1/4, 1/2, 3/4 and 1 ton classification

I have been looking into what defines these different classes but am unable to find anything. Can anyone help?

 

You're referring to the old British measurement formula valid in the mid to late 1800s i believe:

(L-B) x B x 1/2B /94 = tons
or
(L+B)^2 + B/1730 = tonnage or rating

or the Seawanhake Yacht Club Formula:

L x Sa/4000 = "sail tons"

 

Not likely.

The designations refer to the level rating classes within the IOR rule. This was the most competitive keelboat racing for open designs during the 1970s and 1980s.

The QTs raced level at a rating of 18.0, later 18.5 feet. The boats were from about 24 to 26 feet in length overall.

Halves rated 21.5, later 22.0. The boats were about 30 to 31 feet in length.

3/4s rated 24.5 feet. Overall they were about 32 to 34 feet long.

OTs rated 27.5, lated 30.55. The early boats were about 35 to 38 feet long, the later ones 40 to 41 feet.

There were also level classes for the Mini Tons rating 16.0, 20 to 22 feet long, and Two Tonners rating 32.0, about 42 feet long.

The IOR Rule ran to about 80 pages and is still available for a fee from the ORC.