This is a pretty easy step. It takes the Booleans you have made and converts the Boolean operations to a mesh model just as you converted the Subdivision Surface to a mesh model:
Select the Cabin. In the top Add Modifier subpanel, click on the Apply button. This will make the Boolean modification permanent.
Now, repeat this for the other two Add Modifier subpanels.
In the Layers buttons in the 3D View header, select Layer 1 and Layer 2.
Use theMMB to inspect your sloop.
Press 1 to move to Layer 1.
Increment the file name and save the file.
Congratulations, the sloop is well on its way, now that you have finished the hull and the cabin. Making the basic shape of the cabin was very similar to how you made the boat. The big change was using Boolean modifiers. They made quick work out of cutting out the portals and the door.
So with your model, the Difference operation left all of the cabin that was not part of the Door Boolean. It...