At the posted coordinates, you will find two signs, which both use a certain six-letter word. This word is also repeated many times on the sign directly across the channel. This is probably a word that you should keep in mind if you ever head across to the island.
Then, project a waypoint...
- [5]*[5]*[3]*[4]-[4]*[6]+[5]-[1]*[1]-[2]-[1]-[5]+[3]-[3]+[6]*[4]-[6]+[4]*[1]*[2]+[2]-[5]*[6]*[1]-[2]+[5]*[5]+[4]-[6]+[3]+[3]+[1]+[6]*[5]*[3]+[4]+[3]-[1]+[3]*[2]+[2]-[2]+[4]*[3]*[5]+[6]+[3]-[1]+[5]+[2]-[5]*[1]*[2]-[3]*[1]-[3]-[5]-[6]+[4]+[2]+[3]-[1]+[4]*[3]-[1]*[5]+[3]*[1]*[2]+[2]-[3]*[5]*[4]-[5]-[5]+[4]+[6]-[6]+[5]+[1]-[1]*[1]*[3]*[3]+[3]*[1]+[3]-[6]-[1]*[3]-[6]-[3]+[4]+[2]+[1]+[3]+[6]-[5]+[6]+[6] metres
- [5]-[4]-[4]+[2]-[1]+[4]+[6]*[6]+[3]+[1]-[5]*[6]+[3]+[1]+[6]+[3]+[2]+[4]+[1]-[5]-[6]+[2]-[6]*[5]+[4]*[1]-[6]*[4]+[6]+[4]-[3]-[1]+[1]+[2]-[1]+[5]-[2]+[3]-[6]-[1]-[3]-[5]*[5]+[3]*[4]+[1]-[3]+[4]*[1]-[5]+[5]+[2]-[1]+[3]-[3]+[3]+[5]-[4]*[3]-[4]*[2]+[4]*[1]+[6]+[4]-[1]-[4]+[5]+[4]*[5]+[3]*[1]+[6]-[3]+[2]*[5]+[2]+[3]-[1]*[4]-[3]-[5]*[3]-[3]*[6]-[5]-[2]*[6]+[4]*[3]+[2]+[2]+[3]-[4]+[6]*[3]+[3]+[2]+[1]+[5]+0.6 degrees
...where [\(x\)] refers to the numerical value (A=1, Z=26) of the \(x\)-th letter in said six-letter word. Don't forget the order of operations!
You can validate your puzzle solution with certitude.