(Also sorry if this has already been suggested, I tried searching but it was all to vague and I pulled up a ton of unrelated stuff)
I think you should be able to build a little boat like a dinghy on longboats or basically any of the biger ships. Right now docking the first dinghy to a boat is a pain because you can't do it by yourself, and I can't think of any reason why you wouldn't be able to make something that small on a larger boat...in fact you're supposed to be able to build anything else you could build outside on a ship, why not vehicles too?
You should also be able to build all ships in a coaster harbor or jetty. And as a similar idea, how about a new building called a 'garage' that you can build bikes and cars in, and drive them in and out? I think both of those thigns would encourage businesses.
