curising rpms

Dear Fellow Sailors, I have a new-to-me Irwin 28 with a 25hp Kubota diesel engine. Wondering if anyone can recommend the proper RPMs for cruising speed if there is no wind. Also, if the throttle is as far as it can go, (haven’t tried) is this damaging to the engine. I’m a neophyte when it...

Hello, I have a 2001 Hunter 460 with the flex-o-fold prop, previously my WOT was around 3600rpms. This put my cruising RPM's at around 2800. Over the last year i've noticed I can no longer get up to 3600rpm's. I top out around 2900. Thinking this could be because of a running gear or bottom...