Dovetail - A Sea Otter 33' Narrowboat. Dovetail - A Sea Otter 33' Narrowboat. Sea Otter Narrowboats are the Rolls-Royce of the inland waterways. Like all Sea Otter boats, they are constructed from Marine grade BS5083 aluminium alloy. It is a material commonly used where strength and longevity are required. Aluminium alloy is a material favoured by the majority of small commercial craft builders. Dovetail - A Sea Otter 33' Narrowboat. Sea Otter Narrowboats are the Rolls-Royce of the inland waterways. Like all Sea Otter boats, they are constructed from Marine ... read more