Scale speed and rpm

[mariner]

I'm in the process of building a scale Chesapeake Bay deadrise from scratch, (a local workboat used for crabbing and fishing) and have decided to power it with the motor and reduction gear from an electric car. The full size boat I took my lines from is 50ft long x 14ft wide powered by a diesel engine of 2500rpm run through a 2:1 gear reduction turning a 32" dia. 4 blade wheel.
My model is 50" long x 14" wide powered by a 10,000rpm motor through a 3.5:1 gear turning a 2.5" four blade prop.
My question is, to achieve scale speed does rpm have to be scaled down as well or does it remain constant regardless of scale. This may be elementary to many of you but it has been the subject of some lively debates among my buddies and I.http://forums.radiocontrolzone.com/newthread.php?do=newthread&f=289#
Confused

[CG Bob]

You can scale sown the size of the boat and all of its parts and fittings; but water remains constant. The water is creating the same resistance for your model as the full size boat.

Here are a couple of thoughts on scale speed. You can run the model at a true scale speed or at a speed for a scale wake. A model running at a true scale speed appears to be moving much slower, because the wake doesn't look right. A model creating a scale wake looks right, but is moving at slightly faster than scale speed.

[mariner]

My thinking was the same. As you scale down the prop, rpm has to remain constant.
A 1/12 scale prop w/ a 2.5" pitch will travel 2.5" (not accounting for slip) per revolution.
A full scale prop w/ a 30" pitch will travel 30" per rev (again discounting slip) and 2.5 is
1/12 of 30.
I took the boat for sea trials on the power train yesterday and noticed exactly what you said. At true scale speed (under 2 kts) the wake was barely noticeable, only at wot( 4.1kts) did the wake appear realistic. That would be over 50kts full scale!