As a part of our approach to our work, we are always looking for ways to reduce our impact on the environment. After an evening’s discussion with like-minded friends, we started putting our minds to the question “What would a sustainable research vessel look like?” After much mulling and some research, I put our thoughts down on this page to stimulate further discussions.
The catamaran hull design is quickly becoming the preferred choice for new research vessels. There are a number of reasons for this:
- More comfortable ride: catamarans have a softer ride in rough water than V-shape monohulls. When launching from a wave, there is a parachute effect – air is trapped between the hulls, softening the blow and minimizing spray. Catamarans also turn flatter without the lean of a monohull.
- Stability: catamarans have greater stability; they don’t pivot on the centerline like a monohull. Their wide footprint negates the effect of rolling seas, minimizes side-to-side listing, and allows for greater load capacity.
- Increased space: the wider beam of catamarans provides for more deck area and maximum storage.
- Shallow draft: a shallow draft allows access where other boats can’t go. This is particularly important for research ships operating in nearshore environments.
- Fuel efficiency: the twin-hulls of a catamaran have less water resistance than a single, wide bow, producing greater fuel efficiency.
- Safety: a well built and properly designed catamaran is very hard to sink. Not only are the materials used to make most catamarans positively buoyant, a catamaran has two hulls, not one. Should one of the hulls be damaged you still have another one for buoyancy. Catamarans are also superior to monohulls in terms of redundancy. Cruising catamarans generally carry two diesel engines and a diesel generator. An engine failure on a monohull is the end of motoring. Not so on a catamaran. In fact, when motoring, most catamarans only use one engine to conserve on fuel.
- Maneuverability: because most catamarans have twin engines, they are far easier to dock than a single engine monohull. A modern catamaran can do a 360 degree turn in her own length.
- Beaching: catamarans with twin mini-keels are structurally reinforced to take the point loads from small rocks when beached, either accidentally or purposely. Convenient beaching allows easy botton cleaning, hull repairs, and good access to the beach.
Catamarans come in two main types – motor (either planing or displacement) and sailing (displacement). The hull designs are somewhat different for these two types. In general, for a given water-line length, motor catamarans are taller (more windage), narrower (less deck and cabin space), and heavier than sailing catamarans. For our research purposes, we prefer the hull design of the sailing catamaran. With this in mind, we had the following thoughts regarding propulsion:
- To sail or not to sail, that is the question: since neither of us has had any experience in recreational sailing, initially the whole concept of a research vessel with sail power seemed rather pointless. We could easily see all the down sides – the unreliability of wind for sailing, the lack of maneuverability while under sail, and the hassels of taking the sails up and down, adjusting them, and so on. However, after some research and contemplation, we quickly came to realize that even if sails are only used for down-wind traveling, the savings in terms of fuel economy can be very significant. So I think we would keep the sails …
- Engines – having dual engines would be absolutely essential in a research catamaran, as they would be necessary for maneuvering while deploying and towing equipment at a site. They would also be required for travel during days when winds and tides are unfavorable for sailing. We settled on diesel-electric engines as the best choice for engine type, based on:
- Fuel – a number of potential fuels are available for a “sustainable” vessel; however many of them are highly flammable or explosive (e.g., hydrogen, natural gas, ethanol) or require significant advances in technology (e.g., hydrogen) before they can be readily used. As a result of numerous boat fires and explosions over the years, diesel is the preferred fuel for most work vessels. It is much less flammable than gasoline, and diesel engines have a much better safety record than engines which operate using more flammable fuels. Furthermore, a standard diesel engine can run on biodiesel. Unlike petroleum-derived diesel, biodiesel is a renewable energy source, and can be produced from a number of plant sources. While the overall production of biodiesel is less efficient than energy produced using solar cells , it is safely and readily transported, and can be used during times when electrical generation by wind or sun is not possible. Biodiesel has better lubricating properties and much higher cetane ratings (e.g., burns faster) than today’s lower sulfur diesel fuels. Biodiesel reduces fuel system wear and may increase the life of the fuel injection equipment that relies on the fuel for its lubrication.
- Known technology – hybrid propulsion systems have been in use for some time now, and fall into two general categories: parallel hybrids and series hybrids (see Diesel Power Hybrid and What is a Hybrid?).
- Parallel hybrids have an internal combustion (IC) engine driving through an electric motor-generator unit, to a transmission or leg. A parallel hybrid powerplant can operate with electric power alone, with IC power alone, or a combination of both.
- Series hybrids have an internal combustion (IC) engine driving a remotely mounted electric generator which powers electric propulsion motors via a large battery bank. The IC engine operates at its most efficient speed, and can be used to charge batteries or to directly power the electric motor.
Parallel hybrids are more commonly used at present than series hybrids; however series hybrids tend to be more efficient. In any case, when operated at similar speeds (e.g., 7-8 knots), the fuel efficiency of a catamaran with a hybrid system (e.g., a 12.8 m catamaran with a series hybrid system with a fuel consumption of approximately 2.8 L/h ) is significantly greater than that of a monohull with a regular diesel system (e.g., the Moody Blue, which is a well designed 11.9 m monohull operating an efficient Gardner engine, with a fuel consumption of approximately 9.6 L/h).
The main drawback with diesel-electric hybrid systems is battery technology. Current technology uses sealed lead-acid batteries. These batteries are large and heavy, and can significantly reduce the load capacity of a catamaran. However, on the bright side, battery technology is evolving at a very rapid pace to keep up with the demand from electric vehicles. Lighter, more efficient batteries will probably soon be a reality.
- Alternative energy sources – the batteries in a hybrid system (particularly a series hybrid system) can be recharged using a number of alternative energy sources:
- Regeneration from wind power – when the propeller turns in the wake while the boat is under sail, the drive motor automatically becomes a generator and sends electricity back to the batteries.
- Solar cells and wind turbines – if the boat has space available, solar panels or wind wind turbines can be used to recharge the battery pack.
- Dockside plugin – standard AC power can be fed into the battery pack through a battery charger.
Length and Layout
Research vessels require significant load capacity for equipment (e.g., winches, cables, sampling equipment, laboratory equipment). For this reason, it would probably be best to choose a larger (e.g., minimum of approximately 14 m in length) rather than a smaller catamaran. While catamarans have large amounts of deck and cabin space, there is a tendency to overload them with weight. An overloaded catamaran will plough through the water, allowing waves to slap the underside of the deck, and quickly lose its fuel efficiency and speed. Since catamarans are very spacious, there are lots of opportunities to customize the interior and deck layout to suit the particular research needs. Shown below is an example of a layout which we might use (based on a crew of two and sufficient laboratory, computer, and office space to work as a live aboard for extended trips).
The concept of using a sailing catamaran as a research vessel is not a new one – two very successful catamaran research vessels, the Oceana Ranger and the Alguita, are shown at the top and bottom of this page, respectively.