Appendix F
HMS TACITURN AND HMS PORPOISE
Taciturn - speed trials detail 1952
The Taciturn was the first of eight T class converted, to a streamlined submarine with greater submerged power, in a manner similar to the USN GUPPY. However due to the nature of the original direct drive machinery generally employed by the Royal Navy in its submarines at that time, the hull needed to be extended for an extra motor per shaft, with an extra battery was installed in the existing forward hull.
There were 448 cells as opposed to the 502 cells of the Guppy I/II submarines.
The Guppy I/II cells were 6100 Ah at the five hour rate while the T class were 6560 Ah.
Cell dimensions 344.4 x 444.4 x 1082 mm to terminal tops.
Cell weight 450 kg, Total battery mass 201 tons
Battery area calculated at 68.6 M2.
Specifically built for heavy discharges for 30 minutes. Final cell volts 1.67.
18 month life - plus with good management
Speed trial at 90 feet 373 volts Battery amps 12402 amps + Field 29 amps + 400 aux amps. Endurance 34 minutes .5754 shp, 15 knots .598 rpm (average two shafts).
Speed trial at PD 368 volts Battery amps 12447 amps + Field 28 amps + 400 aux amps. Endurance 33 minutes .5718 shp, 13.7 knots .598 rpm (average two shafts). The field amps were at minimum for full speed (29 amps). Maximum field current at the slow end speed ranges (140 amps).
Submerged displacement of the Taciturn was 1,680 tons compared to the Guppy with 2400 tons.
Note the considerable difference in speeds achieved at Periscope Depth and at 90 ft; it is likely this was due to increased wave action increasing drag near the surface.
Also it should be noted that the battery voltage on heavy discharges starts at a particular higher value but progressively falls during the discharge until the stated safe limit is reached. In USN practice for a particular cell type, the specified average voltage over the discharge period is stated along with a lower limiting final voltage that seems to be lower than the figure used for the Taciturn cells.
To maintain a reasonably constant power over the discharge period, the current has to be raised as the voltage falls by adjusting the motor shunt field.
Though not stated, it seems logical that the Taciturn speed trial voltages and currents are those recorded at the end of the 30 minute discharge periods.
PORPOISE CLASS
It may be of some interest to note the battery specification and electrical propulsion arrangement of the 1958 British P Class (and later O Class) were being planned as the Taciturn was being converted.
Two batteries of 224 cells = 448 cells,
Battery cells 7420 AH at the 5 hour rate.
Cell mass 507 Kg. Total 227.14 tonnes
Series/parallel switching of the supply to the twin motors, each 3000 shp.
Max' voltage to motors a nominal maximum of 880 volts.
Maximum submerged speed - 17 knots for 20 minutes.
Submerged displacement 2400 tons.
3-bladed 7ft dia. Propeller, 400rpm
Diving Depth 800-900ft
This form is for you to comment on, or add additional information to this page. Any questions will be deleted. If you wish to ask a question contact the Branch or the Webmaster using the Contact Us page or ask your question on our Facebook Page
