When built in 1909, the Duwamish was a steam powered riveted steel hull vessel. She was 120 feet long, 9.6 feet deep with a 28-foot beam (28 feet wide). The Duwamish is registered at a gross tonnage of 322 tons. Although her decking is steel, it was originally covered in teak. She was built to work in Seattle's waterfront. This consisted of among other things shallow waters and mudflats. Because of this, the Duwamish has no external keel giving her a flat bottom. She was also given a projecting "ram" bow designed to sink burning wooden boats of the day in the event that an uncontrollable ship fire threatened the waterfront.
Prior to 1949, the original design was given several modifications with the most notable being the water manifold was moved above decks to prevent it from flooding the vessel should the manifold break. However, in 1949, the Duwamish underwent a major rebuild that, with minor exceptions, brought it to its current form. Her bow was reconfigured to more conventional lines and her steam power plants were replaced with three Cooper Bessemer 900 hp diesel engines. These were coupled to General Electric 600 volt DC generators. These same GE type generators also serve as the electric motors driving the propeller shafts and two DeLaval centrifugal pumps. The pumps are rated at 11,400 gpm each giving the Duwamish a total capacity of 22,800 gpm. This is equivalent 1.6 tons of water per second. Of the three Cooper engines, one was designated for the shafts only, another for pumps and the third could be switched to either the shafts or pumps. With two engines on the shafts, the Duwamish has a maximum speed of 14 Knots.
The water is delivered via a manifold system that runs most of the length of the boat on either side of the trunk deck. Both sides join by way of two separation valves with one located behind the pilothouse and the other in front of the aft cabin. There are six hydrants as well as three monitors per side along with a monitor on top of both the pilothouse and aft cabin. The aft cabin monitor can deliver 7,000 gpm while pilothouse monitor produces 11,000 gpm. Although the monitors are original, they have been modified to work with a hydraulic control system.
Controlling the propeller shafts and pumps from the pilothouse is done using a telegraph system. Commands are received in the engine room where the engineer is manning two electric control panels.Once the engineer has set the controls, he/she answers back on the telegraph. Steering is electric assist with a mechanical override controlling two (under sized) rudders.
