Navigation of the era

compassimage.jpg Great circle route sailing was quicker but it meant that for 8 - 12 weeks ships masters had to rely on fixing their position using celestial navigation for latitude and in combination were relying on an accurate chronometer (ships clock) to measure longitude.

A ships clock was set on Greenwich time (a known longitude) A navigator would establish local noon with a sextant and check the time difference against Greenwich time. Every hour of difference equates to 15 degrees of longitude (360 divided by 24) every minute equates to 0.25 degrees of longitude (15 divided by 60)

When skies were obscured deduced reckoning was made from the last known position. Deduced reckoning involves estimating forward speed and heading over time to a new position.

Once land was sighted, coastal navigation could be employed. Ships masters used known elevations on marine charts to mark position accurately on approach to the narrow 1.5 km opening into Port Phillip Bay (The Rip)