This article provides a short overview to the development of the manned submersible ICTINEU 3, a work class vehicle with high capabilities for research, ocean observation and underwater intervention, but also suitable for filming and leisure. It has been designed for 1,200m depth and a crew of three: one pilot and two observers (passengers, and will be certified and classified by Germanischer Lloyd).
The challenge has been to achieve a very small and lightweight but at the same time versatile and highly operational vehicle, with the aim to improve the capabilities of existing submersibles in this depth rate. The result is a new generation of manned submersible, a compact vehicle of only 5,300 kg, that is designed to be easy to operate from most research vessels and incorporates outstanding innovations such as a lithium-ion-polymer battery system that will provide the vehicle with a high power capacity.
Ictineu Submarins SL was founded in 2007 to develop and built the ICTINEU 3 manned submersible. The vehicle was named ICTINEU 3 as a tribute to Narcís Monturiol that built the first modern submersible in history, the first Ictineu or Ictíneo in 1859, and the second in 1864.
The aim was to build a new generation of manned submersibles that would improve the observation and operation capabilities, as well as be versatile, easy to operate and maintain. As part of the team that has worked in the development and engineering had no background in underwater vehicles, a completely new approach has been brought to the table in terms of design, construction materials, systems integration and in particular its energy system and automation. In this sense new solutions have been provided that appear to be practical and efficient.
Development and Innovations
In order to achieve a small, lightweight and versatile vehicle with a big field of view and three passengers, many challenges had to be solved during the design phase of the Ictineu 3, and a lot of technology review was needed. In particular, there are several issues where most effort has been put on:
• Weight reduction. A big effort on design and research on new materials was needed in order to drastically reduce weight in several systems. Extensive calculation was done by FEM as well as design optimization and research in new materials, mainly in the pressure hull. Innovation in stainless-steel materials and design have lead to an unparalleled volume to weight ratio of the pressure hull, that weights only 2,714kg (including the two acrylic domes, 540kg) for 3,089 cu. m. of internal volume. Composites (CFRP) have been largely used as structural and constructive material, both outside of the pressure hull (exostructure, tanks, pressure-tolerant containers) and inside. The exostructure and the fairings have been built completely in composite, as a sole body, yet withstanding the requirements of the certification authority. Many years of experience have allowed us to work with different materials and properties, achieving lightweight, high-resistance, fire-proof and electrically isolated parts/elements, suitable both for inside the pressure hull and exterior of the vehicle (in water). Finally, the development of a pressure-tolerant li-ion-polymer battery system has been definitive in the final weight reduction. As a result, the vehicle does not need the addition of syntactic foam.
• Maintenance reduction. Last generation stainless steel has been used for pressure hull so the need for painting and corrosion maintenance has been cancelled. Aluminium materials have been reduced to a minimum, and are never in contact with steel or carbon fiber parts. The use of composite in shells, the conception of exostructure and farings in one sole body, and a practical anchoring and fixing system, allows for a very fast assembly and disassembly of all the systems with very few personnel needed.
• Improvement of performance in navigation. The aim was to built an easy to pilot, safety improved vehicle, with fine control on navigation systems. Apart from diving tanks with 600l capacity, also interior buoyancy tanks have been provided with a capacity of 220 liters. They will allow a fine control of the ascent-descent as well as trimming of the vehicle. If we add eight powerful thrusters, 2.5kW each, to the system, we have a vectorial propulsion system on full six degrees of freedom. Custom-made, pressure-tolerant motor controllers have been designed. They allow for a proportional control on the thrusters and for a pilot-configurable navigation board. The whole must be an efficient and easy to pilot system.
• Improvement of performance in operation. A high power and high energy system has been developed based on lithium-ion-polymer technology. The result is a compact, lightweight and safe battery system that will provide endless capacity to work at a normal load for longer missions (up to 10 hours) and enough power to respond to an emergency with high power requirements. An optimal selection and configuration of thrusters, the proportional motor drives and the architecture of the whole electric system will add efficiency to the vehicle. Power and communications system has been dimensioned so they can adapt to any task and mission requirements, with capability to upload any instrument from the client in an easy and quick way.
• Improvement in safety. Three different active safety systems (manually actuated) have been implemented in the vehicle: diving tanks with 258 liters capacity at 1,200m depth, drop-weigh system (200-500kg), emergency buoy with 1,800m high-resistance rope. As passive safety, design has been used also to improve hydrodynamics and to avoid as much as possible entanglement areas. If we add an electrical system distributed architecture and powerful and efficient energy system, the vehicle gains in autonomy, performance and finally: safety.
The pressure hull is 1.7m in diameter and it has two acrylic domes, one on top (entry hatch) and one in front: 1.5m external diameter, 150º. The front dome is in a very advanced position with respect to the skids/supports, and it has an inclination of 10 degrees forward in respect of the vertical, so the vision on the sea floor is greatly improved. This allows the three passengers a large field of view and excellent capabilities for ocean observation, as well as the possibility to take high quality photography and video recording from inside the pressure hull. An important effort has been done in design for optimization of space and ergonomics have also been taken in account in order to make submersibles a comfortable place to travel and work.
The weigh of the vehicle will be about 5,300kg, so it can be operated from most research vessels, but it can be also towed from harbour if working area is near the coast. Due to shape and diving tanks capacity, passengers can go in/out from water surface in good sea state. As it has a very reduced size it can fit in a 20-ft. container, so it’s easy to transport to the work place by road, ship or air worldwide.
The power system is based on last generation lithium-ion-polymer batteries, which give the vehicle a high power capacity: 42 kWh.
This means it can work 10 hours full autonomy at normal load capacity and will be able to travel up to 20 nautical miles underwater. Battery system is robust and safe and it can be controlled either automatically or manually, as it can be also double checked and monitored for safety.
The Ictineu 3 will have scientific instrumentation on board, and the data obtained will be published so that they can be used by the scientific and oceanographic community.
Sea trials and classification are expected during fall 2013, though the pressure hull pressure test was successfully completed in summer 2011.
Once the vehicle is finished, the company itself will operate the submersible and offer diving services. Operation of ICTINEU 3 submersible can be adapted to any need of the client, either for long campaigns on a mother ship or on a daily basis with the need of only a small surface support vessel. A daily mission of 8-10 hours can be run, and a regular time lapse of five hours will be needed to recharge the batteries, though they can support a fast charge. The company also offers engineering services and the possibility to build new submersibles according to client needs. The design and construction of the Ictineu 3 is the result of nearly 10 years of work. Through this period, the project has counted with the selfless collaboration of many people motivated by the sea, science and technology. Up to 2.000 individuals and organizations have collaborated in a crowd-funding campaign, and a sponsoring opportunity is still open for companies.
(As published in the October 2013 edition of Marine Technology Reporter - www.seadiscovery.com)