The Steamship Authority provides frequent, year-round service to Martha's Vineyard.
This ferry to Martha's Vineyard is based in Woods Hole in Falmouth, MA. We've taken the ferry from Woods Hole to Vineyard Haven.
It's a quick, 45 min ride and there are bathrooms, plenty of seats and food available on board. However, be prepared to pay a bit extra for food on the ferry.
We brought our SUV because we were staying several days and have kids. Although there are buses, mopeds and bicycles available on the Vineyard, it was easier for us to have our own car and the cost is not excessive. It's nice to have your own vehicle, especially if you're traveling with family.
You may also rent a car on Martha's Vineyard, but it is convenient to be able to simply pack your stuff in your car and transport everything (car and all!), rather than lugging bags etc and packing it into a vehicle on the Vineyard.
This very helpful web page gives current status for parking lot availability, weather conditions and estimated wait times:http://web3.steamshipauthority.com/ssa/opsinfo.cfm?Loc=WH
You may also tune your car radio to 1610AM, as you approach the Falmouth area, for updated information
Here are some ideas for family friendly vacations on Martha's Vineyard...
See some beautiful sunset pictures on Martha's Vineyard