In 1870, the Russian Navy launched a warship that was almost completely circular. Designed as a floating battery for coastal defence, the ironclad Novgorod and her sister ship were by all accounts a nightmare to steer. One account said: ‘They went up the Dnieper very nicely for some distance, till they turned to retire. Then the current caught them, and they were carried out to sea and whirled helplessly round and round, every soul on board helplessly incapacitated by vertigo.’Yes, you might say: that’s all very well, but what does this have to do with our Secret 20, which when built should be a long, slim gaffer? Only that should we fail to set up the boat’s backbone – the keel, stem and stern – straight, level and true, the…