A Human Powered Submarine
Richard Donovan Team Leader
Department of Mechanical Engineering
October 8, 2004
Introduction and Background Material
The International Submarine Races was started at Florida Atlantic University in 1989 to "inspire students of the various engineering disciplines to delve into broad areas of underwater technology advancement and to provide them an educational experience that translates their theoretical knowledge into reality, to foster advances in subsea vehicle hydrodynamic propulsion and life support systems, and to increase public awareness of the challenges people face in working in and exploring the ocean depths" The race was held in the water off the Florida coast for the first three competitions (1989, 1991, and 1993), drawing up to 44 submarines. In 1995, the competition moved indoors to the David Taylor Model Basin at the Naval Surface Warfare Center in Bethesda, Maryland. The facility has a width of 15.5 meters and a depth of 22 feet. The course consists of a 30.5 meter run up area, and a 100 meter long course. The 8th ISR competition will also include a slalom race on the last day.
All submarines are designed first of all for safety. Each team is required to have standard safety systems such as bright marking on the fins, a strobe light, and a dead man buoy. Before racing, all submarines must pass both a dry and a wet inspection. They are first inspected in the parking lot outside the model basin and then brought inside for an inspection in the water. Many teams in the past have been delayed by problems passing this safety inspection. In many cases it is because the submarines dead man buoy did not work initially and took time to fix.
Life support is another aspect of safety. The driver is required to have a normal SCUBA tank as well as a reserve supply.
The next design challenge of the teams is navigation. They must design a craft that they can drive in a straight line and control the depth. Even though the race is a straight line, the control planes are an important part of the submarine design. A fast submarine doesnt do well if it crashes into the wall. Since the act of pedaling will cause disturbances in the path of the sub, it is important that the control system can correct the subs course. This year, the slalom race will test the control systems to a higher degree than the straight-line race.
After those criteria, teams generally either try to be fast or original. The categories for the competition are one and two person, propeller, and non propeller driven.
The state of the art for submarine races can best be studied by looking at the statistics from past competitions. The submarines using propellers have so far been the fastest, with the record being 7.192 knots. At the last competition, the fastest one person propeller teams turned in an average speed of 4.916 knots. At the 7th ISR in 2003, the teams showed up with a mix of single propeller, dual propeller, and non propeller designs (figure 1).
The single propeller designs face the challenge of keeping the tilt of the craft constant, as the reaction torque on the submarine would tend to spin it in the opposite direction of the propellers. At the 7th ISR competition, 8 single person submarines used one propeller.
Two of those eight used variable pitch propellers, which can increase or decrease the efficiency of the system to accommodate for the fatigue of the pilot. This serves nearly the same purpose as an automobile transmission. A propeller with a pitch chosen to provide thrust at high vehicle speeds requires a large amount of torque to start. A lot of energy is wasted getting the submarine started. Likewise a pitch that requires minimal torque to start can not provide efficient thrust at high speeds, thus limiting the maximum speed that can be attained by the submarine. In diesel, gasoline or electric powered applications, this is not a problem because the engine has enough power to easily overcome the high start-up torque. However, in a human powered submarine the "engine" torque is limited to what the human driver can produce. The variable pitch propeller solves this problem by adjusting the pitch of the blades to be appropriate for the situation. So far in the competition, all variable-pitch propellers have been manually controlled. However, a method has been suggested using the concept of a "free wing" which would allow the pitch to adjust itself automatically.
Four of the submarines at the last competition utilized counter-rotating propellers. These are good because they counteract the reaction torque that would cause the submarine to have unwanted tilt. Submarines without counter-rotating propellers generally counter the torque in the way they trim the submarine. All of the propeller-driven submarines at the last competition used propellers placed at the rear of their submarine. Non propeller propulsion systems at the 7th ISR competition included a centrifugal pump, a dismus pump, a fishtail, and a swimmer with a dolphin kick. At the 7th ISR competition, all of the teams used a bicycle pedal system for power generation, except for one team that did a proof of concept on a swimmer with a streamlined shell doing a dolphin kick. The fastest one-person non-propeller design in the 7th ISR competition traveled at 3.520 knots. The one-man submarines varied in size from lengths of 9 to 14 feet, and diameters of 22.5 to 36 inches. Weights vary from 75 to 287 pounds.
Progress To Date
This project was originally divided into six main components: propeller, drive train, hull design, frame, navigation, and safety. These have been broken down so that each of the five members of team WildCatfish can research a specific component or aspect. One change is that all aspects of the submarine are being designed simultaneously. Most of the design is finalized. Listed below are the aspects that have been determined. After a few modifications and specific selections, the calculation and construction phase will be ready to commence.
Brian Comber has been designing of the hull and any framework that would be involved. The hull will be a revolved solid to simplify calculations and construction. Airfoil design has been researched for minimum drag while allowing enough room for the most important aspect: the pilots ability to produce maximum possible horsepower. The hull will be made of fiberglass. Many of the systems which do not see high loads will be mounted directly into the fiberglass. The mounts will be laid into the fiberglass during the manufacture of the hull. For the aspects withstanding higher loads, such as the drive train and pilot restraint system, there will be a frame to take the load off of the hull. The frame itself, however, will be mounted on the fiberglass hull in the same way as described above.
Michael Seibert has been designing the drive train. He has also worked in contacting sponsors to donate parts for the completion of this objective. The maximum efficiency is being analyzed for the size and distance of the pedals and moment arm on the pedals. He has designed the foot cages to get maximum horsepower but also easy to get out of in case of an emergency. Michael has also been researching and designing the restraint mechanism to keep the pilot comfortably in the prone position with access to the pedals and the escape hatch. Straps will be used here that are connected to the hull/frame and can be easily removed.
The drive train is heavily dependent on the final designs for the pedal setup and the propeller. Michael Seibert and Timm Strayer have been working together to design this aspect of the submarine. There is a chain that will connect the power input device (pedals) to the gears. The gears will be connected to the drive shaft with a bevel gear, and the drive shaft will connect the propellers.
Timm Strayer has been heavily researching propeller design. The research has been narrowed to two types of variable pitch propellers. One type being analyzed is a pinned propeller where the blade will find the angle of attack on its own based on the location of the pin and the camber of the airfoil. The second design will have a manual shifting rod that will be connected to the drive shaft and a set of bearings that will alter the pitch of the propeller. This is one of the most important aspects left to be finalized with the design of the WildCatfish.
Erin Vogels has been focusing on the control systems and design. Erin has had a difficult task because the design must be altered each time there is a change in the hull, propeller, or restraint mechanism. This aspect will be controlled from a bar at the front of the submarine. A linkage will connect the hand controls to the control planes at the aft of the submarine. The one device will be able to control the elevators and the rudder. There will be a set of planes forward on the hull but will not need a control system because they will be stationary.
The safety aspects of the submarine design are being developed by Richard Donovan. The dead man buoy is normally what delays many teams when they arrive at the competition because it is crucial that it works properly. This will be done with a bicycle or motorcycle break/clutch bar and cable. The handle will be spring loaded and the cable will run through a cable shaft where a pin is inserted into the actual buoy. The buoy is part of the surface of the submarine and the foam buoyancy device. The pin is inserted in the buoy and is pulled out when the handle is released. This launches the buoy to the surface. Consideration must also be given so that the submarine will not become overly negatively buoyant when the buoy is released. The other safety aspect is the escape hatch. It will be located above the diver and held with magnets. This is so the pilot can escape without necessarily turning the release levers (which will break the magnetic connection making it easier to release the top). This area must be decently large and must not have any positive buoyancy. That would make the escape door want o separate the magnets simply by submersion, and it would make the submarine sink when the buoyant door was released.
Many changes have been made in the design of this Human Powered Submarine. The progress to date has explained many of the changes that are critical to entering the construction and calculation phase of this project. Many of the finalized characteristics being used were the same characteristics conceived at the start of this project. They were altered and questioned until there was a sound reasoning and understanding of the construction of each element. One major change is the propeller design. It is because of this change and its implications that propeller design is the last aspect of the sub to be finalized conceptually. Originally, counter rotating propellers were designated for their simplicity. Currently, there are two types of counter rotating propellers that are being analyzed for our sub. This is a change to the drive shaft and complete propulsion mechanism. The design below is loosely based off of helicopter propeller design. The pitch can be manually changed through a shifting rod connecting to slider. The bearing roll in the groove and when the manual rod is moved the bearing slide the pitch adjuster and change the angle of the propeller. The design of the propeller is also very critical for this change because the change of pitch at a small radius from the drive shaft could create more drag if the propeller blade angle was changed.
The second propeller change where the pitch would find itself due to the positioning of where it was pinned to the shaft is still under research for complexity and reliability.
The budget has been altered significantly since the last progress report. With the fact that it will be almost logically impossible to raise $11,000, different ideas were implemented to reduce the cost of this project. Michael Seibert has done research and contacted individuals who are able to make a human powered submarine for approximately $1,000. This was very refreshing news. Many of the designs originally thought to be outsourced to companies to build will be built with Villanova University facilities on Villanova University property. There is still a $1,000 entry fee and hotel rooms will be needed while at the competition. A new approximate budget for this project can be re-estimated to approximately $3,000-$4,000. Christini AWD is a sponsor that will help with parts (reducing the price). There are a number of sponsors who are willing to help with ideas and concepts. This can reduce the budget by having our sponsors suggest materials that are inexpensive yet efficient. The main schedule changes are allowing for more testing. Though proper construction is critical to the success of this vehicle, it will likely fail in a race if the pilot has not mastered the controls and compensated for where real situations deviate from the calculations. The design is expected to be altered through testing. Because of this, it is crucial to have the submarine constructed by early March to allow for sufficient testing. The updated budget sheet the ghantt chart posted below depict the new cost analysis the modifications in the schedule respectively.