Building 11' ribboned Sapele ships ladder. Sides are 5/4 by 6". The 9 treads are 18" wide 5 3/4" deep and 7/8 thick. Treads will sit in 1/2" deep stopped dados.

Obviously all face to end grain glue joints, but would you trust going without fasteners?

I was thinking screw/plug 4 treads (top, bot, middle) but want to get opinions. Thanks.