I want to address the issue of larger size boats first to give people a practical understanding of the problems of using any boat that can’t be hidden. Whether the boat is a 16′ runabout, a 50′ sport fisherman or a 30′ sailboat they all give your position away in daylight and often at night. There is no way to hide and there is no where to go and hide. Even the fastest boat can be cut off by a slow boat in front of it, that boat is caught in the open and bullets are darn fast.
This leaves one option for large craft, massive superior stand off capabilities. If a boat can’t be outfitted with that type of firepower then don’t use it after shtf. There could be some exceptions, for example of an exemption would be, using a large boat at night to cross a body of water and abandon the boat off shore using the dinghy to sneak on shore. If a boat does have standoff ability it still can’t come ashore without losing the tactical advantage.
A large boat must be able to successfully engage multiple fast moving targets (3 or 4) in a 360 degree perimeter 24/7 before attackers close in to small arms range (500yrds) Accuracy must allow for hits on a 1 ft square (the size of a small outboard motor) moving at 40 mph. Okay I don’t have even one mg and certainly not two or three 50bmgs and probably not many preppers do. So scrap the idea of sailing that 50′ sailboat into the sunset.