Building my first plank

Getting ready to build my first plank, having obtained 'some' ash, which has been planed to 5/16" and routed/sawn straight, although pieces are questionable in my estimation (knots).
My existing hull setup uses a 6-1/2" wide plank. Also have a nice piece of rough sawn walnut I want to incorporate. Thoughts/suggestions? Should I change hull to accept 7-1/2" plank? Existing plank is extremely stiff, built approx. 1968. Hull weight is heavy at 85# w/o plank, etc., Skipper is 170#.
I don't have Excel for the plank spreadsheet from IDNIYRA, and don't know a modulus from an ice hole...
Thanks for any and all help, except promoters of Texas Holdem!
Scott C.

The wider the better, I'd g

The wider the better, I'd go for 7 1/2". For a starting point build your plank between 1 1/8" to 1 3/16" total thickness. For your weight you'll want the plank to deflect 1 5/8" and 1 3/4" while you stand on it. The final crown you want is about 2 1/2". To get this you'll have to over bend it about 1/2" to5/8" while gluing it up. It should spring to about 2 1/2" when the clamps come off. Good luck. Bob Gray us4654