Planking by Eye and Riveting

With the garboards on, the boat starts to show its shape. Days three to five hang the rest of the planks: on a Holmsbu-type pram, three more strakes a side, the top one being the sheer strake. Simpler designs use fewer, wider planks: Simon Watts’s pram has only three planks a side, “like a dory” ¹.

Each strake in turn

Every strake repeats the garboard routine:

1. Spile the lower edge from the top edge of the plank already hung, plus the lap allowance.
2. Mark the upper edge by eye, springing a long batten to a line that looks fair from every angle. Planks are usually widest amidships, a few inches wide: Bryan gives 3 1/2 to 5 inches including the lap ².
3. Cut, then bevel the top edge of the plank below to receive it.
4. Cut the gains at both ends.
5. Clamp, check, rivet.

Spread it from above

Traditional Norwegian building completes the planking by eye “before any transoms or frames are installed” ³. Without molds, the shell is pushed and pulled into shape with struts from a beam overhead and spreaders across the hull. Stand back often. Sight down each lap from both ends and from above; a hard spot or a hollow shows up as a kink in the line of the lap. Fix it now, by easing a spreader or re-bending the plank, because frames will lock in whatever shape the planks have.

Riveting step by step

Faering Design, a North American supplier of copper boat fastenings, gives this procedure ⁴:

1. Drill a pilot hole through both planks, one bit size smaller than the nail measured across its flats.
2. Choose a nail at least the total wood thickness plus 3/8 inch long.
3. Drive it from outside while a helper holds the bucking iron against the head, until about 1/4 inch pokes through inside.
4. Push a rove over the point, cup toward the wood, and drive it down snug with the rove set.
5. Clip the nail just above the rove with end nippers.
6. Peen the end over: three light taps around the edge, then 5 to 8 light blows with a 3- to 4-ounce ball peen, while the bucking iron stays on the head.

For planks around 3/8 to 1/2 inch, two thicknesses plus 3/8 inch suggests a #14 nail, 1 to 1 1/4 inches long, with 5/16-inch roves, both stocked by Fisheries Supply ^{5 4}. A pram of this size takes about 500 rivets ⁶, so a two-person team with a rhythm (one outside on the hammer and bucking iron, one inside on the rove set and nippers) matters more than speed.

The sheer strake

The top plank sets the boat’s look. Hang it oversize, then trim the sheer line by eye: spring a batten along the top edge, step back, adjust until the curve sweeps up evenly to both transoms, and plane to the line. A sheer that dips or humps is the one mistake everyone sees.

Fasten the transoms

Once the planking is on, fit the plank ends to the transoms. Trim each plank flush with the transom face, then fasten the gained ends into the transom’s edge. Use copper nails or bronze screws into the transom’s edge, set back from the plank ends, and keep them out of the thinnest part of the gains.

Try it

Rivet a practice joint in two scrap boards before the boat. Try a nail that’s too short and one that’s too long, and see why the 3/8-inch rule exists.