It has been observed on trial trips that ships’ officers are very much interested in the trial course and how trials are run. As there is very little literature on the subject available for general reading and as the experience of a complete trial ls horded few officers, it is quite natural that trials are spoken of only in general terms.
In view of the interest, it is the intention of the following to give reasons for holding trials, requirements for trial courses, special equipment necessary for conducting them, and a brief description of standardization, Free Route Endurance, and Fuel Oil Consumption trials.
Why Trials Are Held
The major characteristics of a warship consist of armament, armor, speed, and cruising radius; the proportion of each in a design being determined by the specific use for which the vessel is intended. The performance of the armament itself is known by proof tests before it is installed. How efficient the whole installation on board ship will be in service cannot be determined by any known short tests. Outside of proper installation on the ship, about the only thing that can be done is to test the foundations and adjacent structure for weakness. To this end structural ring tests are conducted shortly after commissioning. The very nature of armor or protection precludes the possibility of devising reasonable tests to determine its actual efficiency in the finished ship. If it is installed properly, which can be checked by inspection during construction, it is known that its efficiency in action will be somewhere near that intended in the design. However, the last two characteristics, speed and cruising radius, are subject to actual measurement and trials are held on the completed ship to determine them.
When the design of a ship is first settled upon, quite accurate predictions of speed, power, and cruising radius are made. The Experimental Model Basin makes the original predictions for speed and power on the basis of performance of small-scale, self-propelled ship models run in their test tank. Given the power requirements, the Bureau of Engineering predicts equally well the over-all efficiency of the machinery installation, from which the fuel required for the various speeds is calculated. This, added to the fuel required for auxiliaries, divided into the total fuel supply carried by the ship, gives the cruising radius.
Since power developed and efficiency of machinery are paramount requirements which are predicted and can be measured on completion, guaranteed performances for them are incorporated in the building contracts. Monetary premiums and deductions are provided for performance differing from the guarantees. The maximum shaft horsepower developed is determined by a 4-hour full power trial in free route. Efficiency of machinery is determined from a number of 4-hour fuel oil consumption trials in free route at various speeds. The criterion of efficiency in the contract is the pounds of standard fuel consumed by the ship for all purposes per knot of the speeds specified. Since propeller r.p.m. are used at sea to set speed, standardization over a measured course is necessary to get the relation between r.p.m. and actual ship speed for use in the fuel oil consumption trials. Moreover, it is important for the Bureaus and operating personnel to know this, and also the relation between speed and power. For these reasons contracts require full standardization trials for at least one ship of each class being built by a contractor.
The combined trials in free route, standardization over the mile, and other miscellaneous tests and observations comprise, in the case of a privately built ship, the Preliminary Acceptance Trial. This trial is conducted for the Board of Inspection and Survey about one month before the intended completion date of the ship. When a contractor is building more than one ship to the same plans, full trials may be required for only one ship. The others are given such curtailed trials as are directed. Privately-built ships also have a Final Acceptance Trial which is held before expiration of the 6-month guarantee period to ascertain that its performance is still satisfactory. In the case of government-built ships, whatever trials decided upon are known as Official Trials. They are held from six months to a year after first commissioning.
Requisites for Measured Mile Trial Course
- Depth of water.—The depth of water over the course has to be sufficient to permit the highest speeds without appreciable interference by the water bottom on the wave systems established by the ship. The empirical formula 10Xdraft in feet X speed in knots divided by the square root of the ship’s length in feet gives the necessary depth of water in feet quite closely. Moreover, a good depth of water is required for about 4 miles on each end of the course for turns and approaches.
- Proximity to shore.—The course should be about one mile from shore as the greater the distance the less accurate the observations and the more the loss of visibility from adverse atmospheric conditions.
- Weather conditions.—The course should not be handicapped by unfavorable weather conditions such as fogs, continued rains, or strong prevailing winds.
- Tidal conditions.—Tidal flow is undesirable, but, as it cannot be helped, it should be small, regular, and set parallel to the course. A small, steady cross-setting tide is not an insurmountable objection.
- Protection from the open sea.—The course should be sheltered from seas and large ground swells, both of which are conducive to obtaining erratic results.
- Shore line.—The shore line should be free of mooring docks, anchorages, and shallow beaches so that there will be no damage from the waves generated by the ship at high speeds.
- Direction of the course.—An east- west course with range beacons to the north is desirable so that it will not be necessary to pick up beacons against the sun.
- Location of range beacons.—The distance between the front and rear beacons on the land should be over one-half and preferably equal to the distance from the front beacon to the ship’s course. If the beacons are too close together transit of the beacons is so slow at low speeds that timing is erratic. The beacons should have a sky background as it is easier to pick them up and follow them than if outlined against land. The beacons should be visible at least a third of a mile before transit to give the observers time to get ready for observations. The rear beacons should have lights to aid in picking them up against the sun or in hazy weather.
- Location of the course.—The course should be conveniently located for the shipyards or bases using it. Facilities should be available near it for housing personnel and obtaining provisions. The local anchorage should be close to the course. It is also very desirable to have fueling facilities at or near the local anchorage.
- Traffic.—The course should have little or no traffic directly along or crossing it to interfere with runs over the mile.
- Water.—Sea water is preferable, but, if partially fresh, large variations in density from ebb and flow of tide during the day are undesirable. Engine efficiency is increased if the water is cold. The water should be free of floating seaweed, kelp, and timbers.
From the above it can be appreciated that the chances of finding an ideal course
are relatively remote. In times past a great many trial courses have been laid out by the Navy and by private interests. Some laid out for special purposes and others laid out for general use have been abandoned because they lacked one or more of the requirements listed above. The principal courses now used by the Board of Inspection and Survey are:
- West Penobscot Bay, Rockland, Maine (for surface ships)
- Provincetown, Massachusetts (for submarines)
(а) Inner course
(б) Outer course
- Point Vicente, San Pedro, California (for surface ships)
- Point La Jolla, San Diego, California (for submarines)
Of all the courses in the United States, and perhaps in the world, the present one at Rockland, shown on Fig. 1, is considered most satisfactory for deep-water trials. While not perfect, it satisfies most of the important requirements. Its most serious drawbacks are its distance from shipyards, lack of fueling facilities near at hand, occasional fog, and cold weather in winter. From records available it appears that the Rockland course was first laid out in 1905, but the rear beacons were located on the shore line so close to the front beacons that transit of the beacons was very slow. Another difficulty was that the high land on Monroe Island obscured the north rear beacon on north runs until just prior to transit. In 1906 plans were made for establishing the first-class course now in use. On account of delays encountered in purchasing land for the rear beacons, with a number of adjoining parcels for protection to the lines of sight, the new range was not built until 1911. The new beacons have structural steel bases set in concrete and rock. The transit poles are of steel tubing of such size that they all subtend the same arc when viewed from the course. The rear beacons are lighted with 500-watt reflecting lamps for use against the sun or in hazy weather.
The course is buoyed for 7 miles, which is inestimable value in making turns and approaches. The water over the course is of adequate depth except at the extreme end of the southern approach. The course very well protected from the open sea, being exposed only to seas from the southeast. Small ground swells are encountered at the southern end. The tide, which is regular, sets almost parallel to the course and seldom exceeds one-half knot. There is very little traffic in Penobscot Bay. Figure 2 shows the south beacons in profile.
Trials and Equipment for Surface Ships
Standardization of a ship consists of running it over a measured mile in a series of runs at different speeds, at the same time measuring accurately speed, shaft horsepower developed, and the revolutions of the propellers. The data obtained are used for plotting the following curves of performance:
- Speed in knots vs. propeller r.p.m.
- Propeller r.p.m. vs. s.h.p.
- Speed in knots vs. s.h.p.
Typical curves of these are shown in Fig. 3.
The series of runs to obtain data for the curves start at about 9 knots and end at full power, with a number of runs at intermediate speeds. For a destroyer about 10 speeds are selected for full standardization. Three runs over the mile are made at each speed, except that 5 runs are usually made at full power. In computing speed, power, and r.p.m. the first and last runs in a series are given one-half the weight of the other runs. Wind effect is not taken into consideration although it has an effect on the results. Standardization is not accurate when the true wind exceeds 9 or 10 knots parallel to the course. The apparent speed and direction of the wind which are recorded may be used later by the Model Basin when the ship’s performance is corrected for wind effect and reduced to model size for comparison with the original model predictions for speed and power.
The ship is ballasted so that the mean trial displacement is reached at the middle of the full power runs. This does not introduce a large error, as fuel consumption at the lower speeds is relatively small. The full curves resulting from standardization are good only for the displacement at which the runs were made. To obtain figures for all likely displacements it is necessary to standardize at several displacements so that cross-curves can be drawn. However, standardization at heavy and light displacements with straight interpolation between curves for intermediate displacements gives results sufficiently close for ordinary use.
It requires about 12 hours on the course for complete standardization of a high speed ship. Each series of 3 runs below 20 knots takes about If hours, and from there up about 1 hour for each series. The approaches are shorter for slow speed runs, increasing in length for higher speeds. At full power an approach of 3 to 4 miles is required for the r.p.m. to settle down and for the speed to become steady before the mile is reached.
About 16 complete sets of special equipment used by the Trial Board for measuring accurately speed, horsepower, and propeller revolutions are maintained at several of the navy yards. Some time before a ship is to have trials, the Bureau of Engineering orders one of these sets delivered to the shipyard or navy yard for installation. A description of the equipment follows:
- Taylor electric printing revolution counter.—One counter is attached to each shaft in a convenient location. The number dials on the counter are run from a worm ring gear attached to the shaft. An electric solenoid on the counter which is actuated by both the forward and after deck observers at the beginning and end of the measured mile course causes the revolutions showing on the counter dial to be printed on a paper tape. On completion of the run the tape with the readings on it is torn off and sent by messenger to the Trial Board computing-room, where they are reduced to r.p.m.
- Smith Cummings mechanical revolution counter.-—One counter is placed on each shaft as with the Taylor. Through a solenoid actuated by the midship deck observer the counter dials are started at the beginning of the mile and stopped at the end. The two readings are recorded manually on a form provided and sent to the computing-room at the end of each run. The readings of these counters are used only in case the Taylor counters fail.
- Electric torsionmeter.—A torsion-meter is placed on each shaft to obtain the torque exerted. The beginning and end of the mile is signaled by bells and lights operated by the forward deck observer. While going over the mile the galvanometers in the meter receivers are balanced and read about 10 times. The 10 readings on each torsionmeter are recorded on a form and sent to the computing room where they are averaged. From the averaged readings, the revolution counter readings, and predetermined constants, the horsepower is calculated.
- Chronograph.—The chronograph is an instrument designed and manufactured by the Model Basin for timing observations made on Standardization Trials. It is kept by the Board of Inspection and Survey and installed by it on arrival of the Board on the ship. A chronometer with an electric make-and-break circuit is attached to the chronograph. It scratches a half-second broken line on a waxed paper tape which is fed through the instrument at nearly constant speed by an electric motor. The following recordings are marked on the tape and their times counted from the chronograph broken line record:
(a) The moment each of the three deck observers start and finish the mile.
(b) Anemometer readings.
(c) Revolutions of the shafts. (These are obtained from attachments on the counter ring gears. They are used normally for analysis of variations in shaft speed as the ship traverses the mile.)
- Contact makers— There is one contact maker for each of the three deck observers. The forward and after ones, which are on the same electric circuit, actuate the Taylor counters and record on the chronograph time tape. The midship contact maker actuates the Smith Cummings counters and records on the chronograph.
Each contact maker has a receptacle holding a stop watch which starts and stops mechanically as the electric contacts are made. Stop watch timings are recorded on a form and sent to the computing-room after each run, but are not used unless the electric chronograph timings fail.
- Bell and light signal system.—Bells and lights are located in the engine- rooms, boiler-rooms, computing-rooms, etc., wherever data from meters, gauges, etc. are to be taken. The contact maker for them is operated by the forward deck observer who gives a double stand-by signal 30 seconds before the mile is reached and a single long signal at the beginning and end of the mile.
- Anemometer.—An anemometer for recording wind speed is installed near the top of the foremast. It records on the chronograph tape.
- Electric control panel, wiring, etc.— A switchboard equipped with switches, solenoids, etc. for controlling the trial gear is installed in the Trial Board headquarters.
- Calibrated fuel oil meters.—Used for fuel oil consumption trials. Two meters are installed in tandem on each oil line, so that one checks the other. They are calibrated again after trials.
Some time before the trial, the Board of Inspection and Survey makes up a station bill which lists and describes the duties of each observer and computer. This is sent to the ship well ahead for assignment of ship personnel, as the Board itself can fill only a few of the billets.
En route from the shipyard to the trial course it is customary for the ship to hold several rehearsals to familiarize personnel assigned from the ship with their duties. The Trial Board (Board of Inspection and Survey) usually comes aboard after the ship arrives in the trial course area. It brings with it observers’ data-taking books, special forms, small instruments, and the chronograph. Before the trials are to start the ship observers are called together and given final instructions and the data-collecting books. About 10 minutes before the ship comes on the course the observers take their stations.
The r.p.m. to obtain the speeds desired for plotting the various spots on the curves must necessarily be estimated before each series of runs, as one purpose of the trial is to get the relation between r.p.m. and speed. The ship must maintain the designated r.p.m. over the course on all propellers within small permissible limits. After the r.p.m. are designated, control of the runs is in the hands of the forward deck observer. About 30 seconds before the mile is reached he gives a double standby signal on the bells and lights to warn all other observers. At the start of the mile he presses his contact maker which records the Taylor counter reading and the time on the chronograph. At the same time he also gives a single signal on the bells and lights for all below-deck observers to take readings of oil, steam and oil pressures, bearing temperatures, etc. At the end of the mile he again presses the contact maker and gives the bells and lights signal. The other two deck observers, as they in turn pass the beacons, press their contact makers which record the shaft counter readings, the time on the chronograph, and the stop watch time.
Elaborate precautions are taken to prevent the loss of a run from failure on the part of trial equipment or deck observers. The after observer checks on the forward observer. The midship observer is independent of both. If both the Taylor and Smith Cummings counters fail, the r.p.m. recorded directly on the chronograph can be used. In case the chronograph timing fails the stop watch times can be used.
If on a run the times over the mile as recorded on the chronograph by the 3 deck observers differ from each other by more than .3 second, the run is thrown out, and all previous runs at the same speed as well, except that if the second run is thrown out the remaining two can be made providing the time interval between the new second and third runs is the same as that between the first and new second runs. If two observers are within .3 second of each other and the third is more than .3 second out from either of them, the time of the third observer is discarded and the average of the first two used.
After each run all the data required for computing speed, s.h.p. and r.p.m. are assembled in the computing-room and worked out quickly. The final results are available shortly after completion of any series of runs. The results are plotted to give the curves mentioned. The r.p.m. to obtain the speeds specified in the contract for the 4-hour fuel oil consumption trials are picked off the curves.
Four-Hour Endurance, Full-Power, and Fuel Oil-Consumption Trials
These consist of a 4-hour endurance and fuel oil-consumption full-power trial and a series of 4-hour endurance and fuel oil- consumption trials at selected lower speeds, the number of the latter depending on the speed and power of the ship. For a destroyer 6 lower speed trials are usually required.
(1) Full power-endurance and fuel oil- consumption trial.—The main purpose of this trial is to measure the average shaft horsepower developed and the fuel oil consumption. The contracts specify a minimum shaft horsepower. Graduated deductions are made from the contract price for failure to develop the required power, but there are usually no premiums for over power. The fuel oil consumption requirements will be discussed under (2). The s.h.p. must be developed under operating conditions limited by the contract and specifications. Some of these are:
- Steam pressures
- Steam temperatures
- Fuel oil pressures
- Fuel oil temperatures
- Bearing temperatures
- Boiler forced draft air pressures
- Smokeless operation for one hour
- Operation of auxiliaries
- Specified load on ship’s generators
- Water supply systems
- Steam auxiliaries such as heating systems, galley steam, etc.
In addition observations are made of:
- General performance of machinery installation
- Noise in gears
- General noise level in machinery spaces
- Vibration of hull, machinery foundations, piping, etc.
- Stack gases on bridge, etc.
- Ventilation of machinery spaces
(2) Endurance and fuel oil-consumption trials.—The main purpose of these trials is to measure the pounds of fuel oil consumed by the boilers at full power at the speeds specified in the contract. It will be noted that, except for full power, the contract requirements call for pounds of fuel oil used per knot, so that speed (r.p.m. obtained from standardization) and not the s.h.p. developed is used. Premiums and deductions are provided for fuel oil consumption below or above those guaranteed. On a destroyer at low speeds these may amount to as much as $3,000 per pound of corrected fuel oil. The gross amount which can be paid in premiums is limited, while there is usually no limit for deductions. Deductions on any trial can be balanced against premiums earned on others. Operating conditions and observations are about the same as outlined for the full power trial.
Four-hour trials are held in water deep enough to insure no interference of the wave systems formed with the water bottom. The ship is ballasted so that the mean trial displacement is reached at the middle of the trial. If there is a wind or a sea running, one-half of the trial is run under favorable conditions and one-half unfavorable, as less power for a given r.p.m. is necessary with a following wind or sea. When the sea is such that the ship rolls and pitches appreciably it is difficult to operate economically. As premiums and deductions may be very high, it is customary for a contractor to schedule important fuel oil-consumption trials only when the weather is favorable.
The trials are controlled from the Trial Board computing-room. Signals are given at half-hour intervals for recording data by below-deck observers and for getting r.p.m., torsionmeter readings, and fuel oil consumption. The figures are worked out rapidly each half-hour to check on the trial’s progress. The curves of fuel oil consumption versus s.h.p. and speed are shown on Fig. 3.
Miscellaneous Trials, Tests, and Observations
In addition to the main trials described other tests, observations, and procedures are required or scheduled to take place during the trials. Among these are:
- Two-hour 20-per cent overload boiler test.
- Backing standardization. (Two runs over the mile are usual at about 90 per cent of full power backing to get the r.p.m. for astern steering test.)
- Full and reduced power backing tests. The extent of these depends upon the type of ship.
- Quick stop and reversal from full power ahead to full power astern and vice versa. These are spectacular performances involving extreme conditions for hull and machinery. The times to “dead in the water” and the ahead and astern reaches are observed.
- Steering gear tests. The full power ahead tests, which include putting the rudder from hard over to hard over at maximum speed are exciting as the centrifugal force on the turns and the ship’s list combine to produce a feeling of insecurity among those first experiencing the sensation. These ahead tests are a modification of the old “figure eight.” The astern tests impose the most severe operating loads on the steering gear.
- Anchor gear tests. These are held in over 60 fathoms of water. Among other things, they include heaving in anchors with 60 fathoms of chain at the water’s edge, cross connecting, and letting the anchors go on the brakes to 60 fathoms with stops at 15, 30, and 45 fathoms. On this test there is an occasional unanticipated failure which consigns the anchor and chain to Davey Jones’ locker.
- Record of squat at all speeds standardized.
- Maximum angle of roll during steering tests.
- Normal rolling period of ship.
- Consultations with Superintending Constructor, Inspector of Machinery, ship’s officers, and contractor’s representatives on unsatisfactory and uncompleted work.
- Consultations on proposed alterations.
- General inspection of ship.
- Demonstrations as requested of auxiliary machinery and mechanisms.
If the weather has been favorable and the ship’s performance satisfactory, the trials described take about 8 days. The ship has been run under operating conditions probably more severe than it will ever again experience. So there is a feeling of satisfaction and relief when the ship finally ties up at the shipbuilding plant with a “clean sweep” broom at the masthead.
★
The Stone Blockade
During the early days of the Civil War a scheme was devised to seal the harbors of Charleston and Savannah against blockade runners. Gustavus V. Fox, Assistant Secretary of the Navy, went to New York and contracted with a Mr. George D. Morgan for the purchase of 25 old sailing ships. These ships were easily found. The war had disrupted the whaling industry and whaling vessels stood idle in the ports of New Bedford and New London. Twenty-five of these whalers were purchased at prices ranging from $3,150 to $6,500 each. Sixteen of them hailed from New Bedford, eight from New London, and one from New York. Each one was fitted with two holes closed with plugs for convenient scuttling, and then loaded with stone purchased from New England farmers at 50¢ a ton. On November 20, 1861, they left New Bedford and reached their rendezvous at Tybee Island, near Savannah fifteen days later. There they were turned over to Flag Officer, later Rear Admiral Samuel F. Du Pont. Of the twenty-five ships that had left New Bedford but sixteen remained. Three had gone ashore, three had been transferred to the Army, one had put back to New Bedford, and two had been reserved for later use. The sixteen whalers were then towed by steamers, under the protection of armed ships, to the entrance of Charleston Harbor and sunk upon and inside the bar. They were sunk as much as possible at right angles to the current, not in a solid line, but a little distance apart so as to allow for the free passage of the water. Each ship, however, was so placed that the bow of one overlapped the stern of the other. The work was completed December 20, 1861, to the dismay and anger of the defenders of Charleston, who believed this a violation of the rules of civilized warfare. Twenty more ships, similarly loaded with stone, were purchased in New England ports and sunk in another channel leading to Charleston, known as Maffit’s Channel. This sinking was completed January 26, 1862. But nothing came from all this labor and expense. A few months later not a vestige of the ships remained. According to a Union officer, Commander Daniel Ammen, the timbers had been eaten by a marine worm, the teredo navalis, that infested the waters. The stones, released from their confining timbers had sunk in the mud, and blockade runners passed to and fro as they had done before.