Let us say that you are loading in tropical load line zone and destined for a port in summer load line zone.

The entry point of summer load line zone is 10 days sailing and ship's fuel consumption per day is 40 tons.

So from load port to the entry of summer load line, fuel consumption would be 400 T.

Calculate the fresh water in the same way. After 10 days of sailing will you have more, less or same amount of fresh water?

Let us say your fresh water generator produces 15 T of fresh water per day and average consumption of fresh water is 10T. So in 10 days, you will have 50 T of more fresh water.

So you can afford to load 350 T of more cargo above the summer load line. This 350 T will be consumed during 10 days of sailing and you will be at summer load line after 10 days of sailing.

Now how to plan to load this excess 350 T of cargo. 

Let us say summer deadweight is 80000 T. Can you load 80350 T and comply with the load line zones?? 

The answer is No. Because the compliance is not based on the deadweight but on the freeboard (& hence the drafts) at the midship.

Here is how chief officer needs to plan this.

Plan for the point when the ship will enter the summer load line. Enter all the consumable you will have at this point. Which will be 350 T of less fuel from the date of loading and 50 T of more fresh water.

Enter these values in the loadicator. Each vessel experience different amount of SAG when fully loaded. This is by the experience of the ship's crew. Usually, a Suez max size vessel will have around 10 cm of SAG.

Allow this sag while looking at the loadicator drafts at midship.

Once you have the loadicator condition for the point of entry of summer load line, enter all the present values of fuel oil and fresh water etc.

This will be the condition that you have to load at the load port.

When going from the summer load line zone to tropical load line zone, there is nothing extra you have to do. Because you are already in summer load line and you can only load up to summer load line.