I have a trip coming up with a requirement for 14-foot boats - Point Judith Pond on July 23rd. It is open water, 8-miles and subject to wind and waves. I know from experience that folks in longer boats do better. Does that mean that someone in a shorter boat couldn't keep up - not necessarily. But I'd want them to understand the conditions, and I'd want to feel comfortable that they can keep up with the group. Not fun for anyone to be on a trip with the wrong boat. If you want to join a trip with that requirement, you can speak to the leader.
We also have trips on narrow rivers where shorter boats are recommended/required.
Not trying to exclude anyone - just want to make sure that people have the right boat for the trip.