Prop spinning in the current

[QBhoy]

Hi
An interesting question and thoughts sought.
My mooring is on a fast flowing river.
The prop spins in the flow of current. To stop this I leave it in gear. My thinking is that it will stop any un due wear on the drivetrain.
What do we think...am I waiting my time ?

 

[jimmbo]

Well the prop is now acting like a turbine. As for that causing undue wear...The propshaft is supported by well oiled bearings and when in operation is spinning at several thousand rpms...
But it is your boat, you can leave in gear or out of gear, doubt it would make any difference. I would be more concerned about things growing on the hull and out drive and gelcoat blisters after prolonged time in the water

 

[QBhoy]

Thanks Jimbo.
I'm aware that it is lubricated by oil and all that, but don't see the point in allowing it to spin 24/7.
I take the boat out all winter and a few times a year to change the drive oil (hours dependant), clean and polish the hull too. Keeps her running efficiently.

 

[Old Ironmaker]

Then leave it in gear. The question now is would leaving it in gear cause undo pressure on the lower end? Letting it spin on your boat may keep crud sticking to it. How about lifting the prop out of the water when she's docked if you can? I keep it out of the water myself. If my elderly neighbour in 1 slip over smacks my boat docking at our marina I will know exactly who it was. He broke the prop in the boat at the slip to his right, twice. Plus it keeps crud and Zebra mussels from sticking my outboard.

 

[QBhoy]

I had thought about tilting the drive up, but figured that may be worse off, in terms of corrosion. Being an outdrive, it would neither be out of the water completely or in the water completely. When it's trimmed right down, the whole drive is under water, which will no doubt reduce cold corrosion....I like to imagine.

 

[ondarvr]

What is cold corrosion?

 

[roffey]

What is cold corrosion?

I had to look it up.....

https://www.exxonmobil.com/en/marine/technicalresource/marine-resources/engine-cold-corrosion

 

[ondarvr]

From that link it would have nothing to do with an outboard being tilted up. It could have an affect if the motor was never allowed to fully warm up and be worked hard, which is the exact same thing that any motor has to deal with in those circumstances.

 

[JimS123]

My 1984 Family boat has a 9.9 2-stroke Evinrude kicker. At no-wake speed the prop turns real fast. The Owner's Manual has no instructions, one way or the other. Way back when, I called OMC's Engineering dept. and asked whether I should allow this or not and they said definitively, "leave it in neutral and it'll do no harm". Been spinning now for 33 seasons with no harm.

My 2017 Fishing boat has a 3.5 Mercury 4-stroke and the Owner's Manual is very specific about putting it in forward so the prop doesn't spin.

If it were me I would call the manufacturer and ask for their recommendations.

You didn't say what engine you have, but if it is an OB, I'd tilt it up, and if its an I/O I would leave it down - no sense in taxing the rubber boots.

 

[Jim_the_Islander]

Original poster is correct in leaving it in gear to reduce bearing wear. Same thing when trailering down the highway. My manual says leave in gear to keep it from rotating causing wear when your going down the highway.

 

[Silvertip]

One can use simple math to determine the actual rpm the prop is turning in either of the above examples. At 70 MPH (ignoring slip and bearing/lubricant drag) the prop would be spinning very fast compared to being spun by a river current (say 10 mph). So in the first example, I tend to agree that the spinning prop is less likely to get gunked up with algae and slime and bearing wear would be a non-issue. At highway speeds however, the shaft speed would be very quick and it is just very simple to pop it into gear to prevent the possibility of wear. Knowing the prop pitch, current speed and road speed one could determine approximate shaft speed.

 

[jimmbo]

The only propellers I have ever seen spin while going down the highway @100 km/hr were the novelty ones stuck in the hitch receiver.

 

[MH Hawker]

i had a Nissan 60 hp that would spin on the road so i dropped it into reverse, it never caused a problem

 

[H20Rat]

The only propellers I have ever seen spin while going down the highway @100 km/hr were the novelty ones stuck in the hitch receiver.

Most 2-tube pontoons i've seen going down the road will spin the prop if not in gear. Pontoons have a nice wind tunnel going down the center so lots of airflow. (helps that our speed limit is 75 mph/120kph also)

 

[jkust]

Don't know what the OP has but you can't put a Bravo drive into gear if the engine isn't on or so say my Bravo Manual.

 

[QBhoy]

What is cold corrosion?

Happens in a damp cold environment. Basically rust caused by these conditions. It's a well known seafarers term for rusting.

 

[QBhoy]

My 1984 Family boat has a 9.9 2-stroke Evinrude kicker. At no-wake speed the prop turns real fast. The Owner's Manual has no instructions, one way or the other. Way back when, I called OMC's Engineering dept. and asked whether I should allow this or not and they said definitively, "leave it in neutral and it'll do no harm". Been spinning now for 33 seasons with no harm.

My 2017 Fishing boat has a 3.5 Mercury 4-stroke and the Owner's Manual is very specific about putting it in forward so the prop doesn't spin.

If it were me I would call the manufacturer and ask for their recommendations.

You didn't say what engine you have, but if it is an OB, I'd tilt it up, and if its an I/O I would leave it down - no sense in taxing the rubber boots.

Hi. It's an alpha one. I prefer to leave it down because it is fully submerged then...and your valid point about not stretching the bellows ! Well said.

 

[QBhoy]

One can use simple math to determine the actual rpm the prop is turning in either of the above examples. At 70 MPH (ignoring slip and bearing/lubricant drag) the prop would be spinning very fast compared to being spun by a river current (say 10 mph). So in the first example, I tend to agree that the spinning prop is less likely to get gunked up with algae and slime and bearing wear would be a non-issue. At highway speeds however, the shaft speed would be very quick and it is just very simple to pop it into gear to prevent the possibility of wear. Knowing the prop pitch, current speed and road speed one could determine approximate shaft speed.

Can't tell if we are being serious about the prop spinning going down the highway....surely not !

 

[bruceb58]

Leave it down and leave it in gear are my opinions.

 

[QBhoy]

I agree Bruce. Thanks to all who have replied.