Yes, a boat or some other means of water transport will be
required to get to the area of the cache. At an hour or so either
side of low tide this will be above the water level.
Once at the cache site you'll need stout footwear and perhaps
some leather gloves. Do NOT attempt with bare feet! While
placing, both TB and GSV got a scallop slice to the fingers so be
warned.
The easiest spot to start from would be Ravensbourne - see
Parking coordinates. It's only about 400m. to the cache from
there.
As the main challenge is to get to the site, the picture was taken
very close to the cache site.