Knowledge of lever arm distances from sonars, mounted on vessels, to systems such as Inertial Measurement Units (IMUs) and Global Navigation Satellite Systems (GNSS) is crucial for accurate ocean mapping applications. Traditional methods, such as laser scanners or total stations, are used to determine professional survey vessel lever arm distances reliably. However, for vessels of opportunity that are collecting volunteer bathymetric data, it is beneficial to consider survey methods that are less time consuming, less expensive, and which do not involve bringing the vessel into a dry dock. With the development of Unmanned Aircraft Systems (UASs) in the field of mapping, more cost-effective and quicker surveys can be conducted. To investigate the feasibility of conducting accurate horizontal lever arm surveys of vessels, while maximizing time efficiency in data collection, UAS surveys of a vessel with calibrated lever arm distances were conducted using both Structure for Motion (SfM) photogrammetry and aerial LiDAR while the vessel was docked at the pier. Estimates of the horizontal errors, for both methods, were obtained by comparing the horizontal distances between targets acquired by the UAS methods to ground-truth measurements of lever distances from survey-grade laser scanning of the vessel. With the use of Ground Control Points (GCPs), horizontal errors of both the photogrammetry and LiDAR models are on the order of centimeters, with the LiDAR model being slightly higher in horizontal error than most of the photogrammetry models.