Interesting, I've always just put in in reverse. Usually I forget and once I'm sailing I'm NOT going to try to stop the spinning shaft. I never had to mark the shaft, the shaft coupler with bolts up/down indicates the prop is vertical (don't know if that's by design). When sailing in with this config, I never hear any chattering, the force seems constant but after an initial test when I went below, I haven't checked it since different conditions.
PS31#111 Cielo Azul