Planking Method Comparisons
February 26, 2011
Paul in carvel, clinker, cold molded, glue, hand tools, planking, self-fairing, strip planked, traditional

What are the differences, and advantages and disadvantages between different traditional and glued construction methods? (Carvel, Clinker, Cold Molded, Strip Planked)

Traditional Methods: Carvel

Carvel is edge to edge smooth skin with caulked seams. All planks are individually shaped to follow the curvature of the hull. They vary in width along their length in order to compensate for the girth difference between the middle of the hull and the ends, and they are also shaped in their thickness to fit the curvature of the sections. That is, they are hollowed out on the back and rounded on the outside. Carvel works best when planking thickness is 3/4" or greater. It is possible to go down to 1/2" but the caulking has to be done very gently.

Traditional Methods: Clinker (Lapstrake)

Below 1/2" plank thickness clinker comes into its own. Here the planks overlap and there is no caulking. Watertightness comes from the fit of the plank lands and close spaced riveted fastenings. Clinker is generally quicker than carvel as the planks are not shaped in their thickness, only in their width. Clinker is a great way to build small traditional boats.

Both carvel and clinker are done over bent frames in small boats, in larger sizes carvel may be over sawn or laminated frames.

The advantages of the traditional methods are that they are usually the quickest way to build a one off boat. They are to a large degree self fairing, that is because of the natural spring in the wood of both planking and framing, unfairnesses that exist in the temporary molds will show up and can be corrected, or will be self correcting when the molds are taken out. Also it is pleasant work, no glue or fibreglass means no latex gloves or respirators and most of the work can be done with hand tools.

The disadvantages of the traditional methods are that the boat relies on the swelling of the planking to stay tight and if the boat is kept out of the water on a trailer, it will likely leak a little when it is launched until the planking swells again. In larger sizes the wood to build traditionally is getting harder to come by.

Glued Methods: Cold Molding

Cold molding is distinguished from its predecessor hot molding by the fact that the glue will cure without high temperature. This technology came out of World War II when airplane fuselages were made from multiple diagonal layers of veneer laid up over a jig and then baked in an oven. It wasn't until after the war that cold setting glues came along and cold molding was born.

In cold molding most of the planking goes diagonally, in alternate directions with the outer layer running fore and aft to avoid diagonal plank lines showing through. The planks are individually shaped to compensate for girth changes but are thin enough to bend without steaming in both directions. Essentially in cold molding we are building a piece of plywood that conforms to the compound curvature of the hull. Because the planking layers are thin and glued to each other into a monocoqe structure, the finished hull will retain any unfairness that exists in the jig over which it is built. There is no self fairing as in the case of traditional methods and therefore the standard for lofting and jig making must be higher if a quality hull is to result.

There is no question in my mind that of the glued methods, cold molding is the superior system. It is utterly stable, has maximum strength and minimum weight.

The only disadvantages are that there are more hours in a cold molded hull than a conventionally planked one and on aesthetic grounds it is not always the best fit with the character of the boat. The lack of framing and the flawless finish tend to give cold molded boats a too perfect, 'plastic' finish that often makes them indistinguishable from glass hulls. This is often not what we want in a wooden boat and we have to work hard to get some texture back into the thing.

Glued Methods: Strip planking

Strip planking is a glued construction method very popular with amateur boatbuilders because it appears to be a quick method that avoids complex temporary jig work and does not require shaping of the planks. My diatribe on the method farther on in this section of the web site gives my views on this. See more on Paul's opinion.

Hybrid systems

Now we get to the hybrid systems, those which combine features of both traditional and glued systems. This is often the answer when we are looking for a boat with a traditional air but would like some of the advantages of the glued methods.

This was the case with the Tomales Bay One-Design "Jessie". The customer wanted a traditional wooden boat, if I remember rightly he first approached us about a clinker boat. However he was in California, we are in British Columbia and the boat was to live out of the water on a trailer. I was concerned about the potential for drying and leaking if we shipped a conventional clinker boat down to him from here. Instead we planked her over bent frames with two skins of red cedar, one diagonal and one fore and aft fully glued with epoxy. Apart from the run of the inner skin visible in the varnished interior, it looks like a traditional carvel planked hull but we don't ever have to worry about her opening up.

There are many other variations along this line. The boat we built for our own use is also double planked over bent frames, with both layers running fore and aft. (See 22 ft Cutter "Surprise") In larger boats one could also go two diagonal and one fore and aft for an exceptionally strong hull with a traditional interior. That is one I would like to try one day.

So there you have the range of possibilities. Each has its up side and reverse. I would just finish by reminding you that the fun is in the traditional methods. The glued systems all involve using copious amounts of toxic sticky substances, none of which are very good for you. It therefore entails working in gloves or using barrier creams and/or respirators at various stages in the process. This seriously detracts from the experience, believe me.



 

Article originally appeared on Gartside Boats (http://www.gartsideboats.com/).
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