For the most part, in scale models, it is a matter of whether what propeller the real boat used.

I used to use three bladed propellers on one of my destroyers.
For the heck of it, I changed them to four bladed propellers.
What I found, was that I had to put less pitch on the four blade propellers
to make the boat run "scale speed" or the same speed as the three blade propellers.

So, hmmm, the four blade propellers could provide more speed at the same rpm.
Therefore more thrust.

I could also conclude that the four blade was more efficient than the three blade propeller
in this case, but it could have been a crappy three blade prop.
Also in this case, since the top speed of the boat was regulated, the lower pitch of the
four blade propeller made starting and stopping the boat take more time. The boat
could not start or stop as quickly with a lower pitch propeller.

My impression of the number of blades on military ships, is that more blades makes for
a quieter propeller. I am also learning, through David Merriman, that there is a maximum
blade area/propeller diameter that should be maintained.

Not sure if that even helps you, just my observations on the subject.
[&:]