Engine in gear to prevent prop from spinning?

[Captain Caveman]

On another forum, there is a debate going on about whether or not to shift your boat into gear when trailering. Apparently this keeps the prop from free-spinning during the drive, which some argue will heat up and wear out the bearings or ruin the outer propshaft seal (due to not being cooled by water). Apparently this was copied from the Mercury website:

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Q: What precautions should I take when trailering my outboard powered boat with the engine attached?

A: Trailer your boat with the outboard tilted down (vertical operating position). Shift the outboard to forward gear. This prevents the propeller from spinning freely.
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I've never heard of this practice and have never done it. A boating forum is probably the best place for this discussion. Does anyone else do this and if so, let us know why. I'm curious if this is just something that people do or whether it is actually recommended by the motor manufacturers.

 

[reelfishin]

Re: Engine in gear to prevent prop from spinning?

I've heard of it but never paid it much mind. On most trailers, there's probably not enough air flow over the prop being behind the trailer cross members and other obstacles for it to catch enough air to spin. I've driven behind many trailers and haven't even noticed any props just spinning in the wind. I would think that there's enough resistance in the seals and the gear oil to prevent it from free spinning.
Try spinning your prop in neutral by hand, see how long it spins after giving it a good twirl. Most won't make a full rotation.

I have set some in gear to keep the prop in a fixed position so as not to be too close to the road, setting one blade at the 12 o'clock position to gain a few inches of ground clearance just in case I encounter a high curb somewhere, but the that would do nothing to protect the skeg.

I would be more apt to think that leaving the motor in neutral would make it far less likely that the prop would get damaged if it were to hit something while in tow.

None of the above though is substitute for just not trailering with the motor down in harms way.

 

[Silvertip]

Re: Engine in gear to prevent prop from spinning?

At wide open throttle an engine with a 2:1 gear set would have the prop spinning at about 3000 RPM. Although in the water, the engine loading provides much more stress than free spinning at 60 mph on the highway. There is simply too much resistance in the gearing and oil to create heat in an amount to damage anything. What you could say however is that every revolution of the prop brings seals and bearings one more turn closer to failure - but not perhaps in your lifetime.