The correct answer is D) None of these. Heavy vehicles aboard Ro-Ro (roll-on/roll-off) vessels are typically secured using chains and binders, not manila rope, webbing, or buckle/ratchet tensioners. Chains and binders provide a more secure and robust method of restraining heavy vehicles during transport, in accordance with regulations and industry best practices for Ro-Ro vessel cargo securing. The other options listed, while potentially used for securing lighter loads, are not the primary means employed for heavy vehicle securement on Ro-Ro ships.