Efficient, Quiet, Trustable. Marine Twin Propeller Podded Propeller Efficient, Quiet, Trustable.Material: Bronze, Aluminum Bronze, Nickel Aluminum Bronze, Manganese-Aluminum Bronze, Brass, Copper-zinc Brass, Manganese Brass, Aluminum Brass, Stainless Steel,Customized Dimension Available.Blade: 3,4,5,6 Chongqing Perputual's Products have been approved by ABS, BV, CCS, DNV, GL, KR, LR, NK, RINA, ...