat on the mud the work could be done. After scraping, antifouling paint was applied. Several fishermen and their wives worked together to get the scraping and painting done fast within the window of opportunity provided by the low tides.
"Think of it as fishermen's barn-raising. Over two days several boats could fully scrapped, '' Mr. Hall says.