By George Schwarz, Ph.D, Underwater Archaeology Branch, Naval History and Heritage Command
Editor’s note: This is part two in a series of blogs relating to Naval History and Heritage Command’s search for the Bonhomme Richard. You can read part one, here.
The 2016 Bonhomme Richard Survey project collaborators, including the U.S. Navy, French Navy and Global Foundation for Ocean Exploration, launched a survey for the remains of John Paul Jones’s devastated warship on Sept. 3, aboard rescue and salvage ship USNS Grasp (T-ARS 51), approximately 25 miles off Flamborough Head in the North Sea.
Arriving late Friday morning on the mission’s primary target, a mostly-buried wooden shipwreck located during a previous survey, the Naval Oceanographic Mine Warfare Center (NOMWC) and French Mine Clearance Dive Unit deployed small boats to conduct individual operations in separate areas. The first objective was to gather additional information on the shipwreck using side scan sonar systems from NOMWC’s Autonomous Underwater Vehicles (AUV). The second goal was to expand the known survey area using the French unit’s towed side scan system. Naval History and Heritage Command (NHHC) conducted a magnetometer survey directly over the primary shipwreck target to detect and map buried remains of iron objects such as ballast (heavy material, such as gravel, sand, iron, or lead, placed low in a vessel to improve its stability), cannon, and ship’s fasteners.
On-site Operations are Underway
Based on calculated drift models, past survey coverage areas spanning over 900 square nautical miles, and focused investigation of the primary shipwreck target, we were able to create a survey plan, which includes a shipwreck of particular interest. During our remote sensing, the shipwreck of interest, though largely buried under accumulations of sandy gravel basin sediment, revealed sections of intact wooden hull, an encrusted anchor and numerous iron concretions! Gathering more information on the objects of interest and the surrounding area will give us better clues as to the origins of this vessel and better prepare us for possible future diver or remotely operated vehicle (ROV) surveys.
The teams have been deploying in rigid hull inflatable boats, or RHIBs, with their survey equipment, working for several hours at a time before returning to Grasp to recharge equipment, swap crews and download data. The AUVs are launched into the sea and follow a pre-set grid pattern underwater to collect high-resolution sonar imagery, often struggling against the undersea current in the process. The French towed sonar system trails behind the boat at a distance of over 100 meters with the assistance of an onboard winch, and images considerable swaths of the seafloor on each pass. The magnetometer is also towed from one of the small boats, and follows narrow survey lanes to collect information on the presence and density of iron objects on or below the seafloor. The challenge of the towed gear is maintaining steadiness in the North Sea when deployed over 100 meters behind the boat in choppy seas, at a depth of approximately 60 meters. All of these instruments operate within meters of the bottom of the seafloor to obtain high quality and precision data.
Over the past five days, the survey teams have been steadily recording detailed seafloor characteristics over the planned areas of study. When the sea state has been too rough for survey operations, team members have been processing and reviewing collected data, fixing technical problems, and updating survey focus areas.
Beyond the immediate shipwreck area, a number of intriguing targets have been discovered which warrant further investigations. Despite a few weather delays and technical difficulties, this international collaboration continues to build more data and will add considerably to the current body of knowledge gained from past surveys—taking the project researchers another step toward finding Bonhomme Richard’s final resting place. Over the next few days, the teams will continue to work together to map the project areas and gather high-resolution seabed imagery before heading back to shore, where the fieldwork comes to a close and the process of data sorting and interpretation begins…