Sweep or sweep-oar rowing is a type of rowing

Rowing (sport)

Rowing is a sport in which athletes race against each other on rivers, on lakes or on the ocean, depending upon the type of race and the discipline. The boats are propelled by the reaction forces on the oar blades as they are pushed against the water...

  when a rower has one oar, usually held with both hands. As each rower has only one oar, the rowers have to be paired so that there is an oar on each side of the boat. This is in contrast to sculling

Sculling

Sculling generally refers to a method of using oars to propel watercraft in which the oar or oars touch the water on both the port and starboard sides of the craft, or over the stern...

 when a rower has two oars, one in each hand. In the UK the term is less used as the term rowing generally refers to sweep oar. The term pulling was also used historically.

Sweep or single oar rowing has a long history and was the means of propulsion for Greek triremes and Viking longboats. These boats were wide enough for the pairs of rowers to sit alongside each other. Boats can go faster, the narrower they are, because a smaller cross-sectional area reduces drag

Drag (physics)

In fluid dynamics, drag refers to forces which act on a solid object in the direction of the relative fluid flow velocity...

 and wave drag

Wave making resistance

Wave making resistance is a form of drag that affects surface watercraft, such as boats and ships, and reflects the energy required to push the water out of the way of the hull. This energy goes into creating the wake.-Physics:...

 and gives a sharper angle to the bow. The hulls can be kept narrower by attaching riggers to the gunwales, so that the oarlocks can be placed farther out to carry longer oars. A narrower hull means the rowers can not sit side by side and so they sit one behind another. The riggers are staggered alternately along the boat so that the forces apply asymmetrically to each side of the boat. This means a sweep oared racing shell

Racing shell

In watercraft, a racing shell is an extremely narrow, and often disproportionately long, rowing boat specifically designed for racing or exercise. It is outfitted with long oars, outriggers to hold the oarlocks away from the boat, and sliding seats...

 has to be stiffer in order to handle the unmatched forces, and so requires more bracing, which means it has to be heavier and slower than an equivalent sculling boat.

Sweep rowing has to be done with crews in multiples of two - i.e. pairs, fours and eights (sixes and boats longer than eight are not used in competitive racing today). Each rower in a sweep boat is referred to as being on stroke side

Stroke (rowing)

Stroke is a term which has multiple meanings within the sport of rowing. It is used to refer to the action of propelling the boat with oars, to a rower seated in a particular position and to one side of the boat.-Stroke action:...

 (port) or bow side

Bow (rowing)

Bow is a term which has multiple meanings within the sport of rowing. It is used to refer to a rower seated in a particular position and to one side of the boat.-Bow:...

  (starboard), depending on which side of the boat the rower's oar extends. In a sculling boat the riggers apply forces symmetrically. While sculling boats are also in multiples of two, it is possible to have a Single scull

Single scull

A single scull is a rowing boat used in the sport of competitive rowing. It is designed for a single person who propels the boat with two oars, one in each hand....

 or Triple scull.

The primary sweep oar racing boats are as follows.
Eight

Eight (rowing)

An Eight is a rowing boat used in the sport of competitive rowing. It is designed for eight rowers, who propel the boat with sweep oars, and is steered by a coxswain, or cox....

 (8+) : A shell with 8 rowers. Always with coxswain because of the size, weight and speed of the boat - bow loader eights exist but are banned from most competitions for safety reasons.
Four (4-) or (4+) : A shell with 4 rowers. Coxless four

Coxless four

A coxless four is a rowing boat used in the sport of competitive rowing. It is designed for four persons who propel the boat with sweep oars.The crew consists of four rowers, each having one oar. There are two rowers on the stroke side and two on the bow side...

s (4-) are often referred to as straight fours, and are commonly used by lightweight and elite crews and are raced at the Olympics. In club and school rowing, one more frequently sees a coxed four

Coxed four

A coxed four is a rowing boat used in the sport of competitive rowing. It is designed for four persons who propel the boat with sweep oars and is steered by a cox....

 (4+) which is easier to row, and has a coxswain to steer.
Pair (2-) or (2+): A shell with 2 rowers. The Coxless pair

Coxless pair

A Coxless pair is a rowing boat used in the sport of competitive rowing. It is designed for two rowers, who propel the boat with sweep oars.The crew consists of a pair of rowers, each having one oar, one on the stroke side and one on the bow side...

 (2-), often called a straight pair, is a demanding but satisfying boat to master. Coxed pair

Coxed pair

A coxed pair is a rowing boat used in the sport of competitive rowing. It is designed for two persons who propel the boat with sweep oars and is steered by a coxswain....

s (2+) are rarely rowed by most club and school programs. It is no longer an Olympic class event, but it continues to be rowed at the World Rowing Championships

World Rowing Championships

The World Rowing Championships is an international rowing regatta organized by FISA . It is a week long event held at the end of the northern hemisphere summer and in non-Olympic years is the highlight of the international rowing calendar.The first event was held in Lucerne, Switzerland in 1962...

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