Despite her innovative machinery, the Luna was built as a wood-hulled tug with all of the features typical to Boston Tow Boat tugs. Wooden hulls were preferred because they were cheap, relatively long-lived, and had "give" when bumped and crunched by ships and barges. Riveted iron tugs, on the otherhand, could be dented and leak. The welding of steel hulls was also in the early stages in 1930 when the Luna was built and was not preferred by Boston Tow Boat.

The Luna features a one-level pilothouse, side ladderways from the main deck to the boat deck, and two masts that were typical of Boston Tow Boat tugs. The tug was delivered with a white hull, green and brown trim, black rubbing guards, clear varnished deckhouse and pilothouse, and white trim with green upper decks. Fenders were knitted rope at the stem. The stack was black with the white "T" of Boston Tow Boat, a carry over from the original company, the T Wharf Towboat Company in downtown Boston. Click for a schematic drawing of the engineroom.

Principal dimensions
Particulars
Main machinery
Hull Construction
Outfit

Principal Dimensions (top)

• Length, over all timbers and rub rails: 100 feet
• Length, waterline: 90.3 feet
• Beam, overall: 27 feet (approx.)
• Depth of hull, midships: 18 feet (main deck to keel)
• Draft, fully loaded: 12 feet
• Draft, light condition: 11 feet 4 inches
• Air draft, light condition, masts folded: 27 feet
• Displacement, full load: 325 tons
• Displacement, light condition: 315 tons
• Gross tonnage: 165 (hundred cubic feet)
• Net tonnage: 112 (hundred cubic feet)

Particulars (top)

• Typically crewed as Single Shift Day Boat: Master, Engineer, Cook, Deckhand, Oiler (Total 5 persons)
• Occassional Crew as 24 Hour Boat: Master, Mate, 2 Engineers, Cook, 2 Deckhands, 2 Oilers (Total 9 persons)
• Accommodations: 1 master in cabin behind wheelhouse; 2 engineers in stateroom in deckhouse (starboard); 2 mates in stateroom in deckhouse (port); four crew in forecastle on pipeberths.
• Fuel Capacity: 12,000 gallons of distillate diesel fuel (No. 2 grade) (40 tons) in four riveted fuel tanks in the engine room
• Lube Oil Capacity: bulk storage in one vertical, cylindrical tank inside deckhouse
• Potable water: in one rectangular tank in forefoot below forecastle
• Ballast water tanks: none
• The LUNA’s hull is essentially one long compartment, subdivided by non-watertight bulkheads

Main Machinery (top)

• Two Winton Model 130 diesel engines with 6 cylinders, four stroke cycle, 300 rpm, airless (mechanical pressure) fuel injection, approximately 325 hp each, total 650 hp, weighing 21 tons each.
• Two General Electric DC generators, one mounted aft of each diesel engine
• Two General Electric DC exciters, one mounted aft of each generator
• One General Electric DC motor, double armature mounted in series on the same shaft, approximately 650 hp, mounted forward in the engine room
• One switchboard consisting of a stone slate front dagger switch system with rheostat controls mounted in the aft end of the fidley (upper engineroom). Stations controlled generators, exciters, motor, pumps, lights.
• Two DC compressors and four high pressure compressed air tanks for engine starting
• Various DC pumps for: salvage, bilge, fire fighting, fuel oil transfer, engine cooling, fresh water pressure
• Lube oil filters (quadruple container) and lube oil cooler (originally two coolers mounted ahead of each engine)
• Battery box and battery charger in fidley. Batteries provided power to create the compressed air to start the tugboat from a "cold" condition
• CO2 bottles for fire suppression mounted in fidley
• Electro-mechanical steering motor pulling wire through sheaves to aft rudder quadrant
• The propeller shaft runs from the aft end of the motor to a four-blade propeller
• The main machinery was secured to large steel beams that were in turn secured to heavy timbers near the keel and lower frames
• 8 speeds ahead, 8 speeds astern

Hull Construction (top)

• All the wood used in the Luna would extend as a one-inch thick, twelve inch wide board for about 15 miles!
• Hull is substantially crafted from white oak. Frames are on 22-inch centers, created from double sawn futtocks 6 inches thick and 12 inches moulded (depth). Trunnelled together, these frames are 12 inches thick and 12 inches wide.
• Hull exterior is planked with white oak. Four large broad strakes run from the main deck down. Typical side planking below them is 8" by 3".
• The interior ceiling (planking) provided a second layer of water protection and strength and is made of long leaf yellow pine
• Keel, deadwood aft, horn timber, and stem frame are built up of heavy white oak, typically 12"x12"
• Two rubbing guards faced with steel run along the hull, one all the way around the main deck, the other about two-thirds of the way aft
• Main deck wasplanked with Douglas fir
• Boat deck and pilothouse roof are planked with cypress
• The bulwarks were faced with cypress planks; and replaced with white cedar
• The hull is caulked with oakum over cotton, sealed with compound
• Planking and ceiling planing are secured to the frames with locust trunnels ("treenails") that are driven tightly into holes in these structural members and secured with wedges
• Heavy structure, rub rails, knees, and clamps are secured with heavy galvanized iron clinch bolts and drift bolts that are hammered, riveted, or turned into place
• The deckhouse is primarily built of cypress
• The boat deck and pilothouse roof are covered with canvas glued to the decks for watertightness
• The tug’s rudder is fabricated from steel plates

Outfit (top)

• The LUNA has two folding masts. The forward mast carries three "towing lamps": two lit meant the tug was pushing a cargo; three meant it was towing a vessel astern. The original lamps were oil lit and supplied from a locker on the boat deck The aft mast flies the American flag.
• The galley is located in the forward end of the deckhouse, with oil-fired range and oven and early General Electric refrigerator. A table and seats for five people are forward in the galley.
• A single toilet and sink are located in the deckhouse, starboard side
• All accommodation compartments have porcelain sinks
• There is no shower on the LUNA!
• Two cast iron "H bitts" and four quarter bitts constitute the towing gear
• In service, electronics consisted of shortwave (VHF) radio telephone
• A galvanized iron sheetmetal lifeboat was mounted under davits on the boat deck, on steel gallow frames, over a wood-framed skylight. The base of the davits are on main deck.
• Two cowl ventilators on the boat deck pulled air to the engineroom, while a cowl ventilator and a wooden vent on the foredeck pulled air to the focsle and aft to cool the electric motor
• The tug was heated by an oil-fired furnace on the port side of the engine room, circulating water through a hot water radiator system.
• A small lazarette for hawser storage was located beneath the aft deck, abaft the engineroom. A small circular manhole permitted lines to be led up and down.
• The LUNA had no provisions to hold or process waste water or oil