I belive almost, if not all, Artesania Latina ship are double planking. Nevertheless, in case I am wrong or is missing in that kit, buying a second planking, for example walnut, is not expensive at all. Check eBay or Model Expo in USA or many others around the world and you will see it is cheap. Moreover, the Swift is a small ship, so you will not need to much. You can count how many woods planks have you used for your first planking and add a few more. Get the same width of plank.
My very first ship was the Swift from plans following a Spanish Magazine subscription (Modelismo Naval). On each magazine you had pictures of the part to be built. All from scratch. That was in Argentina 30+ years ago. I have a special feeling for that ship..... you can imagine why.
Enjoy it !!!
Daniel