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I agree with Jeff’s summary of the intent of the Seat Back Specification A. fueselage,13:
Seat back shall be flat
2. Seat length must be 11″(280mm) min measured from base of seat along flat on centerline, to crown, No maximum dimension specified
3. Radius specification is at top extent of seatback flat area which is specified by the word “Crown”, min dimension is 2″ (50.8mm)
4. Min width is 4″(101.6mm). Which in turn is 2x min radius when the top of seat forms a complete semi- circle profile (popular). In reality this applies is in the area located between surface of rear deck level and at a point 2″ (50.8mm) down from “crown”
I do not believe an official Interpretation is required, since I have always thought these clarifications were clear in the wording of the Specification. However if the TC Chairman feels an Interpretation would add additional clarity to the Specification I would support that.
I think Richard makes a good point that the corner radius in the green outline in Tomek’s drawing is less than 2″. I think that all radii along the top of the seat back should be 2″ minimum. Otherwise the corners on Tomek’s Green outline could be reduced to sharp corners and create a safety issue. The seat back is directly behind your head in a collision and can cause serious injury. But this could require an Interpretation, or possibly even a Specification change.
If a sailor decides to add some sort of padding to the seat back I believe that should be allowed since it could provide additional safety, or at least comfort. But this additional padding would need to be added to a seat back that already meets the Specification.