I'm more invested in the lore of these comics than I should be. Rarity's a ship captain, Fluttershy and Spike are part of the crew, but I don't know in what capacity. This is the first one I saw which only mentions Fluttershy working on a ship, so initially I thought she was some kind of environmental activist trying to protect marine life. The threesome with Rarity and Spike, however, is explicitly a callback (or call forward, I don't know the order these were published in) to another comic establishing Rarity as captain. Yet another comic has Rarity, Spike, and Vinyl Scratch fucking in a pool, and it's stated that Rarity hired her. Assuming this also takes place on a boat, it alludes to a cruise ship more than anything but isn't outright stated.