Updated Cylinders fit the same applications as the prior models. Improvements over previous models include: Updated styling, a more robust barrel, new sealing systems and materials with excellent resistance to compression set, and new adjustable stainless steel O-ring fittings (ORB). Front Mount Cylinders are balanced and the most commonly used. Recommendations: Single Engines: Single Cylinder: 350 HP-maximum, 65 MPH-maximum HC53xx Cylinder, Single Cylinder: 350 HP-maximum, HC63xx Pro or HC6845S, Dual Engine Non-Counter Rotating: Single Cylinder: 450 HP maximum, 55 MPH maximum. HC53xx Cylinder, HO60xx TiebarDual Cylinder: 600 HP maximum, 55 MPH maximum. HC53xx Cylinders, HO60xx TiebarTriple Engine1 with Counter Rotating: Dual Cylinder: 900 HP maximum, 55 MPH maximum. Dometic has specific steering equipment for boats that are driven aggressively, used in severe conditions or with more than 300 HP per engine. Before ordering, determine the best application for the boat based on hull design, speed, and usage. For higher speed single engine applications, SEASTAR recommends the use of SEASTAR PRO Cylinders. Material: Metal.