Circle Line VII was launched around 1943 at Kearny, New Jersey. She looked similar to the LCI(L) (Landing Craft, Infantry, Large) shown below. These ships were built to transport troops onto beaches, often while under enemy fire.
|In order to land close enough for the men to get ashore from the bow ramps or gangways, a shallow-draft, flat-bottomed hull was needed. Sea chest cooling water intakes were on the sides below the waterline, rather than low on the bottom as on most ships. The sea chests also had an access hatch (seen at right) located in the engine room above the waterline to enable cleaning while underway.|
The propellers and shafting were partially protected with a tunnel-like shape in the hull near the stern. This also kept the draft to a minimum. A large stern anchor was led out as the vessel approached the beach, and was used to help pull the vessel off the sand.
While LCIs were not intended to be disposable, it was realized during the design phase that due to their hazardous mission a significant number of them might be lost. That fact, coupled with the large number of LCIs needed as soon as possible for the war effort, made ease and economy of construction mandatory.
Simple framing and flat plating design allowed relatively inexperienced welders to make solid joints. The fairly small size (just over 150' length) permitted building and side launching in modest shipyards. And standardization of equipment enabled quick mass production.
One major problem was designing the propulsion machinery, which may take many months from calculations to final tests. Enough power was needed (about 1200 HP) to enable the vessel to beach herself and still be able to back off after discharging her troops. Yet the Navy just did not have the time to spare developing a new engine plant.
Fortunately, a quick solution was found. A short time previously, the hull for another vessel type had been ready for testing before its two main engines, of similar horsepower, had been finished. Rather than wait, a test setup consisting of four small engines in parallel was used for the initial sea trials. Although this design was something that was very quickly thrown together (in only three weeks, and long before computer-aided design and manufacturing techniques!), and was only intended as a temporary substitution, it worked amazingly well.
Many engineers at the time were sure that tying four separate engines together into a common reduction gear would develop critical harmonic oscillations that would break crankshafts and cause other problems. But the clever design allowed for that --- by using dry disc-type clutches for each engine with pressure plate spring tension calculated to be just high enough to hold under maximum developed engine torque, any abnormal critical speed vibration would cause the clutch to slip just enough to make the momentary oscillations go out of phase with each other. The individual clutches also enabled engines to be taken off line and serviced without stopping the shaft on that side. I have heard stories of LCIs making it to port on only one or two engines, with parts cannibalized from the others to keep them going.
| The engines chosen for that setup were GM 6-71 diesels,
perhaps the greatest and most important engine design in history.
Manufactured by the thousands for use in buses, they were immediately available, rugged and reliable, as well as simple and easily repairable.
|To minimize the chance of exhaust noise being heard by the enemy before the LCI's neared the beach, the sea water from each engine's heat exchanger was used to both cool and quiet the wet-type mufflers, which were Maxim silencers made with baffles just like the version used to quiet gunfire. The picture at left shows the clear exhaust and cooling water going over the side from the four port engines.|
|Each bank of engines has a gauge board with a coolant temperature gauge, lube oil temperature gauge, lube oil pressure gauge and low oil pressure warning light for each engine. Below them is a tachometer for the shaft on that side.|
|A pair of 2-71's, two cylinder versions of the main engines, is used for the two 20 KW ship's service generators.|
The LCI's main power was 120 volt direct current, distributed through the main switchboard shown here. Although AC power was added by Circle Line to power the concession and other modern amenities, DC is still used for almost all the pumps, steering and other machinery.
The main engines of any vessel are a significant part of the overall cost and design considerations. By using a two-stroke design, the power-to-weight ratio was superior to many of the more common marine engines of that era. The basic idea was developed by the Winton Engine Corporation, in cooperation with General Motors. They developed the Winton 201A for use in railroad locomotives. Winton came up with the first engines with the unit injector, uniflow scavenging, and welded-block construction, all novel ideas at the time. A similar design, on a smaller scale, is used for the 71 series diesels, which in addition to propulsion usage are also very common as generator prime movers on smaller ships. The 71 series was available in sizes from the 1-71 one cylinder (special Navy order for small generators) to V-16 configurations, and is still used extensively today.
So as to further simplify the reduction gear design, it was made without reversing capability. Controllable pitch propellers were used instead. These propellers turn constantly, with the blade angle varying from ahead, through feathering, to astern pitch.
| The pitch motor is located between the forward two
engines. It runs off the 24 volt starting batteries so that the LCI
could maneuver even if it lost both main generators.
The vertical motor turns a horizontally-mounted shaft via bevel gears. The rotating motion is converted to fore-and-aft movement via a screw and traveling nut assembly. This slides a rod fastened to a thrust collar that connects to the main pitch rod and transmits its longitudinal motion to the rotating pitch rod (inner propeller shaft).
The hollow main propeller shaft transmits thrust from the bull gear to the propeller, while the inner shaft or rotating pitch rod extends through the gearbox all the way back to the propeller hub, where it bolts to a triangular rack which meshes with sector gear segments machined into the individual blade shafts where they enter the propeller hub.
Due to the shape of the propeller blades, they naturally seek the ahead pitch as longitudinal tension on the pitch rod is eased. This minimizes stress on the mechanism since the propellers are running ahead most of the time while underway. When a stop or astern bell is ordered, the pitch rod pulls forward to feather or set the blades for backing.
|LCI steering is electric, with either of two motors turning a pinion meshed to a geared quadrant. This turns the tillers on the twin rudder stocks. Electrical limit switches and shock-absorbing springs protect the rudders from shock and overtravel.|
|Each motor has a DC controller with left and right contacts, an accelerating contactor, and dynamic braking contacts that help stop the motors quickly. Both motors also have magnetic clutches to disengage them when off line.|
|To enable emergency steering if both main generators were disabled, a hand steering station on the quarterdeck can be manually clutched in. A sound-powered phone enables the Captain to give steering commands to the aft steering station.|
Listen to LCI 191's eight engines running at cruising speed (MP3 audio)
Listen to LCI 191's eight engines briefly maneuvering (smaller MP3 audio file)
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Copyright © 2002, Brian Bailey, W4OLF
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