Spun prop, spun coupler or neither???

[thunderroad]

69 Mercruiser 160 SN 2497444. On the river yesterday, boat was running fine. We pulled up to a sandbar for a bit. We we left I pushed off until the boat started to drift with the current, lowered the unit, started the engine and put it in gear. We moved a little bit but must have run into a shallower spot. Not realizing exactly what was going on, by instinct I accelerated a little. Not a huge amount, just what I thought I needed to get underway. About the time I realized what must be going on, we got clear of the sand...but we plowed pretty good there for 3-4 seconds.
Nothing seemed wrong at all. We powered at about 3000 rpm for a couple miles, then shut it off and drifted a while. When it was time to go in I powered up and ran up to about 3200. With about 1/2 mile to go, I opened it up. It pulled good until about 3800 then went up to about 4200 almost instantly with no increase in speed. I backed it back down to 3800. Seemed to be pulling fine. Opened it up again and it did the same thing. I first thought maybe I'd spun the prop and wasn't too concerned because it was my "river" prop and I've got a couple others that are better. Then today I had one of those "Oh *****" moments. What if I've spun the coupler instead of the prop? I know all I have to do to find out is slap on another prop and give it a whirl but that's not gonna be possible until early next week and the suspense is killin me. Which is most likely, given the circumstances described?
One variable is that I can't positively swear what position the trim was in at the time. I can't really hear the trim and I don't have a gauge so I usually just trim down until I see the amp gauge bounce a little. Thinkin back...I can't swear that I remember doing that. I THINK the trim was ok because usually when it's trimmed too high it steers hard and pulls a little on the wheel. It wasn't doing any of that.
Any ideas?

 

[180shabah]

Re: Spun prop, spun coupler or neither???

It "broke loose" at 3800 and spun up to 4200 - then when you throttled back a little it settled back to 3800. Is this correct?

If so I doubt that either you coupler or hub are the problem. You would generally have to drop all the way back to idle for the rubber to "catch" again.

Probably damaged the prop blades slightly causing it to lose it's bite in the water.

 

[stonyloam]

Re: Spun prop, spun coupler or neither???

You could give it a sniff. As I understand it (never having experienced myself) if you spun the coupler you should be able to smell the burnt rubber. Don't know if it's true, but sounds logical.

 

[thunderroad]

Re: Spun prop, spun coupler or neither???

It "broke loose" at 3800 and spun up to 4200 - then when you throttled back a little it settled back to 3800. Is this correct?

yes...that is correct. It only seemed to slip above 3800 and was fine everywhere below that...even under acceleration. I didn't actually examine the prop blades for damage.
As for a smell, I put the boat on the trailer within about 10 minutes of this occurence and didn't notice any smell. I have to raise the doghouse to open the doors to unhook the battery and to get my tool box out. I would have had my nose within a couple feet of the coupler area when I dug out the toolbox so surely I would have smelled burning rubber.
I'll look at the prop...but I'm beginning to feel a little better about it all.

thanks

 

[180shabah]

Re: Spun prop, spun coupler or neither???

Put your other prop on and go have a good day on the water...

 

[racinrc14]

Re: Spun prop, spun coupler or neither???

Something very similar happened to me a couple weeks ago. Scared the bejeezus out of me too, since I had recently finished up a lengthy engine rebuild! In my case, I wasn't paying attention to the trim guage before opening up the throttle. I found that if the trim was even just a little to high, the prop would cavitate above about 3200, but would get a good grab below that. After retracing my steps, I realized that I had not trimmed back down after anchoring in a fairly shallow cove. I need to get one of those whale tail thingys I guess.

 

[180shabah]

Re: Spun prop, spun coupler or neither???

I need to get one of those whale tail thingys I guess.

You are kidding, right???