The stepped profile of clinker-built boats is immediately recognisable and has been a popular method of construction for over 1,000 years, writes Richard Johnstone-Bryden.

In more recent times, it has been predominantly used for small wooden dinghies.

However, the method has also been used for an interesting selection of larger vessels, including the 7.9m (26ft) Whitby motorboat Le
Bateau and the mighty Norfolk Wherries.

In a clinker-built boat, the planks run fore and aft, with the lower edge of one plank overlapping the outboard side of the upper edge of the plank below it.

The planks are fastened to the timbers of the boat and to each other with copper nails, which are clenched over washers called roves.

A clinker-built boat is comparatively easy to repair because a damaged plank may be removed and replaced without unduly disturbing the adjacent planks.

In this article, Nat Wilson explains the process while Alastair Robb demonstrates the techniques.

Spilling the plank on a clinker-built boat

1. The featured boat is a replica of the 100-year-old, 10ft River Deben pilot’s skiff, Teddy.

The keel, stem, softwood building moulds, garboards and the first three planks are now in position, showing the distinctive clinker profile.

To begin measuring for the fourth plank on the port side, a spiling plank has been clamped in place, on which the edge of he plank below is marked.

2. The upper edge of the third plank on the lower inside face of the spiling plank is drawn. A flat pen or pencil helps follow contours.

3. Alastair marks the position of the softwood building mould on the upper edge of the spiling plank.

ABOVE: The positions for the tops of each plank are marked on the moulds: Alastair measures to the mark at each point, including the overlap.

4. A dummy stick is used to take a line from the stem to determine the profile of the forward end of the fourth plank.

5. The spiling plank has been temporarily pinned to the larch planking stock.

Alastair places the dummy stick over the line on the spiling plank and runs a pencil along its outer face to mark the lower edge of the new plank.

The positions of the building moulds are transferred to the larch planking stock.

6. The measurements taken in step 3 are measured up from the spiled line, and a wooden batten is used to join the marks and obtain a fair line for the top of the plank.

7. A handheld circular saw is used to cut out the plank.

Boatbuilders usually choose wood with a degree of curve for use as planking stock: once the initial cut has been made, a wooden wedge is inserted to keep the two sides apart as the saw moves along the length of the planking stock.

It’s important to check the edge of the cut plank for a fair line because the lower edge will be clearly visible, as will any imperfections.

8. A plane is used to trim the upper edge of the plank to the exact shape required.

9. The new plank is clamped into position for the first round of adjustments to be marked up.

The plank was deliberately left slightly over-length so that the forward end could be trimmed to length in position using a jigsaw.

A block plane is used to trim the forward end of the plank to the exact shape required.

10. The back bevel for the forward end of the plank is marked up to fit into the Gerald of the previous plank.

‘Gerald’ is the East Coast name for the angled rebate in clinker planking which allows the planks to lie flush at the stem.

11. A bullnose plane is used to produce the back bevel.

12. The shape of the back bevel is fine-tuned to the desired shape with a chisel.

Fitting the plank

1. To achieve a uniform incline, Alastair uses a rebate plane to a square rebate as the first stage of the Gerald, then marks up the second, angled stage.

2. The second part of the Gerald is produced with a bullnose plane, and finished off with a chisel.

3. The length of the back bevel for the aft end of the plank is marked up.

4. Alastair uses a dummy stick to mark out the width of the back bevel.

5. Alastair clamps the plank into position again to mark up the next set of adjustments.

The forward end of the plank is bent into position.

6. The forward end of the plank is clamped into position.

A wooden mallet is used to gently tap the plank tightly into position so that the forward end is hard up against the rabbet in the stem.

The rabbet is the groove into which the plank edges fit.

7. This is one of the wooden clothes peg-style clamps that will hold the plank in position before the final securing process.

These clamps are cheap, and you can even make your own.

8. The plank is clamped to one of the softwood building moulds.

9. The forward section of the new plank is held firmly in place for securing by this combination of clamps.

10. The aft end is secured with a clamp, demonstrating one of the benefits of leaving the planks slightly over-length. Another benefit is the ability to hit the end of the plank without damaging it.

11. Alastair fine-tunes the bevel on the preceding plank to ensure a tight fit against the transom.

12. The bevel is marked up along the top edge, ready to receive the next plank. The fastening process is completed by steaming timbers and securing the planks to the steamed timbers using copper nails and roves.

Reverse clinker construction

The 4.9m (16ft) Singer Commodore speedboat Miss Singer III illustrates an alternative form of clinker construction, developed in 1930 by Eric See.

The outside lapping edge of conventional clinker construction is nearest to the keel or centre line. The projection causes a lot of resistance and skin or surface friction as the boat moves through the water.

While studying clinker construction in detail, Eric observed how water was trapped under the plank lands and did not clear the bottom of a conventional clinker motor launch.

He realised that the amount of resistance offered by the hull of a clinker-built craft could be reduced by reversing the direction of the overlapping planks, so that the upper edge of each plank would overlap the lower edge of the plank above.

The projecting edge would now be the furthest away from the keel or centre line.

As in conventional clinker construction, the overlapping planks are joined together by driving a nail through both planks as well as a washer-like rove.

The nail is then burred or riveted over to complete the fastening.

The principal benefit of the reverse clinker construction method is that it enables the boat to achieve a greater speed, because the step or planes lessen the wetted surface and skin friction.

In addition, the boat has greater stability both in rough weather and while turning.

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