The basic construction of these is to cut a double layer of foamcore to total 1/2" thick in the shape of the hull.
Then I add a layer of white Strathmore illustration board to the hull then I draw on the deck planks with a pencil and straightedge.
Next add the hull sides cut from white thin posterboard. I make this just a bit taller than the hull and taper it up at the bow to get a boat-like profile. It also serves to cover the laminated foamcore hull sides.
Then the rest is a matter of building up wheelhouses out of Strathmore and adding details.
The width of all the boats is about 3-1/2" to 4"...and the length varies:
The Merak is 7" long.
and 3 " wide
The Safieh is 9-1/2" long
and 4" wide at the paddle wheel housings but the actual deck is about 3-1-2"
The Mizar is about 10" long (the railing at the top of the wheelhouse is small straightpins stuck and glued into the deck and then thread makes the rails and its all painted white which stiffens the rail nicely.
and just shy of 4" wide (here you can also see the drawn on deck detail as well as the drawn and watercolored windows, the deck is stained with a wash of tan over the pencil lines. The ladder is plastic HO railroad bit with a wire rail added.
The lengths seem to work well for my 8x5 table but much bigger and the size would become unwieldly. The 4" width dimension seems to work best to give a reasonably slender boat but still have enough room for figures but if you build one of these, test fitting the figures is a must...wouldn't want to have to leave any of the lads behind!