I have a pair of 225HO G2s. They have a plate assembly at the transom, thin aluminium plates which seem to be removable.
Can anyone tell me what it does and if it can or should be removed? (It picks up a lot of barnacles!)
I believe the lower aluminum item that you are inquiring about is the splash plate and on some boats, helps in getting up on plane quickly. If barnacles are a problem, see your dealer for special anti-fouling paint formulated for aluminum.
"There is never just one thing wrong with a boat";
-- Travis McGee, main character in a book series by John D. McDonald
The factory recommends that a properly trained technician service your Johnson or Evinrude outboard motor. Should you elect to perform repairs yourself, use caution, common sense, and observe safety procedures in the vicinity of flammable liquids, around moving parts, near high-temperature components, and working with electrical or ignition systems.
The information offered here is only general in nature and should not be construed as complete factory approved procedures, techniques, or specifications. Always use the proper service manual for your motor, up-to-date service literature, the correct tools, and have an understanding of how to proceed with troubleshooting and repair methods. If you are unsure or uncomfortable with a procedure, a situation, or a technique, enlist the services of a factory trained technician.