Harrel was born in Mount Pleasant, County Down, the son of a land agent. He was educated at the Royal Naval School, Gosport, but was too old to join the Royal Navy as a Midshipman when he took the exam and instead joined the Merchant Navy.
Harrel, whose father was a land agent, was born in Mount Pleasant, County Down. Although he attended the Royal Naval School, Gosport, he was not eligible for naval service as a Midshipman due to his age and joined the Merchant Navy instead.