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?

On Mon, 4 Aug 2003 09:02:02 -0400, "Joe Blizzard"
wrote:

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?

Yeah, "a fair assumption", although if the prop is "dinged" it could
cause the same symptom.

noah

Courtesy of Lee Yeaton,
See the boats of rec.boats
www.TheBayGuide.com/rec.boats

"Joe Blizzard" wrote in message ...
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?


Sounds familiar - I think you've hit it right on the head. Buy a new
prop, and then get the old one re-pressed to use as a backup for the
next time this happens.

FishFan

"Charles T. Low" wrote
I've spun couplers on I/O's - but am not sure if this is analagous.
When I did, the prop virtually just didn't turn, at any speed.

I decided to forego testing and dropped my prop off late yesterday (Monday)
to be rebuilt. The local shop sends them out on Tuesdays, so I wanted to go
ahead and get it in this week's truck so it would be back next week. I asked
about other causes while I was there and was told that a drive coupler could
do something similar, but that I would probably have noticed a hot smell
from that, which I didn't. Fortunately the forecast here is rain all week,
so I don't feel too bad about the boat being out of commission for a few
days.