August 17, 2010

The beauty of lapstrake

(Mainly about Boats: a new column every Monday, Wednesday, and Friday.)

A READER CALLED JONATHAN in Fort Lauderdale, Florida wants to know what I think of lapstrake planking. “I was recently visiting in New England and saw lots of lapstrake wooden boats,” he says. “What’s the advantage?”

Well Jonathan, the first thing is that it’s beautiful. If you like looking at pretty girls, you’ll like looking at lapstrake. It emphasizes all the curves. That’s not actually why boats were built with overlapping planks, or strakes, in the first place, though.

Because each plank overlaps the one below it, the thickness is almost doubled along each edge. That makes it very stiff and strong — suitable for one-design racing dinghies, smallish fishing boats landing on beaches, or ship’s launches that take a good pounding. And because it’s so strong, a lapstrake (or clinker-built) hull is normally much lighter than it’s carvel-planked cousin.

But building in lapstrake is a fine art, and mostly a lost one these days except in a few wooden-boat centers scattered around the country. In the old days the planks had to be finished so finely that they would not leak even in the absence of caulking. These days, a fine bead of polyurethane or polysulphide makes it easier to form a watertight seal along the plank edges but formerly it was the skill of the boatwright alone that kept the water out.

The planking always starts at the keel and works its way upwards. Copper nails with rooves fasten the planks together with a minimum overlap of about 5/8 inch with 1/4-inch planks — and more on bigger boats, of course. At the stem and transom, where the planks come together, the strakes need expert treatment and call for fine woodworking skills.

Older wooden boats without caulking would open cracks along the seams if they dried out for too long, but if they were allowed to soak in water again for a couple of days, the wood would swell and cure that problem.

There isn’t much lapstrake construction around these days, of course, at least not in commercial production, but when fiberglass took over from wood some 60 years or so ago some boatbuilders thought it might be a good idea to produce lapstrake GRP boats.

The problem with that is that fiberglass doesn’t like to make sudden sharp bends, and lapstrake is ALL sharp bends. So they had to fillet the joints between planks into nice gentle curves, which took more material and added weight – and that, in turn, negated one of the main advantages of lapstrake hulls. I expect the construction of a lapstrake mould was also much more difficult and expensive than a plain carvel one. The net result was that a fiberglass lapstrake hull was strong and pretty and more maintenance-free, but often impractical from the point of view of construction and cost.

One-off racing boats are rarely built in lapstrake, despite the weight advantage, because of the added resistance of each lap at slow speeds and because the greater surface area of the hull results in more drag.

One thing that surprises people who have never owned a lapstrake boat is how much noise they make at anchor. Each little passing wavelet smacks into the underside of the laps with great zest, resulting in an unexpectedly loud chorus of noise that owners of lapstrake boats are wont to dismiss as cheerful “chuckles.” But if you’re anchored nearby, in the middle of an otherwise quiet night, you might not be laughing so much.

Today’s Thought
This sort of thing takes a deal of training.
— W. S. Gilbert, Ruddigore

Boaters’ Rules of Thumb #84
Noises in fog. The basic rule is that distant noises in fog sound low and dull. Nearer noises are higher and brighter. Fog carries sound very efficiently so that even faint noises are carried long distances — which makes distance judging very difficult.

A newly released government report reveals why universities are always referred to as “storehouses of knowledge.”

“It is simply that undergraduates bring so much knowledge in,” says the report, “and graduates take so little out.”


Phfrankie Bondo said...

...I don't understand the "sharp bends" in the lapstrake method. Don't the strakes gently follow the hull frame? Where are the sharp bends?...

John Vigor said...

Phrankie, the sharp bends are from top to bottom, as you move from one plank to the next.

John V.

Ken said...

Maybe the word "bends" makes it difficult for Phfrankie to see the sharp edges of one plank overlapping the top edge of the previous plank. And no, the planks do not lay flat against the frames, only the top full length edge of a plank touches the frame in a lapstrake boat.