Used in any era from Ancient Roman onwards..there´s a few still being operated (newly built ones that is..not ones from the ancient romans)
Quotefrom Wiki ;
"A ship mill is a type of watermill. The milling and grinding technology and the drive (waterwheel) are built on a floating platform on this type of mill.
Its first recorded use dates back to mid-6th century AD Italy"
As with the Horse-Powered Ferryboat, These Mills come (came) in a wide range of designs which gives some freedom in creating my own Version.
For a really good write up on Boat mills, Hanging Mills, Bridge mills and all thier varients go HERE. In fact..if your interested in weird and wonderfull machines and "forgotten" Technology, the site is well worth a browse..I mean..who wants to miss out on learning about windpowered chinese wheelbarrows..? :-D
As ever, it´s all scrap material, mostly Card with bits of insulation foam and paperclips, heads of Pins for bolts etc.
To aid with hauling the craft back to the Riverside, I´ve added a windlass to my Boat mill. The Little Cogwheel is from an old Motor driven toy. There is a ratchet to stop the cog going backwards but it´s so small it´s barely visible.
Obviously this will end up in Bodstonia...and it´s shown in "Action" HERE