Number and type of legs
The traditional Olympic triangle course consists of a lap (starting with a beat or work to windward from the starting line to the top, weather or windward mark, a first reaching leg to the wing mark (also known as the gybe mark), a second reaching leg from the wing mark to the bottom or leeward mark), a hot dog (a beat to the top mark with a square run back to the bottom mark), another lap and then a beat to the finish line, which may have one end at the top mark, or may be set beyond the top mark. When the finish line is set beyond the top mark, the sailing instructions need to specify whether the top mark remains a mark of the course on the final leg or whether it is to be ignored. There are generally 9 legs, 5 equal to the length of the windward leg (4 beats and a run) and 4 reaching legs (2 of each reaching leg), so once the leg lengths are known the total course length can be calculated. Roundings are generally to Port. Many sailing instructions only specify the length of the windward leg and the total course length, but see below on the use of the law of sines, trigonometry table and spreadsheets to calculate the angles and other leg lengths.
In trigonometry, the law of sines, sine law, sine formula, or sine rule is an equation relating the lengths of the sides of a triangle to the sines of its angles. According to the law,
The angles of the triangle may not always be perfectly sharp, either, since it is a course.
Length of windward leg and course - time versus distance
Many dinghy classes have a target length for a race for the first boat. This time might take into consideration the age of competitors, how physically demanding the class is and how physically demanding the conditions are. 100 minutes is often used by Herons in Australia as an informal target (not specified in the Sailing Instructions). It is generally accepted that the whole of the course ought be completed in a race to ensure that all points of sailing are tested by competition. This requires consideration of the length of the course for a given class of boat in given wind strength.
When dinghies are sailing in displacement mode (as opposed to planing mode) they will take longer to complete a leg than if they are planing. The relationship between the time taken to complete a beat, compared to a run, compared to a reach will vary between classes at a given wind speed and by a class at varying wind speeds, with a significant change once boats are consistently planing on reaches (and runs).
Empirical evidence for Herons at 8 knots (15 km/h) of breeze on Botany Bay, Sydney with a windward leg length of 0.8 nautical miles (n.n.) saw a beat of 19 minutes, a reach of 9 minutes and a run of 13 minutes (non-planing conditions). With an equilateral triangle the traditional triangle, sausage, triangle, and beat to finish would require a windward leg of approx 15 minutes to allow for a completion time of approx 100 minutes for the first boat. In 8 knots (15 km/h) for a Heron the indicated windward leg length is approx 0.6 n.m..
Any Principal Race Officer wishing to have completed courses within a target time will need timing of completion of beat, reach and run legs over a wide range of wind conditions for the particular class to enable the setting of an appropriate length course (9 times the windward leg length in the traditional configuration described above). Race committees need to ensure that the sailing instructions regarding course length for each particular regatta have taken into account the aims of the Organising Authority in relation to all of target times, course length and course completion and that the achievement of some are not inconsistent with the achievement of the other(s). The possibility of changing leg/course lengths during a race needs to be considered to allow for changes in wind conditions.
The starting line
The starting line often has a bias to the port end (the left end as one looks up the course towards the top mark) of 5 to 10 degrees towards the top mark from what the start line would be if it was straight across the wind direction. This bias encourages competitors to move to the pin end of the line as it is further up the wind towards the top mark. It also provides "cleaner" air to competitors on the port end of the line. With many competitors moving to the pin or port end of the line to be further to windward, there is room for the other competitors to form up along the line, and although they may be further down the wind from the top mark, they are more easily able to tack onto port tack should the wind shift or to get clear air. If there is no bias favouring the pin end, or more particularly if the starboard (committee boat) end is favoured (further to windward), competitors will be encouraged to avoid being on the line away from the committee boat and so the committee boat area becomes very congested and most competitors are not on the start line and do not start until some time after the starting signal as they have been queued up in the area to starboard of the starboard end of the line. Boats generally approach the starting line on starboard tack to maintain right of way over boats on port tack.
The length of the starting line is generally set by reference to the total length or width of the fleet, that is, the number of competitors by the length or width of each boat. While a general rule of thumb is 1.1 to 1.5 times the total length of the fleet, some race officers believe this is too generous according to ISAF. Another rule of thumb is 1.5 to 2.0 times the width of the fleet which is easy to calculate in a one design class, but is generally markedly less than 1.1 to 1.5 times the length of the fleet.
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