It sounds like Maryland applies a strict and simple 50% rule, i.e. if the boat is there more than 182 days a year, they own you. You might want to contact them in writing to find out if it is that simple, or if they provide for vessels in slow transit, etc.
Each state has their own regulations about boats and motor vehicles. Generally, you can expect a local "burden" sometime after you have had a motor vehicle in a state for 30 days. Sometimes that's tax, sometimes that's registration, but yes, it is that short in some states. State and federal rules about "domicile" versus "residence" may also come into play, you'll need to check that out too.
In many states the time period is tolled by moving in/out of their waters, it looks like Maryland doesn't let you cheat that way, they may just be counting days.