Can anyone tell me how far I would have to sail East of Sydney to be unable to see any landmass of Sydney, ie I would see nothing but water?
A rough calculation for the distance to the horizon in nm is 1.2 X sq root of the heights in feet. You need to add your eye height distance calculation with that for the height of the object e.g. the cliffs.www.boatsafe.com/calculate-distance-horizon/
E.g. Eye height 9 ft
Cliff height 81 ft
Square root of 9 = 3 X 1.2 = 3.6nm. Square root of 81 = 9 X 1.2 = about 11. 11+3.6 = 14.6nm
The North Head cliffs are about 300 ft high. Sq root of 300 is about 17 X 1.2 = about 20. Add your eye height calculation and you have the distance you need.
Somewhere around 24 or so nm away and the top of the cliff should drop below your horizon.
Off Pittwater the land is lower so you get the all round ocean view closer in.
this calculator only allows you to enter eye height and distance, but can narrow it down pretty quickly with a bit of trial and error:
dizzib.github.io/earth/curve-calc/?d0=45&h0=3&unit=metric
Earth curvature? ....... NOOOOOOOOoooooo, say it aint so
It's a well know fact that the Earff is flat
Select to expand quotedougham said..
Can anyone tell me how far I would have to sail East of Sydney to be unable to see any landmass of Sydney, ie I would see nothing but water?
depends on the swell height, time of day, fog, rain, etc, oh do it at night,
Why ponder. Just get in your boat and head East, you'll soon have the answer. The real issue is, just how big are the mountain to the West of you. They are what you normally see when approaching a land mass from a sea voyage, not the shore line
Select to expand quoteCrusoe said..
Why ponder. Just get in your boat and head East, you'll soon have the answer. The real issue is, just how big are the mountain to the West of you. They are what you normally see when approaching a land mass from a sea voyage, not the shore line
What mountains, aren't any mountains on the east coast of Australia.
Try the west coast of South Island NZ 
Select to expand quotesamsturdy said..
If the Earth was flat, cats would have knocked everything off it by now.
Of course it's flat and we are about to be knocked off the edge 
