About the design
The Mark IV, designed in 1953, had finer bows than the Mark II to improve windward performance in waves, and wider with more flared topsides. The development of self bailers allowed the IVa to have a lower freeboard. 

The winner of the 1957 Burton Cup was N1357, a IVa, and four more of the first 8 boats were Mark IVs or IVa's 

Designer: Ian Proctor

Builders: No current