Spun Hub and I didn't hit anything?

[Reg312]

Hey - This weekend we were cruising nicely WOT (5200 rpm) and out of nowhere revs climbed and extra 500 rpm and pontoon slowed down. So I throttled it down to 3000 rpm and toon was still moving at a decent speed and made in safely to dock. Turning left or right would cause the prop to lose its bite and motor would rev up. Pulled the prop off .. it looked fine. No signs of hitting anything. Put on an beat up prop and toon performed well for the condition of that used prop. The prop I had on was a 13 x 11 RH Michigan Wheel thats barely 2 years old. So did I really spin a prop or are Michigan props poorly designed or do props just wear out after a few years? Should I replace this with the same prop?

1991 lowes 20' pontoon with 1991 40 hp Johnson T&T.

Thanks for any info given.

 

[Texasmark]

Re: Spun Hub and I didn't hit anything?

No biggie, using a magic marker or something that will survive the testing, make a mark from the brass splined insert straight out to the edge of the hub of the prop. If you have a spun hub, the prop and the hub will run at different rates. Therefore, after a short run, pull the prop nut and washer off and look at your scribe lines. If they are no longer aligned, you have a spun hub. If they are still aligned you need to look elsewhere.

Props will run for 10's of years!

Mark

 

[Sea Rider]

Re: Spun Hub and I didn't hit anything?

If prop hub has been poorly vulcanized or with vulcanizing issues during it's manufacturing process, expect prop failures at any time lenght specially while running constantly at wot. Props and shoes are not eternal...

Happy Boating

 

[MH Hawker]

Re: Spun Hub and I didn't hit anything?

I have ran MW props for years with no problems.

 

[Reg312]

Re: Spun Hub and I didn't hit anything?

Thanks for the reply's. I'll mark it next weekend to see what happens. We were tubing with it the weekend before for a few hours and a 40 hp pushing a 20' toon is pretty slow so figure 8's were in order to enhance the tubing experience. I wonder if doing something like that would put enough stress on the prop to make it spin in the hub.

 

[petertay]

Re: Spun Hub and I didn't hit anything?

Sent my old 13-inch steel prop to Midwest Props last week to be rehubbed. They turned it around the same day. $58. Nice cost compared to buying a replacement.

 

[Jimbski]

Re: Spun Hub and I didn't hit anything?

I have a 6 hp, 4-stroke Tohatsu motor that is 6 years old. After annual maintenance, I would tighten the prop nut 1/4 turn past "hand tight". Last year, I experienced spun prop so I made alignment marks and put on a new prop and hand tightened it as recommend by a local marine mechanic. My boat is v-hull and gross weight pushed by the motor is only about 300 pounds including the motor. 15 minutes at wot( 14 mph) was ok, but then motor suddenly increased rpm while decreasing speed. Everything seemed ok at 8mph (half wot). When I took the prop off, the marks were not aligned. I reinstalled the prop, but tightened the prop nut to 17 Nm (150 inch pounds) as recommended by a service manual, and went for a test drive. It seemed ok for most of the ride (wot), but a slip here and there. Since the water was choppy, I thought it might be due to cavitation, but the alignment marks had moved again. Did I encourage spun prop when I put on the prop nut hand tight? Is this prop hub ruined? Does it matter if a new prop is "hand tightened" versus tightened to 17 Nm?
Jim

 

[Sea Rider]

Re: Spun Hub and I didn't hit anything?

Really doesn't matter. I usually tight nut by hand untill fully seated on washer, then with wrench adjust slight more untill shaft hole is aligned to nut's cuts evenly as to insert a greased split pin effortlessly. If prop spuns again, it's bad manufacturing and probably made in...you know where.

Happy Boating

 

[Jimbski]

Re: Spun Hub and I didn't hit anything?

Really doesn't matter. I usually tight nut by hand untill fully seated on washer, then with wrench adjust slight more untill shaft hole is aligned to nut's cuts evenly as to insert a greased split pin effortlessly. If prop spuns again, it's bad manufacturing and probably made in...you know where.

Happy Boating

Thanks for reply. I will discuss it with my prop's supplier.
Jim

 

[Reg312]

Re: Spun Hub and I didn't hit anything?

Finally got back to the lake with identical new prop in hand (Michigan 13 x 11 RH). Marked and put the old (spun) back on a took a test drive. Higher RPM, lower speed, And lost all bite turning left or right ..... but when I pulled the old prop marks were STILL LINED UP. Put New prop on and tested it. Prop did fine. Had bite all thru rpm range and in turns. But I could only get it up to 4800 rpm at WOT whereas the old prop would run at 5200 rpm before it stared having issues.
So what happened since hub doesn't seem to be spun?
Are the rubber spokes weakened under higher torque?
Why the lower RPM with the new prop?
I did notice a loader exhaust note and a tad more vibration with the new prop.
Any insight on this greatly appreciated.

 

[Texasmark]

Re: Spun Hub and I didn't hit anything?

Prop torque is against the brass splined insert, not against the hub. On my 90 Merc with a manual reading of 55 ft-lbs you aren't going to get that pushing againgst rubber. So on the Tohatsu you had a prop problem with the hub.

On your identical prop, something had to change. On the 4800 vs 5200, same everything, I'd say the prop was already slipping somewhat unloading the engine and giving you the extra rpms. With it slipping you could realize the increased rpms and still retain the same speed.

Obviously the twisting "moment of inertia" at higher rpms would be higher than at lower. You have more HP against which the prop is having to work so the work function is increased.

This sounds like a fluke, but by chance possibly the marks spun but wound back where you started....just a chance fluke.

What is the essence of the tower in the thumbnail? That doesn't look like an OMC 40 hp. What does it have to do with the question? You had me chasing a ghost there for a minute.

I left OMC years ago, but aren't they listed at 5000 rpm at WOT +/- 500? That said I guess 4800 isn't too bad.

On Michigan wheels, they were here when I started boating 50+ years ago and still going strong. Looks like their quality survived the ultimate test.....time! Back in the early days, if you wanted something other than OEM alum for a prop MW in bronze is what you had for a selection, 2 or 3 blade. I had several and never a problem.

 

[Reg312]

Re: Spun Hub and I didn't hit anything?

Thanks Texasmark. Tower of power my 1st attempt a boating a few years ago. Near end of season it was running a little rough but thought it would make the year. 2 weeks later scored #2 cylinder. Learned a lot since then. I pay more attention to my motor now that I'm a little more informed. I just never changed my thumbnail. Looks cooler than a thumbnail of a pontoon with a OMC hangin off the back.

 

[Texasmark]

Re: Spun Hub and I didn't hit anything?

Thanks Texasmark. Tower of power my 1st attempt a boating a few years ago. Near end of season it was running a little rough but thought it would make the year. 2 weeks later scored #2 cylinder. Learned a lot since then. I pay more attention to my motor now that I'm a little more informed. I just never changed my thumbnail. Looks cooler than a thumbnail of a pontoon with a OMC hangin off the back.

Yessssssss