Rodd -
I left Tashmoo this morning and the shoal spot is actually about 20-40 feet outside the red buoy at the entrance between the breakwaters, out in Vineyard Sound. Didn't do a detailed survey but I'd guestimate it's a sandbar about 30 feet wide. If you daw 5 feet I'd recommend you go at half tide or higher, preferably on a rising tide. It's soft ( hit it with my centerboard, which popped up) so maybe you could plow through if you grounded.