Hi Boxedup. I keep my Tartan 3700 at Britannia, and I am not the largest boat there. Pegasus takes five feet of water, so I have an hour or so on either side of dead low when I can't negotiate the channel from the town dock to the marina. They have been trying to get the town to dredge the harbor for years, but so far the problem of what to do with the spoil has not been resolved.
The tide problem is a pain for a day sail because you must deal with it twice in one day, but not that hard to work around for a weekend trip. On the plus side, it is the most wind sheltered marina I have ever docked at, which is good because the fairways are narrower then most marinas. It is probably the most pricey marina on the North Shore, charges based on size of slip not boat, but this year they have many vacant slips, so some under the table deals may get done.
Britannia has some issues with management like most larger marinas, but like most of the boat owners there, I stay because the location and general lay out are so good.