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. It takes a short time to load as it's a GIF image)
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 snappier photographs of how to do it! (click here).
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