Expansion of bottom planks - P O cedar

[Fletch]

Last fall we built a replica of the Julius F, the boat Buzz Holmstrom used to run the Colorado River in 1937. The boat is considered the apotheosis of wooden river boats in the southwest among many guides. We built the boat using Port Orford cedar. The material had air dried in Flagstaff for four years after having been milled in Coquille, Oregon. The story of our construction project as well as our commemorative run down the Rogue River can be viewed at http://www.riverstouch.com/ Now, here's our problem: the bottom planks have expanded a full inch. The rivets and clench nails have not sheared, near as we can tell. And there are no leaks. We think we have a solution figured out, but my question is this: how could we have avoided this problem in the first place?
Thank you. Roger

[RGM]

As my old friend and ex-coworker Dave points out, the Port Orford Cedar made quite a jump in humidity going from the PNW, then air dried in Flagstaff for about 4 yrs, then stuck in the water. You say the planks swelled an inch overall. Would that be about 1/8" per plank? How wide are the planks? Are they flatsawn (sounds like it) or vertical grain? I guess if it were me and I was going to do this again I would consider using narrower planks, and I would be sure that they were vertical grain/quartersawn. Good luck.

[Fletch]

The cedar planks 10" wide by 3/4". Total expansion is about 1/4" per foot, or just under 1/4" per plank. The result of this expansion has been a separation from the frames at the chine. The planks are cvg.

I suppose one "cure" would be to keep it wet, pull the screws, bring the sides back in where they belong, then rescrew and retrim the
bottom. Then allow the huge gaps to form when it is dry, and count on dropping the boat in the river a week early for the next trip.