The X-99 was designed by Niels Jeppesen and built by X-Yachts and first launched in 1985 with 605 built. Oak frame: Hull no 1 -to 259 and hull no 270, 263 and 267 Steel frame introduced 1990 Hull no 260 and onwards except 270, 263, 267 Alu. framed windows introduced 1991 (MK I) Hull no 288 and onwards except 290 and 310 Volvo engine introduced 1991 (MK I) Hull no 288 and onwards except 290 and 310 MK II introduced 1996 Hull no 500. From there on the MK II was sold with slightly different features as two windows, needle rudder bearing and a different water pass design. The class was recognised by the International Sailing Federation from the late 1997 to November 2010 during this period the class was entitled to an official World Championship.
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 Class symbol | |
| Boat | |
|---|---|
| Crew | 6 |
| Draft | 1.75 m (5.7 ft) |
| Hull | |
| Hull weight | 2,980 kg (6,570 lb), Ballast 1,300 kg (2,900 lb) |
| LOA | 10 m (33 ft) |
| LWL | 8.5 m (28 ft) |
| Beam | 3 m (9.8 ft) |
| Sails | |
| Mainsail area | 32.3 m^2 |
| Jib/genoa area | 30 m^2 |
| Spinnaker area | 78 m^2 |
| Former class of World Sailing | |