INSTALLATION OF THE FIRST bow thruster in a standard American Great Lakes bulk freighter was completed recently at Fraser-Nelson Shipbuilding & Dry Dock Co. of Superior, Wis. The Motor Ship Henry Ford II, 14,000-ton ore carrier, has been equipped with a 500 hp controllable pitch propeller type bow thruster to increase the vessel's maneuverability in confined channels and in docking and undocking situations.

The Ford's bow thruster is a KaMeWa type manufactured by BirdJohnson Co., South Walpole, Mass., and is the first unit of its kind on the Great Lakes to be direct-driven by a Diesel engine.

Bow steering devices are relatively new on the Lakes-the first thruster units having been installed in two self-unloading vessels in 1961. The following winter (1961-62) four more self-unloaders were equipped with electrically-driven thrusters.

A bow thruster, simply speaking, is a transversely mounted propeller located in the middle of a tunnel that extends through the ship from side to side near the bow and below the waterline. The KaMeWa thruster features a controllable pitch propeller that can force a stream of water out either side of the tunnel thus impart

May 1963

ing lateral motion to the forward end of the ship. The unit is fully controlled from the ship's pilothouse, and the direction, either left or right, and the degree of force, can be regulated with a single lever.

Head-on view of M/S Henry Ford II in dry dock showing bow thruster tunnel openings in each side.

BOW STEERING

The M/S Henry Ford II, built in 1924 at Lorain, Ohio, has a 612 foot length, 62 foot beam, and depth of 32 feet. A normal ship must rely on forward motion through the water to provide steerageway, but with the bow thruster the head end of the vessel can be swung to right or left regardless of whether the ship is moving, stopped, or moving at dead-slow speeds.

This ability to "steer" the bow will be a big advantage when it is necessary for the ship to negotiate tight 90°, and even 180°, bends in rivers leading to some of the ore unloading docks. Also, where narrow canals must be traversed, and bridge abutments cleared while the ship moves at slow speed, the thruster will enable the captain to make adjustments in ship's heading without increasing speed through the water. Landing alongside docks and lock walls will be accomplished with much less rubbing and bumping by use of the thruster, and backing for long distances will be facilitated. There are a number of docks on the Great Lakes where the big ore carriers must turn 180° in confined basins as they leave in order to line up for the harbor entrance.

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HULL ALTERATIONS

The bow thruster is located in the blind hold, just aft of the forepeak bulkhead. It is approximately 36 feet back from the stem and 5 feet above the keel. The tunnel, 44 feet long and 5 feet 51⁄2 inches inside diameter, was fabricated in shipyard shops out of 3/4 inch steel plate. The tunnel flares out into a truncated cone where it joins the hull on port and starboard sides. Special cut-aways at the after side of the tunnel opening give the entrances a tear-drop shape. This is designed to avoid having the tunnel act as a scoop when operating in ice.

The tunnel is fully submerged

at ten foot draft. There are no protective grids at the tunnel entrances.

THRUSTER

The KaMeWa design consists of a steel tunnel, 88-inches long, cylindrical in section, with two sets of tripod vanes internally arranged to support the propeller and drive assembly. Between pod ends, the propeller rotates with four planar shaped blades that are fully controllable from zero pitch to maximum pitch in either direction without change in direction of rotation of the propulsion machinery.

Full thrust of the Ford's 500 hp unit when operating at its designed speed of 325 r.p.m. is 13,200 pounds. Pitch reversing time is 12 seconds.

PRIME MOVER

Propulsion machinery for the bow thruster consists of a Cummins supercharged Diesel engine that will develop 500 b. hp at 1,800 r.p.m. The

Lever that actually controls direction and amount of thrust is located near front window of M/S Henry Ford II's pilot house, so Captain can operate the bow thruster without leaving his usual conning position.

engine is located in the Thruster Room a few feet aft of the tunnel and is connected to the thruster by a power takeoff. A clutch is provided to permit running the Diesel engine for warmup or servicing without operating the bow thruster.

Starting air for the Diesel, and air for clutch and thruster controls, is supplied by the ship's main compressors. A 3,000 c.f.m. axial blower furnishes air to the Thruster Room area. Engine exhaust is piped through a stack along the after side of the forward cabin and exhausts to atmosphere above the pilothouse. Special engine mounts and hospital type muffler keep vibration and noise at minimum levels. A hydraulic pump and control unit is mounted adjacent to the bow thruster that contains the control valves for delivering oil to the pitch changing mechanism in the propeller hub. The hydraulic controls and main propulsion shaft reach the propeller pod through the support

vanes.

PILOTHOUSE CONTROL

All control functions for the thruster and Diesel engine are handled from the bridge.

Mounted on a bulkhead in the ship's pilothouse is a control and indicating panel for the bow thruster. On it are start and stop buttons for the pitch control hydraulic pump, start and stop for the Diesel engine, and engage and disengage buttons for the clutch. These controls are interlocked electrically to insure proper sequence of starting and stopping procedure. Indicators on the panel show pitch position (left, right, or midships), tachometer for Diesel engine, low air or hydraulic pressure alarms, and high temperature alarms.

The pneumatic signal lever that actually controls the setting of propeller pitch and speed of the Diesel engine (in full synchronization), is located on a small stand alongside the engineroom telegraph. The Captain can operate the thruster control lever without leaving his usual conning position.

The thruster will not be operated while the ship is running in the open lake, but will be started up, the clutch engaged and the propeller turning in zero pitch, ready for instant use, when approaching maneuvering situations.

KaMeWa IS SWEDISH INVENTION

The name KaMeWa is derived from Karlstads Mechanical Works, of Sweden, which first developed controllable pitch runner blades for water turbines back in 1921. Adapting the hydraulically operated propeller for ship propulsion followed and the first such

BOW THRUSTER tunnel on M/S Henry Ford Il showing tear-drop shape of hull aperture, and KaMeWa reversible-pitch propeller unit in center of tunnel.

installation was made in 1937. KaMeWa propellers are used for main propulsion in ships both large and small throughout the world. It has only been in recent years that the principal has been incorporated in bow thruster design.

The six American Great Lakes selfunloaders that are now equipped with bow thrusters include Columbia Transportation Division's J. R. Sensibar and W. W. Holloway, and Boland and Cornelius' J. F. Schoelkopf, Jr., Detroit Edison, Fred A. Manske, and Harris N. Snyder. In addition, the converted T-2 Canadian ore carrier Lake Winnipeg has a motor-driven KaMeWa thruster, and the U.S. Engineers hopper dredge Markham (stationed on the Great Lakes) has a bow thruster of a different design.

SHIPBUILDING NOTES

U.S. private shipyards had 54 major ships of 647,900 gross tons (757,192 d.w.t.) building or on order, according to the Shipbuilders Council of America. Only 15 large merchant vessels were ordered last year as compared with 34 during 1961. Total major merchant orders received during the past years amounted to 113 ships, or an average of 22 ships a year for which 13 private shipyards regularly compete. During 1962 U.S. shipyards delivered 27 ships totaling 379,233 gross tons as compared with 25 of 369,000 gross tons completed in 1961. Of the 54 ships now on order, 39 are general cargo liners, 8 are tankers, 4 are passenger-cargo ships and 3 are ferryboats. The only order for new tonnage placed during December was for two 14,642-ton-d.w.t. cargoships for American Mail Line, to be built on the West Coast. Total launchings for the year numbered 36 of 415,800 gross tons.

By Loren M. Smith

Second Officer, SS Illinois

This article on true motion radar contains the views of Mr. Smith only, and does not necessarily represent the official views of the U.S. Coast Guard. His discussion of this topical and important subject is presented here because of its possible interest to the reader. A true motion plot standing alone does not give a full picture of the navigational problem; usually the conning officer will want to know these basic items:

(a) Is there danger from the targets? i.e.: What is the closest point of approach (CPA) and its time.

(b) Is the target changing course and/or speed?

In order to find the CPA from a true motion plot it is necessary to accomplish a vectorial subtraction of own ship's true velocity from the target's true velocity. On a relative motion plot the CPA may be estimated by merely extending the line of target relative motion to its closest point. With a true motion plot the estimation of CPA by eye is difficult and in some cases rather deceiving. Where the tracks of own ship and target ship diverge, there is no problem as the

CPA is already past. Where they converge, however, CPA is in the future and will NOT be at the intersection of the tracks due to different distances and speeds of the vessels from that "intersection."

Changes of target course and/or speed may be seen from either true or relative plots just as readily, but determination of a target's new course and/or speed is much quicker from a true motion plot. However, again, to determine the effect of this change on CPA it will be necessary to obtain a vectorial solution on true motion, whereas relative motion plots will give the solution directly. It should be noted that a change in own ship course and/or speed will cause an error in the true motion plot unless promptly corrected for.

A full picture is obtained by maintaining both true and relative motion plots. If it were a matter of being able to maintain only one of these plots, on the open sea, I would select a relative motion plot due to the ease of obtaining the most important CPA information directly.

The plotting of own ship's track as always "up" might be possibly con

fusing in comparison to plotting own ship's track relative to North always being "up." Also, the latter presentation allows automatic correction for changes in own ship's course.

Some true-motion "setups" available commercially have a true motion presentation with long persistence so that target past positions show up as "tails" and allow rapid observation of target course changes with no plotting. In using long persistence scopes it is also necessary to have true motion stabilization so as to prevent land masses from "smearing"-particularly on short range scales. Some installations provide a range and bearing "bug" that is placed on the PPI target and then is also automatically printed on a relative motion plot (on a paper roll). Having both true and relative motion radar presentations with long persistence would give a maximum of information without manual plotting. If the long persistence is obtained by SCAN conversion, the displays may be viewed in daylight and the length of persistence can be adjusted as desired, and the picture can also be erased instantly, if necessary.-ED.

A NUMBER OF months ago I was assigned to the SS California, the first of four improved Mariner-class ships built for the States Steamship Co. at the Newport News Shipyard.

Equipped with the latest in electrical and hydraulic gadgetry the ship had on its bridge one of the first triRADAR installations to be installed on a freighter. The installation was composed of RCA 3-cm. and 10-cm. relative motion consoles with a unit of TRUE MOTION (TRUMOT) physically placed between the two other sets in the combination. Their location on California's bridge is illustrated in figure 1.

None of the licensed deck officers including myself had any prior experience with TRUMOT, so our emotions were slightly mixed at seeing this very complicated array, the general attitude being best described as one of doubtful fascination.

As the ship normally transits between Pacific ports, we had ample time to get acquainted with the rig. Our doubts slowly faded, giving way to natural acceptance of TRUMOT. Maneuvering situations in which we

were involved were solved with precision and accuracy by employing TRUMOT without, in most cases, touching anything but a few knobs on the instruments themselves and a

ABOUT THE AUTHOR

LIEUTENANT SMITH, USNR-R, is a graduate of the California Maritime Academy, Class of 1956. After active duty in the Navy on board destroyers and in the Navy Oceanographic Office he shipped as third officer on the SS C. E. Dant and, in a similar capacity, on the maiden voyage of the SS California. Mr. Smith is presently second officer on board the SS Illinois.

grease pencil. Thus we were able to obtain the TRUTH from TRUE MOTION easily and simply.

DISPLAY AND TECHNIQUES

I think it can be stated without much contradiction that the average merchant ship bridge is a poor area in which to attempt to receive and evaluate display information from radar.

During the day this space is bright, so that even with the radar scope hooded the display cannot be immediately recognized. (In some earlier radars it was virtually impossible to correctly read the true bearing dial with the hood in place.) At night the situation is different but can be equally as distressing. The mechanics of transferring display information to a maneuvering board or plotting sheet left much to be desired. A flashlight held under the chin was a common procedure before ultraviolet and luminous plotting ideas were marketed.

Naval ships do not have these problems to contend with, as they have radar units in their chartrooms and/ or combat centers which are manned

by personnel who are not part of the bridge watch. These people collect, evaluate, and disseminate all tactical and maneuvering data and transmit this to the bridge. Watch personnel then evaluate the situation and maneuver the ship accordingly.

On the merchant ship, all of these functions are handled by one manthe Deck Officer. This requires a system from which target information can be readily determined and acted upon on the bridge of a merchant ship. TRUMOT has, for the most part, eliminated shoddy transferral methods previously subscribed to and allows the watchstander to retain most of his information right on the face of the scope. This can be done because both true course and speed are available to him through the "wonderful world of electronics."

Several versions of the TRUMOT idea are now on the market. Although each manufacturer has a different method of slaving TRUMOT to the masters, the concept of TRUMOT remains the same, and all TRUMOT is in Plan Position. In order to have a target move along its true course and speed you are required to develop, by some means, a "navigational plot" where your own ship also moves along true course and speed. The latter is accomplished in TRUMOT by a computer within the set itself with the manual adjustment of ship's speed being made by the operator.

A typical situation of relative versus TRUMOT is illustrated in figures 2 and 3. In this example initial tar

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330

340

get's course and speed were 270, 15 knots. At time 06 target's course was changed to 320 to show how much quicker the change appears in the TRUMOT presentation than that of relative. In relative motion (RM) one might possibly have had doubts about the accuracy of the 06 plot, thereby considering target's course and speed to be somewhat less than the actual values. Of course successive plots would rectify this error, however the point is that TRUMOT detected the change almost instantaneously. Parenthetically it is interesting to note that under certain

conditions when minimum ranges are used and low sea state is experienced, own ship's as well as target's wake, can be observed when TRUMOT is slaved to the higher definition 3-cm. console. This, then, is just another way in which target maneuvers can be detected when operating the unit in TRUMOT.

Versatility varies, of course, with different installations, however I believe most TRUMOT units can be operated in the following manner: As we saw in the TRUMOT illustration in figure 3 the own ship presentation starts at the bottom of the scope and

progresses upward at actual ship's speed (which is preset manually). To make it easy these presentations are generally "head up" so that the ship will track bottom to top no matter what heading is assumed.

The unit on the California has three modes from which to select-RM on center (as in the conventional type RADAR), RM off center, and TRUMOT. The range at which you can operate the TRUMOT unit is always the same or less than the range taken by the master console but never more than 16 miles. Manufacturers of TRUMOT with the RM offcenter mode will recommend that this mode be used to search. In this mode the sweep will originate not at the center of the scope as in the RM on center mode type but in a position between the physical center and bottom of the scope, usually about "5 miles" from the bottom. The sweep origin will remain fixed in this position with no bottom to top movement as there would be were the TRUMOT mode of operation used.

There are a number of advantages to be derived in operating the unit in the RM off center mode. In the first place your viewing range ahead is increased by approximately 10 miles without a decrease in the definition and bearing accuracy. Also, a shift to the TRUMOT phase is natural from the RM off center idea because the origin of the sweep begins in the same place in both modes. You can readily see how smoothly a TRUMOT problem can commence after initial CPA has been found in RM offcenter.

In figures 4 and 5 a typical problem is shown with illustrations in all modes of display. Figure 4 shows the RM oncenter display and figure 5 shows how the problem would look and be solved using a combination of RM offcenter and TRUMOT. Notice that in figure 4 had the set been in RM offcenter and had the target been of sufficient reflective quality, it might have been possible to exceed the 16mile initial contact range and permit an earlier solution.

After 12 minutes of plot (excessive for illustration's sake) a CPA, as well as the distance at which the contact will pass ahead, is found. (Please bear in mind that even though plotting simplicity and convenience is stressed here there will be times when a black and white plot might be an advisable thing, especially where another ship is burdened to keep clear.)

Now, in the example, the modes are switched from RM offcenter to TRUMOT and the tracking of the contact along his true direction and at his true speed begins. In figure 5 this mode change was made at time 12 and this time so marked (in this case with the letters "TM"). This is done so that the operator knows where one leaves and the other begins thus eliminating possible confusion between the RM and TRUMOT phases.

At time 18 target has changed course to 180 and it is apparent that if each ship remains on its respective course they will pass clear. At time 30 your ships are passed and the range is opening. So, for 30 minutes you have been aware of every movement the other ship has made. Needless to

say, timely and up-to-the-minute information such as this is fast becoming a very desirable and necessary commodity. Relative speeds of 50 to 60 knots during a meeting situation are not uncommon today, and things can develop all too quickly.

It is at this point, I think, that we can get more specific and describe some of the mechanical and electrical features of the TRUMOT unit which enable us to complete a problem in true motion.

Bearings are taken by a mechanical cursor and read on an azimuth scale in RM oncenter; they are also taken with an electronic flasher originating at sweep center and are read in a separate counter on the face of the unit in all offcenter modes.

Ranges are fixed and variable in all modes originating at sweep center.

View Time In Trumot depends on both the range scale used and the speed of the ship. Units having a maximum range of 16 miles in offcenter modes have 26.4 miles of viewing area ahead, because the center of the sweep starts 10.4 miles below the physical center of the scope. As the presentation moves from bottom to top in the TRUMOT mode the sweep is automatically reset when it reaches 4.0 miles from the top giving the operator 22 miles of viewing distance at his own speed (66 minutes at 20 knots).

Own Ship Reset To Start Trumot Sequence can be accomplished manually at any point during the sweep's travel upward on the face of the scope but is automatically reset when sweep