A good rule of thumb is 1/8" of rode diameter for every 9' of hull length. So while 3/8" ride will certainly hold a 25-footer, I find 7/16" or even 1/2" rode to "feel' and deploy far easier on the hands .... as me, myself, and I be both the Captain and windlass! I'm sure 8-plait line is easy on the hands too, as that stuff is soft to the touch ...