Thank you. Yes, I am aware of that rule. There does not appear to be any rule on length and width of the rudder. I also could not find a limitation on length and width of the skid fin regarding electric hydro 1/10th scale.NAMBA Rule book. Section 28. 7.b.iv
If you're building a 1/10 scale, I recommend you read section 28.7 completely. There are limitation in that class you won't find addressed anywhere else in the rule book.