Exam Question
(a) Explain why a Spectacle Frame and Boss Plates are fitted to twin screw ships. (8)
(b) Make a simple sketch of a Spectacle Frame showing how it is attached to the ship structure and to the Boss Plates. (8)
Class 4 (4th Engineer)
SC&S
📅 Jan 2026
Reference Answer
### Part (a): Purpose of Spectacle Frame and Boss Plates (8 Marks)
A Spectacle Frame (or A-Bracket) and its associated Boss Plates are critical structural components fitted to twin-screw (or multi-screw) vessels for the following fundamental reasons:
1. **External Support for Propeller Shafting**:
* In twin-screw designs, the propeller shafts exit the hull at a significant distance from the ship's centerline and at an angle. This results in a long, unsupported overhang between the hull exit and the propeller.
A Spectacle Frame (or A-Bracket) and its associated Boss Plates are critical structural components fitted to twin-screw (or multi-screw) vessels for the following fundamental reasons:
1. **External Support for Propeller Shafting**:
* In twin-screw designs, the propeller shafts exit the hull at a significant distance from the ship's centerline and at an angle. This results in a long, unsupported overhang between the hull exit and the propeller.
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