Double planking: pros & cons

[Glider]

I have read several threads on double planking, but did not get a full picture. When I think about double planking (longitudal), I see the following points:
Pros:
+ More water-tight (but not for the rabbet seam?)
+ Wood quality is less critical
+ No (re)caulking needed
Cons:
- Less rigid (and probably less strong, for the same thickness)??
- Less durable (if water is trapped between layers)
- More difficult to build
- More difficult to repair

Is it correct? I'm building single-chine 36' boat, and just thinked about this method...

P.S. When I say that double planking is "less rigid" I mean that it's more easy to bend 2 layers of 1" planks (not glued together) than do the same with one 2" plank. I'm not sure about this.

[ 02-28-2006, 08:44 AM: Message edited by: Glider ]

[Dan McCosh]

I think you have most of the pros and cons. The rigidity is not really an issue, however, as the stiffness of the structure after being fastened would be at least as good as a single-planked hull. The technique was considered a luxury feature, more costly due to the waste in lumber and additional labor involved. i think with some new sealants available, it would be even more superior today.

[Glider]

I suppose there may be some specific issues with the single-chine hulls:
1) Isn't it much more easy to fit planks? May probably use standard stock without almost any squaring (fitting).
2) How seam at chine should be treated? Caulked?
3) Should diagonal (cross) planking be used for both layers on bottom sides?

[ 02-28-2006, 09:24 AM: Message edited by: Glider ]

[seo]

N. Herreshof built many boats double-planked above the waterline, often cedar or cypress under, mahogany over, then single planked with yellow pine below the wl.
Double-planked hulls finish well, don't show seams, and the double planked hull contributes to the panel stiffness of the structure, which is lacking in carvel planked. Lots of extra work.
The credulous mind might accept the idea that strip planking with resin/fiber over is a modern derivative. Certainly cold molded is related to double planking (and ashcroft).
One of the problems with having a very smooth shiny fair hull is that people say "it looks like fiberglass." Hell, if I wanted a boat that looked like fiberglass, I'd a bought one...
seo