I am not familiar with the Carius design, but here are some broad generalities about the construction type that you are describing.To start with, there are a lot of ways to build a wooden boat and each have their own advantages and disadvantages. I am a big fan of many types of wooden boat construction for a lot of reasons. Properly constructed a wooden boat can offer relatively low maintenance and low cost especially for a custom boat, or where the owner is doing much of their own work.
Strip planking has been around for a very long time but really first really achieved popularity in the late 19th century as machine sawn lumber became readily available. In traditional construction, strip planking is generally edge fastened, meaning that the planking is fastened plank to plank through the edges of the plank, rather than through the face of the plank into a frame which is how conventional carvel planking is fastened. Because of the potential for splitting the planking, Strip planking generally requires thicker planking resulting in a heavier (but not necessarily stronger) hull than any other type of planking.
Strip planking takes a bit less skill to construct because the individual planks do not need to be spiled (cut to shape)and depending on the design also can take less time as well.
Because of the greater planking thickness and mechanical fasteners, Strip planking can often have glued edges which can allow a hull to dry out without leaking. Glued strip plank hulls require far less framing than a carvel or lapstrake hull because they behave in a similar manner to a monocoque such as steel or fiberglass, but with a distinct strength bias parallel to the grain of the planking.
The biggest disadvantage to strip planking is the extreme difficulty in repairing it. Because it is edge fastened you cannot make simple repairs because you can''t get to the fastenings. Strip planked boats are more often than not fastened with ferrous fastenings between the planking (Because they are so fastening intensive and the fastenings are somewhat protected) This tends to greatly limit their lifespan to something resembling 20 or so years. The great frequency of joints also makes Strip Planked boats more prone to rot than other planking forms.
As to the specifics of the boat in question, Western Red, and Port Orford are generally considered the best quality planing materials for strip planking with white cedar a somewhat distant runner up.
The sheathing sounds like it is there simply as a moisture barrier, to increase
paint lifespan, and to increase the abrasion resistance of the hull over cedar which is a pretty soft wood. It does not sound structural because if it was structural you would expect the interior the hull to be glassed as well and you would not expect internal framing. There can be extremely serious rot problems with strip planking that is glassed on only one side and so the way that this boat is constructed is generally discouraged if durability is an issue. Also glassing on one side encourages delamination of the glassed side over time and so at some point this boat will need to be re-glassed.
I also question the choice of framing materials. Fir is a pretty marginal material for athwartship framing on a strip planked boat. Unless well sealed, fir is pretty rot prone and also fir tends to be a little brittle and becomes more rot prone and brittle with steaming. The rot issue is very important as the fastenings for the plank to frame connections generally allows water access to enter the core of the frame and rot it out invisibly.
I would be expecially concerned with the choice of cedar for the floor timbers. Floor timbers have a tough job to do in a stripped planked hull. They are the single means of distributing the major keel and
rig loads athwartship across the joints in the planking. They need to be sturdy, tough and very rot resistant. That would not fit my description of yellow cedar.
So my strongest advice is to find a marine surveyor who really knows wooden construction and have him do and extremely careful survey of this boat. The fact that the edge fastening materials are not mentioned really concerns me. In strip planking that is the most critical element in predicting how well a boat will stand up over time.
Respectfully
Jeff
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