Very excited to come across this project as it's been on my mind to examine the amount of Brighton pier that can be viewed from Worthing. At 8" per mile squared Brighton pier should be 66 feet beyond the curve.
Why not measure from the beach rather than above the water? Also, why not just photograph or video Brighton from Worthing? As 66 feet of the pier should have disappeared behind the curve the pillars, at least, should not be visible. What about using a board painted with a 1 foot wide bands of contrasting colours? (Such as used against Mark Sargent by a US TV News program). From beach level under the pier none of it should be visible so it would be interesting to see how much is visible.
Please keep me in touch with the expected date and time of experiment as I would like to be there to witness it, if possible.
I assume you will be measuring distances from pier, GPS location and GPS height. Are there any tide marks on the pier structure like on the pier's vertical support columns. You could record lowest tide positions and water positions when the actual sightings get taken. Therefore if someone wanted to repeat this experiment they would know what height the sea level was. All the best, its unlikely that I will be meeting up to this.