Lightweight Dialog

Lightweight Definition Dialog.

It is to be noted that only one lightship definition is allowed for within a Calc project and this is then associated with all of the different deadweight loading conditions that are subsequently created. Hence you can only accept and not modify the system assigned title of Lightweight Definition. Calc will not prevent a User from including more than one Lightweight node within the Application tree, however the internal files and the Edit command will only operate on one single Lightweight file, namely the first one that is created.

You can, if he wishes, group the various input items into different categories by name, for example into hull steelwork, outfit steelwork, superstructure/deckhouses, outfit systems, machinery, , and can carry the refinement to whatsoever level that he has some data for and/or has confidence in. The input data does not need to be sequential and several different items can be simultaneously distributed over overlapping lengths of the hull,

For each weight item, you specify:

1. A Name to simply help in identification.

2. Its Weight, (tonnes or tons).

3. Its centroid, defined by the LCG, TCG, and VCG, which are measured relative to the vessel's origin (units: meters or feet). you must provide an entry for each LCG position, however the TCG and VCG items can be given zero values. (Clearly an item that is symmetrically disposed about the vessel’s centreline will have a TCG of 0.0.)

4. A value of free surface moment, FSM, if necessary, (units of: tonnes-meters or tons-feet).

5. The Aft ext and Fwd ext, which are the extents of the item over which its weight should be spread, measured relative to the vessel's origin (units: meters or feet). The lightship weight distribution is made up of trapezoidal items, the number being dependent upon the detail required. Note the LCG of the item should lie in the mid third of the defined extent of the item. Thus the distribution can be uniform or triangular over the defined extent. Large local weights could be distributed over a relatively small length, which would be consistent with the physics of real objects, however you could also input the same dimension for the Aft and Fwd extents if he wishes to simulate a point weight.

A summary of the current total lightweight, the corresponding overall centre of gravity position, and the FSM, is displayed at the bottom of the dialog. This summary is automatically updated following each complete row of data entry.

By clicking on the appropriate report results icon you can obtain a plot of the corresponding lightweight distribution.

The ShipWeight program from BAS Engineering (http://www.bas.no) is useful for producing a good lightweight estimate and longitudinal weight distribution. This program can output a file that can in turn be read into Calc by clicking the Import ShipWeight button.

Clicking the Export ShipWeight button, enables you to write a ShipWeight type file, which can in turn be re-imported into Calc. The ShipWeight file is a simple TAB delimited file that can be read into, for example, MS Excel.

A Lloyd’s Register type distribution can be generated, by clicking the LR Distribution button. This will bring up a dialog, where you can enter the parameters for constructing this, ie weight, centre of gravity, block coefficient, and parallel midbody. A number of weight items, identified by the prefix, LR, will be entered in the table. These will approximate the LR distribution. The number of these items can also be specified by you. You also have the option of deleting all existing items, or just adding to those already defined.