The engine in this boat had defective mountings, and was vibrating severely- so much so that the alternator cables, as shown, had been torn from their connectors.
Ironically, the customer- new to the world of boating- hadn't actually noticed. Assuming flat batteries to be part of the boating experience, he had installed a large genset on the back deck of his narrowboat, and a 50A battery charger inside.
Since rectifying the problem, towpath dwellers in the Chiltern area of the GUC are enjoying a sound night's sleep!