Hm, I think we need to revisit this "Buzzards Bay 21" topic. First
off, what is a "Buzzards Bay 21"? What defines it? Why do you think
that #547s, #573s, and #574s are "Buzzards Bay 21s"?
Note that they are very different boats. #547s Onagh and #574s are
both finkeel raceabouts built from the same model (No. 305). #573s
Terrapin, on the other hand, was really designated by HMCo as a
"Buzzards Bay 21 Class". But she is a keel and centerboard boat, no
finkeel, and she was built from another model (No. 313).
Thus, there was no Herreshoff-built Buzzards Bay 21' one-design class
(like, say, the BB15s or the BB18s).
There was, however, a very active class of 21' WL knockabouts and
raceabouts racing in Buzzards Bay after the turn of the century.
My guess is that #547s Onagh, #548s Radiant, #555s [Cancelled], #573s
Terrapin, #574s Arethusa, #611s Illusion, and later possibly the
Beverly YC Raceabouts #696s Foraminifer, #701s Foraminifer, #705s
Saracen and #707s Pollywog were all designed for this class. I am sure
one could find more details in the yearbooks of the Beverly Yacht
Club.
Bill Beardsley, might you be able to shed more light on this topic?