The IRSA Marblehead (M) class is probably the most exciting to sail with its moderate size and light weight combined with high maneuverability and stability. The rule is essentially a box rule with minimal constraints. A modern M will usually be made almost entirely of carbon fibre - hull, foils, spars and fittings. The class was the first to adopt hi tech construction in the early 90s and development since then has been limited. This permits almost all boats built since then to be compete well in modern fleets.
The class is quite often referred to as the "Formula One" of radio sailing. Internationally, the Marblehead is second in numbers only to the IOM class, and has been a high performance racing class for many years, even pre-dating radio control, using vane steering. It is a very high tech class using up to 6 rigs per boat, including swing rigs.
World Championships are held in conjunction with the Ten Rater Class every two years. Here in Australia, we have fleets of Marbleheads in all states apart from the ACT, and until recently WA. In WA, a small group of skippers are starting to get back into sailing Ms. National and State Championships are held annually around the country.
Class details:
Open class, box class
Carbon hulls, foils and spars
Hull length 1.3 m
Displacement 4.5 to 5.5 kgs
Draught 660 mm
Sail area 0.5161 m²
Further details about the class can be found at the website of IRSA Marblehead page