These two aren't the traditional water convexity experiments. Experiment 6 is about the tops of boats being level as they traveled. Experiment 7 is about the horizon being level with a long straight piece of wood.
I let you go with Experiment 7, although curve or "not level" is quite the same in my opinion.
But experiment 6 is truly a level experiment: Trying to prove, that two piers and the mast head of the ship traveling between those two is "level". But again, this experiment is very inaccurate. Valuable parameters are omitted: The Tide. There's no hint how long the experiment lasted and no hint what was the state of the tide, which is quite high in the English Channel!
Look at the bottom of this page and search for "Eddystone" -- http://www.sacred-texts.com/earth/za/za33.htm
Rowbotham describes how the observation of lighthouses may be inconsistent at times, and depends on how calm the environment is. When the Eddystone lighthouse is visible from the location described it contradicts the Round Earth theory.
I cannot follow that deduction, that waves lower than the observer and the observed object will obscure significant parts of the object.
My opinion: The viewing distance in question is quite near the value, what is given by the curvature of the globe earth model.
Variations of atmospheric refraction may lessen or increase the viewing distance, so that depending on weather conditions Eddystone lighthouse may be sometimes visible.
As described in settled weather a density/temperature gradient may build up above the water, which gives high refraction values and so increasing the viewing distance. Where as in windy weather, with agitated sea, a temperature/density gradient will not build up above the water, so decreasing viewing distance.