Two-Ram Steering Gear with Spherical Bearings
(a) Arrangement of Rams and Tiller, Including Fittings:
A two-ram steering gear utilizes two hydraulic cylinders (rams) to control the movement of the rudder. Here’s a breakdown of a typical arrangement, including fittings:
- Rams: The two rams are typically positioned symmetrically on either side of the vessel’s centerline, often mounted on the hull structure. They consist of a cylinder body, piston rod, and end fittings.
- Tiller: The tiller is a lever arm attached to the rudder stock. It acts as the point where the rams apply their force to turn the rudder. The tiller can be a forged or fabricated steel structure designed to handle the forces exerted by the rams.
- Ram End Fittings: The piston rods of the rams connect to the tiller using suitable fittings. These fittings can vary depending on the design but typically involve:
- Clevises: U-shaped yokes with a pin connecting them to the tiller. The clevis allows some angular movement at the connection point.
- Fork Heads: A forked end on the piston rod that connects directly to a pin on the tiller.
- Trunnion Mounts: In some cases, trunnion mounts might be used, where the piston rod is supported on a fixed pin on the tiller, allowing for some rotational movement.
- Tie Bar (Optional): In some configurations, a tie bar may connect the two piston rods at their ends to ensure they move in unison and distribute the load evenly across the rudder stock.
(b) Why Spherical Bearings are Required on Ram Ends:
Spherical bearings are essential on the ram ends connecting to the tiller for several reasons:
- Angular Misalignment: Ships experience flexing and torsional movements due to wave action and hull stresses. Spherical bearings allow for a small degree of angular misalignment between the ram and the tiller, accommodating these movements without binding or placing undue stress on the rams or tiller.
- Self-Alignment: Spherical bearings can automatically adjust to slight variations in alignment between the ram and the tiller, ensuring smooth and efficient force transfer.
- Reduced Friction: These bearings have a low coefficient of friction, minimizing friction losses at the connection point and maximizing the effectiveness of the hydraulic force.
- Increased Load Capacity: Spherical bearings can handle high radial and axial loads, making them suitable for the forces exerted by the rams.
- Reduced Maintenance: Compared to plain bearings, spherical bearings require minimal maintenance due to their enclosed design and self-lubricating properties (in some types).
Overall, spherical bearings provide flexibility, reduce friction, and handle high loads, making them crucial components for a reliable and efficient two-ram steering gear system.