prop spins in cold water?

[HJWiseman]

1978 Evinrude 9.9 HP has been setting for 15 years. Took it to a dealer to be checked out before use, they changed the lower unit oil and gave it an "A-OK". Went to use the boat at Lake Taneycomo (a cold water lake below Table Rock dam) and all went well for about the first 20 minutes after that the engine would over rev and the speed of the boat would decrease. Seemed like a classic spun hub, was able to return to dock at low speed. Got home & pulled the prop, no visible damage. Marked the hub and prop to verify spun hub. Went to a local river and tried for an hour to get a repeat performance to what happened at the lake. I was not able to get the hub to spin in an hour of trying with repeated hole shots, etc. My question is can cold water cause the hub to spin but in normal temperature water the hub would work as it should. That doesn't make sense to me. Does anyone have any ideas as to what else I should be looking at? Hate to go out in a boat that I'm not sure of. Thanks.

 

[Willyclay]

Welcome to the iboats.com forum. The members here are great and the experts, which I am not, can help you with any problem. How cold is the "cold water" where the problem showed itself?

 

[Sea Rider]

Being a 36 year oldie prop and for my boating peace of mind would get a new one right away. Prop hubs don't last forever...

Happy Boating

 

[GA_Boater]

Being a 36 year oldie prop and for my boating peace of mind would get a new one right away. Prop hubs don't last forever...

Happy Boating

As I found out last week when my just barely broke-in 50 years young prop spun the hub. With no warning, I went from cruising about 20 MPH and 3500 RPM to revving and speed dropping off. I was able to run about 1500 RPM and 5.5 MPH the eight miles back to the dock. Talk about watching paint dry! If it would stop raining, I could test the new prop.

HJ - I think it was just coincidence in the colder water. One thing is cold makes the hub rubber harder and that could be the reason. Curious - Any idea what the river and lake water temps were?

 

[HJWiseman]

The water temperature of Lake Taneycomo is about 48 degrees and the river I tried to test the prop in later was in the low 70's.

 

[GA_Boater]

Forgot to :welcome: you. :sorry:

I guess you could try another run on the lake, with another prop because your symptoms sure sound like a spun hub.

 

[Texasmark]

Only positive answer I could give you would be material thermal dynamics. Most materials shrink to some degree with decreasing temp. Course the alum has a much higher thermal coefficient of temp than rubber so the grip should get better cold as the alum would shrink down onto the rubber better.

Possibly the prop developed rubber shrinkage over the years and the rubber surface glazed and as such couldn't grip the alum like it should initially. After you spun it for awhile, you wore the glaze off it and it was able to develop enough friction between the two surfaces to stay put.....like sanding off a glazed surface so you can paint it and have the paint stick.