User:NZMKZ/sandbox.rowing

Rowing Article

Design Factors

The classic shapes of rowboats reflect an evolution of hundreds of years of trial and error to get a good shape. Some factors to be considered are waterline length, speed, carrying capacity, stability, windage, weight, seaworthiness, cost, waterline beam, the fullness or fineness of the ends, and trim. Design details are a compromise between competing factors.

Width and Height

If the waterline beam (width) is too narrow the boat will be tender and the occupant at risk of falling out, if the beam is too wide the boat will be slow and have more resistance to waves. Overall beam (width) is important. If the rowlocks are too close together the oars will be difficult to use. If the rowlocks are too far apart then the boat will be overly large and rowing will be inefficient, wasting a rower's effort. Sometimes on narrow, faster rowboats for protected waters outriggers are added to increase rowlock separation. Many traditional rowboats have a beam of about 135 cm (4+7⁄16 ft). Most modern rowboats between 2.4 m (8 ft) and 4.6 m (15 ft) have a maximum beam of 1.2–1.3 m (4–4+5⁄12 ft).

If the freeboard (height of the gunwale above the waterline) is too high then windage will be high and as a result, the boat will be caught by the wind and the rower will not be able to control the boat in high winds. If the freeboard is too low, water will enter the boat through waves. If the boat is designed for one person then only a single rowing position is required. If the rower is to carry a passenger at the stern then the boat will be stern heavy and trim will be incorrect.

Weight

To have good width and the height that ensures the balance of the rowboat, a weight can be added in the bow, alternatively, the boat can supply a second rowing position further forward for this purpose. For a boat to have three separate thwarts and have adequate space for each occupant then the boat has to be of a certain minimum size. A 2.4-meter (8 ft) pram dinghy can carry 4 passengers on 3 thwarts in flat seas. The ideal size of a good row boat intended for distance rowing is 5 m (16 ft).

Most modern style rowboats are considerably lighter than traditional clinker-built style. Many 3.7–4.6-meter (12–15 ft) row boats are about 32–45 kg (70–100 lb). A pure rowing boat built for speed will have a narrow transom 61–84 cm (2–2+3⁄4 ft) and be very narrow at the stern waterline, while a rowboat intended to use a small outboard motor of 2–5 hp (1.5–3.7 kW) needs a wider transom to support the weight of the engine and operator in the stern. Small short shaft outboards need a transom height of 38 cm (15 in). Often the aft thwart is moved forward 30–36 cm (12–14 in) from the stern to give better weight distribution and balance if the boat is being operated solo with an outboard.

Stability

Water line beam is important for stability. Most general purpose rowboats' water line beams are 0.9–1.2 m (3–3+11⁄12 ft). Stability is very much influenced by the seat height as the rower makes up a big percentage of the total weight. Most general purpose rowboats have a main thwart height of 25 cm (10 in) above the keel. Wider boats can have higher seats. Older rowers with stiff or sore backs benefit from 28 cm (11 in) high seats. The Finnish Savonian type rowboat is very narrow and fast, having a very sharp bow and stern, with beam around 110 cm (3.6 ft), but also dangerously tender and prone to capsize easily in inexperienced hands.

Perforemence

Spring in the keel or rocker influences how a rowboat performs. Longer, slender race boats have less rocker of about 7.6 cm (3 in). A short 2.4-meter (8 ft) pram dinghy has a rocker of 15–18 cm (6–7 in). Boats with less rocker are easier to row and faster in flat or nearly flat water. However, in any waves a boat with 13–15 cm (5–6 in) of rocker will be more seaworthy—rising over waves rather than going through them. A boat with more rocker can change direction easily whereas a straight keel boat will track well in a straight line but resist turning. High sided and fine-ended boats, such as dories, are affected by wind. Their trim can be altered by using a plastic container of water attached to a rope that can be moved to the bow or stern as need be. Long-distance rowers can keep up a steady 20 strokes per minute compared to a racing shell which can be rowed at 32–36 strokes per minute by fit athletes. A rower can maintain 40 strokes per minute for only a brief period. Longer, narrower rowboats can reach 7 knots (13 km/h; 8.1 mph) but most rowboats of 4.3 m (14 ft) can be rowed at 3–4 knots (5.6–7.4 km/h; 3.5–4.6 mph).

Many old rowboats have very full ends (blunt ends); these may appear at first glance to be bad design as it looks slow, not fast. However a full-ended rowboat will rise to a sea and not dig in as a finer hulled boat might do, thus a compromise needs to be made between the factors of speed and of seaworthiness. This style of rowboat was designed to carry a bigger load and the full sections gave far more displacement. Also older boats were often very heavily constructed compared to their modern counterpart, hence weighed far more. A rowboat designed as a tender carrying occupants to a boat on a mooring might tend to be short, whilst a rowboat for use on rivers and to travel long distances might be long and narrow.