You have noticed that the drafts you see on your screen in LOCOPIAS do not match the actual drafts. Possibly the actual weight of the vessel may differ from the data entered in LOCOPIAS. As the light ship weight is approved by the Classification Authorities, it is not allowed to simply change them. However it is possible to add a correction weight, so that the drafts in LOCOPIAS match better. This manual describes a step-by-step procedure to check the defined loading condition in LOCOPIAS and create and use correction weights.

Procedure correction of light ship weight according the actual drafts

Step 1: Measurement of the drafts

The first step is to measure the drafts on all six draft marks, i.e. both starboard and port. Points of attention:

Determine the drafts by means of a freeboard measurement (digital measuring devices can deviate!)

Step 2: Check tank filling

Now it is important to check whether all tanks have been filled correctly, in accordance with reality. Otherwise, the creation of correction weights is of little use. In another loading condition, this correction will no longer be correct. Points of attention:

Use the correct filling for all tanks, including potable water, gas oil, waste water, water ballast, etc.
Do not forget the residual water in the ballast tanks.
The weight of the cargo must correspond with the loading list.
If required, adjust density for current temperature (density = weight / liters at actual temperature)

Step 3: Observation of the problem

Now the input data in LOCOPIAS correspond exactly to reality and the actual drafts have been measured, you can observe what the problem is. Possible deviations:

Draft
Trim
List

Step 4: Definition of correction weights

Now the correction weights will be created.

First click on [weights] and then click on the [check-displAce] function.

Weights, check-displAce

You must specify the actually measured drafts of the front and rear draft marks. Note: Here the mean of starboard and port side is requested. List is taken into account later on. By clicking on [OK] the correction weight is calculated.

Correction weight calculated

Now select both check marks and click [OK]. You will now see your correction weights in the loading condition: Note: You may need to scroll down because the corrector weights are added at the bottom of the list.

Correction weights in the loading condition

Step 5: Fine-tuning correction weights

Now we turn on the hydrostatics window in the weight module to look at the results. This can be found at the top of [Window]→[Result windows].

Result window

It then appears as follows: (You can reposition this window) Sometimes only the mean value per draft mark is shown, not starboard and port side separately.

Hydrostatics

You may not be satisfied with the results yet. For example, because the ship has list, or because the ship is deflected. We can now "play" with the properties (weight, Center of gravity in Width) of the correction weights until we are satisfied with the results. The effect of the changes can be seen directly in the hydrostatics window. Examples for the specific cases, such as list and hogging/sagging, are given below. Here too, you can continue to tweak until you are satisfied with the results.

Adjusting weight and centre of gravity in width

Trim

You can adjust the trim by adjusting the weight of the correction weights. For example, if you increase the weight aft with 5 tons and decrease the weight fore by 5 tons, the ship will trim astern. You can adjust these weights with small steps until the desired trim is reached.

Adjusting trim with weight

List

The actual list may differ from LOCOPIAS. We can correct this by adjusting the position of the correction weights in transverse direction. If you do not have separate starboard and port draft marks in LOCOPIAS, we will first have to calculate the actual angle of inclination. If separate PS and SB draft marks have been defined in LOCOPIAS you can skip this step. As an example, we assume that your ship is 10cm deeper on port side. Assume you have measured:

	SB	PS	Difference
Draft mark aft	2.60m	2.49m	0.11m
Draft mark mid	2.55m	2.45m	0.10m
Draft mark fore	2.40m	2.31m	0.09m

We first calculate the average difference on all marks: (0.11 + 0.10 + 0.09) ÷ 3 = 0.10m If your ship is 9.60m in breadth, the angle of heel is now: inclination = sin^-1 ( 0.10 ÷ 9.60 ) = 0.549 degrees. If you have trouble with this calculation, you can also perform this calculation online at this website.

Calculate angle of inclination online

Then enter the two numbers in the red circles. Use the button in the blue circle to perform the calculation. The angle of inclination can now be read in the green circle.

In this case, the desired heeling angle is 0 degrees. We move the correction weight to port side (negative) and observe the effect.

Corrective weight to port side

Now we adjust the transverse center of gravity until we find the desired heeling angle. After several tries, we find the desired position in breadth of the correction weight:

Desired breadth

Hogging / Sagging

In LOCOPIAS the ship is simply assumed as a straight beam, which is a standard approach for loading software. A correction on the draft as a result of deflection (Hogging / sagging) is therefore not taken into account. You will have to adjust the correction weights such that the deviation on all draft marks is minimized.

An example Assume you have measured:

	SB	BB	Mean
draft mark aft	3.120m	3.120m	3.120m
draft mark mid	3.155m	3.155m	3.155m
draft mark fore	3.100m	3.100m	3.100m

Below you can see the correction weights that LOCOPIAS has created with corresponding drafts. So on the mid draftmark there is a deviation of 4.5cm, on the other draft marks there is 0cm deviation. The mean of all draft marks in LOCOPIAS is (3.120 + 3.110 + 3.100) ÷ 3 = 3.110m. This should be (3.120 + 3.155 + 3.100) ÷ 3 = 3.125m.

Created correction weights

So the draft of the vessel must slightly increase, or in other words, the correction weights have to be heavier. We make both correction weights a little heavier. After trying a few times we find the following situation:

Desired situation

Modify correction weights in the database

Now that you are satisfied with the determined correction weights, these must be saved in the database. The database can be accessed via the ‘Weights’, ‘Database’ and ’Edit database’.

Edit database

If all is correct, you will already see the correct correction weights. In Step 2 you have already placed these correction weights in the database by checking a check mark. However, the adjustments in step 5 have only been made in the current loading condition. We now take over all values of the correction weights in the “database weight items”.

Edit database

Use the correction weights for every new loading condition

In case of any new voyage/loading condition, the correction weights must be used again. You can retrieve the correction weights from the Weights module in the database with the [Read dataBase].

Read database

The following window will now appear:

Read database

By selecting a correction weight and clicking on [OK], the correction weight is added to the current load condition. You should do this twice so that both correction weights are included in the new loading condition.