Is 21HP on the Ericson 35 ok?
Paul, I am not clear on what are you trying to say when you say, "One reason for heftier horsepower in the current crop of designs is the need to deliver race boats to the the start at 10-12 knots, because you can''t get the fifteen guys needed to sail the thing until its actually race time."
If you look at the current crop of raceboats they actually take smaller crews than earlier IOR boats. A 35 footer in IOR days may have had a crew of 7 or 8. Today 43-35 raceboats can have crews of 5 (J-105) to 6 or so on a IMS or OD25. These are also easier boats to sail single handed or with limited crews than many similar sized cruising boats. Modern raceboats get by with smaller engines typically powering throught saildrives, which despite their variuus negatives are a bit more efficient in using a given horsepower.
Of course the Ericson 35-3 never was really was a race boat but was more of a performance cruiser with a rig that was a bit harder to handle than modern fractional rigs with non-overlapping jibs. As to the various HP differences, this is not a cut and dry issue. Diesels from the early 1970''s (as might be found on Ericson 35 mk1''s) tended to produce more torque at a lower RPM than more modern engines. To calculate horsepower in a rotating shaft, you multiply RPM x Torque X a constant. HP matters less on a sailboat engine than torque. Since these slow turning high torque engines produced similar torque to the current breed of lower torque, higher RPM engines modern engines appear to be more powerful, they really do not necessarily produce more usable power.
The extra HP is useful as modern boats do tend to have higher capacity alternators and the like that sap power.