The ORC decided that the rule should "....permit the development of seaworthy offshore racing yachts...The Council will endeavour to protect the majority of the existing IOR fleet from rapid obsolescence caused by ....developments which produce increased performance without corresponding changes in ratings..." When first introduced the IOR rule was perfectly adequate for rating boats in existence at that time.
However yacht designers naturally examined the rule to seize upon any advantage they could find, the most noticeable of which has been a reduction in displacement and a return to fractional rigs.
[1] The idea of holding a Half Ton Classics Cup first arose at Cork Week in 2000 when the Crew of 'Sibelius' (FRA) including Didier Dardot and his wife and the crew of 'SpACE Odyssey' (IRL) including Shay Moran, Enda Connellan, Terry Madigan and Vincent Delany agreed that it would be a great idea to organiser a bi-annual event for Half Tonners under the IRC handicap system with the venue rotating between France, England and Ireland.
In fact Didier Dardot was unable to persuade La Trinite or any other French clubs to organise the first event.
[2] By 2017 it was evident that only expensively optimised boats were capable of winning the Half Ton Classics Cup.