The Fulmars were introduced to replace the Westerly 31s - Berwick Longbow Pentland and Renown - and in performance terms were unequalled at the time (The Fulmars that is, not the W 31s!).
Keel Width 97" (measurement point not stated)
The Westerly Owners Association Definitive Guides
A presentation that Roger gave to the RYA London and South East Conference
Lots of Fulmar stuff here Richard Spencer's Fulmar Inadee site