Submarine Taniwha - Design Report

New Zealand’s ﬁn driven, human powered submarine 2015

Prepared by: Ben Pocock, Gerrit Becker, Christopher Walker, Sanjay Surendran, Alex Cashen, Jonathan Chaplow, Andreas Tairych, Iain Anderson Contents

1 Scope 1

2 Introduction 1

3 Background 2 3.1 Inspiration ...... 2 3.2 History ...... 3 3.3 Design Philosophy ...... 3 3.4 Knowledge Retention ...... 4

4 Submarine Systems 4 4.1 Overview ...... 4 4.2 Hydrodynamics ...... 6 4.3 Hull and Chasis ...... 8 4.4 Nose cone ...... 9 4.5 Control Surfaces ...... 10 4.6 Control Mechanisms ...... 13 4.6.1 Elevator Hydraulic System ...... 13 4.6.2 Rudder Hydraulic System ...... 14 4.6.3 Feedback Mechanisms (Detent) ...... 14 4.7 Buoyancy Control ...... 16 4.7.1 Electric Pump System ...... 16 4.8 Propulsion ...... 17 4.8.1 Fin Design ...... 17 4.8.2 Pedals ...... 19 4.9 Pilot ...... 19 4.9.1 Egress ...... 19 4.9.2 Ergonomics ...... 20 4.9.3 Air Supply ...... 21 4.10 Safety ...... 22 4.10.1 Emergency Pop-Up Buoy ...... 22 4.10.2 External Facing Pressure Gauge ...... 24 4.10.3 Hatch Attachment ...... 24 4.10.4 Strobes ...... 25 4.10.5 High Visibility Mohawk ...... 26 4.10.6 Foot Restraints ...... 26 4.11 Electronics ...... 26 4.12 Trolley ...... 27 5 Preparation and Procedures 28 5.1 Testing ...... 28 5.2 Team ...... 29

6 Conclusion 30

7 Future Work 30 7.1 Automated Ballast System ...... 30 7.2 Novel Drag Reduction ...... 30

8 Appendix 31 8.1 Taniwha Photos ...... 31 8.2 CFDImages ...... 33 Taniwha Design Report 2 INTRODUCTION

1 Scope

This document outlines the design and development plan for the human powered submarine Taniwha. It also provides information on the team’s motivation to compete in the International Submarine Races and some of the non-technical challenges associated with the project.

2 Introduction

The submarine Taniwha is a single person, human powered, wet submarine. It was built in the Biomimetics Laboratory of the University of Auckland and has the privilege of being the only Southern Hemisphere competitor in the ISR. The team consists of undergraduate and PhD students, post-doctoral researchers and academics from around the university. The project started as part of a wider goal to advance the field of underwater human movement and first competed at the European International Submarine Race (eISR) in 2014. Thrust is provided by pedal driven fins mounted to the top and bottom of the submarine, inspired by the Leatherjacket fish (Parika Scaber). Innovations in Taniwha includes the following advances and features:

1. A very thin (approximately 2.5 mm) hull - With such a thin hull the entire submarine (minus scuba bottles) can be carried by 2 people.

2. Screw attachment of the two part hull - The screw attachment allows quick and easy hull removal for access to the internal chassis. With this feature all major submarine systems can be easily altered or upgraded.

3. Adjustable ballast trim - A motorized constant volume ballast adjustment system can move up to 2 kg of water fore or aft; a useful feature for ﬁne trimming and for diving the sub downwards or steering its nose upwards from the bottom.

4. A coupled double Hobie Mirage ﬁn drive - The pilot, with one pair of feet can operate two ﬁn sets that are coupled to work synchronously.

5. Hydraulics - Dive planes, rudder and safety buoy are controlled using hydraulic actuators.

6. A push-out nose cone - This added safety feature allows the pilot emergency escape through the front of the submarine. The nose cone, attached to the hull front using magnets with locator pins, can be pushed oﬀ from the inside.

1 Taniwha Design Report 3 BACKGROUND

3 Background

3.1 Inspiration

Although we can stay underwater with an aqualung for about an hour or so we are greatly impeded by our low speed and lack of manoeuvrability. A diver’s top speed is about 1 m/s [1], quite slow when in tidal currents that can exceed 3 m/s and very slow compared with marine mammals such as the Bottlenose dolphin that can swim up to 6 m/s [2]. We are held back by limited muscle-power, a land-based physiology and the high drag that our bodies and equipment create. Our dream is to produce a human-powered submersible that will augment our ability to swim and overcome these issues. Our human-powered submarine Taniwha represents our first “fin-kick” in this direction. Taniwha is driven by fins, like its Polynesian namesake, a mythical malevolent water spirit in the shape of a large fish. Fish use their fins for several functions: clearly they provide propulsion but can also be folded back for gliding, and used for steering and braking. They impart great manoeuvrability en- abling navigation in close proximity to rocks and weed. There is no need for a gearbox; the action is direct from the limb to the fin. If we were like fish we would be able to move around effortlessly, feeling and responding to minute pressure changes in water [3] and sending it back- ward in an efficient way. Propellers are also efficient but it would be virtually impossible to match the manoeuvrability of fish and the multi-functionality of the fin with a propeller driven craft. It would also be impossible to feel the water through a gearbox. The successful deployment of a fin driven sub is clearly a far-reaching goal and we are no where near doing this yet. We are starting our exploration using our submarine.

Taniwha’s fin configuration is inspired by the NZ Leatherjacket (Parika scaber): a triggerfish that uses wave-like ripples along dorsal and anal fins to create thrust for manoeuvring and forward swimming. They steer with a tail that acts like a rudder (Fig. 1). We have not attempted to mimic the wave-like ripple of the Leatherjacket but we have arranged human powered fin propulsors in corresponding positions on the top and bottom surfaces.

2 Taniwha Design Report 3 BACKGROUND

Figure 1: A young New Zealand Leatherjacket (Parika scaber). Swimming thrust is developed from wave-like movement of the dorsal and anal ﬁns with the tail acting like a rudder. (Photo: I. Anderson)

3.2 History

Work on Taniwha 1.0 started in mid-July 2013 in preparation for the 2nd European Interna- tional Submarine Races to be held in Gosport UK, July 2014. The hull design evolved from the geometry of a 3 m long streamlined solid of revolution model that was tested in the David Taylor Model Basin at Carderock Maryland [4]. The design philosophy of Taniwha 1.0 was to maximise manoeuvrability by having large control surfaces. The elevators were positioned forward of the centre of gravity to mimic pectoral ﬁns. This did provide excellent manoeuvrability but caused a positive feedback loop and instability at higher speeds. The ensuing collisions also caused breakage of some key components making the submarine more diﬃcult to control. Despite this, Taniwha was awarded the eISR trophy for ”Best Non-propeller Performance”.

3.3 Design Philosophy

From the experience gained at eISR a new design philosophy has been developed. For the 2015 preparations reliability and simplicity have been encouraged. Reliability is achieved by designing failure modes, building fail-safes and frequent testing. Design decisions were mostly

3 Taniwha Design Report 4 SUBMARINE SYSTEMS based on qualitative analysis and empirical data rather than stringent quantitative design. Quantitative analysis has its place and was used where appropriate. This combination allowed for rapid innovation and ensured the development was in-line with the actual goals. An example of the design philosophy is the rudder; CFD and other quantitative methods were used to find the most efficient shape for the rudder. A larger rudder gives more turning force, but the magnitude of force actually required was unknown. Therefore the correct size of the rudder, required to sufficiently change the submarine’s trajectory, had to be determined empirically through testing.

3.4 Knowledge Retention

The first step in preparing for ISR 2015 was to ensure that all of the knowledge gained and lessons learned from building Taniwha 1.0 were retained. The nature of a university based project is to have a high turnover of people. If not properly managed this can easily result in a loss of knowledge from year to year. In an effort to combat this, several protocols have been created. The submarine team is part of a wider society of students and staff with interests in underwater engineering; this broadens our shared knowledge base. Each system that is developed is documented with special sections for lessons learned and results from tests of designs that did not make it into the final product; this limits duplicated effort. At the beginning of each development cycle new team members are introduced to past members and a proper hand over takes place.

4 Submarine Systems

4.1 Overview

The submarine has been designed for rapid development and as such is inherently modular. Most of the sub-systems attach to chassis which is able to be completely removed from the hull.

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Figure 2: a: Nose cone, b: Chassis, c: Control Handles d: Main Air Supply, e: Hull, f: Front Ballast Tanks, g: Main Hatch, h: Drive Mechanism, i: Safety Buoy and Safety Boy Release, j: Rear Ballast Tanks, k: Rudder, l: Elevators and Stabilisers.

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4.2 Hydrodynamics

The hydrodynamic forces are created by the relative movement of the submarine and the ﬂuid it operates in. Detailed explanations of the principles of hydrodynamics are beyond the scope of this report but it is important to discuss the main points that guided the development process. The major forces acting on Taniwha are shown in Fig. 3. Inertial forces are not shown.

Figure 3: Free Body Diagram showing coordinate system and forces acting on the body. FD : Dragforce, FH z : Bodylift, FH y : Bodyturningforce, FB : Buoyancyforce, FG : F orceduetogravity, FT 1andFT 2 : T hrustforce, FS : Stabiliserforce, FE : Elevatorforce, FR : Rudderforce.

The weight and buoyancy are not dynamic forces but are just as important. It is well established that the buoyancy force works in the opposite direction to gravity and is equal to the weight of the displaced fluid. The weight force is simplified to a single force acting at the centre of mass distribution known as Centre of Gravity (CG) and is equal in magnitude to the sum of all of the weight components. The buoyancy force is similar but acts at the centre of volume distribution called the Centre of Buoyancy (CB) and equal in magnitude to the volume of displaced fluid multiplied by the fluid density and the gravitational constant. It may not be immediately obvious what constitutes displaced fluid in a wet-Submarine. One could argue that the fluid contained within the submarine hull is not displaced when the submarine is static. However, when considering the contained fluid in a moving submarine there will clearly be a separation of the contained fluid and the surrounding fluid. For this reason, despite the fact that the contained fluid is neutrally buoyant, it must be considered in the buoyancy and weight force components. In the real case there will be additional fluid that is set into motion around the outside of the submarine and some of the contained fluid will flow

6 Taniwha Design Report 4 SUBMARINE SYSTEMS through the openings (joints, drain hole, etc.) but these variances are considered negligible at this stage. Qualitatively the aim of the weight/buoyancy relationship is:

• Neutral buoyancy, weight force equal to buoyant force. This is to prevent the submarine drifting in the z-direction and minimises the force required to maintain desired depth.

• CG should be directly below CB. This is the only stable position for a submerged body because any displacement in the x- or y-directions will cause a moment that will rotate the body. If CG was directly above CB the body would not rotate but a small shift would create a moment that would eventually invert the body.

• The strength of the static righting moment increases as the magnitude of the forces increases

• The strength of the static righting moment increases as the distance between CG and CB increases.

The driving force is provided by the Hobie Mirage drives located at the top and bottom; see section 4.8 for more details on the propulsion mechanism. Having similar drives arranged this way means that the force provided in the x-direction by the top drive creates a positive moment on the body, the force created in the z-direction by the top drive creates a negative moment on the body; the bottom drive gives the opposite results. The magnitude of the resulting moment is dependent on the drive phase, acceleration of the body, relative velocity of the drive to the coupled ﬂuid and how accurately balanced the drives are. This makes it a complex reaction that is likely to cause instability if additional control measures are not implemented. The guiding qualitative design principles are:

• Match drives as accurately as is feasible to minimise destabilising moment

– By coupling directly together to match phase – Similar drives

• The drives should be equidistant from CG with one above, one below and both behind.

During testing it was found that if the submarine gets too close to the top or bottom surface the edge eﬀects were signiﬁcant enough to cause the submarine to turn into that surface. The

7 Taniwha Design Report 4 SUBMARINE SYSTEMS boundary effects decrease the efficiency of the drive that is near the surface, decreasing the moment on the body allowing the opposite drive to become dominant. The effected zone has been measured at approximately 300mm from the drive’s zenith. The issue is overcome by the dynamic stability provided by the elevators. As discussed below the stability provided by the elevators is proportional to the fluid velocity so the edge effect phenomenon is usually only an issue during launch and is therefore easily compensated for by using proper launching technique. Of course the edge effect is also proportional to distance to the boundary so it is still advisable to stay clear of the surfaces. For this reason the submarine requires additional equipment to get away from a surface in the event of a breach or bottom hit.

4.3 Hull and Chasis

The geometry of the hull was based on one of the models studied as a potential post-WWII attack submarine design [4]. The low length to diameter ratio of Model 4154 met transport space constraints while maintaining a low surface area body. The model was a solid revolution so the aft portion of the was modiﬁed to smoothly transition into the rudder (Fig. 4).

Figure 4: The raw shape of the hull used to make the mold.

The submarine structure contains a separate hull and chassis to allow for a high level of cus- tomisation and development. The hull is made of 2.5mm epoxy – glass fibre composite, moulded using a vacuum infusion process. The technique allows for higher fibre content in the composite by more effectively infusing the epoxy resin. In turn this increases specific strength and lowers the chance of brittle failure. The mold for the hull was created on a five axis CNC-mill by

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Jackson Electrical Industries, the vacuum infusion equipment was provided by the Centre for Advanced Composite Materials (CACM) of the University of Auckland. The chassis is built primarily from marine plywood sealed with epoxy resin. The purpose of the chassis is to provide mounting points for the equipment rather than to add stiffness to the hull which is already sufficiently rigid. Therefore the light weight, easy to work with and already water proofed marine ply is an appropriate building material. The hull is molded in two pieces, split along the top and bottom longitudinal lines. The starboard half is bolted to the chassis, the port half is connected only to the other section of hull. This allows for easy access to the submarine’s internals for development, repair and maintenance. Additional access is possible through the hatch in the port quarter. This hatch is magnetically attached and is designed to allow easy access to the hydraulic control system. A transparent acrylic nose cone forms the front portion of the submarine, giving the pilot an unobstructed view. A drain hole has been cut in the lowest portion of the hull to allow water to escape as it is lifted from the water. The 110 mm diameter hole has proven to be sufficiently sized. The major dimensions of the hull are: 3073 mm long, 1340 mm tall with drive fins fully extended, 693 mm tall without drive fins and 860 mm wide.

4.4 Nose cone

The nose cone forms the front portion of the submarine and is made of clear acrylic. It was vacuum formed over a positive mold with the same profile as the original model. The nose is sufficiently sized to give external divers full view of the pilot’s head. The nose is attached by friction pins and magnets which allow for its removal without release handles (Fig. 5). The magnets are used to relocate the main attachments if they become dislodged. The mounting faces of the connectors are shaped to match the profile of the hull and nose cone. The complex geometry of the connectors is made possible by 3D printing. The space vacated by the removed nose is large enough to extract the pilot in an emergency and is the quickest way to access the pilot’s head. This has been experimentally confirmed. In 2014, Taniwha had a hemispherical nose which was one tenth of the cost of the large hydrodynamic cone currently used. An analysis of the effect on the drag co-coefficient shows a reduction of 17.5% with the new nose (Fig. 6).

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Figure 5: The male connector (blue) is bolted to the nose cone and friction ﬁts into the rubber grommet (black) mounted in the female connector (green) which is bolted to the hull. Each connector has a magnet (grey) built in.

Figure 6: Left: Pressure proﬁle on hemispherical nose cone. Right: Pressure proﬁle on hydrodynamic nose cone

4.5 Control Surfaces

The control surfaces of the Taniwha consist of stabilisers and elevators on each side of the submarine as well as a rudder in the back. The stabilisers are ﬁxed horizontally at the rear

10 Taniwha Design Report 4 SUBMARINE SYSTEMS quarters of the submarine; they create a moment that restores the pitch angle if it is offset. Early testing proved that if the whole surface rotated then the lift created at small control angles would cause the pilot to over-correct. However if the size was reduced then the self righting moment was insufficient. The solution is to split the control surface into a fixed stabiliser and a rotating elevator. The elevators are mounted directly behind the stabilisers and are controlled by the pilot to steer the submarine in the vertical direction. CFD analysis was performed to determine the most effective proportions for the two sections. To be effective the stabilisers must create a stronger moment, and in the opposite direction to, the body lift force. The stabilisers and elevators are both part of a single NACA-0006 profile. The NACA-0006 profile was chosen because, at typical Reynolds numbers, it has low efficacy at small angles which will prevent small alignment errors from causing stability issues; note the low gradient between -2o and 2o in Figure 7.

Figure 7: Lift coeﬃcient versus control angle at 2 m/s

The stabilisers are connected to the submarine by a system of aluminium tubes and u-proﬁles. To allow for easy attachment of the ﬁns, two 20x20 mm bars are glued in the center of the wood.

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These can be easily slid on to the 16x16 mm bars protruding out of the submarine and locked with bolts. A single bar runs through the back of the submarine connecting the stabilisers on both sides of the submarine to increase stability. The elevators can be rotated by ±10◦. The rotation is initiated by a hydraulic system connected to the control handles in the front of the submarine and an aluminium bar connecting the two elevators in the back of the submarine (Fig. 8).

Figure 8: Attachment of the control surfaces. Left: left and right control surfaces connected by an aluminium bar, right: Cross-section of one elevator and the mounting bars

The rudder in the back has a drag reducing NACA-0006 profile modified to be compatible with the location. The submarine shape is also modified in the back in order to allow for simple attachment of the rudder. All control surfaces are made of solid marine plywood. They have been manufactured by milling the wood into approximately the correct shape, then sanded to the correct profiles. These are covered with epoxy resin to prevent water from penetrating the wood. Finally the epoxy layer has been painted.

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Figure 9: Milling the control surfaces. Left: milling the rough shape of the elevators, right: milling slots for aluminium bars to mount stabilisers to the submarine

4.6 Control Mechanisms

4.6.1 Elevator Hydraulic System

The water ﬁlled elevator hydraulic system consists of a hydraulic cylinder that connects to an arm that is clamped around a shaft that rotates the elevators. The system is tuned to rotate the elevators 10 degrees either way of the neutral position as this is the stall angle for these surfaces. The hydraulics, control arm, shaft and bearing mounts are all built in a single unit (Fig. 10) to limit relative movement and therefore maximise control accuracy. By having a self-contained unit the system could be designed and evaluated while outside the submarine and during the actual making of the system allowing pool testing to continue on the other systems. The shaft is machined at each end to constrain rotational alignment from left to right; misalignment here would induce roll. The elevators are removable from the shaft to make shipping easier and enable design iterations. The shaft is attached to the hydraulic piston by a solid aluminium arm that uses two bolts and an aluminium plate to clamp around the shaft and hold it at a constant position. This system allows for tuning of the elevator’s neutral attack angle.

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Figure 10: The hydraulic cylinder acts on the lever which is clamped to the shaft and turns the elevators.

4.6.2 Rudder Hydraulic System

The water filled rudder hydraulic system utilises a hydraulic cylinder connected to the rudder by a fixed length aluminium arm (Fig. 11). The arm orientation is fixed at the cylinder side but free to pivot at the rudder end. The rudder itself pivots about the frame and has a connection that emerges at a right angle from the rudder. This means that the rudder will rotate about the frame pivot if the arm moves and the arm can only move if the cylinder stroke changes. The hydraulic cylinder has a limited stroke meaning that it was possible to constrain the rotation of the arm. As with the elevators, the rudder turns only as far as the stall angle as determined by a CFD analysis.

Figure 11: The hydraulic cylinder acts on the jogged rod pushes/pulls the rudder lever. The push rod is jogged to clear other components in the submarine.

4.6.3 Feedback Mechanisms (Detent)

The control surfaces are driven using hydraulic master-slave cylinder systems. After changing course, it is essential for the pilot to quickly return the control handles on the master cylinders

14 Taniwha Design Report 4 SUBMARINE SYSTEMS back into their neutral position. Mechanical detents are ﬁtted to the slave cylinders to provide the feedback necessary for this action. When the pilot moves the control handles back into neutral position, a spring loaded pin is pushed into a corresponding groove in a plate, and locks the slave cylinder into position. From this position a certain force has to be applied to the master cylinders if the pilot wants to move the control surfaces out of neutral again. Similar mechanisms are used to lock control spools in manually actuated hydraulic valves into position. To avoid oxides building up in the clearance between the block and the pin, all components were made from stainless steel and plastic. To remove detent parts for repair work, none of the hydraulic control components have to be disassembled. Slotted- or oversized holes allow for alignment with the hydraulic controls. Figures 12 and 13 show the detent systems for the rudder and elevators respectively.

Figure 12: The rudder detent’s grooved plate (green) is attached to the slave cylinder body (not shown). The block containing the pin (white), spring and adjustment screw (blue) is mounted to an arm connected to the cylinder rod.

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Figure 13: The elevator detent assembly is attached to the chassis while the grooved plate (green) is mounted to the rudder hydraulics. Tension adjustments are made with the adjustment screw (blue).

4.7 Buoyancy Control

Taniwha is designed to be close to neutrally buoyant when the ballasting systems are not installed. Closed cell foam blocks and lead weights are used to create a stability moment as discussed in section 4.2. Tuning done with these elements is coarse and cannot be altered quickly. A specialised system is used for ﬁne tuning of the submarine’s trim.

4.7.1 Electric Pump System

The constant volume trim system is made of tanks positioned fore and aft which are partially filled with water. Electric pumps move the water between the tanks, air is displaced in the opposite direction through bleed tubes in the top of the tanks resulting in a shift of the center of mass (Fig. 14). Pumping is done by two 70 W, 12 V-DC diaphragm pumps controlled by an On-Off-On rocker switch located within reach of the pilot. The pumps are powered by a 9.6 V-DC, 3300 mAh power supply to bring the volume flow rate to a useful range. The start up current draw of the pumps is 7.3 A. However, under normal operating conditions a draw of 2.3 A is expected. With the assumption of satisfactory draw for the first 80% of battery charge expected run time is 69 minutes of continual use. The switch was sealed in epoxy resin, to prevent water flowing into the circuit. The control

16 Taniwha Design Report 4 SUBMARINE SYSTEMS box is rated IP-68 with additional seals on the cable glands.

Figure 14: A schematic of the trim adjustment system

4.8 Propulsion

Drive force is created by matching pairs of Hobie Mirage drives mounted to the top and bottom of the submarine. The drives are designed by Hobie for pedalling kayaks and have been modiﬁed to suit Taniwha. In keeping with the Taniwha design philosophy these drives provide environmental feedback and intuitive control by having minimalistic mechanisms between the user and the ﬁn.

4.8.1 Fin Design

The drives work by moving the stiff leading edge of the fins in a reciprocating arc motion. The resistance of the water causes the fins to flex; the deformed shape creates a lift force which provides thrust as demonstrated in Figure 15. Due to the arc motion of the fins the tip is travelling significantly faster than the base so this is where most of the force is generated. Taniwha uses the Hobie ST Turbo Fins. These fins are longer and have a different foil geometry to the standard fins and have proven to be more effective. The optimum fin stiffness can be found by applying Blade Element Momentum theory and computer simulation (Fig 16), verified by testing.

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Figure 15: The fin deflection can be seen as the pilot starts to take off

Figure 16: ANSYS modelling shows the deflection of the drive fins and the fluid velocity profile as the drives pass though the zenith

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4.8.2 Pedals

The Hobie drives facilitate a stepping motion which is more ergonomic than cyclical motion which would require a larger vertical area within the submarine. This would restrict the use of space around the pedals as well as require additional leg room for the pilot. With tight size constraints this would not be ideal. Furthermore with rotational motion a dead zone exists where input force is not eﬀectively transferred into torque (Fig. 17) [5]. Due to this phenomenon only one third of the muscle power is eﬀectively used. Comparatively, coupled linear motion, as used on the Hobie Mirage drive, produces 50% thrust with each pedal cycle.

Figure 17: Resultant force versus angle for constant input force[5].

The position of the pedals relative to the pilot is important for safety and eﬃciency. The majority of the leg’s muscle power develops when it is almost fully extended. The pedals can be adjusted to accommodate each pilot to improve performance and prevent hyper-extension of the leg.

4.9 Pilot

4.9.1 Egress

The pilot has two points of egress (Figure 18). The main exit channel is through the hatch located at the top of the submarine. This is the largest transit point allowing the pilot to

19 Taniwha Design Report 4 SUBMARINE SYSTEMS exit/enter either foot first or head first depending on preference. The second point of transit is through the transparent acrylic nose cone located at the front of the submarine. The nose cone attachments (Fig. 5) show a grommet and magnetic system allowing the structure to be pulled off without the need for a more permanent securing. The evacuation process for emergency divers is outlined below:

1. Unpin the latch by pulling the orange tether. Pull the tether to lift oﬀ the hatch. Emer- gency divers will now have access to the back and legs of the pilot

2. The pilot’s head can quickly be accessed by removing the nose cone. The nose cone is removed by pulling it away from the hull. This is especially useful if the pilot has consumed all of their air.

3. The pilot is not attached to the submarine, however his feet are slipped into straps of the pedals and his arms are placed through shoulder straps. These straps will automatically disengage if the pilot is pulled or moves toward the hatch although care should be taken to prevent entanglement. Once the pilot’s feet and shoulders are free the pilot can be pulled out through either egress point.

Figure 18: Emergency Exits in the Taniwha

4.9.2 Ergonomics

The pilot wears an H-Bomb wetsuit donated by Ripcurl. This is a 3 mm surfing suit designed for both flexibility and warmth. The notable manoeuvrability stems from the use of E3 neoprene, the lightest and most flexible neoprene commercially available. 3 mm thickness limits the amount of compression at depth, giving the pilot a higher level of stability relative to a 5 mm

20 Taniwha Design Report 4 SUBMARINE SYSTEMS or 7 mm suit. Titanium backing which houses two heating elements allows the user to dive in environments typically too cold for a standard 3 mm wetsuit. The heating elements are powered by interchangeable batteries contained in the suit and should supply 2 hours of continuous heat. Shoulder straps have been installed for the pilot to push against while pedalling. Both hands of the pilot are used for control. The straps are attached internally to either side of the hatch and extend over the shoulders of the pilot down to below their waist where they are attached to the chassis. Ergonomic handles were made to suit the pilot by the method described in section 4.10.1.

4.9.3 Air Supply

The pilot has access to two separate breathing systems within the submarine: a 5.75 litre main tank and a 2.75 litre pony bottle. The pony bottle with regulator is used as a back-up and can be clipped onto the pilot. During setup and ballasting the pilot can source air from support divers to save the submarines supply speciﬁcally for racing. The regulator assembly attached to the 5.75 litre aluminum tank includes 2 pressure gauges: one within easy view of the pilot and one that can be viewed from the outside by the supporting divers (see section 4.10.2). The submarine tanks have been hydro-statically tested within the last few months prior to the race; the regulators, BC’s and tanks have also been inspected before shipping to the race. Regulators used by the support divers all have a back-up 2nd stage for use by a buddy with a pressure gauge attached to the high pressure port. All regulators are subjected to an annual check-up by a qualiﬁed repair/maintenance technician. Tank Main Spare Make Catalina S40 SP12. TC-3ALM204 Catalina S19 SP12. TC-3ALM204 Manufature Date Dec. 2012 Dec 2012 Working Capacity 5.76 litres 2.72 litres DOT 3A12957 3A12957

Testing has demonstrated that the 5.75 litre supply is fully adequate for the race. Based on an oxygen consumption rate of 2.1 litres/min (measured on experienced divers subjected to moderate exercise) [6] 11 litres/min of air would be required. The submarine bottle has a cubic capacity of 1132 litres (40 cu ft at 3000 psi). With a requirement of 50 Bar remaining (286 litres)this gives about 76 minutes at moderate exercise. Metabolic rates can be double or greater at higher levels of exercise (measured on treadmill and bicycle) [7]. This gives an

21 Taniwha Design Report 4 SUBMARINE SYSTEMS expected usage of 22 litres/min or 38 minutes of tank time. Exhaust air exits through strategically placed holes in the submarine. Additionally there is a small gap between the nose cone and the hull where exhaust air can escape.

4.10 Safety

4.10.1 Emergency Pop-Up Buoy

In line with the race rules Taniwha has a buoy which deploys when the pilot releases a dead- man switch. The trigger for the buoy is a spring loaded button on the rudder control which the pilot holds down with his thumb. The button is connected to a hydraulic cylinder which drives the buoy’s release mechanism (Fig. 19). The default position of the release mechanism is to release the buoy ensuring that any fault in the system will cause deployment. When released the buoyancy of the buoy causes it to accelerate toward the surface, bringing with it a 10 meter, brightly coloured, ﬂoating tow rope. This tow rope is stored on a reel mounted to the submarine chassis directly below the safety buoy. The reel is mounted securely enough to allow the submarine to be lifted by the tow rope.

Figure 19: Safety Buoy and release mechanism

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To make the ergonomic handle a mold of the pilot’s hand was taken using modeller’s clay, the mold was then digitised and 3D printed in PLA thermoplastic. Provisions for the trigger hydraulics were modelled in before printing (Fig. 20).

Figure 20: left: The safety buoy trigger is made up of a small hydraulic cylinder inside an ergonomic sleeve (black) with a button (red) attached to the piston.) Right: A cross section view of the handle, button and trigger hydraulic.

The latch is operated by another water ﬁlled hydraulic cylinder connected in parallel with the trigger cylinder. As the trigger hydraulic extends, the latch hydraulic retracts. The buoy is restrained by a sliding latch plate with key holes which interface with T-shaped locks on the buoy (Fig. 21). When pressure on the trigger is removed the latch spring (Figure 21 green) causes the hydraulic to retract and the latch plate slides toward the front of the submarine, moving the open section of the key slot in line with the T’s, thereby releasing the buoy.

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Figure 21: left: The safety buoy is locked by the latch plate (red) engaging the tabs (blue) right: The safety buoy is released

4.10.2 External Facing Pressure Gauge

An outward facing pressure gauge allows support divers to monitor the pilot’s air supply. The gauge is attached to the pilot’s ﬁrst stage by an extra long hose which runs to the top, port corner of the nose cone. The main pressure gauge runs to the control panel in clear view of the pilot.

4.10.3 Hatch Attachment

A Clip-on-System has been developed for easy attachment and removal of the hatch. On one side of the hull, the system consists of two bolts attached to the hatch itself. These can easily be inserted in slots on the submarine’s side of the connection (Fig. 22). The other side of the hull has a detent system. The detent is placed on the inner side of the submarine’s hull. The female adapter of the system is mounted to the inside of the hatch (Fig. 23).

24 Taniwha Design Report 4 SUBMARINE SYSTEMS

Figure 22: One side of the hatch clip-on-system. Bolt (yellow) that is inserted in the slot (green). Both attached to the inside of the hull and the hatch (grey)

Figure 23: Cross-section of the detent system. Detent (blue) can be moved inside the detent mount (yellow) and clipped into the female adapter (green). Holding force is applied by a spring (orange). Detent mount and female adapter are both connected to the inside of the hull and hatch (grey)

4.10.4 Strobes

Strobe lights are mounted to the top and bottom to increase the visibility of the submarine. The strobe is USCG approved, with an expected battery life of 20 days. The location of the strobes ensures the ﬂash can be seen from 360 degrees, above and below.

25 Taniwha Design Report 4 SUBMARINE SYSTEMS

4.10.5 High Visibility Mohawk

The top of Taniwha has a white stripe to increase the visibility in low light conditions. The main colour scheme is matte black so the teeth decals and Mohawk are white for maximum contrast and visibility.

4.10.6 Foot Restraints

The pilot’s feet are restrained by slip in straps. The restraints do not clip in so the feet can just slip out during exit or in an emergency. This feature has been tested during the emergency evacuation drills. See section 4.9.1 for the emergency evacuation procedure.

4.11 Electronics

In addition to all the mechanical features of the submarine, electronic components where added in the submarine for this year’s race. Being inside the submarine with a very limited field of view, it can sometimes be difficult for the pilot to judge the direction, tilt angle and the current position of the elevators and fin. Therefore an electronic sensory unit has been implemented providing the pilot with all necessary information. The unit consists of a tilt sensor, a sensor for the current elevator state and a safety buoy deployment light (Fig. 24).

Figure 24: left: display showing the current tilt angle of the submarine and the elevator state, right: electronics unit consisting of a: display unit, b: battery compartments, c: waterproof connection for sensor attachment, d: tilt sensor mounted to bottom nose cone connection

26 Taniwha Design Report 4 SUBMARINE SYSTEMS

The tilt sensor that has been developed is using a 3-axis-gyroscope to determine the current tilt angle of the submarine. To reduce signal noise as well as the influence of acceleration, the raw values are being manipulated by a running-mean filter. The calculated tilt is being displayed in the cockpit as positive or negative degrees. While the elevators already have a feature to slightly lock them in the centre position, a second system has been implemented to show the current elevator state in the cockpit. This electronic unit uses Light Dependant Resistors (LDRs) to accurately measure the current elevator position. A third electronic unit is a simple switch connected to the dead man system controlling the emergency buoy. This switch turns on a warning light in case the safety buoy is accidently being deployed. Overall, these newly designed features provide a simple feedback of the submarine’s current position to the pilot. The unit is powered by 3 Trustfire batteries supplying an output voltage of 10 V.

4.12 Trolley

Transporting a three metre long submarine requires a stable and robust trolley. The design, pictured in Figure 25, is an aluminium box structure with padded adjustable supports for holding the submarine.

Figure 25: Aluminium trolley holding the submarine at the 2015 NZ Hutchwilco Boatshow

27 Taniwha Design Report 5 PREPARATION AND PROCEDURES

The aluminium box openings allow the structure to be ﬁlled when submerged in water. This reduces the buoyancy ensuring the trolley will sink when loading the submarine into the pool. Four wheels with 360o freedom allow a high level of manoeuvrability. This is especially useful when navigating through narrow corridors and around sharp corners.

5 Preparation and Procedures

A stringent testing and training regime has been vital to give Taniwha the best opportunity at the 2015 ISR. Thorough testing is essential for the development style employed by the team.

5.1 Testing

Weekly testing ensured all participants in the Taniwha team had comprehensive experience underwater with the submarine. A minimum of two support divers were required before the submarine would enter the water. This allowed for at least one person in front and behind the submarine at all times (Fig. 26). A third person would ﬁlm the training exercises for post-analysis. Testing varied considerably depending on the progress of the submarine. Initial stability tests involved the submarine attempting to recover from various oﬀset angles to head in a straight line. Manoeuvrability drills included 90 degree turns in the horizontal plane and porpoising. Accuracy training forced the pilot to manoeuvre to meet a support diver.

Figure 26: Testing in the Westwave Dive Pool

28 Taniwha Design Report 5 PREPARATION AND PROCEDURES

Caution was taken with every new pilot to ensure an emergency plan was in place and to minimise risk of harm. Pilots would first enter and exit the submarine in the shallows. Emergency egress drills were practised before taking the submarine lower. These drills involved support divers providing air and aid with egress to the pilot. Furthermore the pilot would then repeat the exercises at depth before beginning the submarine test. This procedure gave the pilots sufficient time to acclimatise to the cramped environment of the submarine. The majority of the testing has taken place at Orakei dive pool, an Auckland diver training pool. While this pool has sufficient depth, it limits the runs to six metres. The speed and stability of the submarine were difficult to test as terminal velocity was not achieved. On occasion testing occurred at Westwave Dive Pool in Henderson, Auckland. This pool increased the run size to 25 m allowing the team to more accurately assess the submarine’s capabilities. This was also a good experience for the pilot to test the controls of the submarine over a substantial distance. Overall the submarine team is now well practised and ready to race in the 2015 ISR.

5.2 Team

The team consists of six members, all with a minimum open water divers certificate from the Professional Association of Diving Instructors (PADI). The primary pilot, Christopher Walker, and secondary pilot, Sanjay Surendran, both have advanced open water licenses. They are both well experienced with piloting the submarine from weekly training sessions. The support divers, Sanjay Surendran, Karay Atalag, Iain Anderson, and Gerrit Becker all have extensive experience with preparation and setup of the submarine. Once in the water the six pneumatic cylinders for the controls need to be filled and bleed. Ballasting is done next; as the pilot is slightly negatively buoyant, the submarine should be slightly positive before he gets in. Coarse adjustments are made using lead weights placed low in the submarine, then the trim is finely tuned by the pilot using the trim tanks (see section 4.7). Communication protocols have also been set up between the support team and the pilots. An array of sign language gestures are used to communicate testing procedures, strategy, instructions and safety checks. At the surface there will be a manager out of the water and one support diver on the surface to pass on communication to and from the rest of the underwater team. Ben Pocock is the head engineer on the team and will ensure everything is ready to go and sorted outside of the water. Additionally Ben has his open water license and can be a support diver if required. Gerrit and Iain will alternate between the role of surface support diver.

29 Taniwha Design Report 7 FUTURE WORK

6 Conclusion

The Taniwha was built at the Biomimetics Lab of the University of Auckland and is the Southern Hemisphere’s only racing submarine. Experience from the first race participation at the eISR in Gosport 2014 has shown the way forward and lead to rapid innovation towards this year’s race. Existing features such as the submarine’s extreme lightweight hull of only 2.5 mm thick epoxy - fibre glass composite, the simple attachment of the two part hull and the coupled Hobie Mirage fin drive have been improved and augmented by newly designed innovations. These include an adjustable ballast trim, hydraulic controls and a push-out nose cone as well as an electronic feedback unit. Experience gained through this year’s development and testing have provided the team with confidence to participate in the 13th ISR in Carderock this year.

7 Future Work

7.1 Automated Ballast System

An automated ballasting system is currently being designed and is expected to be completed by the end of 2015. The system uses a microprocessor and Digital PID controller to activate the existing diaphragm pumps. This system will take some responsibility of depth control away from the pilot.

7.2 Novel Drag Reduction

For future work a part of the team is working on novel drag reduction technologies. A ﬁrst approach to this is the use of special hull coatings. The Biomimetics Laboratory is in a good spot to get some inspiration and help on this matter from nature. The surface structure of marine animals’ skin has already been analysed by multiple research facilities and found to be useful for drag reduction. Using materials based on shark’s skin, for example, provides a simple solution towards the goal of increasing the submarine’s speed. Another approach that has been taken is the analysis of the control surfaces. Changing their shape and size can reduce drag signiﬁcantly. In order to attach the rudder to the back of the submarine, the submarine’s shape had to be altered in a way that increases the drag slightly. Being able to change it back to its original shape by changing the shape of the rudder can undo this increase in drag.

30 Taniwha Design Report 8 APPENDIX

8 Appendix

8.1 Taniwha Photos

Figure 27: Through the nose cone hole

Figure 28: The control hydraulics as seen through the rear hatch

31 Taniwha Design Report 8 APPENDIX

Figure 29: Safety buoy latch and control hydraulics

Figure 30: Main air supply in it’s cradle

32 Taniwha Design Report 8 APPENDIX

8.2 CFDImages

Figure 31: Velocity proﬁle

Figure 32: Velocity Proﬁle in x-y plane

33 Taniwha Design Report REFERENCES

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