ITTC Recommended Procedures and Guidelines

Transcription

1 Page 1 of 10 Table of Contents Speed/Power Trials PURPOSE DEFINITIONS RESPONSIBILITIES Shipbuilders Responsibilities The Trial Team PROCEDURES Trial Preparation Shipbuilder s Support Requirement: Space Requirements Ship Inspection Preparation for the trials Ship Inspection Reporting of Results and Distribution of Information Hull- and Propulsor Survey Instrumentation Installation and Calibration Instrumentation Installation Instrumentation Calibration Check Trial Conditions Wind: Sea State: Current: Trial Conduct: REFERENCES Updated / Edited by Approved Specialist Committee on Powering Performance of 24 th ITTC Date Date 24 th ITTC

2 Page 2 of PURPOSE The general purpose of this procedure is to define basic requirements for the preparation and conduct of speed trials. The primary purpose of speed trials is to determine ship performance in terms of speed, power and propeller revolutions under prescribed ship conditions, and thereby verify the satisfactory attainment of the contractually stipulated ship speed. The applicability of this procedure is limited to commercial ships of the displacement type. The procedure is to provide guidelines to document the trial preparation prior to the conduct of a full scale Speed/Power trial, to define the responsibility sharing among the parties who take part in the sea trial for the smooth preparation and execution of the speed trial to establish a guideline for conducting inspections for the purpose of installing instrumentation prior to the conduct of a full scale Speed/Power trial, to establish a baseline of the ship hull and propulsor condition prior to the conduct of a full-scale Speed/Power trial;(hull and propulsor surveys are recommended to allow an evaluation of the trial results for scientific purposes), to install and calibrate trial instrumentation for full scale Speed/Power trials, to define acceptable limits for trial conditions needed to validate hydrodynamic design and/or satisfy contractual requirements, for acceptable conduct of each speed trial. 2. DEFINITIONS Ship Speed is that realized under the contractually stipulated conditions. Ideal conditions to which the speed would be corrected would be no wind (or maximum wind speed according to Beaufort 2) no waves (or waves with maximum wave heights and wave periods according to Beaufort 1) no current deep water smooth hull and propeller surfaces Docking Report: Report that documents the condition of the ship hull and propulsors (available from the most recent dry - docking).

3 Page 3 of 10 Trial Agenda: Document outlining the scope of a particular Speed/Power trial. This document contains the procedures on how to conduct the trial and table(s) portraying the runs to be conducted. Trial Log: For each run, the log contains the run number, type of maneuver, approach speed by log, approach shaft speed, times when the maneuvers start and stop, and any comments about the run. Propeller Pitch: the design pitch also for controllable pitch propellers. Running Pitch: the operating pitch of a CPP Brake Power: Power delivered by the output coupling of the propulsion machinery before passing through any speed reducing and transmission devices and with all continuously operating engine auxiliaries in use. Shaft Power: Net power supplied by the propulsion machinery to the propulsion shafting after passing through all speedreducing and other transmission devices and after power for all attached auxiliaries has been taken off. 3. RESPONSIBILITIES 3.1 Shipbuilders Responsibilities The Shipbuilder has the responsibility for planning, conducting and evaluating the trials. Speed Power - Trials may be conducted by institutions acknowledged as competent to perform those trials, as agreed between the Shipbuilder and the Ship owner The Shipbuilder has to provide all permits and certificates needed to go to sea. The Shipbuilder is responsible to ensure that all qualified personnel, needed for operating the ship and all engines, systems and equipment during the trials have been ordered. The Shipbuilder is responsible to ensure that all regulatory bodies, Classification Society, Ship Owner, ship agents, suppliers, subcontractors, harbor facilities, delivering departments of provisions, fuel, water, towing, etc., needed for conducting the sea trials, have been informed and are available and on board, if required. It is the Shipbuilder s responsibility that all safety measures have been checked and all fixed, portable and individual material (for crew, trial personnel and guests) is on board and operative. It is the Shipbuilder s responsibility that dock trials of all systems have been executed as well as all alarms, warning and safety systems. It is the Shipbuilder s responsibility that an inclining test has been performed and/or at least a preliminary stability booklet has been approved, covering the sea trial condition, in accordance with the 1974 SOLAS Convention. The Shipbuilder is responsible for the overall trial coordination between the ship's crew, trial personnel, and the owner representative. A pre-trial meeting between the trial team, owner and the ship s crew will

4 Page 4 of 10 be held to discuss the various trial events and to resolve any outstanding issues. The Shipbuilder has, if necessary, to arrange for divers to inspect the ship s hull and propellers. The Trial Leader is the duly authorized (shipbuilder s representative) person responsible for the execution of all phases of the Speed/Power trials including the pretrial preparation. 3.2 The Trial Team The trial team is responsible for correct measurements and analysis of the measured data according to the state of the art. The trial team is responsible for the following: a. Conduct ship inspection, if possible or necessary. b. Provide, install and operate all required trial instrumentation and temporary cabling. c. If previously arranged, provide the ship master and owner s representative with a preliminary data package before debarking. The contents of the data package will be determined in consultation with the owner s representative at the initial pre-trial briefing. d. Provide a final report after completion of the trials in accordance with any agreement between the shipbuilder and the ship owner. 4. PROCEDURES 4.1 Trial Preparation Shipbuilder s Support Requirement: Prior to the trials the required instrumentation has to be installed. The assistance of the ship s or shipbuilder s crew will be required when making electrical connections to the ship's systems and circuits such as heading, wind speed, wind direction, and rudder angle synchronous repeaters. The following support is requested from the Shipbuilder to properly prepare for the trials: a. Provide access to the ship for trial instrumentation. b. Assistance is required for the following electrical connections: Gyrocompass Wind meter Rudder angle indicator Log Speed Propeller Pitch c. Vary the output level of each of the above measurement sources to ensure the proper operation and alignment of the test instrumentation Space Requirements Spaces and an electric supply adequate for the trial equipment will be required for the trial instrumentation and computers.

5 Page 5 of Ship Inspection There are three stages of a ship inspection: in-house preparation, the actual inspection, and the reporting of results and distribution of information to the various parties involved in the trial Preparation for the trials Review shafting dimensions, propulsion plant specifications, etc. Review trials agenda, if available Ship Inspection Inspect hull- and propeller surface condition, if possible. Inspect ship s instrumentation for accessibility. Determine routes for cable runs/data transfer conduits between trial room and bridge or control area. Contact the Engineer on duty to discuss trial instrumentation requirements. Inspect machinery spaces as applicable Reporting of Results and Distribution of Information Document all pertinent information related to the ship inspection a) Last date of cleaning. b) Means of cleaning. c) Propeller roughness measurement, if available, which should include average, standard deviation, distribution along the blades, and existing physical damage. d) For a clean hull; documentation indicating manufacturer and kind of paint used, paint layer thickness and, if available, roughness measurements (average, standard deviation, and distribution along the hull) should be provided. The majority of this information may be contained in the docking report. e) For a dirty hull, documentation indicating visual observations of any fouling and date of last dry-docking should be provided. 4.3 Hull- and Propulsor Survey A roughness survey is recommended to document the conditions of the ship hull, appendages, and propulsor(s) prior to the start of the full-scale speed/ power trial. Cleaning may be required if fouling is found to be such that it would bias the trial data. Ideally, roughness surveys should be conducted prior to the trials. The average hull roughness should not exceed 250 µm (µ = 1x10-6 m) (6.35 mils) and the average propulsor roughness level should not be greater than 150 µm (3.81 mils). 4.4 Instrumentation Installation and Calibration Instrumentation Installation The installation of instrumentation should be scheduled at a time of minimal conflict with ship operations.

6 Page 6 of 10 The bias limits of the instrumentation used for the measurements should be known and assessed. The instrumentation used for the on-boardmeasurements must be calibrated before application on board. If this is not possible, for some reason, the consequences of this should be highlighted in the final trial report. Electrical calibration is recommended for the torque measurement device and, in case of use during the sea trials, for the thrust measurement device. Further a calibration should be done for the pick ups and the respective amplifiers used for the measurement of the rate of revolutions. A calibration of a (differential) GPS-System is not possible without excessive measures, but at least the function of the device should be checked before use on board. If portable radar tracking or (differential) GPS is utilized, a Receiver/Transmitter (R/T) unit or GPS antenna is to be installed. In case the soft ware program used for the evaluation of the data received does not allow for varying positions on the uppermost deck of the ship the antenna should be placed in a location along the ship s centerline as close to the ship s CG as possible. This location will ideally be located on a mast or site that is clear of obstructions, such as the ship s superstructure Instrumentation Calibration Check All shipboard signals to be recorded during the trials must be adjusted to zero or should have their zero value checked (e.g. for a (D) GPS-device) after the instrumentation installation is completed and prior to the trials. The zero values of the torsiometers, the thrust measurement devices and the devices for the measurement of the rates of revolutions must be checked before the trial runs start and after they have been finished. As part of the pre-trial calibration, the torsion meters zero torque readings must be determined since there is a residual torque in the shaft, which is resting on the line shaft bearings. This might be done in different ways; one possible way is to use the jacking motors. The shaft is jacked both ahead and astern and the average of the readings noted. The zeroes are set at the midpoint of the torque required to jack each shaft ahead and the torque required to jack each shaft astern. An allowance is normally made for frictional losses in the stern tube bearings. As part of the pre-trial calibration for a ship equipped with controllable pitch propellers, maximum ahead pitch, the design pitch and the maximum astern pitch should be determined and then the ship indicators should be adjusted to reflect the measurement. 4.5 Trial Conditions Speed/Power trials require accurate position data. The use of (D) GPS provides great latitude in choosing a trial site. Regardless of the instrumentation utilized for obtaining positional data, the operational area should be free from substantial small boat traffic. The tracking range should be agreed between the Trial Director and the ship s master. Draft, trim and displacement of the ship on trials should be obtained by averaging the ship draft mark readings. The ship should be brought into a condition that is as close as possible to the contract condition and/or the condi-

7 Page 7 of 10 tion on which model tests have been carried out. This will allow for the correction of the displacement and trim with respect to the trials that were conducted and will be applicable to the suggestions outlined in the ITTC Procedure for the Analysis of Speed/Power Trial Data. Draft, trim and displacement should be obtained at the beginning and at the end of the trial. This may be accomplished using a loading computer or by taking a second draft reading. The accuracy of the draft readings and the method used to establish draft and displacement underway will be compared in port by direct draft readings both port and starboard in conjunction with a liquid load calculation. Displacement should be derived from the hydrostatic curves by utilizing the draft data and the density of the water. Environmental factors may significantly influence the data obtained during sea trials; consequently, these factors should be monitored and documented to the greatest extent possible: High wind and sea states can force the use of excessive rudder to maintain heading, and thus cause excessive fluctuations in shaft torque, shaft speed and ship speed. Sea states of 3 or less and a true wind speed below Beaufort 6 (20 Kn) are the desired conditions for sea trials. When working under the time constraints of a contract, corrections to the trials data can be made in accordance with the recommendations provided in the ITTC Procedure for the Analysis of Speed/Power Trial Data for sea states less than or equal to 5. For sea states greater than 5, corrections to the trials data can be applied but are not considered reliable from a scientific standpoint. The local seawater temperature and specific gravity at the trial site are recorded to enable the calculation of ship's displacement. An acceptable minimum water depth for the trials where the data do not need to be corrected for shallow water can be calculated using: h > 6.0(A m ) 0.5 and h > 0.5 V 2 (1) with A m = midship section area, [m 2 ] V= ship speed, [m/s] The larger of the 2 values obtained from the two equations should be used. Current speed and direction should be determined in the test area by prognostic analysis. When current speed and direction is unknown, the ship s global drift (also including wind effect) in some cases might be determined by a 360 turning test conducted at low ahead speed to magnify any environmental effect. The runs should be conducted into and against the waves; i.e., head and following seas, respectively. To ensure that tests are performed in comparable conditions, the data between reciprocal runs should be reviewed for consistency and/or anomalies. Individual speed runs conducted in the same conditions should be averaged with their reciprocal runs to take into account global drift.

8 Page 8 of 10 In accordance with ISO the following, general recommendations can be given: Wind: Wind speed and direction shall be measured as relative wind; continuous recording of relative wind during each run is recommended. Care has to be taken whether the data derived from the wind indicator are reliable; checks, such as parallel measurements with a portable instrument, comparison of the data received from the wind indicator with wind speeds and directions received from local weather stations sufficiently close to the actual position of the ship or, if possible, calibration of the wind indicator (taking into consideration the effects of boundary layers of the superstructure on the measured values) in a wind tunnel are recommended. It is suggested that wind force during the trial runs under no conditions should be higher than Beaufort 6 for ships with lengths equal or exceeding 100m and Beaufort 5 for ships shorter than 100m Sea State: If possible, instruments such as buoys or instruments onboard ships (e.g. seaway analysis radar) should be used to determine the wave height, wave period and direction of seas and swell. Considering usual practice the wave heights may be determined from observations by multiple, experienced observers, including the nautical staff on board. During the trial runs the total wave height (double amplitude), which allows for the wave heights of seas and swell (see ISO 15016), should not exceed 3m for ships of 100m length and more and 1,5m for ships with lengths smaller than 100m Current: Current speed and direction shall be obtained either as part of the evaluation of run and counter-run of each double run, by direct measurement with a current gauge buoy or by use of nautical charts of the respective trial area. It is recommended to compare measured data with those included on the nautical charts. 4.6 Trial Conduct: All speed trials shall be carried out using double runs, i.e. each run is followed by a return run in the opposite direction, performed with the same engine settings. The number of such double runs should not be less than three. This three runs should be at different engine settings. The time necessary for a speed run depends on the ship s speed, size and power. Steady state conditions should be achieved before the speed runs start. It is recommended that the time of one run should be as long as possible but should at least be 10 min. The ideal path of a ship in a typical speed/power maneuver is shown in Figure 1:

9 Page 9 of 10 Min. 10 min Steady Approach Steady Approach Min 10 min Figure 1 Prior to the trial, the data specified below shall be recorded, based on measurements where relevant: Date Trial area Weather conditions Air temperature Mean water depth in the trial area Water temperature and density Draughts Corresponding displacement Propeller pitch in the case of a CPP It is recommended to retain a record of the following factors, which should prove useful for verifying the condition of the ship at the time of the speed trial: Time elapsed since last hull and propeller cleaning Surface condition of hull and propeller. The following data should be monitored and recorded on each run: Clock time at commencement Time elapsed over the measured distance Ship heading Ship s speed over ground Propeller rate of revolutions Propeller shaft torque and/or brake power Water depth Relative wind velocity and direction Air temperature Observed wave height (or: wave height corresponding to observed and/or agreed wind conditions) Rudder angle Ship position and track

10 Page 10 of 10 Data such as ship s speed, rate of revolutions of the propeller, torque, rudder angle and drift angle to be used for the analyses shall be the average values derived on the measured distance. (2) ITTC Procedure for the Analysis of Speed/Power Trial Data (3) ISO REFERENCES (1) ISO 15016, Ships and marine technology Guidelines for the assessment of speed and power performance by analysis of speed trial data