Estimating Weight

Estimating weight

1. Filtering the coefficients in the graph

One of the strong features of ShipWeight is the possibility to do logical selections of the coefficients to be plotted in the graph. This makes it easy to plot only the relevant coefficients in the graph and thus obtain a good regressionline and a good coefficientfor estimating.


2. Graph options

Under the Graph menu in the estimation dialog, many options are available for displaying different information in the graph.


3. Saving settings in the estimation window

The menu makes it possible to save settings in the estimation window so that the next time you enter the weight group you retrieve the same settings in the window as you had when you last saved your settings.


4. Starting a new estimation

When starting a new estimation, selecting the reference ships is the important issue


5. Starting a new project based on the results from the estimation

When the weight activity turn from estimation into a weight take off (WTO) activity, we establish a new project.

There are two philosophies for the weight control activity;

· start with an empty project and enter weights toward 100 %

· start with the estimate and continuously replace weights with more exact (reliable) ones.

In the last-mentioned case, we will always have 100 % in the database.


6. Taking uncertainty into account

In the estimation area, the right-hand column contains information about the standard deviation. The standard deviation can be given either as an absolute value or as a percentage. To switch between these ways of showing the uncertainty, select the Std. Dev. in the estimation dialog.

The deviation of the selected estimation coefficientis calculated from the spread of the coefficients around the regressionline. If the number of coefficients is less than three, the deviation cannot be calculated. Then a value based upon subjective judgment can be manually entered into the grid.

If some of the other parameters are uncertain, an uncertaintyvalue should be entered into the grid to the right parameter value. When all parameters have got appropriate uncertainty value attached, pushing the button in the estimation areagives the total uncertainty for the weight in this weight group, and this value is stored.

By the use of successive calculationsthe uncertaintyfor a weight group containing subgroups, will be calculated on the basis of the uncertainty of the subgroups.

Even though the uncertaintyis an approximate method to obtain the uncertainty for a weight and even if you have to set the values yourself for most weight groups, there are several reasons to take the uncertainty into account. First of all you will be able to use your resources where they are most needed.

When selecting Most uncertainunder the Std. Dev. menu in the main window, ShipWeight will take you to the weight group where a further estimation and splitting of the group will give the greatest impact on the total result. This will help you to focus on the weight groups that really matter at any stage of your estimation. Secondly, taking uncertainty into account will give you a basis to compare the uncertainty between different projects.

7. The estimation dialog

From the Estimate button in the toolbar or by selecting Weight… on the Estimate menu, the estimation dialogbox will pop up.

The estimation dialogcontains four major areas, the graph areaat upper left, the plotted ships list at the upper right, the estimation areain the middle to the right and the comparison area in the lower part of the dialog.


8. Using the remainder group in estimation

Combining known and estimated weights
It is possible to estimate weight groups consisting of sums of sub-weights. This is particularly useful when some of the weights are known while others must be estimated. If an estimate is carried out on a weight group containing data in any of its subgroups, the difference between the estimated value and the values of the subgroups automatically will be added to the Remainder-subgroup.
For example: you are to estimate the weight group M1 (Machinery), but already know the weight of some of its subgroups e.g. M1.1 (Diesel-engine for propulsion). Make sure to enter the known weights of the subgroups. Then estimate the weight group M1. The difference between the estimated weight for the group and the weight of the subgroups is added to M1.R (Remainder machinery).

Dynamic Remainder: Freezing the above weight-group
It is possible to keep the value of the above weight group unchanged while estimating. This is done by adjusting the Remainder according to the new estimate. To activate this mode, select Freeze wgt.grp. over on the Estimate menu or press the corresponding button in the main window (key).