Model, of the 'S.S. Ermack' stern frame, rudder and prop-shaft housing
Wood model stern frame and rudder of the "S.S. Ermack"
These models (scale 1:24) represent the steel castings made in 1898 by the Darlington Forge Co.Ltd. for the stern frame and rudder of the quadruple-screw ice-breaker 'Ermack'.
The stern frame was a combined rudder and sternpost; the latter portion had a boss for one of the three after propellers, and the former the gudgeons for the rudder. On each side of the screw aperture, the vertical sides of the casting had bevelled faces, to ease the passage of any obstructing masses of floating ice. Near the heal of the sternpost was an abutment and scarf for attachment of the after ends of the keel plate. The fork made by the upper part of this casting formed the lower boundary of a recess provided in the stern of the vessel. This served to house the bow of any ship which required towing into an ice-bound harbour, or which was required for use as an auxiliary in forcing a channel.
Both the box and stern frames had the usual rebates for the attachment of the shall plating. The internal gulleting of the castings was reduced to the minimum required for efficient riveting, so as to strengthen these parts which had to with stand exceptional stresses. A number of transverse and longitudinal ribs or flanges served to connect the castings to the general framing of the ship. The rudder, also shown in position, was a single steel casting, and was provided with stops to limit its angle of turning. The actual weight of the stern frame casting was 7.9 tons; that of the rudder casting was 12.7 tons.