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.