Section 8 Sternframes and appendages

8.1.1 Sternframes, propeller bosses and shaft brackets may be constructed of forged or cast steel, or may be fabricated from plate.

8.1.2 Forgings and castings are to comply with the requirements of Pt 3, Ch 5 Fore End and Aft End Structure and Pt 3, Ch 4 Longitudinal Strength of LR’s Rules for Materials respectively.

8.1.3 Cast sternframes, rudder horns and solepieces are to be manufactured from special grade material, see Ch 4, 2 Castings for ship and other structural applications of the Rules for Materials. Cast bossings can be manufactured from normal grade material, see Ch 4, 2 Castings for ship and other structural applications of the Rules for Materials.

8.1.4 Sternframes, shaft brackets, etc. are to be effectively integrated into the ship’s structure and their design is to be such as to facilitate this.

8.2.1 The scantlings of sternframes are to be determined from Table 5.8.1 Sternframes. The scantlings for sternframe configurations other than described in this Section, and for cast steel sternframes, will be specially considered, but the strength is to be at least equivalent to a fabricated sternframe.

Table 5.8.1 Sternframes

Item	Parameter	Requirement
		Forged or roll steel	Fabricated steel
(1) Propeller posts	A	for L ≤ 60 m : 0,8T cm2	-
	A	for L > 60 m : 32T cm2	-
	t 1	-	12 + 0,11L mm
	r	-	18 + 0,17L mm
	l	-	150 mm
	W	-	100 mm
	t W	-	5 + 0,05L mm
(2) Sternpost in twin screw ships and non-propelled ships	A	for L ≤ 60 m : 0,7T cm2	-
	A	for L > 60 m : 28T cm2	-
	t 1	-	8 + 0,07L mm
	r	-	12 + 0,11L mm
	l	-	150 mm
	W	-	100 mm
	t W	-	5 + 0,05L mm
(3) Propeller shaft boss	tb
(4) Solepieces (open type sternframe) supporting the lower rudder pintle	Z T	c.f.Ar(V + 5,6)2 × (a/b – 0,15) × 0,95 a/b cm3 see Note 4
	Z V	0,5Z T cm3
(5) Double arm shaft brackets	Z T	(16 × 10–6 × D ts 3) + 8 cm3
	N	≥ 0,05e mm
	M:N	between 2,5 and 5
Symbols
L, T are as defined in Pt 3, Ch 5, 1.4 Symbols and definitions 1.4.1 a, b, c = distances, in metres, as shown in Figure 5.8.2 Open sternframe e = length of the longest shaft bracket strut, in mm f = coefficient dependent on type of rudder profile and rudder angle, see Table 12.2.5 Rudder coefficient f in Chapter 12 for rudder angles in excess of 45° no higher factors than those for rudder angles of 45° need to be applied. k o = material factor, = (235/σo) (24/σo) t 2 = 10 mm for a propeller shaft boss integrated in the sternframe or supported by a single arm bracket and t 2 = 0 for a propeller shaft boss supported by double arm shaft brackets. t b = finished thickness of boss, in mm t 1, r, l, W, t W = scantlings of stern post, in mm, as shown in Figure 5.8.1 Propeller posts A = cross-sectional area of forged or rolled steel stern post, in cm2 A r = total rudder area, in m2 D ts = Required mild steel diameter of tail shaft in way of the boss, in mm M = the breadth of the shaft bracket strut, in mm, for e, M and N, see also Figure 5.8.3 Shaft brackets N = the thickness of the shaft bracket strut, in mm V = maximum service speed with the ship in loaded condition, in km/h Z T = section modulus against transverse bending, in cm3 Z V = section modulus against vertical bending, in cm3
Note 1. In fabricated sternframes the connection of the propeller post to the boss is to be by full penetration welding. Note 2. Solepieces supporting movable nozzles will be specially considered. Note 3. The support of a solepiece by a fixed nozzle arrangement will be specially considered. Note 4. The length 'a' of the solepiece should be taken as not less than 0,4b in the formula for Z T.

8.2.3 Fabricated sternframes are to be strengthened by transverse webs, spaced not more than 700 mm apart.

8.2.4 Solepieces are to be carried well forward and efficiently scarfed into the keel. Special care is to be taken to avoid any stress-raising details at the point where the solepiece enters the shell plating.

8.2.5 Stern posts and rudder stock lower bearings are to be connected to floors of which the thickness is to be increased by 2 mm, above the thickness required by Pt 3, Ch 5, 7.2 Bottom structure.

8.3.1 The finished thickness of the propeller boss in single and twin screw ships is to comply with Table 5.8.1 Sternframes. The length of the boss is to be adequate to accommodate the aftermost shaft bearing, and to allow for a proper connection to the propeller post or shaft brackets.

8.4.1 Where the propeller shafting is exposed for some distance clear of the hull, it is to be supported adjacent to the propeller by independent brackets having two arms. The use of single arm brackets will receive special consideration.

8.4.2 Shaft brackets are to be designed to ensure a satisfactory connection to the internal hull structure; hard spots are to be avoided. Bracket arms are generally to be carried through the shell plating, which is to be locally increased in thickness, see Pt 3, Ch 5, 2.4 Shell plating 2.4.5. The connection of the arms to the bearing boss and shell plating is to be by full penetration welding.

8.4.3 The scantlings of double arm shaft brackets are to comply with the requirements of Table 5.8.1 Sternframes. The scantlings of single arm brackets will be specially considered.