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Old 13-02-2020, 10:03   #1
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Shifting gear box

When shifting a hydraulic transmission from forward to neutral and then to reverse or visa versa, how long in time before shifting so as to not damage the tranny? My feeling is the prop does not stop spinning immediately when going through neutral to forward or reverse and could cause damage when spinning if dropped into gear. My tranny is by no means oversized for the engine horse power and I don’t want to hurt anything. So what do you al think?
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Old 13-02-2020, 10:12   #2
rbk
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Re: Shifting gear box

I wait a good second or two before shifting but if you’re moving in any direction your prop is spinning so unless you coast to a dead stop each time before you shift you will always be shifting against or with a moving prop except when leaving the dock or anchor. Probably not the best idea to slam it into reverse from full ahead on a daily basis but in the odd emergency it shouldn’t do any damage. Make sure your damper plate is in good order and clean fluid, those are things you should be worrying about.
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Old 13-02-2020, 17:46   #3
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Re: Shifting gear box

In the case of the typical engine/prop that we see with sailboats, it's more important to wait a few seconds between gear selection and allow the engine RPM to drop before shifting ( if possible). The engine components have much more mass and inertia than the propeller has, and if shifting is undertaken at high RPM, damage to the transmission or damper plate is likely to occur.

On the other hand, it's common practice in the heavy duty workboat world ( with 6' and 7' propellers) to use shaft brakes on the prop shaft to stop prop rotation in neutral before shifting because otherwise the propeller inertia would immediately stall the engine.

So, what to do when shifting.....? Keep an eye on the engine RPM and don't shift at elevated RPM.
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Old 14-02-2020, 02:47   #4
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Re: Shifting gear box

Quote:
Originally Posted by DougR View Post
In the case of the typical engine/prop that we see with sailboats, it's more important to wait a few seconds between gear selection and allow the engine RPM to drop before shifting ( if possible). The engine components have much more mass and inertia than the propeller has, and if shifting is undertaken at high RPM, damage to the transmission or damper plate is likely to occur.

On the other hand, it's common practice in the heavy duty workboat world ( with 6' and 7' propellers) to use shaft brakes on the prop shaft to stop prop rotation in neutral before shifting because otherwise the propeller inertia would immediately stall the engine.

So, what to do when shifting.....? Keep an eye on the engine RPM and don't shift at elevated RPM.
Indeed.
B-W Velvet Drive specifies 1,000 RPM as MAXIMUM shifting speed.
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