There seems no end to the genres of things I've developed fondness for, antique drawings of ships being high among them! This one I especially love for its combination of three things in one.
The larger ship on the front I believe is a Blackwall Frigate, developed in the 1830s for the India and China trade and popular for the Opium trade, and known for its black hull with a white stripe.
It seems conceivable that the second, inset ship, with Portland written on the side, is the PS Portland, a side-wheel paddle steamer built in 1890, which infamously sank during the Portland Gale blizzard of 1898, claiming the lives of all on board. (I might think this drawing were a bit older than that, so am not 100% sure, but it looks a lot like it.
And then on the reverse, oriented in the other direction, is a math problem calculating the number of days a man was idle considering that he made $37.50 total over fifty days, receiving 75 cents per day worked and loosing $1 per idle day!
All beautifully done, with a very finely tipped ink pen, mostly blue on front and black on reverse. 7 1/4" x 5 1/4". The writing on reverse is a bit visible through the paper, but I don't think much detracting, and there is a bit of staining/darkening near top left, again pretty minor.