InsertformulahereHull speed is a common rule of thumb based on the speed/length ratio of a displacement hull, used to provide the approximate speed potential of the hull. It is the speed of a deep water wave whose wavelength is equal to the waterline length of the hull. Hull speed is typically not a term used by naval architects (they use, instead, a specific speed/length ratio for the hull in question) but is often used by amateur builders of displacement hulls, such as small sailboats and rowboats. A rule of thumb is an easily learned and easily applied procedure for approximately calculating or recalling some value, or for making some determination. ... The Froude number is a dimensionless number used to quantify the resistance of an object moving through water, and compare objects of different sizes. ... A displacement hull is the type of hull used by large ocean-going vessels and sailboats. ... Ocean waves Ocean surface waves are surface waves that occur in the upper layer of the ocean. ... The wavelength is the distance between repeating units of a wave pattern. ... This is a sailboat term for the length of a boat at the point where it sits in the water. ... It has been suggested that this article or section be merged into Naval Architecture. ... Look up amateur in Wiktionary, the free dictionary. ... Diagram of Sailboat, in this case a typical monohull sloop with a bermuda or marconi rig. ... The GB coxless pair of Toby Garbett & Rick Dunn at Henley Royal Regatta 2004. ...

The concept has to do with the effect of drag from the water on the hull. With all else being equal, a longer boat will have a higher hull speed. In yacht racing this is demonstrated by looking at handicap ratings such as PHRF; generally speaking longer boats have higher handicap, although there are other factors. Please wikify (format) this article or section as suggested in the Guide to layout and the Manual of Style. ...

History

The quantification of the speed/length ratio is generally credited to William Froude, who used a series of scale models to measure the resistance each model offered when towed at a given speed. Froude's observations led him to derive the Froude number, which allows experimental observations performed on scale models to be applied to full-scale vessels. The hulls of swan (above) and raven (below). ... The Froude number is a dimensionless number used to quantify the resistance of an object moving through water, and compare objects of different sizes. ...

The speed-to-length ratio is traditionally expressed in knots of speed (V) and feet of waterline length (LWL): A knot is a unit of speed abbreviated kt or kn. ... This is a sailboat term for the length of a boat at the point where it sits in the water. ...

Use

The speed/length ratio is strictly only useful when comparing different scalings of otherwise identical hulls whose drag is dominated by wave drag. However, for many hulls, a generic speed/length ratio will provide a good general estimate of the speed potential of the hull when it is operating in displacement mode. This is commonly called the hull speed, and this term is commonly found in the boating community and among amateur builders, though it is not used by naval architects or engineers. Wave making resistance is a form of drag that effects surface Watercraft, such as boats and ships, and reflects the energy required to push the water out of the way of the hull. ...

The hull speed limit does not readily apply to certain types of hull which are not primarily limited by wave drag. Examples of these craft are:

• Very long, narrow hulls such as rowing shells, flatwater racing canoes and kayaks, and multihulls such as catamarans and proas. In these hulls, skin drag is often far greater at the normal operating speeds than the wave drag.
• Boats which operate in a semi-displacement mode where the hull shape provides some lift. In these hulls, the lift reduces the displacement, providing a reduction in the quantity of water moved and a corresponding reduction in wave drag.
• Small, highly powered boats such as sailing dinghies and personal watercraft, which can easily plane. These hulls quickly and easily surmount their bow waves, and rely entirely on dynamic lift when planing.

Some boats, such as the proa, have both a narrow hull and are capable of operating in a semi-displacement or planing mode. Very large vessels, such as supertankers, are also generally limited by skin drag. This is not due to any special property of the hull, but rather to a low power to displacement ratio, which keeps the vessels operating at speed/length ratios well below the hull speed. University of Vermont 8-oar shell In watercraft, a shell or racing shell is an extremely narrow, and often disproportionately long, rowing boat specifically designed for racing or exercise. ... C-1 sprint canoe, with K-1 sprint kayak behind. ... A multihull is a ship or boat with more than one hull. ... It has been suggested that Catamaran History be merged into this article or section. ... R. M. Munroes 1898 proa A Proa is a multihull vessel consisting of two (usually) unequal parallel hulls, superficially similar to an outrigger canoe. ... The lift force, lifting force or simply lift is a mechanical force generated by a solid object moving through a fluid. ... 2 GP14s, a Topper and a Graduate Dinghy sailing is the activity of sailing small boats by using (1) the sails and (2) underwater foils (centreboard and rudder). ... Categories: Stub ... A Musto Skiff, planing on a fast reach A planing boats hull skims across the surface of the water rather than pushing through the water in the way a traditional displacement hull works. ... A supertanker is an unofficial nickname that applies to a certain class of tanker ship built to transport very large quantities of liquids; in practice this typically refers to crude oil. ...

The most commonly used hull speed constant is the wave propagation speed for the hull length, and it serves well for traditional sailing hulls. In English units, it is expressed as:

Or, in metric units: Look up si, Si, SI in Wiktionary, the free dictionary. ...

In reality, speed/length ratios of real hulls vary from as low as 1.18 for blunt hulls such as barges to over 1.42 for long, thin hulls. Also, since hull speed takes into account only the wave making resistance, large hulls (over 200 ft or 60 m) will be more limited by other forms of drag[1]. Self propelled barge carrying bulk crushed stone A barge is a flat-bottomed boat, built mainly for river and canal transport of heavy goods. ... Wave making resistance is a form of drag that effects surface Watercraft, such as boats and ships, and reflects the energy required to push the water out of the way of the hull. ...

References

• http://www.afaisouth.com
• A simple explanation of hull speed as it relates to heavy and light displacement hulls
• Hull speed chart for use with rowed boats
• On the subject of high speed monohulls, Daniel Savitsky, Professor Emeritus, Davidson Laboratory, Stevens Institute of Technology
• Low Drag Racing Shells