Prop advice..too much data!

[jroach]

I was browsing through some threads and ran across one about the boat topping out at 25knots (+-) at full throttle. One of the replies suggested that the prop might be slipping which lead me to 1000 other threads about props.

I have a 19' Sorrento, 4.3L. I bought a few props back in the day when it was new (original owner) and was wondering if there is an expiration date (arbitrary or ???) for the rubber impact . I can't say for certain how many hours I have on this prop but I only have 416hrs on the meter. It's a 15x17, AL, stamped "Michigan Wheel". I think the prop might be 35+ years old. I primarily use it for water skiing/wake boarding and less than . I've attached some pics but it looked pretty good (to me). I did notice a little "sparkly" metal dust on the outer washer.

 

[Arminius]

The hubs generally don't slip, just another common misconception. The replacement design has a plastic insert that will fail permanently to preserve your drivetrain and prop if the propeller is caught and seized by underwater debris. The bond between your prop, the rubber insert, and the hub could fail but then you couldn't go anyplace and would have to have it rebonded or replaced.

Incidentally, saw a new 22' fiberglass hardtop pushed by a 175 hp, naturally aspirated, Merc OB at the marina yesterday. Brand was not familiar but the owner was proud and I bet it was pricey. Said you couldn't get a hardtop for years but this did not look like a dedicated fishing rig. "Just enough power to put it on the plane" Ghost of Jim Morrison is singing, "Summer is almost over!"

 

[Skybolt]

I was browsing through some threads and ran across one about the boat topping out at 25knots (+-) at full throttle. One of the replies suggested that the prop might be slipping which lead me to 1000 other threads about props.

I have a 19' Sorrento, 4.3L. I bought a few props back in the day when it was new (original owner) and was wondering if there is an expiration date (arbitrary or ???) for the rubber impact . I can't say for certain how many hours I have on this prop but I only have 416hrs on the meter. It's a 15x17, AL, stamped "Michigan Wheel". I think the prop might be 35+ years old. I primarily use it for water skiing/wake boarding and less than . I've attached some pics but it looked pretty good (to me). I did notice a little "sparkly" metal dust on the outer washer.

No expiration per se' but as the vulcanization gets older it gets softer and less able to hold as well as it once did. It's elasticity tightens up and gets "brittle" so to speak. Sometimes just the force of the engine acceleration can break it loose.

That's not to say I would get rid of the your older props. Just know what may happen so if it does happen, you know what's going on.

 

[Arminius]

No expiration per se' but as the vulcanization gets older it gets softer and less able to hold as well as it once did. It's elasticity tightens up and gets "brittle" so to speak. Sometimes just the force of the engine acceleration can break it loose.

That's not to say I would get rid of the your older props. Just know what may happen so if it does happen, you know what's going on.

As to the "Reel Nauti", very nice! In the future we will have robots to work the ropes.

 

[Skybolt]

As to the "Reel Nauti", very nice! In the future we will have robots to work the ropes.

Thank you, but not so sure about the 2nd part.

 

[Scott215]

If I had a Chance to save my lower unit I definitely would

 

[Lazy Daze]

Yes, absolutely, prop hubs can spin. As the rubber loses it's elasticity, it doesn't "bind" the metal hub to the propeller as well. The rubber hub is simply pressed into the cavity and it makes the connection between the propshaft/metal bug and the actual propeller. They can be re-hubbed (repaired).

As noted, the tipoff when this happens is the RPM's will shoot up higher than you would expect for a given speed. Hi load requirements such as hole shot and WOT exacerbate it.

That rubber hub is about the best looking 35-year old hub I have even seen. It practically look new. Looks can sometimes be deceiving, but based solely on that pic, I'd say it's fine.

 

[GypsmJim]

When my boat was new I did my own performance curve and plotted it on excel. In other words, GPS speed vs rpm.

I do it every year to see if anything needs my attention. It never has. My last boat had the original prop when I sold it after 35 years.

If you suspect a prop is slipping, mark the shaft and hub and go run the boat. If the lines don't correspond any more, your prop is slipping.