On many conventional ships a stem bar, which is a solid round bar, is fitted from the keel to the waterline region, and a radiused plate is fitted above the waterline to form the upper part of the stem. This forms what is referred to as a ‘soft nose’ stem, which in the event of a collision will buckle under load, keeping the impact damage to a minimum. Older ships had solid bar stems which were riveted and of square section, and as the stem had no rake it could cause considerable damage on impact because of its rigidity. Small ships such as tugs and trawlers may still have a solid stem bar extending to the top of the bow, and some existing large passenger ships may have steel castings or forgings forming the lower part of the stem. A specially designed bow is required for ships assigned ‘icebreaker’ notation and additional scantlings are required for the stems of ships assigned other ice classes.
The solid round bar is welded inside the keel plate at its lower end, and inside the radiused stem plate at its upper end, the shell being welded each side (Figure 36). It is necessary to support that part of the stem which is formed by radiused plates with ‘breast hooks’, i.e. horizontal plate webs, between the decks and below the lowest deck, in order to reduce the unsupported span of the stem. Where the plate radius is large, further stiffening is provided by a vertical stiffener on the centre line.
The thickness of these plates will be in excess of that required for the side shell forward, but the thickness may taper to that of the side shell at the stem head.