zelmo,
I too have wondered about this. I have a 2005 Xpress X21 bass boat with a 250 Yamaha on a tandem axle trailer with surge brakes. My trailer registration card lists a GVW rating of 4,000 pounds. When I first bought my boat, I asked two different dealers if I needed to have the trailer inspected; both said "No, because you have surge brakes, not electric brakes".
Over the years, I have had several PA State Troopers pull alongside me and take a long look at the hitch and tongue area of my trailer. Not once have I been stopped for no inspection sticker. My guess is that they were looking to see if I had my chains crossed, or maybe I was just lucky?
That being said, I did see a thread on the Hull Truth boating forum (
https://www.thehulltruth.com/boating...nspection.html ) where someone near Lake Erie was asking about trailer inspections because the Troopers were ticketing guys without trailer inspections. Unfortunately, the thread didn't indicate if the trailers being ticketed had bass boats or cabin cruisers. My guess is that they were big boats on big trailers.
If you are interested in reading the law…
here is a link to the PA Motor Vehicle Code, Title 75, Chapter 47, Inspection of Vehicles:
https://www.legis.state.pa.us/cfdocs...&div=0&chpt=47
here is a link to the PA Transportation Code, Title 67, Chapter 175, Vehicle Equipment and Inspection, Subchapter G. Recreational, Semi, and Utility Trailers:
https://www.pacodeandbulletin.gov/Di...hapGtoc.html&d
Keep in mind that the gross weight is the total weight of the trailer, the boat, and its contents.
Good luck! (I'm still confused.)