Before the era of the motor car, the streets of London were full of horse-drawn carriages of various types, which would require a lot of fuel in the form of hay from the farms of Essex and Kent in particular.
In a trade where cargoes earned money according to their weight, a barge with a hold full of hay would not earn very much, so it became a general practice when loading a hay stack onto a barge, to build it up on deck to a height of about 12 feet. In time special barges were built for this trade which were wider (beamier), were shallower in the water (so they could get up shallow creeks further) and with reduced size hatches (to give more deck space for the bales of hay).
They had to use reduced sail on the main and fore-sails and the skipper at the wheel had to be guided by the mate on top of the stack , as he was unable to see where he was steering.
Having taken the load to its destination, the barge would want, if at all possible, a return cargo, and this often took the formed of the by produts from the hoorses - the manure - to take it back to the fields, where it was used as fertiliser.
This model won a Bronze Medal at the Model Engineer exhibition.
I have recently built a keel, and re-installed radio-control gear into this model, and she has been out sailing several times this year.