The posted coordinates will bring you to a well-worn informational sign which provides information about different types of boats you may see out in the bay. While some of the information on the sign may be difficult to read, you should have no problem locating the information you need to find the final cache, which can be found at the coordinates below. While what you need to do may not make a lot of sense now, once you get to the sign you should easily be able to determine how to get the numbers you need.
North 41° 40.EFG West 071° 18.HIJ
E = Coast Guard Boat + Sloop
F = Research Vessel - Lobster Boat - Ferry
G = Recreational Fishing Boat + Fast Frigate
H = Quahog Skift - Tug Boat - Ferry
I = Coast Guard Boat + Recreational Fishing Boat
J = Tug Boat + Fast Frigate
The cache you seek is a typical magnetic silver nano hidden nearby. You shouldn't have too many issues finding this one even with people around, but take into consideration that this is a very popular spot to visit year round. Please replace the cache exactly as found per the hint and remember to bring a writing utensil. Hope you enjoy!
If you need to, you can check your answers here: GeoChecker.com.