Moonglow Bay

The cost of the tow back to town is 10% of the total shells you currently have. So, to unlock this achievement you need to earn enough shells to have at least 5,000 shells, e.g. by selling fish meals. During one of the missions in chapter 3, you have to renovate the Library which coincidentally costs 5,000 shells, so you could do it at this point. However, this is not necessary and it can be done at any time after you have access to the boat and radio.

Once you have reached this amount, use the save/load menu to save your progress. Next, go out to sea in your ship, go inside the cabin and use the radio with the telephone icon (press ) to call Abi for a tow back to town. Once you are in the boat shop, you will unlock this achievement. Now, go back into the "save/load" menu and load your save file (select the save and press , , ). You will now still have all of your shells and this way you will not negate the Versus the Sea achievement if you haven't finished the story yet.

Optional: if you make sure that your ship is fully functional before calling for a tow (you can buy repairs at the boat shop if needed), you will unlock this achievement simultaneously