This was another name for the Polychrest, before it was launched:
"'...The projector, Mr Eldon, was a most ingenious man, and he spent a fortune on his plans and models.'
"An interesting experiment indeed: he had heard of her. She was known as the '>Carpenter's Mistake, and no one in the service had ever imagined she would be launched. ... What extraordinary combination of interest had managed to get her off the stocks, let alone on to them? She had head and stern alike, two maintopsailyards, a false bottom, no hold, and sliding keels and rudders."