I would jst like to say I have been involved with the sea and ships all my life . I am now 57 years of age and sailed many oceans including Antarctica. 
I can tell you without any hesitation this beatiful planet we are lucky enough to live on is certainly a very large globe !
Anyone who has plotted a course accross an ocean particularly in the north or southern hemisphere knows that diverging lines of longitude and the distances between them decrease nearer the polls !
Yes tides are another subject that proves the globe and thankfully we can predict tines and heights of water due to the path of the sun and moon !
The number of times I have witnessed a glorious sunset at sea .. this huge fireball sinking over the horizon until disappearing and not getting smaller as some say ! Witness this then look yourself in the mirror and say .. no it got smaller until it vanished from view !
Also  for me observing lighthouses  as I aproaching them from afar you only see the sweep of light as the lighthouse itself is below the horizon . Slowly but surely the nearer you get the more appears .. I have not gone into any deep mathematics..  a lot of which is used in navigation on a globe but just wanted to highlight  a couple of things anyone can see anywhere anytime .. take a look and then ask yourself .. how can this work on a flat earth ?