Double Planked Cedar and Fir

[hm0316]

I would appreciate any pros and cons on longitudinal double planking of a hull with cedar inner planks and fir outer planks. Thanks. hm0316

[Chan]

Pretty common. Even more common to strip plank with wrc and cold mold 2 layers with fir.

[GregH]

Chan-

Please continue: I'm curious about the 2 cold-molded layers of Fir, as opposed to say 2 of cold-molded layers of WRC. Greater strength, impact resistance??? Thanks

[Bob Smalser]

The problem is the seasonal movement changes between Doug Fir and the typical light cedars aren't at all close, and as a minimum will strain the fasteners, shortening longevity to one degree or another. The heavy cedars like Port Orford and Alaska Yellow are a much closer match, but the woods are expensive and harder to find than lightweight Western Red.

If I had to use a light cedar, I'd use flatsawn WRC and VG DF to get as close a match as possible. The worst case of flatsawn DF and VG cedar is almost enough to pull the boat apart when combined with old planks, deteriorated paint and too long on the hard. With even minor neglect, it's possible to achieve two inches or more difference in movement between the two planking layers every 10 feet of linear expanse.

Otherwise you might contact Dave Fleming. His ideal is DF below the waterline and cedar above, which could be done with double planking as well as single. Gets the tougher but less stable wood in the water were its MC will be relatively constant, and the stable wood on top where it alternates between getting wet and baking in the sun.

Strip planking is a different critter entirely.

[hm0316]

Bob, thanks for your insights. My earlier reply apparrently did not post, so I will try again. The double planking is a rebuild of what was orignally mahogany over Port Oxford cedar. The originally planking is still in place above the water line and the cedar/fir is below the waterline. The fir is quarter sawn Douglas Fir (stair tred material) and the cedar is Eastern white cedar. Orange shellac was used between the cedar/fir layers in the rebuild. The boat has generally been stored wet, but will be moved to Maine and hauled for the winter in the future. Any thoughts you may have would be greatly appreciated. Many thanks, hm0316

[Bob Smalser]

The double planking is a rebuild of what was orignally mahogany over Port Oxford cedar.

The originally planking is still in place above the water line and the cedar/fir is below the waterline.

The fir is quarter sawn Douglas Fir (stair tred material) and the cedar is Eastern white cedar.

And what is it that needs fixing?

Qsawn DF shrinkage factor is 4.8% and flatsawn cedar is 5.4%. That's a close match.

[hm0316]

Bob, thanks for the reply. Probably I should have been clearer. As far as I know, nothing needs to be fixed. The issue is going from keeping the boat is in the water year round to Maine where the boat will be out of the water 6-7 months a year. I was worried about how the two different woods might react. hm0316

[Bob Smalser]

The cedar-fir will be fine below the waterline, providing the boat isn't left out of the water long between May-September. Keep the paint up on the POC-mahogany topsides.

[hm0316]

The cedar-fir will be fine below the waterline, providing the boat isn't left out of the water long between May-September. Keep the paint up on the POC-mahogany topsides.


Bob, thanks. hm0316

[hm0316]

Bob, your explanation inspired me to read some of your other posts. You know a lot about the demensional stability of wood. I think I am beginning to understand. POC, mahogany and Douglas Fir (at least some kinds) are pretty close. I'm still a little unclear on whether "Eastern White Cedar" is the same as "Northern White Cedar", but if it is then it appears Eastern White to be closer to Douglas Fir in the tangential direction than the the radial. I may be completely off. hm0316