Difference between revisions of "Renouf Torpedo Tactical Instrument"

Revision as of 13:30, 12 March 2011

The Renouf Torpedo Tactical Instrument was a pretty ingenious family of Torpedo Control instruments designed by Lt. Cdr. Edward de Faye Renouf of H.M.S. Conqueror (1911) described in the Annual Report of the Torpedo School, 1917.^[1]

It was proposed in 1917 and foreseen as being delivered in 3 types of increasing complexity and function: A, B and F.

Geometric Theory

• 

  Figure I^[2]

• 

  Figure II^[3]

• 

  Figure III^[4]

In Figure I, if your target, located at S, is not moving, a torpedo fired from position O will hit him if it is within a circle drawn about S whose radius (OS) equals the maximum range of a torpedo at the given speed setting.

In Figure II, if your target, located at S at the moment of firing, is steaming along line AB, a torpedo fired from position O can reach him if it is anywhere within a circle drawn about the impact point, E with a radius equal to the endurance of the torpedo. The limiting range circle, then, will always be centered on the impact point, and distance SE and OE are going to be proportional to the speed of the enemy and the speed of the torpedo, respectively. The centre of the torpedo circle must move in the direction the enemy is steaming by a distance SE, which is equal to the SpeedOfEnemy * MaximumTimeOfFlightOfTorpedo, as both torpedo and target will travel for the same duration between firing and impact.

The geometry of the case described above is independent of scale, owing to the similarity of triangles. In Figure III, consider if we move point O well within the extreme range circle and observe that director angle SOT has the same angles as does SXE (the director angle pertaining to the extreme range case). The enemy inclination would be the same in both cases, as would the director angle required to produce the hit.

Mechanical Design

Base Plate Schematic^[5]

To save time and space, Renouf instruments typically portrayed three torpedo settings at once by having three colour-coded torpedo circles. The scale chosen was 4,000 yards to an inch. The primary structure was formed by a flat base plate with a speed scale for the target ship, adjustable by a knob. The instrument always depicted the target ship steaming left to right across the bottom as indicated by an arrow.

The Base Plate

The red, fixed circle drawn at 10,000 yards from S is meant to suggest the effective range of secondary armament that the attacker might fear. The radial lines drawn every 10 degrees can be read from either of two scales to treat them as:

• enemy inclinations in attacking problems, or those where the enemy is the ship depicted at S
• relative bearings to the enemy for defensive calculations where we consider our own ship to be at S.

This somewhat schematic diagram shows how each of 3 link gears (suggested in gold here) might advance its respective torpedo range circle a different distance along AB according to the different times of flight for the different torpedo speeds as enemy speed is dialed in. Thus, in this implementation, point S is always in the middle of the lower edge of the instrument, and the circles are advanced different distances, displacing their centers (the impact points) rightward toward B. The torpedo rings are painted in white at portions where firing would be unwise owing to:

• low striking angle of torpedo against hull
• low relative speed (when firing from astern)
• ease of evasion, as the enemy is nearly combing the wake already
• deleterious effect of enemy course estimation errors^{[Citation needed][6]}

This is similar to how the Renouf instruments effected this, but even the simplest Mark added no fewer than 4 bars to depict various tactical considerations.

The Position Bar

Type A^[7]
Set to show an attacker making 26 knots, intent on firing from 11,000 yards and 45 degrees off the bow of a target at a present range of 20,000 yards and making 17 knots with circles for torpedoes reaching: * 18,000 yards at 21 knots * 15,000 yards at 25 knots * 11,000 yards at 29 knots

The Position Bar (shown in orange) was pivoted at point S and scaled along its length in thousands of yards. It would be swung to the proper angle to indicate the target's inclination (in attack mode) or the threat's relative bearing (in defence mode). A slider along the scale would be positioned to estimated range, and this bore a pivot point (referenced below). A disc about the hub at S would be referenced later, with the Course to Steer bar, and a small switch (shown in green) would indicate whether the attack from coming from port or starboard (as the instrument always depicts an attack from port).

The Desired Track Bar

The Desired Track Bar (shown in pink and pivoted from the position pointer on the position bar) depicted the proposed movement of the attacker to reach his preferred firing position. It pivoted from the position pointer and was graduated in "DISTANT TO RUN IN THOUSANDS OF YARDS" from the position pointer. A sliding Desired Position Pointer on this bar could be slid to a position to indicate the position the attacker would like to attain. The orientation of this bar and the placement of its pointer, then, would indicate a proposed firing position on the base plate relative to S.

The "Course to Steer" Bar

The "Course to Steer" Bar' (depicted in blue) pivoted around S and was graduated in knots on the same scale used on the target speed scale. A pointer near its hub indicated on the graduated disc at the base of the position bar. This would indicate the relative bearing the attacker would have to place the target to achieve the desired attack position indicated by the desired position pointer.

The Resultant Track Bar

The 'Resultant Track Bar (depicted in pink on the left) was on a pivot that was free to slide along the target's speed scale. It was graduated in "time in minutes to run 1,000 yards along the desired track bar."

"A Type" for Attack

This type, illustrated above, was the simplest. It was intended for use in cruisers, light cruisers, flotilla leaders, and destroyers. Its emphasis was delivering a torpedo attack.^[8]

It could determine:^[9]

• whether torpedo fire was possible from the present position
• when fire was possible, which torpedo setting would be most advantageous
• how to steer to attain a specific desired firing position
• how long it would take to attain that firing position
• the deflection setting for the torpedo deflection sight

Determine whether you can fire a torpedo now

This could be worked out as follows:

1. place the position bar to the inclination (or bearing, if you are the target) of the enemy
2. slide the position pointer to the present range
3. set the estimated enemy speed by the knob (this would advance the torpedo circles)
4. the attacker is able to fire using any torpedo setting if the position pointer falls within its torpedo circle

Determine the best setting for the torpedo

Generally, this was held to be the fastest setting, or the smallest circle the position pointer falls within, subject to inviolable orders for torpedo settings or other vital tactical considerations (such as wanting the torpedo to over-run).

If, however, one wanted to allow for the enemy turning away, one could examine which setting would suffer least from it by rotating the position bar anti-clockwise by an amount equal to the turn away expected. This represents the situation if the turn were made now, and so the smallest circle from this new inclination would represent the best choice.

Determine course to steer to achieve attack position

This could be worked out as follows:

1. place the position bar to the inclination of the target
2. slide the position pointer to the present range to the target
3. set the estimated enemy speed by the knob (this would advance the torpedo circles)
4. position the desired track arm and its desired position pointer
5. position the resultant track bar to the speed of the target and make it parallel to the desired track bar
6. rotate the "course to steer" bar so that attacker's speed is indicated on the resultant track bar
7. the pointer on the course to steer bar will indicate the relative bearing the target should be placed on to achieve the desired attack position

Consider the configuration of the instrument in the illustration above. It is set up to work an attack problem where

• initial range 20,00 yards
• initial estimated inclination 100 degrees right
• initial estimated enemy speed 17 knots
• desired attack position 11,000 yards at an inclination (bearing?) of 135 degrees right
• our speed is 26 knots

This will require a run of 13,000 yards with the enemy bearing 70 degrees red. A time to run 1,000 yards along desired track is about 2 minutes, so time to attain our desired position is about 26 minutes.

Type A Example 2^[10]

In another example, Example 2 shows an attacker making 25 knots, intent on firing from 13,000 yards and inclination 135 right of a target at a present range of 25,000 yards and inclination 170 degrees right and making 18 knots. The instrument shows that the attacker will have to run 17,000 yards after bringing the enemy to bearing green 50. As the time to run 1,000 yards will take about 45 seconds, the attacker will have to cruise for a little under 13 minutes before it will achieve the attack position.

Determine how long will it take to achieve attack position

When the "Course to Steer" bar is swung to meet the resultant track bar at the attacker's speed, a triangle of velocities is formed in which the length of the resultant track is the movement of the attacker during his approach to firing. It is graduated in time to run 1,000 yards along the resultant track. The distance to be made along the desired track can be read from the position of the desired position pointer and then multiplied by the figure indicated on the resultant track bar to obtain the total time required before the attack can be made.

Determine the deflection setting for the sight

Renouf Instrument Deflection Sliderule^[11]

A slide rule was fitted to the side of all Renouf instruments to allow the torpedo sight deflection (the target speed-across if attacker were at rest, or TargetSpeed times sin(Inclination)). The slide in this rule (marked at inclination angles, 0 to 90) had an arrow at its 90 degree mark which would be positioned to indicate the enemy speed. When this was done, the target inclination on the slider would be opposite the knots of deflection on the fixed speed scale, which was graduated from 1 to 32 knots.

"B Type" for Battleships

Renouf Type B^[12]

This type was intended for use aboard battleships and battlecruisers. The emphasis here was primarily defensive, but could also be used for attack calculations if torpedo circles of one's own torpedoes were substituted for those of the enemy. ^[13]

The Type B was issued with 2 sets of torpedo circles, one for British torpedoes and one for what were thought to be possible settings for German torpedoes which were deemed equivalent to British 21-in Marks V and VI.^[14]

Otherwise, the Type B was nearly identical to the Type A, adding just one more bar.^[15]

The Avoiding Bar

The new bar, called the Avoiding Bar, was pivoted on a slider free to slide along the base line. It was marked in "time in minutes" for a given speed of attacking torpedo, with zero being at the pivot. The slider for the avoiding bar had a fixed semi-circular graduated disc that could be read off a pointer on the bar in either degrees or compass points.

The design was such that when the avoiding bar's slider was moved to the center of the torpedo circle in question and aligned to point to where the position bar crossed the torpedo circle, it was then parallel to the torpedo track and the pointer would show how many points the target would have to turn, and in which direction, to comb the torpedo track if it were fired at that moment. The avoiding bar's pivot slider could then be slid until it meets the position pointer, and the running time in minutes of the torpedo read off.

The "B" augmented the functionality of the "A" by permitting these defensive problems to be illustrated:^[16]

• are we within range of enemy torpedoes?
• if so, what course change is sufficient to cause them to fall short?
• what is the track angle of the enemy's torpedo, in case I want to comb the wakes?
• how long until his torpedo crosses my track?

Determine if we are within range of the attacker's torpedoes

This is the same as the first attack problem illustrated on the Type A above if we apply our own speed to the target ship and align the position bar to the enemy bearing.

Determine a course change that will allow us to draw out of range

This could be easily worked by setting the instrument as above. One would then swing the position bar until the position pointer fell outside of all torpedo circles. The bearing the position bar now indicates is the bearing one must place the attacker on to place him out of range at the present moment. Another way of stating this is that the angle you have to adjust the position bar to place the attacker outside the torpedo circle is the angle you must turn away from him.

Determine the track angle of the attacker's torpedo

The prospect of choosing to comb the wake of an incoming torpedo requires one to understand that, referring to Figure III at the top of the page, that the torpedo has to travel along the line XE.

Special note was drawn to the observation that a torpedo at a track angle of 90 degrees which was 500 yards distant could not be avoided by use of the helm.^[17]

Determine how long until the torpedoes cross our track

Referring to Figure III at the top of the page, if the torpedo is fired from point O, the running range of the torpedo is the length of line OT. If we divide this length by the running speed of the torpedo, we will determine the torpedo's time-of-flight.

Renouf Type B Example^[18]
Example

If we consider the example image:

• enemy destroyers are plotting at 14,000 yards, bearing 40 degrees
• the enemy is equipped with a torpedo that can travel 15,000 yards are its 25 knot setting
• avoiding bar's pivot is slid to the center of the appropriate torpedo circle and rotated to where the position bar crosses the torpedo circle
• the avoiding bar indicates a turn of 6 points toward the enemy will comb the torpedo track
• the avoiding bar is then slid along the base line to the dotted position when it crosses the position pointer and indicates it will take 11 minutes for the torpedoes to reach our track

Attack by multiple ships^[19]
Example

"F Type" for Flagships

Renouf Type F^[20]
Shown the "Course to Steer" fittings in place.

This was for use in flagships, and was the most complex model, as it was oriented toward torpedo attack and defence not at the ship level, but the level of a division, a squadron, or even three squadrons. It could also help identify, from the perspective of the fleet being considered, safe and unsafe arcs for one's own torpedo fire.^[21]

The device had 3 sets of fitting supplied:

• "Course to Steer" fittings to perform all functions of the Type B
• "Squadron" fittings (which included the avoiding bar) for attack and defence of a division, squadron, or 3 squadrons
• "Own Torpedo" fittings to deal with hazards posed by friendly torpedoes

The Type F's torpedo circles were worked independently from one another, not together as in Types A and B. Its base line ran down the centre of the base plate, essentially doubling the size of the instrument and allowing threats from the starboard to be depicted naturally.

"Course to Steer" Fittings

The device could work a new problem (in attack and defence forms) over the Type B when the fleets were on converging courses, namely "how long before attacker is in position to fire?"^[22]

The process was as follows:

• Advance torpedo circles to speed of target fleet
• Set attacker range on the position bar
• Set attacker direction by his bearing (on defensive problems) or by the target's inclination (on attack problems) on position bar
• Place desired track bar to course of attacker
• Set resultant track bar pivot to speed of target fleet
• Place "Course to steer" bar parallel to desired track bar
• Turn resultant track bar so its reading edge cuts speed of attacker on the "course to steer" bar
• Read off time to run 1,000 yards on resultant track bar
• Turn desired track bar parallel to resultant track bar and read off range to run on resultant track bar to reach the pertinent torpedo circle
• Multiply time to run 1,000 yards by this range to run to determine how long before attacker is in torpedo range

"Squadron" Fittings

Renouf Type F^[23]
Shown with "Squadron" fittings in place.

Fleet Bar

This bar is depicted in magenta in the figure and can slide and rotate through a pivot fitted on the central base line of the instrument. "It is graduated in thousands of yards each way, which divisions represent the space occupied by two ships in line."^[24]

Position Bar

This is depicted in orange in the figure, and is graduated in thousands of yards. Rather than pivot on the central base line, its pivot is on the sliding fleet bar. The position pointer is the pivot point on which rides the squadron bar. A second, simpler slider located nearer the hub is called the destroyer position pointer.

Squadron Bar

This is depicted in magenta in the figure and is pivoted on the destroyer position pointer which in turn rides on the position bar. "It carries three small bars on the underside, each of which represents a squadron of eight ships. Each squadron is pivoted at the leading ship..." This arrangement permitted the squadron bar and its underslung 3 squadrons (depicted as white lines in the illustration) to be arranged in any manner relative to the primary pivot on the base line.

History and Deployment

Unknown [TO BE CONTINUED - TONE]

See Also

Footnotes

Bibliography