As a Chartered Engineer, his first job came about when it was discovered that Denis Doyle's yacht Moonduster was floating above her 'marks', having been built less heavily than had been intended her designer, Germán Frers.
Castro advised that lead be attached to the underside of the coachroof and had a hole drilled in the keel to reduce her stability, which gave the vessel an exceptionally good handicap for a boat of her size.
He was appointed by a member of Royal Cork Yacht Club to redesign the J24, with the aim of producing an exciting sports boat.
The client expected a bigger mainsail, a new deck moulding and an effective keel to give greater stability.
Castro's designers work with many boatyards internationally, including the Royal Huisman, Jongert, Palmer Johnson, Neptunus, CS Yachts, Laser, and Jeanneau, Beneteau, Galeon, Focus, Williams, etc.