Hello all!

After we discussed the deployment of a piston core I opened the flood gates for questions!. Not surprisingly I have been asked quite a few questions about ISIS. I can understand people being interested in ROV's - this is the reason I got interested in oceanography!

ISIS is an amazing bit of kit, but I understand that a lot of people know little about how exactly she works and what we use her for. A few of the questions I have bee asked are from people who know a lot about ROV's - "Do we use a TMS?", "Do we deploy using the ship's A-frame" and other technical questions relating to ISIS's operation.

Firstly a bit about ISIS. If you want to know more about ISIS I have already written a comprehensive articleabout the actual ROV that can be found by click HERE

ISIS is a remotely operated vehicle (ROV) designed and built by Woods Hole Oceanographic Institution's Deep Submergence Laboratory to allow scientists to have access to the seafloor without leaving the deck of a ship.

ISIS is a single-body ROV system. A 10-kilometer (6-mile) fiber-optic tether delivers electrical power and commands from the ship down to ISIS, which then returns data and live video imagery.

ISIS is equipped with sonar imagers, water samplers, video and still cameras, and lighting gear. ISIS manipulator arms collect samples of rock, sediment, or marine life and place them in the vehicle’s basket or on “elevator” platforms that float heavier loads to the surface.

Pilots and scientists work from a control room on the ship to monitor ISIS’s instruments and video while manoeuvring the vehicle. The average ISIS dive lasts 21 hours, though operators have kept the vehicle down for dives spanning two days.

General Information Depth Capability: 6,500 m Tether: 35 m, 20 mm (0.8 in) diameter, neutrally buoyant Size: 3.4 m (134 in) long, 2.4 m (96 in) high, 2.2 m (88 in) wide Weight: 3,675 kg (8,100 lbs.) in air (approx.) Maximum Sampling Transect Speed: 0.2 knot on flat bottom surface, 0.1 knot up-slope Maximum On-Bottom Transit Speed (no sampling): 0.5 knot Maximum Vehicle Speed (on site, within tether range): 1.5 knots forward, 0.5 knot lateral, 1.0 knot vertical Descent/Ascent Rate: 35 m/min Propulsion: Six brushless DC electric thrusters, each providing 250 lbs of thrust

Deploying ISIS

I'm going to start at the beginning - planning a dive and launching ISIS and over the coming weeks elaborate on different parts of our dive cycle.

Planning and Deploying ISIS

An ISIS dive starts long before ISIS (we refer to her as "The Vehicle") touches the water.

Firstly a dive must be thoroughly planned - no ISIS dives are ever ad hoc! A successful ROV cruise relies on a healthy interaction between the Principle Scientist (The Boss of all scientists onboard), ROV team (Guys who fly and maintain ISIS) and the Master (Godlike figure responsible for the safety of the ship and all those onboard).

The Principle Scientist defines the scientific mission of the expedition and conveys to the ROV team what equipment needs to be employed on ISIS in order to meet the scientific goals of each dive and ultimately the cruise. It is standard practice for the Principle Scientist to keep the entire scientific party aware of the cruise objectives and to provide advance notice (24-hour basis) of the operations plan.

Above:The scientific party and ROV team sit down and discuss the 24hr ROV plan during exploration of Hess Deep in the Paciifc

For each dive the Principle scientists plans a route and purpouse for the dive. A dive may be a simple transit from A to B filming and taking pictures of creatures and geological features encountered enroute.

Other dives may involve a more hands-on approach when collecting biological samples or deploying experiments. These type of dives may require special tools and storage boxes to be attached to the vehicle for both collecting and storing these samples safely. The principle scientists will discuss with the ROV watch leader the equipment required for each dive.

The weight of each piece of equipment added to ISIS must then be calculated. We cannot simply cram ISIS full of scientific equipment. At all stages throughout an ISIS dive we want ISIS to remain positively buoyant (i.e float) and for this reason we are limited to the amount of equipment she can carry.

ISIS's foam pack has a set amount of buoyancy - each additional bit of equipment we add reduces the vehicles buoyancy in water. The reason for keeping the vehicle positively buoyant is so that in the unlikely event that Isis’s tether was to break (and we loose the ability to control her) she would float to the surface where we could recover her.

If ISIS was negatively buoyant and her tether broke she would sink to the seabed. We would then have to call in another ROV to rescue her - a costly (and somewhat embarrassing) job, especially as not many ROV's are able to operate down to the depths that ISIS can work.

The worse case scenario would be if ISIS was neutrally buoyant - i.e she doesn't sink or float, instead she would stay at one level in the water column and float with the current - if this happened it would be very unlikely we would ever see her again.

However, ISIS can also be too buoyant! When ISIS dives we use her vertical thrusters to propel her downwards through the water. If ISIS is not carrying any equipment she is naturally very buoyant in water and the two vertical thrusters have to fight against this high level of buoyancy to get ISIS down to the seabed.

To combat an extremely buoyant vehicle we attach special expendable weights which allow us to dive without putting as much strain on the thrusters and burning them out - although we still ensure the vehicle is buoyant!

When it comes to returning to the surface these weights can be jettisoned making us more buoyant and allowing the vehicle to come to the surface with less effort on the thrusters

So as you can image we take weights very seriously when working with ISIS and everything we add or remove from the vehicle is carefully monitored and its weight added or subtracted from a spreadsheet that calculates our buoyancy

Once the dive plan has been filed we look at things that may affect the dive. We will discuss with the scientific party the terrain we are likely to encounter (as this may effect camera and lighting positioning) - when working on a canyon wall the lights may be adjusted so that we aren't dazzled by there reflection of the flat surface. There are lots of factors we take into account based on the experiences of the team operating if different environments

We also need to contemplate currents, visibility, and what human "junk" may be present. In shallow coastal water there may be fishing nets and fishing lines that have become snagged on underwater obstructions.

In addition, vast numbers of communication cables that have been laid over the last century-and-a-half also criss-cross the world's oceans. Before a dive we consult submarine cable charts make sure that we are no operating in the vicinity of any underwater communications cables.

The position of cables laid more than 15 years ago before the widespread introduction of GPS is always a big unknown – imagine trying to figure out your position accurately in 1910 (when there was a massive boom in underwater cable laying) – some of the recorded positions are miles off!!

Other factors we will consider are how close are we to shipping lanes? This may require the bridge to broadcast special messages to nearby ships detailing that we are conducting science operations and have limited manoeuvrability.

With the dive plan and necessary equipment drawn up it's time to prepare the vehicle for the deployment.

Once all the equipment is added we undertake a detailed check of the vehicle. This involves powering up ISIS and testing all systems to ensure that they are functioning correctly - lights, cameras, thrusters, science sensors, manips, tool tray, swing arms, beacons etc. The science equipment and experiments are checked to make sure they are secure on the vehicle. Last thing you want is a science system to fall of during a descent/ascent and be lost!

Above: We have various basket configurations depending on the dives. The left image shows a basket configured for coring with a selection of push cores (tube like devices) and box cores. A downward looking camera (Pixelfly) is also positioned on the right-hand side of the basket for taking pictures of the seabed as we pass over it. The Right image shows a large selection of push cores and our suction sampler which is a device for "hoovering" up samples from the seabed - these samples are then stored in plastic containers.

All the wires on ISIS are contained within oil filled tubes - the reason for this is oil is inert and non-conductive and does not compress at depth. Naturally, salt water and electricity do not go together very well and if they come in contact they tend to cause problems. So for that reason all electric cables are stored in these oil filled lines. We actually use biodegradable environmentally friendly oil in the tubes. Before a dive the team check that there is enough oil in the compressors which supply these tubes.

One of the most decisive factors in ROV operations is the weather. ISIS can manage a lazy 1 knot on the surface. She is not particularly happy working in rough seas and we generally don't deploy in anything exceeding 25 knot winds and 2 meter swell. Before a dive the watch leader will look at the weather conditions and forecats and decide if it is practical to deploy ISIS.

A normal deployment involves a minimum of six people. Two of the ROV team are positioned on deck and another two team members in the control van fulfilling the roles of Engineer and pilot, two of the ship's crew are also in attendance to add floats to Isis’s tether.

Above: The deck team usually consists of two ROV team members. One member controls the Winch/Launch & Recovery System via the deck unit and the other monitoring ISIS's movements in the water and communicating instructions to the control van. There are two team members in the control van - Engineer and pilot. The Engineer checks all systems on the ROV are healthy as the vehicle is deployed. The Pilot controls the ROV's movements based on the deck teams instructions during the deployment

The first part of a deployment is confirming the ship is "on station" - i.e in position and that the officer on the bridge is happy with us to begin ROV operations.

The first action is to pick ISIS from her plinth and positioning her over the water. With the vehicle over the water and away from the deck team she is powered up.

Once the control van team has powered up the vehicle and are happy that all the systems are functioning and ready for the dive, they inform the deck team they are ready to begin the deployment.

Above: ISIS on her plinth	Above:: ISIS is lifted and "latched into" the Launch & Recovery System (LARS)	Above: The LARS pivots placing ISIS over the water.	Above: ISIS is rotated to match the ship's heading

With the control van team ready and the ROV positioned over the water the deck seek permission from the ship’s bridge to deploy the vehicle into the water.

Once clearance is given by the bridge ISIS is lowered into the water.

Once in the water the vehicle is rotated 90 degrees anticlockwise from the ship's heading.

ISIS is connected to the surface via a thick metal cable known as a tether or umbilical.

There are number of problems with being connected to the ship via a cable. Naturally as the ship rolls due to wave action the movement is transferred down the cable to ISIS - tugging and pulling her. Having a long cable also creates a lot of drag - as ISIS moves about at depth she may be dragging over 6000m of cable above her!

To stop this tugging and drag we need to "decouple" ISIS from the ship and allow free swimming. There are two methods for decoupling ROV's from a ship - TMS (Tether Management System) or using floats. After experimenting with both methods we have adopted using floats.

So once ISIS is in the water we need to add the floats that will decouple her from the motion of the ship.

These are simple rugby ball shaped floats that are latched closed on the wire. These floats add buoyancy onto the wire and create the S-bend shown below:

As the ship rolls the majority of motion is removed in the right-hand proportion of this s-bend and ISIS is able to free swim.

During deployment the deck team will attach 9 floats at regular intervals along the first 50 or so mteres of cableas ISIS slowly drives away from the ship.

Once all the floats have been added ISIS is usually about 50-60m away from the ship.

Before diving it is common practice to see how buoyant the vehicle is. The pilot stops thrusting upwards to keep the vehicle on the surface and watches to see how ISIS sits in the water.

Once the deck team are satisfied with ISIS's position and her buoyancy they ask the bridge for permission to dive. Once this is given we begin the dive.

The pilot thrusts the vehicle downwards using the vertical thrusters whilst the deck team pay out cable and match ISIS’s dive speed. For the first 250m of the dive we control the winch that pay's out ISIS's tether from the deck where we can view the whole ISIS deployment system and make sure that there are no problems and till sufficient tension has built-up on the wire.

Once we are satisfied everything is working and there is sufficient tension, the control of the winch is then switched to the controls in the control van where we can monitor the winches and lars via CCTV.

Usually at around 50m we are able to track the ROV’s position using the vehicles onboard USBL beacon. This communicates with a receiver on a special pole that sticks out from the bottom of the ship and allows us to calculate ISIS’s position in relation to the ship and then give it a GPS position.

We then continue diving- the Engineer matching the pay-out speed of the winch with the descent rate of the vehicle as she thrusts downwards…..