Is some hub slippage normal?

[RSchendel]

I am running an old SMC 43 9 x 10 prop on my 1958 18HP Evinrude 15024. The boat is a Lund C-14 Aluminum. The max HP is 20.

Last week, I decide to try a new prop I purchased on eBay (there is another thread for that topic), and marked the back of the inner hub and prop with a sharpie to see if I could detect any hub slippage. The marks are no longer aligned after about 20 minutes at WOT. I did not detect any obvious slippage, but there are some clues.

- A couple of months ago, I lot of weeds got wrapped around the lower unit. The outboard revved up high with little progress. When I removed the weeds, it seemed fine.

- The RPMs float between 4400 and 4500 on a small inductive tach at WOT. I am uncertain if this is just the flaky tach or if it is a sign that the hub is slipping slightly.

Assuming no object has been hit, is some hub slippage normal or does it always mean the prop should be replaced or re-hubbed?

 

[ufm82]

Re: Is some hub slippage normal?

Hubs should not slip and if they are slipping, they will only get worse. When you ate the weeds and the engine revved, that was just the effect of the weeds interfering with the prop's ability to get a "bite" on the water. That happens anywhere on any prop, including trolling motor props.
You aren't running a high horsepower engine so if the marks were not aligned after only 20 minutes, it's just a matter of time before the hub loses its grip and you have issues. Hub slippage is not a thing to live with. It costs you performance, mileage and in the worst case scenario, can strand you somewhere or force you to run home at idle or so- making for a very long afternoon.
If the hub slipped at all it needs to be rehubbed.

UFM82

 

[Sea Rider]

Re: Is some hub slippage normal?

- The RPMs float between 4400 and 4500 on a small inductive tach at WOT. I am uncertain if this is just the flaky tach or if it is a sign that the hub is slipping slightly.

Electronic inductive tachs shows nervous, slight erratic readings compared to needle ones, a (+.-) 100 rpm reading is normal and the tach is working fine.

Happy Boating