Building a Hozugawa Ayubune Model in 1/10 Scale – Part 3

My illustration of the ayubune, based on plan drawing by Douglas Brooks (with his permission). Position and size of details shown here are only approximate.

Counting up all the major planks, transom, and beams, this Ayubune model will be made up of only 17 pieces:

  • Shiki (bottom) – 3 pieces
  • Omote no tate ita (bow plank)
  • Todate (transom)
  • Tana (hull planks) – 4 pieces, 2 on each side
  • Omoteamaose (bow platform)
  • Tsunatsuke (lit. rope attachment) – Bow beam
  • Omote no funabari (forward beam) – 3 pieces
  • Tomo no funabari (aft beam)
  • Tomoamaose (stern platform)
  • Transom Strake

In addition to these, I made patterns in paper for obtaining the proper angle for the lay of the hull planking. I have yet to decide at this point just how I’m going to fix the hull planks to that angle. But, there’s time before that needs to be deal with.

My second illustration of the ayubune. I’ve labeled most of the parts here, but haven’t been able to get the names of all of them yet.

The bottom, or shiki is the first major assemblage. I’m following Douglas Brooks’s build, where he built the shiki from 3 pieces. But, he points out that the Japanese boatbuilders tended to use smaller widths of boards, so they could efficiently replace boards damaged from operating in the rapids of the Hozu river. The same is true of the bow plank, which in this case might be more commonly built from 2 pieces, with the seam running parallel to the centerline of the boat, but off center.

In any case, for this model I decided to build using some 3mm sugi, Japanese cedar, which comes out to about 1 sun thick planks on the real boat. I think I could have gone with thicker wood, up to 1.5 sun.

If confused about shaku, sun, etc., see my Japanese measurements page.

As I mentioned before, sugi is a bit difficult to work with. Were I to build this model at a smaller scale, I’d consider using hinoki, or it’s western equivalent, Port Orford cedar. I want to build this model as the Japanese boatbuilders do, so sugi it is.

I cut the bottom planks in such a way as to optimize my limited supply of wood. The widest plank is the center plank, which I made 1.45 shaku (remember, there are 10 sun to 1 shaku, so that’s 14.5 sun) wide. The other planks then came out to be about 0.8 shaku wide. All shiki planks were cut about 11 shaku long.

I don’t think it really matters how wide the center plank is. In this case, it is the same width as the bow plank, which I’ve seen done before on real boats. I think this is simply a matter of convenience, since the center plank and the bow plank can then be simply be cut from the same piece of wood.

Next, I drew registration lines for the mortises in the two outer bottom planks. These will end up on the bottom of the model, so some might feel this an unnecessary detail. On one of Douglas Brooks most recent Ayubune, which he built for an American customer, I noted that he had the mortises on the inside of the boat so as to be more noticeable.

Using the same techniques I experimented with in my last post, I marked and cut the mortises in the outer bottom planks. And, while I was cutting wood, I went ahead and made the bow plank, which is very simple. On a boat this size, this can be made from a single piece.

Everything turned out well enough that I decided to go ahead and glue up the bottom planks. The plugs still have to go in, but I felt confident enough at this point that the plugs wouldn’t cause me any difficulties.

I shaped a piece of wood cross-grained to cut the plugs from, as I don’t want end grain showing for the plugs. They should be very subtle in appearance. Of course, all this is going on the underside of the boat, so it’s pretty well all unseen detail anyway.

With all the plugs glued into place, the whole thing was left so they could dry securely before trimming. Once dry, I put my “wide” tipped Japanese chisel to work. I’ve now accumulated a half-dozen of these tools. My largest straight tip is 4.5mm or about 3/16″, but this particular line goes up to 7.5mm or about 5/16″.

Trimming the plugs

Before and after plugs trimmed

During the process of adding and trimming the plugs, some plugs came loose. I discovered that clamping the glued-in plugs wasn’t good enough, so for the repairs, I cut the plugs first, glued them into place, and them tapped them home with a small jeweler’s hammer. This made sure the plug fit tightly, all the way into the mortise.

Tapping the plugs to make sure they’re fully seated

This is the way I’ll be putting plugs into place from now on. Also, when dry, I have been putting a drop of water on each plug, with the idea that it will swell and make a tighter fit. I don’t want to wet them too much, as the wood glue I use is not waterproof. Too much water may dissolve the bond.

After the bottom was completed, I cut the transom, and then the project sat for a while until I could figure out how I could put the pieces together without any frames or ways to secure the pieces into position long enough for me to glue them together and also be able to be mark off patterns for shaping the hull planks and, of course, fastening the hull planks into place.


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