This module generates an inclining test report or a light weight check report. After entering the measured data of the test, the lightship weight is calculated including the position of the CoG (Center of Gravity). In this manual, mainly the operation of the program will be discussed, altough in particular the last section is brought under your attention, for that is the place where some computational backgrounds are discussed.
General data and settings
Here the general data of the inclination test or light weight check can be given, from which quite some will speak for themselves. That is just textual input — such as for ‘Condition outside water’ or ‘Number of persons present’ — which can be given and which will be printed on the measurement report. However, a number of calculation settings require some elucidation:
- Density of outside water
- This is the density (the specific weight) of the outside water (in ton/m^{3}) during the inclination test or light weight check, so it is not related to the design density as given in Density outside water.
- Inclining test or light weight check
- Here is defined what type of calculation is made and thus what type of report is generated. Furthermore it should be noted that, when an inclining test is selected but only the zero measurement is defined or there are no test weight defined at the zero measurement, that automatically a light weight check is calculated.
- Calculation with correction for sagging
- With this switch the method of calculation of the volume (and hence the weight during the inclining test or light weight check) and Longitudinal Center of Buoyancy can be chosen. Obviously, sagging can only be taken into account when drafts/freeboards have been measured at at least three locations. At a calculation without correction for sagging a straight waterline is determined as close as possible to the measured drafts. At a calculation with this correction a parabolic waterline is constructed. In both cases the waterplane construction is done with the least squares method.
- Correction of trim & VCG on CoG
- Please read for the background of this issue first the discussion at ‘With free-to-trim effect, including the effect of VCG on trim’, see Stability calculation method. The point is that trim & VCG on the one hand, and LCG & TCG on the other hand have a mutual relationship. In conventional calculations this effect was taken into consideration, but here in PIAS it can be incorporated. If one should wish the results of the elaboration of the inclining test to be fully compatible with those of the loading conditions, then this setting here in Incltest should be set the same as the referred setting in Config. Please note that if the ship has a heel angle during the light weight check then it is advised to use this option.
- VCG for correction of trim & VCG on CoG
- If this ‘Correction of trim & VCG on CoG’ is switched on, the VCG should obviously be known. When elaborating an inclining test that is always the case, because then the VCG is just computed! However, when only a light weight check is done, then the VCG is not known, so it must be user-specified, which can be done here. If the VCG is not known exactly, then one should be satisfied with an estimation.
- Determination of G'M
- At an inclining test, multiple measurements of G'M are performed. From these measurements the single resulting G'M must be determined. The probably most evident method is to take the mean of all measurements. An alternative comes up if we plot the measured angles of inclination against the heeling moments — such a graph is included in the inclining test report as produced by Incltest. If, subsequently, a straight line is drawn through these points, the inclination of this line represents G'M. That straight line is being determined by the least squares method, so this is also the name of this alternative method.
- Note
- Application of the least squares method showed at some point a difference in outcome between the G'M as calculated by PIAS, and as determined by a Bureau Veritas program. Further analysis revealed that what is called in the latter ‘least squares’ is in reality simply the mean.
- Selected wind contour for pictures in report
- The output of Incltest may contain a side view of the ship, where draft, trim and sagging are depicted. For such a sketch a wind contour can be used — as discussed in Wind contour — and at this setting one may specify which contour to use for this purpose.
- Trim and heeling angle for sounding/ullage of tanks
- Here can be given which trim and heel are to be used for the determination of tank volumes based on measured sounding or ullage. As a rule, these will be according the drafts, which have only been recorded once, at the zero measurement, in which case the setting will be ‘Taken from zero measurement’. In practice, it might occur that preparations are not yet ready for the zero measurement, while there is time available to gauge the tanks. For such a case the alternative setting ‘As defined below’ is available. This choice will enable the last two rows of this menu, where trim (in meters) and heeling angle (in degrees, positive to SB) can be given as they have been recorded during gauging of the tanks. In the case that ‘Taken from zero measurement’ is used then the last two rows will show there respective values from the zero measurement.
Inclination measuring equipment particulars
This is a simple form where inclination gauging particulars can be given. PIAS support ten such devices, of two types:
- A conventional pendulum, from which name and length should be specified.
- An (electronic) inclinometer — an inclination gauge — e.g. the one as integrated in PIAS through module Inclmeas. From this equipment only the name has to be given.
Measurements
This table contains the heart of the matter, here the measurements are being entered in PIAS. The first row is always present in this table, which is the so-called “zero measurement”, which fixes the initial condition. For each measurement there is one line, which contains:
- The name of the measurement.
- Whether the drafts of this measurement deviate from the zero measurement. For the zero measurement the drafts or freeboards obviously have to be given, because, as a rule, they are valid for the entire test. Deviant drafts are a bit of an exception (but will be processed in PIAS properly, if being given).
- Whether or not one whishes to use 1 total moment. In the majority of cases it will probably most convenient to give for each individual test weight its position, and to let PIAS add their heeling moments. In such a case a user does not give 1 total moment.
- If one does wish to give 1 total moment, then in the 4^{TH} column that moment (in tonmeter) can be specified relative to centerline.
- In the last columns the measured inclination angles are being given. Either as angle in degrees, in case of an inclinometer, or as the stroke in meters of a pendulum. These angles and strokes should be given relative from the zero measurement.
- In due time, this input form will be equipped with a function to import and utilize inclination angles as measured by Inclmeas. The graph of the measured angle vs. time will then also be included in the inclination test report.
With the text cursor on the row of a measurement, one can with <Enter> continue to input forms of freeboards/drafts and inclining test weights, as dicussed just below.
Measured freeboards/drafts
This is the input form of freeboards and/or drafts, which contains seven columns:
- The first column is called ‘Measuring point’, where the name of this measuring point can be given.
- In the second and third column the longitudinal and transverse positions of the measuring point are given.
- In the fourth column, ‘Ref.height from base’, the reference height of the measuring point is given.
- In column five ‘Measured type’ is given, in case of a ‘Reference point’ it can be specified, if the measured value is defined as a ‘Freeboard’ or ‘Draft’. In case of a draftmark only a ‘Draft’ can be used.
- In column six the ‘Measured value’ can be given. If a draft is entered, it will be added to the reference height (at the longitudinal and transverse position of this measuring point), and if a freeboard is given it will be subtracted from the reference height. In this fashion the measured position of the waterline at this measuring point is specified.
- In seventh column the draft form base is shown. This only for your information and cannot be modified.
With [New] one always creates a ‘Reference point’. For reading on a draft mark the function [Draft marks] is available. With this function one can read draft marks, as defined in PIAS as discussed in Draft marks and allowable maximum and minimum drafts. If the specific measuring point is a draft mark then the columns 1 to 5 have been filled with data from the defined draft mark and for that reason cannot be modified.
Locations of inclining test weights
In this form the inclining test weights are defined. At the zero measurement inclining test weights can be added or removed, in all the other measurements only specific data can be changed. Inclining test weights which have been create in the zero measurement are available in all the other measurements.
In PIAS two types of inclining test weights are supported, a conventional solid weight (such as a block of concrete or a barrel filled with water), or a tank. From each inclining test weight should be given:
- The name, preferably unique.
- The type (solid weight or tank. In the latter case it must have been defined in PIAS module Layout).
- The weight in ton, in case of a solid weight.
- If this test weight was on board during draft reading.
- A further textual description.
With [New] one always creates a test weight of type ‘solid weight’. For adding weights of type ‘tank’ the function [Tank list] is available. Here is a list of all the tanks that can be used as a test weight. This function does the same as the function with the same name in Loading — which is discussed in Define/edit weight items under function [Misc].
The particulars to be entered for a specific type of test weight are:
- From a (conventional) solid weight the longitudinal, transverse and vertical position of its CoG is given, relative to APP, centerline and baseline. The ‘weight’, in metric tons, of the solid weight has to be defined only once at the zero measurement.
- From a tank used as inclining test weight the (weight-) content can be given. Here the user has the choice to use the most convenient parameter from weight, percentage of filling, volume, sounding or ullage. Souning and ullage are only available if the tank in question has a properly defined sounding pipe, see Sounding pipe.
Weights to be added, subtracted or relocated
When conduction an inclining test or light weight check, not each and every weight will be on its final position. In practice always some weight adjustments will have to be made, commonly called weights to add or to deduct. That can be done by this menu option, which is subdivided in three catagories.
Weights to be added to lightship
Weight to be added to light ship, where for each weight item the name, weight and CoG should be given.
Weights, present on-board during the test, not belonging to light ship
Weight, present on board during the test, not belonging to light ship. Just as with the previous category this can be simply unconnected items, with name, weight and CoG. However, one can also use the function [Tank list], as described in Locations of inclining test weights, to add weights of type tank, as defined in PIAS (with Layout). If feasible, this feature is certainly convenient to use, because then giving just a percentage of filling, or sounding or ullage will suffice, and be used to calculate volume and CoG of the tank content, taking into account heel and trim.
Weights, present on-board during the test, but not on their final position
Weights, present on board during the test, but not yet on their final position. In this menu for each item the weight should be given, as well as its position during the test as well as the final position in light ship.
Print measurement report
Prints the inclining test or light weight check report, below an example is included.
File management
Backups of inclining test data can be be made and restored here, please refer to Data storage and backups for more details.
Print pre-2017 measurement report
Prints an inclining test report or light weight check report, according to the method as being applied by PIAS until december
- For an elucidation on the differences between the methods of then and now, reference is being made to Compatibility with the pre-2016 program version. This option is included for backward compatibility reasons only; now lacking the pre-2017 program version, there would otherwise be no possibility to produce a test report with an elder data file, while with this option there is. Obviously, this option does not work when the input data haven been defined with the contemporary program version.
Background and computation method
A brief elucidation on the computation of GM and KG
For a pendulum measurement applies:
\( GM = \frac {(Testweight_N . TCG_N - Testweight_{N-1} . TCG_{N-1}) . Pendulumlength} {Displacement . (Pendulumstroke_N - Pendulumstroke_{N-1}) } \\[6pt] \)
and for an inclinometer:
\( GM = \frac {(Testweight_N . TCG_N - Testweight_{N-1} . TCG{N-1}) . 1 Radian} {Displacement . (Inclinationangle_N - Inclinationangle_{N-1}) } \)
- Applicable to measurement N, with respect to the previous measurement (N-1).
- For measurement N=1 the previous measurement is the zero measurement (after all, N-1 is zero in that case).
- TCG is the transverse center of gravity of the inclining test weights. Test weight (ton) and TCG (m) are taken from the total of inclining test weights.
The vertical center of gravity (VCG) is computed by:
\( VCG = KM - G'M - GG' = KM - G'M - \frac{FSM}{displacement} \\[6pt] \)
where:
- The KM is determined at the draft and trim of the zero mesurement and the angle of inclination of the current measurement (unless one or more measurements independent drafts have been given, in which case the KMs for those measurements are determined for those drafts).
- G'M is that from the measurement itself.
- The free surface moment FSM is the total of all FSMs (so, from the weights to be decuted, as well as potentially the inclining test weights).
- The VCG of ‘ship during inclining test’ (in the final ouput sheet) is computed with the average of all VCGs (of all measurements and all measuring devices), or with the least squares method, dependant on the applied setting.
- Furthermore, in a inclining test with solid test weights it is assumed that the light ship VCG (including the test weights) is constant during the test. However, if (also) tanks are in use as test weights then this assumption would not be realistic, and will the VCG of the ship (excluding test weights) be computed per individual measurement.
- Because small differences in KM, displacement, trim, etc. between the measurements are included, this can produce a small difference to the classical method, which assumes that these data are constant throughout the test.
Compatibility with the pre-2016 program version
The design of the original version of Incltest was drawn up around 1988. In the course of the years, quite some changes and extensions have been made, but the basic structure has roughly remained the same. Comments and desires of many users have been collected over the years, and haven been used in the implementation of a completely new module which replaced the elder one in December 2016. Many of these changes do not affect the basic methodology of input and calculation, however, there is one essential difference that needs to be explained in more detail:
In the elder Incltest module the movements of the inclining test weights as well as the pendulum stroke or measured inclination were given with respect to the previous measurement. In this new module the positions of the inclining test weights are given in the ship's coordinate system, and the stroke / inclination relative to the zero measurement. With old inclining test data, movements and pendulum strokes are in first instance interpreted in the old way, so that the calculation yields the same results as previously. All the old inclining test data can be found in File management. Old measurement reports, if available, can be printed with the menu option Print pre-2017 measurement report. If one would like to use the old inclining test data then one can restore the data with use of Restore data from backup. The restored data is then immediately interpreted in the new fashion, and the calculations will (consequently) no longer be correct. One should now re-enter movements and strokes in the new convention.
It is not possible to, proceed according the old method, and newly defined inclining test data cannot be interpreted upon the old method.