carvel planking with thin planks

[Mohan Pakkurti]

hello!

I am curious about techniques for carvel planking thin planks (9mm or 3/8 inch) and wonder if there are any good techniques for this. I want to avoid strip planking and other techniques that require chemicals etc, and rely on the expansion of wood to keep the seams closed.

A boat designer mentioned a technique called "rolled seam carvel planking". Are there are any good references for this technique?

Does anyone have any tips about techniques for carvel planking thin planks?

Thanks for any tips or comments.

Warm regards

Mohan

[lewisboats]

Carvel planked hulls rely on material stuffed in a beveled gap and pounded in to wedge the planks, then a coating payed into the seams to waterproof everything. I don't think you would be able to get this in anything less than 3/4" thick planking and certainly not in 3/8" thickness. At that thickness you would be better off with a lap construction, rivetting the laps together. I have also seen the laps bolted together with small bronze or perhaps brass machine screws and nuts...Glued lap is another option.

What size boat are you contemplating? If it is quite small, you may get away with simply the plank expansion and calking compound.

Steve

[alan white]

Seam batten construction allows 1/2" or 7/16" planking thickness. Battens a bit thicker than the planking (say, 5/8") are let into sawn frames at the seam centers. No sealant is used between planks, but a flexible caulk could be used to bed planks to battens. The process also calls for fasteners between frames along the seams.
I'm currently involved with an old 19 ft. Chris Craft runabout. Refastening consumed 1500 bung replacements, far more than would be found on a thicker carvel hull. Planks, of vertical grain Phillipine mahogany, are about 7/16" thick, and up to 6" wide. Although the boat is over fifty years old, even in the dry winter shop the average seam joint is about 1/32". No rot was found anywhere on this hull, except a small area under one spray rail, which was dug out and relaced with a wedge "dutchman".
Plank thickness on a carvel hull has more to do with boat size, hull shape, frame spacing and intended use than any limits of scale.
The lower limit is a practical one, determined by the willingness and talent of the builder to accurately bevel the outer edge of each thin plank. Conceivably, one could build a microscopic carvel hull if the tools existed to do so.
Frame spacing should be quite close, perhaps 8"-10" with 7/16" planks, I think. Seam batten method, using the same thickness, could get away with 24" centers, but of course steamed frames shouldn't be notched for battens, so the frames should be hefty and sawn rather than steamed.
Another way is to use sawn frames at 24" to 32" intervals for 7/16" thickness planking and say, 5/8" x 5/8" steamed ribs between at 8" intervals, which will dispense with ribbanding or molds. It seems this would be an excellent method to use if the boat hull is hard chined (but developed) like a planing runabout, which might have a single gusseted chine log/ frame joint, flared bow, and tumblehome stern. It would use rivets rather than screws, ideally, except at the sawn frames, which could be screwed or nailed. I like nails (bronze ring nails) better because countersunk screw heads can split thin wood if they over-tighten.
Which brings up a very important thing to consider------ in hanging planks that are smaller and thinner, the tools used to drive home nails or screws or rivets should be lighter. What feels like gentle snugging could actually be the same relative tightening as would take all your strength on a bigger fastener/plank.

Alan

[waikikin]

From vague & distant memory some of the older blokes I did my time with spoke of carvel dinghy building for our aussie skiff classes etc & apparrently use a caulking wheel to press the cotton into the seam or in other cases would bevel fit the planks so tight inside & out but bruise the plank edge with a marking gage like contraption that had a brass or bronze screw driven into it then the head cut off it & rounded off to make a semi circular bruised groove in the plank edge to accept the cotton as the planks where fitted up. these guys where fantastic tradesmen & only rarely would they have to go back to the bench to reshape any plank- they'd spile it, cut it free hand on a table circular saw- set so the blade only came out of the planking stock by 1/8 or so, bevel it & fit it, doing a oncer was some thing of pride. Regards from Jeff

[gonzo]

Strip planking doesn't need any more chemicals than carvel. It relies on the edge fasteners for structural integrity.