Page 24: of Maritime Reporter Magazine (April 15, 1973)

Some Recommended Practices For

Successful Sea Trials

Sea Trials Are Expensive And Time Consuming But Are Necessary

To Prove That A Ship Will Perform Satisfactorily In Service. The

Author Points Out The Reasons For Many "Do's" And "Don'ts" For Good Results

Robert L. Jack*

Trial Agenda For First Ship Of A Class

Event

Depart shipyard

Pre-trial conference

Calibrate compass and RDF

Drag shaft for zero torsionmeter reading

Conduct standardization trials

Conduct turning circles

Conduct "Z" maneuver

Conduct non-extraction water rate

Conduct fuel rate

Conduct ahead steering

Conduct emergency steering

Drag shaft for zero torsionmeter reading

Conduct crash ahead from astern

Conduct crash astern from ahead

Conduct astern endurance run

Conduct astern steering

Conduct boiler overloads

Conduct automation demonstration

Conduct anchor-handling test

Calibrate shaft torsionmeter (during event 19)

Post trial conference

Arrive shipyard

Sea 'trials are expensive in terms of time, equipment and manpower.

It is probably the only time during the life of the ship when operation- al data, some from special instru- mentation, is documented for all of the ship's systems. It, therefore, appears shortsighted >to undertake such a comprehensive and expen- sive effort without taking every reasonable precaution to ensure that the recorded results will be as accurate as possible.

By carefully sequencing the trial events, this operation can be con- ducted with a minimum loss of time and the chance of mechanical failure.

Where one trial event bears a technical relationship to another, thought must be given to their proper order. In addition, care must be taken to schedule events in such an order 'that possible damage to the plant or its equipment is mini- mized.

Table 1 shows a suggested, if not typical, trial agenda for the first ship of a design. Where appropri- ate, a generous time allowance has been provided to prepare for sub- sequent events. It will be noted that total underway time from de- parture to arrival back at the ship- yard (allowing eight hours to and from the trial area) is approximate- ly 40 hours. Experience has shown, however, that the actual time for merchant-ship trials often ap- proaches three days for the first ship of a class. With proper pre- trial preparation, the agenda in

Table 1 could easily be met.

Trial Supervisor

All trials should be under the direction of a trial supervisor for the contractor. He should have full authority and should be in charge of the trials and all trial personnel, including the captain and chief en- gineer of the ship. Failure to es- tablish this clear line of authority can result in tpoor trial results. For *Mr. Jack, Office of Ship Construc- tion, Maritime Administration, pre- sented the paper summarized here be- fore a recent meeting of the Chesa- peake Section of The Society of Naval

Architects and Marine Engineers. Mr.

Jack has represented the Maritime

Administration on trials of hundreds of ships. example, practically every trial captain tends to follow the same course on every trial regardless of the purpose of the trials or the prevailing weather. One captain did all of his navigation by radar and refused to go beyond range of land.

Consequently, these trials were conducted in waters of varying depths. The accuracy of the tor- sionmeter readings and resulting horsepower calculations under such conditions are greatly impaired.

After the ship is safely at sea, the trial supervisor should have full say as to which course should be followed, the power to be de- veloped, the scheduling of events, the directions to the helmsman dur- ing maneuvers, etc. unless over- ruled by the captain solely for safe- ty reasons.

Likewise, the engine room should be under the control of the operat- ing engineers but only as directed by the trial supervisor. Except for emergency situations, no'changes in plant operating conditions should be undertaken by the engine crew unless so directed by the technical supervisor in charge of the trials.

This applies to minor plant ad- justments as well as operation of auxiliary systems.

Shaft Calibration

The question has often been raised as to the necessity for the calibration of shafts as a prere- quisite for accurate horsepower de- termination. It is obvious that if unchallengeable horsepower data is desired, shaft calibrations must be undertaken. There is a 37-per- cent chance of an error exceeding one percent in using an assumed modulus. This should be consider- ed unacceptable. This is particular- ly true where the shipbuilding con- tract includes a bonus-penalty pro- vision in the order of $50,000 per 0.01 pounds of fuel per horsepow- er-hour. This corresponds to near- ly $25,000 >for each percentage point of horsepower accuracy, which in turn is the same as each percentage point of shaft calibra- tion accuracy.

Torsionmeters

Unless the propulsion system is electric drive, the horsepower must be determined by a torsionmeter attached to the propeller shaft. The variable mutual - inductance - type

Table No. 1—Typical

Event No. Time 1 8:00 AM 2 3 4:00 PM 4 6:00 PM 5 6:45 PM 6 10:45 PM 7 11:15 PM 8 12:15 AM 9 2:00 AM 10 6:00 AM 11 6:30 AM 12 6:45 AM 13 7:45 AM 14 8:00 AM 15 8:15 AM 16 9:15 AM 17 10:30 AM 18 1:00 PM 19 2:30 PM 20 2:30 PM 21 22 11:30 PM instrument should be used exclu- sively for trial purposes. Descrip- tions of its design, installation, calibration and zero determination are presented in Section 5.5 of The

Society of Naval Architects and

Marine Engineers T&R Bulletin •C2. Other types of horsepower meters, installed as permanent ship's instruments, do not have suf- ficient accuracy and reliability for use as trial instrumentation.

Shaft-Revolution Counters

The determination of the shaft revolutions is quite straightfor- ward and is usually routinely ac- complished with great accuracy and reliability using special dual trial counters as described in Bul- letin C2. However, these mechani- cal devices are not infallible, and a back-up for this essential data can be readily provided by merely taking hourly readings of the ship's counters.

Fuel-Oil Meters

If fuel economy trials are to be conducted, reliable and accurately calibrated twin fuel-oil meters must be used. Experience has proven beyond any doubt that these me- ters must be calibrated with fuel of approximately the same flow, temperature, and viscosity as that to be used on trials. Attempts have been made to calibrate such meters with water or other fluids and ap- plying correction factors for vis- cosity. Without exception, such calibrations have proven to be worthless. It is believed that the only facility with the capability of calibrating with Bunker C fuel is the Naval Ship Engineering Cen- ter, Philadelphia Division. Fortu- nately, this facility also has a sup- ply of reliable meters that are avail- able to any ship contractor on a loan basis for a reasonable fee.

These meters, or others calibrated by NAVSEC Philadelphia, must be used where accurate fuel measure- ment is a factor.

Radiometric Equipment

Radiometric equipment was first used on commercialship trials 20 years ago for the standardization of the S'S United States. Since then, this equipment has revolu- tionized the procedures used in conducting not only standardiza- tion trials but also such maneuver- ing tests as turning circles, Z ma- neuvers, and crash stops. The re- sult has been greater accuracy with less effort and a significant saving of trial time.

In addition to plotting the move- ment of the ship in respect to two stations, the instrument also re- cords time in seconds and shaft revolutions, as well as the ship's heading 'by means of a connection to the ship's master gyro system.

The result is a permanent and ac- curate record of ship location, heading, and rpm versus time over an almost unlimited time frame.

The owners of the equipment boast of an accuracy to within 10 feet in (Continued on page 28) 26 Maritime Reporter/Engineering News