It uses somewhere just below 1000 pieces. If I had chosen to make a sternwheeler of a perhaps more recognizable, larger type, those with three or more decks and two smoke stacks, then I think it would have become to big to be a viable set. But there are a few prototypes that look pretty much like this. Most of those prototypes seem to be quite modernly diesel powered though, but this model of mine is steam powered!
The possible set would include, at a minimum, around four mini figures: two crew members and two passengers. Mini figures are about the most expensive types of parts for Lego to produce, so we will have to keep the number down somewhat.
The steam engine workings can be checked out nicely since the whole port side of the ship is hinged and can be folded out like this! Here you can also see the long steam pipe that leads from the central boiler to the two cylinders in the stern. Even though it cannot be seen clearly in this picture, one of the cylinders, the one where steam enters first, is larger than the other.
You can also see the steering cabin, the small cafeteria in the stem, the coal box, a shovel on the wall, the luggage compartment, and a small crew area with a table beside the cylinders in the stern. The passengers have their main area on the upper sun deck.
Here is an image from the stern, which shows the paddle wheel clearly. There are working pistons which move back and forth if the paddle wheel is turned. The hexagonal pieces used here were invented quite recently by Lego, originally for use in a combine harvester!
As you can see here, there are small bulbs in the bottom of the hull so that the ship can be pushed on the floor or a table without leaving ugly marks; this should increase playability.
I include the MLCad .mpd file for those who want to experiment with that. All connections should be functional if I haven't made any mistakes.
Quoting Henrik Jensen
Lovely riverboat, with many fine details. Here's a suggestion. Let the paddle wheel be driven by a wheel under the bottom of the boat so that it turns when the boat is pushed forward.
Yeah, that's a great idea! But I'm not sure how to do it technically without changing the appearance of the ship... there would need to be a chain to the paddle wheel, which would seem to suggest a diesel engine and not a steam engine. Unless I can create working pistons... will have to think about it a lot, but it's a great idea, as I said -- thanks!