Washburn & Doughty, a boat builder based in East Boothbay, Maine, USA, has been selected by Louisiana-based Harbor Docking and Towing to build two new 93ft (28.3m) hybrid Z-drive tugs, called Harbor Assist Vessels (HAVs). The new HAVs will feature Caterpillar Marines stem-to-stern hybrid propulsion system, which includes twin Cat 3512E main engines, each producing 2,550hp at 1,800rpm, two C18 generator sets, sparking 565kW of electrical power, a C7.1 generator set, producing 200kW of electrical power, shaft lines, MTA 628 azimuth drives with Cu-Ni-Al bronze 2,800mm propellers and water-cooled thruster motors. The system also includes the switchgear, variable-frequency drives (VFD) and a fully integrated control system. The main engines power the main thrusters via a shaft line. Between the main engine and the thruster there is a main clutch mounted in a bell housing attached to the engine. On the back end of each thruster there is a thruster motor operated by a VFD controller. The system has four main operational modes: electric, diesel, hybrid and FiFi (firefighting), whereby the firefighting pump is powered from the front of starboard main engine power take-off (PTO). The vessel will have three main deck lanes, for a capacity of 23 cars or a mix of cars and trucks, as well as 250 passengers and accommodation for six crew members. We are proud to have earned Harbor Docking and Towings business and we look forward to working with them on this innovative project, said Bruce Doughty, Washburn & Doughtys chairman. Cats hybrid system is a great fit for our 93ft tugs. The vessels are scheduled to be delivered in Q4 2018 and Q1 2019 respectively.