Go to the project you want to export

Open Project | Export | Data File...

Open Export | Export Project
Select a Directory where you would like to store your data file.
In the string for where you have stored your datafile add a file name at the end and .xml
Copy the path and the name of the file so that you can past this in when importing the file again.
Click Export project to xml. 

Now there will be a file ready to import in the location you selected.

If you would like to import that file copy the path and the name of the file. 

Open Project | Import | Data file ...

Go to the Import tab and select Project Import
Past the location and the file name into the XML Project file box.
Write in the new project name and select Import Project to ShipWeight. 

Open the project you created.