The following comes from the book, How ? (or Spare Hours Made More Profitable for Boys and Girls), published in 1887. The plot thickens around Figure 7, but with a little luck, I'm sure you can do it. (Be patient. The instructions take a short time to load as they are GIF images of the book's pages, but hopefully in the time it has taken you t read this they have loaded).
While the instructions call for a 3 inch x 4 inch piece of paper, I've found the US standard 8.5 inch x 11 inch works just fine. I suspect A4 would do also.
While I like the above, as they were printed in the midst of the Paper Boat era, you can find some even more detailed step-by-step instructions with photographs of how to do it! (click here).
And for extra credit and if you want to move on from making paper boats, you could try a 19th Century Paper Hat.
Everything here is © Ken Cupery 1997