J/30 Class Association Forums J/30 Forum The Boat, Sails and Equipment Prop pitch

Is it true that the Class spec for the prop was created for the 13 hp Yanmar. And if so, isn't the 14p a bit under powered for the 15 hp (1984 model)as noted in another discussion. I feel the 14dx14p is under propped for me. ie. Black soot on transom, 6.6 kts in smooth water at 2800rpm