I know this is kind of long, sorry about that. But it took me a bit to get importing to work and this works for me on all play mode types. Some of these steps may not be needed but this is how I did it. Hopefully it helps ^_^
I download the sment. file then I throw it into my Starmade folder (no specific location just inside the folder). Then open the game client, click "start game" so it takes you to the screen where you would enter your name and or server IP's, then at the top of that menu go to Tools, then Open Ship Catalog Manager. When it opens click import and it should by default have you looking inside your Starmade folder where you put your file. Find the name of the file you downloaded and put in there and click it. It will NOT show up on list right away but don't worry. Close the client fully and re-open it (if you want when you open the Open Ship Catalog Manager now it should show the name of your import). Next start up your game in whatever mode you play in (ive tested this on single player, public servers, and a private hamachi server and it worked on all). After you are in game travel to any shop. When within shop range open up the menu (using "I" "B" or "N" whichever you prefer) then click the Catalog tab.
THIS is where most people don't put instruction. When in the Catalog tab you will see 3 tabs INSIDE Catalog near the top of the menu "Personal" "Available" and "Admin" GO TO Personal and on the top right of that Personal Catalog you will see a green "Upload entry from local" button. Click that and it will ask you to type in the name of the ship you want to import (all of the available ships should be in [----] <---brackets type the name in EXACTLY as it is in the brackets (if more then one name spaced by a comma just type in that one name for the on you want, not every name possible). Click OK and on the top left of your screen you should see it uploading after it uploads gift it a few seconds and it should now show up on you personal list. Click the name on the list and it will open up a BUY button (along with others). Make sure you have enough money to cover the "price" and click buy. It should appear somewhere near you (I always look for the blue arrow that pops up after it spawns, the blue arrow that shows near by "friendly" ship cores). AND THATS IT you now have a imported ship in your game to fly around in a conquer your enemies.
I really hope this helps everyone. And ill answer and more questions to the best of my ability.