Suggestions for dimensional scale lumber sizes.

[doctorwayne]

Don't forget that the track on a wooden bridge is supported, beneath the ties, more-or-less directly under the rails, so those members need to be the heavy ones. For a wharf, their ends would most likely sit atop wooden pilings driven into the lake's bottom - cap timbers, as on a pile trestle, would usually sit atop the piles, with the rail support timbers atop them. As MountainMan points out, the depth of these members will be dependent on their span and on the load carried (which includes the surrounding deck area and the "live" loads of the train. I'd say that looking at a pile trestle should give you appropriate spans for your wharf - at least the part of it under the track, and then you'll be able to safely operate that steamer.

Wayne