I kayaked in Acadia National park about twenty years ago with some guides. We kayaked out of Bar Harbor. It was amazing.
If you aren't up to speed on hypothermia, I'd read up and take it very seriously. The guides warned us over and over against tipping the kayaks. The water there is extremely cold. I live very near Lake Michigan. Lake Michigan is cold and deep, but it ain't nearly as cold or deep as Bar Harbor. This summer in Leelanau county (on Lake Michigan) there were 16 "dry drowings" and counting. A dry drowing is basically death by hypothermia. You can "drown" even while wearing a PFD.
I hate to be such a downer, but until this summer I wasn't nearly as concerned about hypothermia as I was drowning. And, I figured I wear a PFD, so I'm fine. Cold water can be really dangerous. The guides were saying (if I remember correctly) that the water temp I. July was around 53 degrees. They said you got anywhere from 12 to 20 minutes in the water.
Anybody who knows different feel free to chime in. I'd suggest a wetsuit at the very least, but probably dry suits.
Nancy & I kayaked off Stonington, probably around 2002, to get a taste of cold water paddling--we live in FL and had never done any. The water off Stonington was about 54-55 deg. The intent was to prepare us for paddling in Alaska. Frankly, paddling out of Stonington was no prep for the water temps in Alaska, which were in the range of 37-39 deg. When you paddle in waters as cold as Alaska, the danger of hypothermia is very real, but the "involuntary gasp" when you capsize and contact such cold water causes real drowning very quickly. Of course, if you survive that first contact with water, you only have a 10-15 minutes before you are incapacitated sufficiently, so that you cannot climb back into your boat or any boat, even if it were available. You must be pulled from the water to survive. A high-quality, absolutely dry drysuit (good fitting latex gaskets) with suitable clothes underneath is the only thing that is going to keep you alive for any time in AK waters. Some kayakers in very cold water also wear rubber skull caps (like shower caps) to avoid that involuntary gasp if they capsize. In Maine coastal waters, you will have more time, the involuntary gasp may not be a problem unless you are in poor health, but the same concerns prevail.
On one of our trips into Glacier Bay NP in AK, a female Park Ranger had been out solo paddling and was capsized when a whale approached too close (or vice versa.) She survived. I don't know what she was wearing.
Of course, AI/TI sailors probably don't have to worry much about falling into cold water. Still, they must be able to keep warm to enjoy their sail. I would think a drysuit would be appropriate in Maine waters.