Monday, December 21, 2009

Finishing the Hull

Things have happened quickly the last few days on the boat.  In the interests of time I will just post photos from the last three days and throw captions under them.  My apologies for the brevity but remember, you should always be able to click on a photo and enlarge it.  Take a look around.

We fit the gwa gwa at either end using the suri noko method, after planing to the best fit possible, running a saw through the seam several times to make the fit perfect.

This is new for readers of this blog: The endgrain joint of the gwa gwa, which is a very shallow V-shape, is pounded with a hammer, compressing the fibers so that after the pieces are put together these fibers will expand and make the joint absolutely watertight.  This method is used in other ways throughout Japan.  I have been wondering how we were going to handle this large endgrain joint.  Shimojo san pounded this to a point where the cedar had been compressed at least 1/8".  He worked a little more gently near the edges so not to split them.  Then he very lightly planed the high spots and we put the piece in place and did several more passes with the saw in the joint.

Helping and researching at the same time: I brace the gwa gwa while Shimojo san pounds the endgrain while I take notes on this method.

Shimojo san said that in the old days, the sabani's planking came together along the bottom near the bow.  He said that the gwa gwa was much smaller and the seam ran level (as indicated by the batten).  Shimojo san said that this plank seam underneath the bow was very weak (but partly the result of very wide planking material).  The current form evolved and Shimojo san believes it greatly improves the boat.

Planing the forward gwa gwa to a rough shape.

The gwa gwa dogged down with staples.  We've glued it to the planking (even glued the endgrain).  Then we installed huundu and bamboo nails.

A detail of the huundu and nails holding the gwa gwa aft.

As of yesterday, awaiting final sanding.

Spent over half the day sanding the hull, 60 grit followed by 100 grit.

In the old days it was shark liver oil, which I am told you could smell at a great distance (and it didn't smell good).  Now we are using soybean oil, the kind used for cooking tempura.  We put a generous amount on the boat at the end of the day today.  Shimojo san said it could soak up plenty.  I am not sure if we will put more on tomorrow or not, because we are turning the hull over tomorrow.  Seems that an oily boat would not be a good candidate for rolling over, but I will find out.


  1. Dear D.:

    I am doing my best to stay up with how this project is preceding. I do so look forward to reading it each time. You are covering so much information that American and Most European wood workers are unfamiliar with. "Killing wood", (I have forgotten the japanese word for this, could you ask Shimojo san?) is a very old, (and forgotten,) technique, that actually goes back, as some much does, to the Nile Valley 1000's of years ago. Tell Shimojo san that those ancient boat builders on the Nile River would be honored to see traditional techniques are living on. I just "killed wood" on a joint the other and those watching thought I had lost my mind when I got my hammer out and started smacking portions of the joint!!! It is wonderful that you are doing this, I hope you have all the details recorded for posterity. If I ever can steal the time and can pull my notes together, you and I should finish a book together updating modern wood workers to the lost and ancient methods of the East and Middle East, the true heart of working with wood.


  2. Thank you, Douglas!

    I've been wondering, since the bottom was fitted how the end plank joint was done, expecting some type of joinery. But here we have proof, once again, that simple is best.


  3. To answer Jay and perhaps others, the Japanese verb "to kill" is "korosu" and I have heard this technique called "kigoroshi" (ki+korosu, or wood+kill) and Shimojo san has called it korosu. I need to make sure he doesn't have a local term for it, however. I remember my first "real" Japanese boat, the seaweed boat, and we lavished all this attention on sawing the planks seams, and then we stood the planks on edge and my teacher started pounding them! But even my barrel maker teacher of the tub boats used a version of this technique. To answer Jay's email: We carefully fitted those endgrain joints, probably made at least a dozen passes with the saw. Then we pounded. He lightly planed the high spots then we did the sawing technique about four more times. I do wonder about his putting the hard glue in the seam. It seems to defeat the purpose of letting the endgrain spring back. I'd say stick the timber in a bucket of water and then fasten it on! In the West, I would definitely reach for a non-drying bedding compound here, one that would let the wood spring back without resistance. Of course in the old days here (not that long ago) there would have been no glue. Shimojo san also said that he would have pounded both faces of the joint, but he feels that this is not necessary with the glue. By the way, I have never seen anything analogous to bedding compound used by boat builders in Japan.


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