So I'm cruising down the Kanawha River in my '77 T-bird 18' trihull with the
Merc 165 humming nicely at about 3500 RPM and there's a little lurch and a
big increase in RPMs. My keen nautical sense told me that something was
wrong, so I immediately throttled back. After stopping, looking dumbly at
the back of the boat and not seeing anything suspicious, I tentatively
advanced the throttle and everything seemed normal until I got up to about
3000 and I again got a surge in RPMs and loss of power. I tried this a few
more times and got the same results, so I putted home at low speed. This
sounds to me like a spun propeller hub. I took the prop off, but, as
expected, there are no visible signs. I know I can verify it by putting
index marks on the hub, putting it back on, and taking it out for a spin,
but is there really any point in going to that much trouble? In other words,
is there anything else that could give me the exact same symptom? I'm
assuming that if it was a problem with the gears or the sliding clutch in
the drive or something in that area, that I'd have some accompanying
mechanical noise, vibration, and/or symptoms at low speeds. Is this a fair
assumption?