Another prop issue

[Mfribley]

So earlier in the summer I was out with the wife we were checking out the houses on an island in our lake and I was changing the station on my Pandora and didn't notice the shallow rock bar that I was approaching(we were 100 yards off shore) and I well F***** my propeller up beyond repair and my luck was no one was on the lake for a tow so it was a long very slow trip back to the boat launch.

I started looking online for a new propeller and was at a loss as mine had no discernable make or model number, no pitch so I searched and searched to no avail I should mention that I have an old 1972 johnson 125hp and there are tons of props for that model online however my boat is only rated for 85horse max.... So I didn't want a propeller that would cause extra torque and strain the transom more ( I suppose your asking why is he running a 125HP on a boat rated for 85HP.... The short answer is it came with the boat and ran like crap I spent the summer fixing and tuning the motor up and my goal is to trade down find someone who wants more power or sell it and put the money on a used 85HP)

Anyways I found a used propeller on craigslist for $50 in great shape and thought what the hell after talking with the guy he said it was rated for Johnson V4 engines and was off an 80HP johnson side by side comparsion to my old one they looked damn close..and it fit my lower unit like a glove

So I mounted it and took the boat out didn't go to far or fast but things seemed fine however tonight I went out to the middle of the lake and drift fished for lake trout for about 2 hours when I went to head home I gave it throttle and it ran great for a few min and then the engine got loud and I wasn't going anywhere I checked still had the propeller turns out I spun the hub

So my question is what would cause a spun hub without hitting anything?

Any advice on buying a new propeller that would have low torque the boat is a 16FT fiberglass sea sprite tri hull

Is there a chart to cross reference propellers and HP

Any advice would be great

Mike

 

[jimmbo]

Don't worry about the 125hp straining the boats transom, the max torque between it and an 85 is pretty close(the 125 only had 7 more cubic inches of displacement than a 1969 -78 85hp), it does occur at a higher RPM, so the 85 actually has better holeshot.

You say you spun the hub? How did you verify it?

You say the prop you bought was for an 80hp. The 80hp V4s were of a totally different design, and used a completely different gearcase and prop and a prop for it would never fit a Post 1968 V4.

A 16 ft boat would probably use a 19 or 17 inch pitch. Your engine WOT range is 4500 - 5500, it is preferable to prop it to run upper portion of that range.
Prop chart from an OMC accessary book

 

[Mfribley]

Thanks jimmbo

The propeller was working great initally I started heading in for the night started off and things were great...after about two minutes the I lost all forward motion and the engine roared, I immidetly put it into neutral thinking I had lost my propeller or something I killed the engine and l raised it the propeller was still there so I put it back in the water and it would go slow but if I pushed it to a certain point it would do the same thing... So very slow trip back to the launch...


I'll admit I googled the symptoms and it pointed to a spun propeller so I went and pulled mine the center around the splines appears to be protruding also looks like rubber is melted around the splines and the backside of the propeller is worn almost as if the aluminum was rubbing something

 

[jimmbo]

You did ensure there was a thrust washer on the prop shaft when you installed the prop?

 

[QBhoy]

Presumably it's not the same hub you used again after the last propeller strike ?

 

[Mfribley]

No Title

There was a thrust washer on the shaft however the new propeller shredded the rubber down to aluminum rubbing on aluminum...

The "new" propeller was a take off so it had the hub and splines already in it

Here are a few picture's

 

[jimmbo]

Looks like your going to need another prop. Your current thrust washer has seen better days, should be replaced. There should also have been a washer/spacer between the prop and prop nut. Whatever brand of prop you get, make sure to get all the hardware( hubs, inserts, washers, etc) as different brands sometimes are slightly different.