We just had this discussion with a customer who has a 2859 Bayliner diesel. WOT RPM should be around 3600, and his boat tops out at 3000 RPM. He says he knows, but since he never runs at WOT throttle it's okay. Since he cruises at onlt 2000 RPM he feels he's fine.
No amount of discussion woudl disuade him, and he used to work at one of the large marine retailers, so you would think he would know better. His answer was that he understood, but that he know better.
All we could do was shrug and wish him well.