T Class Conversion

Figures

Fig 1

The ‘T’ class conversion engines were, to the best of my knowledge, unaltered from when they were fitted in the unconverted submarine .Nominally 1250 bhp each side. Despite reports, the evidence indicates they were not converted to super charging, indeed the gain quoted was hardly worth the complication and expense.

Note the links for the alternative positions have to come from the battery isolating links thus preventing any possibility of placing the Nos 1 & 2 batteries in parallel with Nos 2 & 4 batteries.

Fig 2a and 2b

The two drawings Figs 2a and 2b are an educated deduction from the text from BR 1965 (1953) and anecdotal information from a former crew member. There may be errors in the placement of certain pieces of equipment but if this so, they are of such a nature as to make no difference to the understanding of the propulsion circuits of the "T " class conversion.

They are drawn principally to make the associated notes on BR 1965 and the First of Class trial data 1952 for HM Submarine TACITURN, more understandable, lacking the missing manual drawings.

There were two of these identical motor controller mechanisms per side, one for each tandem motor. They were installed longitudinally in the bottom of each fore and aft cubicle connected to their associated controller wheel by a control rod system, they were really a large multi-stage rotary switch.

Provision was made to work the controller directly with an emergency handle at the bottom of the cubicle, if the main system failed

The only difference between forward and aft controllers, was that the forward control wheel was smaller than the aft wheel, as shown in Fig 3c.

When in electric drive with the engine clutch open and the motor clutch closed the two mechanisms could be clutched together and operated in tandem by the large aft control wheel. This was a sensible arrangement when on high speed submerged electric drive with one watch keeper per side.

Fig 2c

This circuit shows the basic switches used in older RN submarines to place batteries, tandem motors and armatures, in series or in parallel to obtain a number of speed ranges. The 'T' class conversion used the grouper switch as shown to implement the battery group switches, the tandem motor group switches and the armature group switches. The first two, with duplicated knife blades for the heavy current, were operated mechanically by control wheels, the latter with single blades, by handle similar to the unconverted submarines but installed in a cubicle.

Examples of the armature group switch may be seen on the open switch board of the preserved HMS ALLIANCE.
Also on the ALLIANCE switchboards, the single change switch next to each main armature group switch, is nothing more than another group switch split in two with a section on each switch board, used for placing all four armatures, two per shaft, in series for the lowest speed range. Not used in my experience of some years.

Fig 3a

The only clear drawing I have from BR 1965 ('T' class submarine conversion) of a motor cubicle, is this one showing the control platform side of the starboard forward motor control cubicle.

It is clear from the text and the obscured general arrangement drawings, that the aft cubicle would have been much the same ,but with the starboard Tandem Motor Group Switch and a similar operating wheel and other small switches and indicating instruments. I also deduce the cubicle layout would have been as shown in the small sketch I have added below. The panel shown would have been at the LH shoulder of the operator facing the main control panel, with the blank LH side of the cubicle facing the gangway.

The two large combination ammeters (charge/discharge) were for No1 and No2 battery sections (on the starboard side) LH top.

They had maximum scale readings of 2000 amps charging and 10,000 amps discharging.

Fig 3b

The Port Switchboard - Control panel was essentially identical to this drawing. I have added the forward and aft motor control cubicles to illustrate the general layout. I understand that unlike the unconverted ‘T’ class submarine, two electrical propulsion watch keepers were required per watch. An Leading Electrician’s Mate and an Electricians Mate. In addition the late Captain Coote when CO of TOTEM, reported he had a Commissioned Electrical Officer .See his book “SUBMARINER”, regarding this apparent waste of a highly skilled technical officer.

Fig 3c

This drawing is merely a magnified version part of Fig 3b to show more clearly the control clutch sighting window and the hand clutch operating lever .

Tables

This table with data concerning the aft propelling motor, is associated in BR 1965 with the table that follows about the forward motor acting as a generator supplying the aft motor. It should be noted the speed figure I have added of 7.9 knots –350 rpm, is taken from the Snorting knots /rpm graph for two engines FIG VI “TACITURN “speed trial data. It should noted that the forward motor rpm are for the diesel/generator configuration and the after motor rpm is the propeller shaft rpm. The motor clutch being open.

A significant increase on the tabulated charging current of 500 amps, would have been achieved by a relatively modest decrease in speed, due to the speed/power cube law say 5.5 knot/250 rpm.

This table is associated in BR 1965 is associated with the previous table on charging while snorting.

The comment on available engine power may be in reference to rpm in snorting conditions

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