I also found more detailed description of the Hjortspring boat's design and construction, some of which contradicts my interpretation of the painting that appeared in the previous post:
The Hjortspring boat with its peculiarities was the result of a very skilful builder's work. It is a round-bottomed boat made of five overlapping planks stitched together, midships 20 ins. broad and 5/8 ins. thick, which are joined to two end-pieces each hewn from a solid block. The bottom plank projects like the end of a runner outside the boat proper, and between this runner and the elongated "noses" of the end-pieces these remarkable vertical end-posts are fitted. When hewing the planks cleats were left into which thin ribs were attached with bass binding. Ten thwarts in the narrow boat gave room for twenty paddlers, and it is believed that the craft was used for warlike purposes.With its overlapping planks, this boat is approaching subject matter that this blog typically eschews: it appears to be in the line of development to the lapstrake boat that's at the heart of the western boatbuilding tradition. The description of the end-pieces does seem to be similar to those of the Polynesian five-part canoe, which I had discounted in my previous post.