Strake

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Diagram of typical modern ship exterior plating. A single strake is highlighted in red.

A strake is part of the shell of the hull of a boat or ship which, in conjunction with the other strakes, keeps the vessel watertight and afloat. It is a strip of planking in a wooden vessel or of plating in a metal one, running longitudinally along the vessel's side, bottom or the turn of the bilge, usually from one end of the vessel to the other. On a longboat, one strake will typically be made up of numerous planks running end to end.

Special strakes[edit]

Garboard strakes and related near-keel members.

The strake immediately adjacent to the keel is known as the garboard strake. There are two, one on each side of the keel.

The uppermost continuous strake along the topsides is called the sheer strake. In old vessels, a rubbing strake was built in just below a carvel sheer strake. It was much less broad but thicker than other strakes so that it projected and took any rubbing against piers or other boats when the boat was in use. In clinker boats, the rubbing strake was applied to the outside of the sheer strake. The strakes adjacent to the garboard are referred to accordingly as the first broad and second broad. Each strake thereafter has its own special name such as bottom strakes, lowers, bilge strakes, topside strakes, and uppers. Many current pleasure craft reflect this history in that they have a mechanically attached (and therefore replaceable) rub rail at the location formerly occupied by a rubbing strake, often doubling to cover the joint between a GRP hull and its innerliner. A stealer is a short strake employed to reduce the width of plank required where the girth of the hull increases or to accommodate a tuck in the shape. It is commonly employed in carvel and iron/steel shipbuilding, but very few clinker craft use them. After determining the widths of strakes amidships (there are three categories), a quantity can be determined for all these strakes. This quantity is then divided into the height of the stem to determine the width of the average hood-end. This width must be twice the hood-end's thickness or it will not be able to carry its fasteners. If the hood-ends are not wide enough, the quantity is dropped by one until the resulting revised width is strong enough to carry its fasteners. Stealer is actually a misspelling of the word steeler; the plankers borrowed the word from their peers in the foundry, where forgers would strengthen a piece of metal by steeling a different metal to the original piece. In wooden boats the hood-end is strengthened by making it wider, thus providing more wood mass with fewer hood-ends. A device was needed to compensate for the drop in strakes that actually reached the stem. The device was a strake that was stooped short of the stem by burying its forward butt end into a notch chiseled into a through plank. This strake was called a steeler by the plankers and a drop plank by the liners who originated it by counting strakes during the lining off process.

Construction[edit]

Where the transverse sections of the vessel's shape are fuller, the strakes are wider. They taper toward the ends. In many larger vessels, to avoid ending with very narrow strakes, two are normally converted to one toward their ends. This one is known as a stealer or stealer strake. It was one of these which was also shaped to fit the concave line of the hull, under the counter at the sternpost. Historically, these had to be shaped by carving from an especially thick plank of wood (known as a short strake or plank). When someone was describing the epitome of thickness, he thought of the metaphor, thick as two short planks.

In very small boats, strakes can be made of one continuous piece of wood. Usually, they are made of more than one piece of wood or metal scarfed or butted together similar to brick wall construction. In metal vessels, the modern practice is to butt-weld them with full penetration welds.

In a riveted steel ship, the strakes were usually lapped and joggled, but where a smoother finish was sought, they too might be riveted on a butt strap, though this was weaker. In modern welded construction, the plates are normally butt-welded all round to adjoining plates within the strake and to adjoining strakes.

Wooden vessels[edit]

Wooden planks can be scarfed into a strake by suitably tapering the thickness of the adjoining ends. Traditionally, the adjoining faces were coated with mixed white lead and grease, then held together with copper rivets. It was important to not have the plank end as thin as a feather edge and to have the outboard thin edge at the after end of the joint. In later times, after adhesives had been developed by the aircraft industry, the joint might be made with resin glue and no rivets. In heavier carvel work, the joint would be a butt, riveted to a butt strap. Even large clinker vessels had scarfed strakes as in this form of construction; the strakes contribute a significant proportion of the structural strength of the boat as well as keeping it water-tight.

Assembling the strakes[edit]

Two methods used to plank a wooden hull are: carvel in which the edges of the strakes butt against each other, using an internal frame structure determining the boat's shape, and clinker (lapstrake) in which the adjoining strakes are held together on an overlap and the varying widths and angles of overlap determine the hull's shape.

Carvel construction, more traditional in the Mediterranean than in north Europe, produces a relatively smooth hull surface but needs caulking to make it watertight. It is relatively heavy, due to the mass of the required internal framing. Carvel boats are planked up onto pre-erected frames which become part of the boat.

The second method is clinker. This is the technique, traditional in the north, from which early aviators derived monocoque technology,[1] as it produced relatively light but strong boats. Normally, the boats are built from the garboard up so that the upper plank overlaps the lower on the outside. That overlap is known as the land (hem) and it is held together by clenched copper rivets. In the twentieth century, the boat might be built of plywood and the strakes glued together, without clenched nails. Medieval boats are more likely to have been riveted with iron nails. To rivet the lands, the planks in the two adjoining strakes are pierced, a nail inserted from the outside and a rove (roove, burr[2]) punched over the inside end of the nail. The latter is then cut off some way proud of the rove, and the tip is clenched over the rove.

At the hood-ends of the strakes, where they approach the stem, they are let into each other with geralds (chases, gains). In these, the land of the lower strake is tapered to a feather edge at the end of the land where it is supported by the rebate formed by the apron. The strakes then meet the stem flush, which is also referred to as being hooded.

When the shell of the boat is complete, the strakes are stiffened by the insertion of steam-bent timbers. These, too, are riveted to the planking through the lands. The timbers (ribs[3]) spread the load on the strakes and tie them together, reducing the tendency of the relatively thin strake to split. With glued-ply clinker construction, the timbers are unnecessary.

Steel ships may be plated as clinker-built vessels but were more usually built with strakes alternately in and out. The modern method is to butt-weld the strakes to each other. (The plates comprising each strake are also butt-welded, end to end.) This leaves a smoother finish and is lighter.

Sources[edit]

  1. ^ Garson, Paul (May–June 2018). "Art Deco on Wheels: 1930 Majestic". Motorcycle Classics. Retrieved October 6, 2018.
  2. ^ "Glossary of Nautical Terms: roove / rove [burr]". Practical Boat Owner (https://www.pbo.co.uk). 2010-01-03. Retrieved 2018-11-17. Roove (rove) A saucer-shaped copper washer which fits over a copper boatnail before it is riveted up tight. Also known as a rove or a ruff, though in the USA it is known as a Burr.
  3. ^ "Glossary of Nautical Terms: Rib". Practical Boat Owner (https://www.pbo.co.uk). 2014-11-11. Retrieved 2018-11-17. The ribs of a wooden boat are sometimes called Frames, usually if cut to shape, and sometimes called Timbers, usually if steamed to shape. You will appreciate that only wood of small scantlings is likely to be bent, so timbers are small and frames large.