On racing setups, with pitches of 25" and more it is normal for the motors to be started in gear to make it easier on the lower end. I know of people that have striped gears over a summer like this but shifting into gear after starting, the inertia of the prop weight and high pitch realy does a number on the gears!
Under water, (hydrodynamics) The Blade area has way more significance than the Weight of the prop due to the fact that under water, gravity has 2/3rds less effect. 18lb. prop out of water weighs 6lbs. under water.<br />They both have a rubber hub to absorb shift impact, and the weight has very little to do with it.
I agree that the weight under water is less but then a SS prop will still have more inertia to overcome, the specific graity of aluminum is about 2.5 and SS is about 8, 3.2 times heavier! But , yes, the blade area is the predominant factor so a high pitch prop will give more 'clunk' to the gear case.
