A mounting system rigidly attaches a towing frame to a vessel deck, and includes a base having an arcuate top surface and a bottom surface conforming the deck. A joint member rigidly attached to the towing frame has an arcuate surface mating with the arcuate top surface of the base. The joint member has a cavity and a threaded bore extending through a wall for accessing the cavity. The threaded bore of the joint member is aligned with a bore extending through the base. A threaded shaft extends through a hole in the deck, through the bore in the base, and is threaded into the threaded bore of the joint member. A fastener attached to the shaft is used to bias the joint member against the base, and base against the deck for rigidly securing the joint member and thus the towing frame to the deck.