Chine (boating)

Achinein boat design is a sharp change in angle in thecross sectionof ahull.The chine typically arises from the use of sheet materials (such assheet metalormarine ply) as the mode of construction.

Rationale of chines

Using sheet materials in boat construction is cheap and simple, but whereas these sheet materials are flexible longitudinally, they tend to be rigid vertically. Examples of steel vessels with hard chines includenarrowboatsandwidebeams;examples of plywood vessels with hard chines include sailing dinghies such as the single-chinedGraduateand the double-chinedEnterprise.Although a hull made from sheet materials might be unattractively "slab-sided", most chined hulls are designed to be pleasing to the eye andhydrodynamically efficient.

S-bottom hull (A), compared to a hard (B) and soft (C) chine hull

Hulls without chines (such asclinker-builtorcarvel-builtvessels) usually have agradually curvingcross section.

Ahard chineis an angle with little rounding, where asoft chinewould be more rounded, but still involve the meeting of distinct planes.Chine log constructionis a method of building hard-chine boat hulls. Hard chines are common inplywoodhulls, while soft chines are often found onfiberglasshulls.

Traditional planked hulls in most cultures are built by placing wooden planks oriented parallel to the waterflow and attached to bent wooden frames. This also produced a rounded hull, generally with a sharp bottom edge to form thekeel.Planked boats were built in this manner for most of history.

The first hulls to start incorporating hard chines were probably shallow-draft cargo-carrying vessels used on rivers and incanals.

Once sufficiently powerful marine motors had been developed to allow powerboats toplane,it was found that the flat underside of a chined boat provided maximum hydrodynamic lift and speed.

Boats using chines

Royal NavyWorld War IImotor torpedo boat(MTB)planingat speed on calm water showing its hard-chine hull. Note how most of thebowof the boat is out of the water.

Thescowin particular, in the form of the scowschooner,was the first significant example of a hard-chine sailing vessel. While sailing scows had a poor safety reputation, that was due more to their typical cheap construction and tendency tofounderin storms. As long as it sailed in the protected inland and coastal waters it was designed to operate in, however, the sailing scow was an efficient and cost-effective solution to transporting goods from inland sources to the coast.A good example of this is thegundalow.

Working in the same inland waters as the sailing scows was the laterriver steamboat.River steamboats were often built using the same hard-chined construction methods of the sailing scows, with a flat bottom, hard chine, and nearly vertical sides.

Thepuntis one of the simplest hard-chine small boats. Consisting usually of a single plank for each side, with a square bow and stern, the punt was in essence a tiny scow.

Various types of chine hulls

Different numbers of chines

The simplest type of chine construction is the single-chine "V" shape, with two flat panels joined at the keel (A). This type of hull is among the simplest to build, but they lack stability on a narrow "V" and may lack freeboard on a wide "V". Single-chine hulls are generally only seen onmultihullsailboats, which often use two deep V-shaped hulls connected byakasto provide mutual stability.

The two-chine hull (B), with aflat bottomand nearly vertical sides, was the first hard-chine design to achieve widespread use. This design provides far more stability than the single-chine hull, with minimum draft and a large cargo capacity. These characteristics make the two-chine hull popular forpunts,barges,andscows.

The three-chine hull (C) is probably the most common hard-chine hull. Having a shallow "V" in the bottom and near-vertical panels above that, it approximates the shape of traditional rounded-hull boats fairly well. This hull is common, even in fiberglass designs where employing chines offers no advantage in construction.

Designs with higher numbers of chines (D), often just calledmultichinehulls, are also common. By increasing the number of chines, the hull can very closely approximate a round-bottomed hull.Kayaks,in particular, are often composed of many chines, required for the complex shapes needed to provide good performance under various conditions.

It is possible to refer to the different hulls by the numbers of the flat panels that make up the boat. Thus A is a two-panel boat, B is a three-panel boat, C is a four-panel boat and D is an eight-panel boat.

Two planks joined by a chine log

Plank hulls

Plank hulls use wooden supports placed along the chines calledchine logsto provide strength where the chines joined. Beams are then attached to the chine log to support planks running parallel to the chine, while cross-planked sections such as a typical scow bottom may be attached directly to the chine log. This method of construction originated with the sailing scowand continues to be used today, primarily in home built boats.

Chine log construction works best for hulls where the sides join a flat bottom at a right angle, but it can be used for other angles as well with an appropriately angled chine log. Builders of small boats such as punts, where the plank thickness is large compared to the size of the hull, can dispense with the chine log and nail intersecting planks directly into one another.

Plywood hulls

A chined hull built out of plywood will often be designed to keep most of the lengthwise joints between the plywood sheets at the chines, thus making the building process easier. While chine logs (often just called chines) can be used for plywood boats,another common technique replaces the chine logs with afiberglassandepoxyfilletjoint that provides both connection and stiffness to the joint; this method is most commonly calledstitch-and-glueconstruction.

Padded v-hulls

A padded V-hull is a hull shape found on both purerace boatsand standard recreationalcraft.A variation of the more commonV-hull,which has a V-section throughout the length of the vessel, a padded V-hull has a V-section at thebowsand the forward part of thekeelwhich then segues into a flat area typically 0.15 metres (5.9 in) to 0.25 metres (9.8 in) wide. This flat area at the rear is the "pad", and is said to providehydrodynamic liftmore efficiently due to very low deadrise planing surface (compared to the vee hull lifting surfaces). This highly efficient lift helps to unwet the less efficient V-section's hull, thereby dramatically reducingdrag (force).As the boat's speed increases, hydrodynamic pressure beneath the pad causes the hull to ride higher in the water, so that eventually the boat will be riding solely upon the pad area.

At low speeds these hulls ride and handle similarly to a comparable V-hull; but at high speeds the padded hull can both out-accelerate and have a higher top speed than a similarly powered V-hull. Piloting a padded V-hull requires considerable skill, since at high speed the hull is riding upon a small pad. The driver must make slight, accurate steering inputs to maintain level progress, as otherwise padded V-hulls tend to "chine-walk".As speeds increase, chine-walk becomes more pronounced and may lead to loss of control unless the driver is able to compensate for it.

See also

• Strake
• Smooth curve hull

External links

• Hull Technology in Hydrostream Boats
• Vee Pad Hull Design by Jim Russell
• Chine Walk in Performance Hulls by Jim Russell