Can I/O's freewheel?

[rubenova]

Are there any issues, lubrication, water intrusion, or other, with running one of two engines off and the vessel moving? How fast for how long? I'm interested in single prop Mercruiser or Volvo-Penta's. If this has been answered already I apologize (I did several unsuccessful searches).

[gonzo]

No problem at all. The lubrication is circulated by the lower gears as they turn.

[rubenova]

Thanks Gonzo. Is there any worry of water being pushed into an open exhaust valve? By the forward motion or the boat rolling around?

[powerabout]

A volvo yes but for a Merc only the Bravo can freewheel

[rubenova]

Thank you powerabout. That shines light on the lubrication.

I'm very new to the idea of water cooled exhaust and would like to know how they work. I worry that the forward motion will, above a certain speed, pressurize the cooling system enough to get water into the engine. Is this a concern under, say 15 knots? What about if the boat takes big roll with the engine off?

Thanks in advance all, excuse my ignorance

[powerabout]

Only if you have a water lift muffler where you need exhaust gas to lift the water could you fill it up.
Any exhaust that has a downhill flow from the water injection cant really have a problem

Re the windmilling the prop, any drive that has the gearshift in the lower unit means when its freewheeling the propshaft is not driving any gears nor any thrust bearing so you have the end of the propshaft dog clutch splines wearing themselves into the gear that is stationary and on the other end a small bearing just to support operation when in reverse is doing far more work then it was engineered to do

[rubenova]

That's good news! I will look for a Volvo, or Bravo.

[IMP-ish]

What happens if you freewheel an alpha drive?

[powerabout]

Originally Posted by IMP-ish

What happens if you freewheel an alpha drive?

post#6

[CDK]

Originally Posted by IMP-ish

What happens if you freewheel an alpha drive?

Powerabout paints you a dark picture.
Although the mechanical description is correct, the lower gearcase is filled to the brim with hypoid oil, so there is no metallic contact between the parts and forces acting upon them are virtually zero.

I've had twin Alpha-1 drives for over 25 years and used to cruise at 8-9 knots on one engine. Even installed a second power steering pump so I could use either engine for that purpose. Only when the weather turned bad I used both engines to get home at 25 kn. Over the years all sorts of problems belonging to the Mercruiser concept developed, but none related to freewheeling.
When after 12 years in seawater the walls between exhaust and cooling circuit in one manifold started to crumble, I bought a new pair that received the same treatment for 13 years until they were replaced with a propulsion system of my own design.

[IMP-ish]

Originally Posted by powerabout

post#6

Thanks for that.
My brain skipped when I saw muffler in that post and I missed it the first time. Thanks for the technical explanation.

[IMP-ish]

Originally Posted by CDK

Powerabout paints you a dark picture.
Although the mechanical description is correct, the lower gearcase is filled to the brim with hypoid oil, so there is no metallic contact between the parts and forces acting upon them are virtually zero.

I've had twin Alpha-1 drives for over 25 years and used to cruise at 8-9 knots on one engine. Even installed a second power steering pump so I could use either engine for that purpose. Only when the weather turned bad I used both engines to get home at 25 kn. Over the years all sorts of problems belonging to the Mercruiser concept developed, but none related to freewheeling.
When after 12 years in seawater the walls between exhaust and cooling circuit in one manifold started to crumble, I bought a new pair that received the same treatment for 13 years until they were replaced with a propulsion system of my own design.

Thanks, that's what I wanted to ask next, what can you get away with. Would coming home on one take weeks off an alpha drive's life.
Or would seeing if a boat would plane with one engine out kill the other drive in short order.

[powerabout]

its a wear thing,
It would take a long time to kill it as the parts grinding each other are all hard cased
Just puts very fine filings in your gearbox.
Regular oil changes would overcome that issue