Figure 1. The sternwheel paddle steamer Natchez IV approaching her berth at the Toulouse Street Wharf, New Orleans, December 10, 1995.
Figure 2. The boiler room showing two oil-fired Cleaver Brooks firetube boilers which provide the Natchez IV with high pressure steam.
Figure 3. Tandem compound engine showing starboard high pressure steam chest, 15" high pressure cylinder, and piston valve.
Figure 4. Tandem compound engine showing starboard low pressure steam chest, 30" cylinder, piston valve and connecting rods.
Figure 5. Compound engine showing starboard low pressure cylinder, piston rod and pitman.
Figure 6. Paddlewheel showing port-side pitman and crank.
STERNWHEEL PADDLE STEAMER NATCHEZ IX
by Damian Nance
( I.S.S.E.S. Bulletin Vol. 18 No. 2)
For the past twenty years, the sternwheeler Natchez IX has been offering visitors to New Orleans, Louisiana, the rare opportunity to experience the "Old South" aboard a Mississippi river boat. With her classic lines and appealing design (Fig. 1), she is rightly considered one of the most attractive of the slowly growing fleet of replica steamboats in the United States. One of only six completely steam-operated sternwheelers now working on the river, the Natchez IX is a reminder of the hundreds of such vessels that plied the Mississippi in bygone days.
Owned by the New Orleans Steamboat Company, the Natchez IX was completed in March, 1975, for a cost of $4.7 million by the Bergeron Shipyard, located in Braithwaite, Louisiana. She is 286' long, with a 40' beam, an 8' draught, and a gross displacement listed as 1,384 tons. Despite all-steel construction, required by current U.S. Coast Guard regulations, Natchez IX presents the appearance of a classic Mississippi steamer. Her tall stacks, high decks, and pilot house located amidships well aft of the stacks are typical of late nineteenth century steamboat designs used on the lower Mississippi. Engines and paddlewheel shaft are from an older vessel, which further adds to her historical authenticity. Running fully half her length, the sweeping lounge on the second deck, with its paneling, brass chandeliers, and live Dixieland music is a nostalgic sight indeed!
Power for the sternwheel is provided by a pair of horizontal tandem compound engines, each having a 7' stroke. These engines were custom built about 1925 for the sternwheel towboat Clairton, and served until 1965 pushing barges for U.S. Steel. Installed in Natchez IV, the engines are now open to the public. Piston valves control steam admission to both high and low pressure cylinders, which have diameters of 15" and 30" respectively. At 16 rpm, the combined power from both engines is rated at 1,600 horsepower. High pressure steam at 200 psig is provided by two oil-fired Cleaver Brooks firetube boilers (Fig. 2). One of these is usually sufficient for normal operating conditions, with the second boiler standing by in reserve. When cruising at 10-12 mph, consumption of number 2 fuel oil is reported to be approximately 100 to 125 gph.
Steam is supplied to the engine's high pressure steam chests through a single throttle valve, where it is directed first to one side of the high pressure pistons, and then to the other by piston valves (Fig. 3). While boiler steam is applied to one side of the high pressure piston, the partially expanded steam on the opposite side is exhausted to the low pressure steam chest (Fig. 4) where it is directed to the proper side of the low pressure piston by another piston valve for further expansion. At the same time, the steam on the other side of the low pressure piston is exhausted into the surface condenser, where circulating river water removes much of the steam's remaining heat. The cooled steam condenses and creates a vacuum on the exhaust side of the low pressure piston, which adds to the force of the expanding steam on the other side, and thus increases engine power and efficiency. Lubricating oil is filtered out of the condensed steam, and the condensate is returned to the boiler at a rate of 20 gpm for re-evaporation. Color-coded connecting rods drive the Walscheart valve gear, opening and closing the valves with the appropriate lap and lead time, and provide a means of reversing the engine.
The piston rods emerging from the stern ends of the low pressure cylinders are terminated in massive crossheads, from which their movement is transferred to the sternwheel cranks by way of connecting rods or "pitmans" as they are usually called by Western Rivers engineers (Fig. 5.). The two cranks, located on opposite ends of the sternwheel's hexagonal axle (Fig. 6) are set at a 90 degree angle (quartered) to obtain a more uniform turning moment. Constructed in five 14-spoked segments, the sternwheel measures 25' by 25' and is of all-steel construction (except for the paddles, which are made of oak planks).
From her berth at the Toulouse Street Wharf, located in the heart of the French Quarter, the Natchez IV operates three two-hour trips daily, plus a longer evening dinner cruise. Steaming forth aboard Natchez IV on one of these short but nostalgic river cruises, heralded by music from her 32-note calliope and deep echoing blasts from her melodious 3-note chime whistle, is an experience without which no trip to the "Big Easy" is complete.
Editor's Note: The Delta Queen Steamboat Company's recently completed American Queen, has twin tandem compound engines with rpm, cylinder size, and stroke dimensions exactly equal to Natchez IV. The American Queen operates with 275 psig at the throttle, vs 200 psig for Natchez IV, yet claims only 1,400 horsepower for both engines, versus Natchez IV's claim of 1,600. Using a card factor of .8 and a ratio of expansion of 4, I computed American Queen's indicated horsepower to be only 1,321. For Natchez IV using the same assumptions, engine dimensions, and 200 psig, I compute the MEP = 101psi and 969 indicated horsepower for both engines. I think the claimed horsepower of 1,600 is high. What do our readers think?