the usual brutality
Walton is referring obliquely to the wide-spread practice of flogging to keep discipline aboard ship. It had been a serious issue in Great Britain during the Napoleonic Wars, a spur to the mutinies that took place in the British navy at Spithead and the Nore in the spring of 1797. The Shelleys' friend Leigh Hunt wrote several attacks on the practice in his weekly newspaper The Examiner. The ship's master would have the responsibility for maintaining order, and what most attracts Walton to this veteran mariner is his capacity to do so without violence.