In general I think this comes down somewhere between semi-formal and business casual-

Late July in Maine even on the ocean can get warm during the day, and there could be a chill with a sea breeze at night. Please check the weather and dress accordingly.

For Men, only Jim is required to wear Pants AND Shirt AND Tie AND Jacket.
All others are required to wear a shirt at minimum. NO JUMPERS ALLOWED.

For Women, we're hoping it is a garden party/dinner/dance sort of day. Best bet is to have some layers available.Ceremony will be outside on grass, Reception is inside with a tent out back.