(viii) Hull

Double. Outer of white cedar, inner of mahogany. No armour protection. Aluminum alloy deck plating abaft torpedo tubes.

(ix) Engines

Three Mercedes Benz, Type M.B. 501, 4-stroke Diesels, each marked M.B. 501, followed by engine number, year of construction and date of last test.

Cylinders : 20 arranged in "V" formation.

Bore : 180 mm. (7.087 in.)

Stroke : 250 mm. (9.843 in.)

N.I.D. Note - The strok of engines in "S 53" was given as 300 mm. (11.8 in.) in C.B. 4051(41) page 13.)

Horse-power : 2,000 at 1,630 r.p.m.

Supercharger : None.

Fuel Pump : Bosch. One to each cylinder.

Cooling : Fresh water. 800 litres (176) gallons.

Exhaust : Underwater exhaust used during passages. Auxiliary exhausts (two to each engine) used for starting engines.

Starting : Air.

R.P.M. Indicator : Graduated up to 2,000 r.p.m.

R.P.M. and Speeds : (a) All three engines (boat fully loaded):-
Emergency speed, 37-38 knots.. .. .. .. .. .. 1,630 r.p.m.
Utmost speed, 34 knots.. .. .. .. .. .. 1,550 r.p.m.
Full speed, 31 knots.. .. .. .. .. .. 1,480 r.p.m.
Three-quarters speed, 26 knots.. .. .. .. .. .. 1,400 r.p.m.
Three-fifths speed, 26 knots.. .. .. .. .. .. 1,150 r.p.m.
Half speed, 19 knots.. .. .. .. .. .. 980 r.p.m
Slow speed, 15 knots.. .. .. .. .. .. 750 r.p.m
Dead speed, 12-13 knots.. .. .. .. .. .. 600 r.p.m

Centre engine only :(boat fully loaded)
Emergency speed, 20 knots.. .. .. .. .. .. 1,630 r.p.m.
Utmost speed, 17 knots.. .. .. .. .. .. 1,550 r.p.m.
Full speed, 14-15 knots.. .. .. .. .. .. 1,480 r.p.m.
Three-quarters speed, 26 knots.. .. .. .. .. .. 1,400 r.p.m.
Three-fifths speed, 10 knots.. .. .. .. .. .. 1,150 r.p.m.
Half speed, 9 knots.. .. .. .. .. .. 980 r.p.m
Slow speed, 8 knots.. .. .. .. .. .. 750 r.p.m
Dead speed, 6 knots.. .. .. .. .. .. 600 r.p.m

Survivors said that "S 71" would have been capable of two or three more knots after undergoing the long refit for which she was due.

(x) Endurance and Consumption

Twenty-four hours of full speed on 18 m3 (15.3 tons) of fuel.

(xi) Auxiliary Engines

Two Diesels, each of 15 h.p.
Manufacturers: Motorenwerke Mannheim.
R.P.M. : 800-850.
Used for compressors and generation of electricity.

(xii) Fuel Tanks

Number: Seven.

Total capacity: 21.3 m3 (12.7 tons).

Normal fuel shipped: 15 m3 (12.7 tons).

Position:
In compartment 3: Two outer tanks each containing 3.8 m3 (3.2 tons);
One centre tank containing 1.7 m3 (1.4 tons);
In compartment 6: Two forward tanks each containing 4.0 m3 (3.4 tons);
In compartment 1: Two after tanks each containing 2.0 m3 (1.7 tons).

(xiii) Lubricating Oil Tanks

Two amidships, port and starboard, each containing 500 litres (110 gallons).