Love Musky's comment re following the oil trail.
Richard - now now, the guy's a new member and may not realise you're taking the pi**.
When I started boating in the late 60's we didn't even have Decca - that was only on hire for fishing boats (at some cost). Decca to purchase arrived around 1980 and GPS maybe ten years or so after that. Pity they did away with DF - always preferred compass, log and DF.