Tech Notes
Index

Have you measured your J-Dimension lately? The reason I ask is because that measurement, length from forward edge of mast at mast step to forestary tack point, is used as a basis for calculating "rated sail area", whisker/spinnaker pole length, spinnaker mid-girth measurements and such for your sails and PHRF type racing handicap ratings. While measuring the "J" on my "white hull" First 21.0 Classic, I found it to be 7.58 feet (7' 7") while the factory specs on the First 21.0 model are 7.87 feet (7' 10"). Why the three inch difference in "J" when all the other dimensions ("I", "P" and "E") are exactly the same? Curious, I inspected my friend's First 21.0, "blue hull model". The First 21.0 has an aluminum bow stem plate to which its standard jib furler and luff tape is attacted, as well as a bow pulpit stanchion base. That stem plate also features mooring line feed "chocks". On my First 21.0 Classic, there is no stem plate and the bow pulpit stanchions are secured to either side of the bow stem. The forestay "chain plate" on the Classic is through bolted flat on the deck with a plywood backing plate underneath. As such, you can install a bow light on the deck prow in front of the jib tack plate. On the First 21.0, the stem plate prevents that, so the bow light is welded on the bow pulpit rail. Why is this and is the jib sail area the same on both models? I concluded this. The Classic does not feature roller furling jib gear. Therefore, it does not require the extra 3 inches for the furling drum apparatus. Thus, the jib tack point on the First model is some 6 or more inches higher on the forestay (to allow space for the furler drum). If it's any relief, I surmise Beneteau figured out this difference and set the Classic forestay tack 3 inches back from where its located on the First 21.0. By doing so, they ensured the sail area and "one design" aspect of the two models would be kept in tact; notwithstanding the differences in keels and rudders (5' 11" swing on F21.0 vs. 3' bulb keel on F21.0C and double rudder on F21.0 vs. single rudder on F21.0C). Moreover, you can fly the same sails on either boat and know that the rig, hull and all other dimensions on the two models are essentially equal. I post this here because it's a frequently asked question and you may have to explain it to your PHRF Chief Measurer or Rating Committee some day (as I was required to do). On that, you should receive a 6 sec/mi. extra PHRF "credit" for the Classic "shoal draft" keel. And, for both boats, you should receive a 9 sec/mi. "credit" for using a ODR max headsail of 100% (vs. PHRF standard of up to 155% genoa). Hope this helps.
 
 
 
 
 

Title: J Dimension on Classic vs. First 21.0 
Model(s): First 21 Classic 
System(s): Racing & Handicap Rating; Tech Specs 
Author: Terry F. Ellis