THE Z H T A PROJECT TECHNICAL PROPOSAL January 20, 1988 OBJECTIVE: TO SAIL A RADIO CONTROLLED/COMPUTER CONTROLLED MODEL OR DRONE SAILBOAT ACROSS THE ATLANTIC OCEAN. THE PROJECT IS TO BE COMPLETED IN MINIMUM LEAD TIME AND WITH MAXIMUM PROBABILITY OF SUCCESS. COST OF THE PROJECT IS TO BE KEPT MODERATE. I. THE BOAT General Considerations: The design selected must be strongly built, readily available on the used boat market, and well ballasted in proportion to its sail area. That is, the design should not rely heavily on moveable crew weight for righting moment. Hull, deck, rig, and appendages must be capable of withstanding a knock-down or roll-over. On most available boats this will probably require some reinforcing of the rudder, and replacement of spars and standing rigging. Full keel/attached rudder configuration has the advantage of being less susceptible to fouling by sargasso weed or other floating objects, and less likely to sustain rudder damage. Fin keel/spade rudder configuration (possibly including a bulb keel) has a considerable performance and control advantage, especially downwind. Size: Several factors determine the minimum feasible size of the vessel: 1) Must be large enough to carry off-the-shelf navigation, computing, steering, and communication equipment without serious degradation of performance. The costs and long lead times associated with miniaturization are to be avoided. 2) Must have sufficient deck area for the required solar panels for battery charging. 3) Rig must be able to support a masthead wind instrument cluster. 4) Backstay must be a reasonable length for a short-wave radio antennae. 5) It may be desirable for the vessel to carry passengers during testing and de-bugging. 6) The model should be visible to other vessels, so as to avoid risk of collision. Several factors also determine the maximum feasible size: 1) Vessel must be small enough to rig and test with minimum lead time. 2) Sails must be small enough to withstand serious abuse in adverse weather conditions. 3) Rig must be small to withstand roll-over with minimum probability of damage. 4) Reefing systems should be kept simple, and the number of sailplan configurations required during the voyage should be kept to a minimum. 5) The probability of being spotted by other vessels should be minimized, so as to reduce the risk of the vessel being "rescued" or otherwise interfered with. 6) Vessel should be easy to transport and store. 7) Vessel must be acquired quickly and at moderately low cost. 8) The danger, real or perceived, of causing damage to another vessel must be minimized. Preliminary evaluation of the above size parameters suggests a vessel size of between 16 and 24 feet. Candidate stock designs include: Full keel designs: Cape Cod Bull's Eye (16 ft, 1350 lb.) Cape Dory Typhoon (18 ft, 2000 lb.) Pearson Ensign/Electra (22 ft, 3000 lb.) Fin keel designs: Zypher (16 ft, 500 lb.) International 110 (24 ft, 1000 lb.) Wylie Wabbit (24 ft, 700 lb.) II. STEERING Steering will be controlled by an electrically-driven compass- referenced autopilot. Wind vane type self-steering is ruled out because of size and weight, vulnerability to wave damage, difficulty in making automatic adjustments, susceptibility to fouling the pendulum with floating objects, and the difficulty in providing redundancy in the event of failure. Several suitable off-the-shelf autopilot systems are available, specifically the Autohelm 2000 or 3000. Although these units are reasonably reliable, some redundancy is necessary. One possible actuator configuration is to install two or three tillers on the rudder stock (all below deck level). Each tiller will have its own steering actuator. An electrically controlled clutch device will couple only the active tiller to the rudder, and only the actuator on that tiller will be powered. Similarly, two or three control units will be available. On-board diagnostic software will determine which tiller/actuator set and which control unit should be switched on. III. NAVIGATION The model will carry one satellite navigation unit, plus one additional satellite unit or one LORAN unit. Both of these systems are available off-the-shelf for the recreational boating market, complete with a standardized data output interface. There will also be two remote-reading compasses, and two knotmeter/log units. These devices will send data to the on- board computer for maintaining a dead reckoning position, and/or used in conjunction with the SATNAV or LORAN units to utilize their built-in DR capabilities. The on-board computer software will make course decisions based on wind direction and speed measurements, the current vessel position, and the pre-programmed or transmitted routing strategy. IV. INSTRUMENTATION In addition to the navigation instruments (knotmeter, log, and compass), the model must also be capable of measuring wind speed and direction. This could be a standard yacht masthead instrument cluster, or possibly a heavier commercial anemometer and remote direction indicator. Although the yacht type unit is less expensive, lighter, and consumes much less power, these devices have a poor reliability record and cannot be expected to survive a roll-over. To allow for the possible loss of wind measurement capability, the model will also measure its heel angle. This information, combined with course, speed, sail trim settings and reef configuration, will allow the on-board software to estimate wind speed and direction with reasonable accuracy. A short wind test maneuver, performed hourly, might be used to improve the accuracy of this wind estimate if the masthead cluster is lost or malfunctions. V. COMMUNICATION AND TELEMETRY The primary communication system will be via short-wave radio, pre-tuned to transmit and receive "packets" of digital information at selected times. Even at a relatively slow data transmission rate and with sveral repetitions, these transmissions will only take a few seconds for each contact between the model and the land-based communications station. A range of frequencies can be used to maximize the probability of making a successful contact under varying propagation conditions. It will be desirable to use one ham station on the east coast of North America, and one station in England, linked by telephone to the central control and information center. Satellite bulletin boards may also be extremely useful, but antennae aiming will not be possible from the vessel. Contacts will be attempted on the order of twice daily. Transmissions from the model will include: 1) Present position from DR. 2) Last SATNAV/LORAN fix. 3) Present vessel speed and heading. 4) Present wind speed and direction. 5) Heel angle, sail trim settings, and reef configuration. 6) Battery condition and charge/discharge current. 7) Time history of items 3,4,5,6 since last contact. 8) Results of diagnostic routines. Transmissions to the model will include: 1) Routing strategy modification, based on weather information available on shore. 2) Modification of time and/or frequency of next contact attempt, if necessary for propagation conditions or security. 3) Initiate switch to arrival mode, initiate real-time control with specified parameters. 4) Modify arrival waypoint if necessary. In addition to long-range communications, a VHF radio (approximately 25 mile range) may be installed as an interference-avoidance aid. This radio would be activated once the model is at sea, and continuously monitor channels 13 and 16. If a call from another vessel is detected, the radio would return a taped message explaining the nature of the voyage, along with a request to report the model's position. VI. SAIL HANDLING Sail trim: In order to minimize the possibility of tangles and fouled rigging, running rigging must be kept as simple as possible with 1:1 sheets and control lines where possible. Linear actuators, similar to those used for the autopilot tiller control, will be used to adjust sheets. Note that the duty cycle of an actuator used in this way is extremely intermittent, and their reliability should be far greater than that of the actuators used for steering. The mainsail will be controlled by a single-part sheet and one or two actuators. The jib will be most likely be a conventional non-self tacking working jib, with an actuator controlling each sheet independently. This arangement will probably offer the least possibility of a tangle, maintain good trim through the widest range of wind speeds and angles, and work well with roller furling. A single- sheet arrangement with a boom or tacking track might still be an attractive alternative, however. Reefing: The jib will be roller-furled around a rigid luff- support spar. Although luff-support reefing/furling systems are subject to reliability problems on larger vessels, the approach here will be to use a grossly oversize system. There will be only two positions for the jib: furled and unfurled. The furling spool will be driven by a continuous chain drive from a small electric motor. There will be one fairly deep area reef in the mainsail. A linear actuator will slack the halyard, tighten the reef clew, and tighten the reef tack simultaneously. No lacing lines will be used. In order to insure smooth working of the mainsail luff, steel lugs will be sued at the inboard end of each batten. A lubrication system will introduce lubricant into the track. In moderate weather, the reef will be exercised about once a day to prevent salt build-up or freezing of moving parts. All actuators and servo-motors for trim and reefing will be located either inside the main boom, or in a special shallow compartment located just below the main deck, sealed from the rest of the model's interior. Because a small amount of water will enter this compartment through the ports where control lines penetrate the deck, here must be provision for draining or pumping this water overboard. VII. POWER Electrical power will be provided by several large lead-acid deep discharge type storage batteries, maintained by solar panels on deck and possibly also on the model's starboard side. Approximately 100-150 watts of peak rated charging power will be required for a summer crossing, which entails approximately 20-30 square feet of solar panel area (using off-the-shelf marine solar charging panels). For a winter crossing, it is estimated that approximately three to four times the peak rated charging capability will be needed, unless other power-economizing measured are taken. A low power mode will be available to the model, with reduced steering input, less frequent sail trim, and possibly delayed or abbreviated radio contact. VIII. ON-BOARD COMPUTER The on-board computer will probably be an off-the-shelf MS-DOS laptop computer, selected for reliability in adverse or more computers will be installed for redundancy, although only one will be environmental conditions. Two operating at any one time under normal conditions. IX. DEPARTURE/ARRIVAL Departure and arrival will require real-time steering control from an escort vessel. This will be accomplished by sending course instructions to the autopilot by means of conventional designated radio control frequencies. If the model reaches the designated arrival waypoint before the escort vessel is on station, then the model will heave to and send an intermittent homing signal on VHF frequencies.