I’m getting ready to glass on 9x5 plywood keel fins. They are 5/8" wide at the base. Do I need to beef up the amount of rope and the number of 6 oz. panels to avoid cracking?
you haven’t stated you much rope you’d use normally - how can we say if you need more? Generally, I’d not put 'em on any stronger than you were doing regular fins (as if many people are still glassing on fins in this day). They are shorter than single fins so the torque at the base is less, and they have a wider base to better resist the torque, so you could use a little less reinforcement on your keel fins. This won’t mean they can’t be broken, of course.