Power and Propulsion
The fundamental flavor of this project precludes nasty pollution-belching 2-stroke outboard motors (which are fast becoming illegal anyway, and rightly so), but we obviously need auxiliary propulsion if we are not to be entirely at the mercy of fickle winds and currents. I mentioned the sail earlier – a 21-foot freestanding aluminum mast carrying a 93 square-foot sock-luff roller-furling vertically battened main, with an 8-foot boom on a gooseneck bearing to allow free mast rotation.

A couple hundred miles on a Fulmar-19 with its deployable pedal drive unit convinced me: the way to human-power a boat is with leg muscles, not arm-powered paddles. A Microship can cruise about 4 knots with a small SpinFin drive unit made by Bob Stuart... faster than paddle-powered kayak cruising speed despite considerably more weight and three times the number of hulls.

Each Microship carries one of these pedal thrusters, mounted outboard on the starboard side and retractable into a nacelle when not in use (or when it’s necessary to access the prop through a hinged, gasketed access port for cleaning or replacement). Since the unit is side instead of center mounted, the pedals are of the “double throw” variety; the SpinFin’s input shaft is coupled to a removable machined assembly in the shape of a squarish ‘S.’ Removability is key – remember, we need to be able to sleep in the hulls.

The thruster itself is an elegant piece of engineering. A 5/8" stainless shaft on the left side of the device carries crank rotation and serves as a turning axis for deployment (via a lever inside the hull with adjustable latches and emergency kick-up release). Molded to the end of the shaft is a stepped collar of filled epoxy and glass, carrying the roller bearings as well as a 90-tooth drive gear, coupled via 1/4"-pitch chain to a 10-tooth cog on the propeller shaft. A tensioned idler reduces the cross-section of the unit to the minimum necessary to pass the chain (which makes a 90-degree twist), and the prop is a slender 13" two-blade unit. A molded skeg protects this from bottom contact, and the internals run in a light oil bath to keep it quiet and prevent corrosion.

The other auxiliary power source is solar – with each boat carrying a massive Solarex 480-watt folding photovoltaic array. Under optimum conditions, this can generate over 32 amps of 12V power, which is approximately full thrust for a Minn-Kota 42EX electric motor. Pivoting down when needed from the port afterdeck just behind the arch, this robust thruster is indexed into a steering motor that allows manual or computer control of propulsion angle, with hall-effect position feedback.

The solar panels themselves are a dominant feature of the finished boat – the size equivalent to nearly a ping-pong table on each side, filling the spaces between hulls and overlapping the crossbeams. They are hinged to the center hull by locking pins emanating from the “gunwale bellies” next to the cowling, and are bungeed to rails on the amas to allow flexion in response to cyclic heeling forces or the odd slamming wave. Nonskid tape covers all non-active area to make moving around a bit safer, but the basic way to stroll between cockpit and dock is on the nonskid-coated back of a folded panel – each side’s array consists of four separate panels, hinged into two pairs. This not only allows retraction in rough conditions, but complete pack-away removability for security when we’re away from the boats.

One of the problems, of course, is that these things have to handle body weight – which, on a boat, can be amplified considerably by the dynamics of ungracefully falling down. To yield the best stiffness-to-weight ratio, we specified ultralight Solarex modules... fragile Tedlar sandwiches of photovoltaic cells without the usual aluminum or stainless backing. We then vacuum-bagged fir-framed substrates of 1” Divinycell foam core, backed by 10-ounce fiberglass, and topped by a sandwich of 4mm okoume marine ply and 6-ounce satin glass. The solar panels themselves were then simply glued to these light but beefy structures which support hinges, latches, internal wiring channels, and all mounting hardware.

(Note from June, 2003:  The foam-core solar array turned out to be a bad idea, as the panels overheat in the sun... though they work fine in the dark.  A current project is to create a new solar structure that sheds heat more effectively.)

The electronic challenge here was to manage thruster power in such a way that we don’t inadvertently kill the marine deep-cycle battery on each boat... cruising along at maximum power would, with no solar input at all, drain a fully charged battery in about 3 hours (defining a cruising range in swimming-pool conditions of about 15 miles). Normally, of course, there will be some input from the solar array... as well as some battery charging current and additional load imposed by the systems in the console. Responsibility for intelligent power management is the domain of three embedded microprocessors on the Shipnet control network: every few seconds, they perform a complete power budget analysis, tweak battery charging levels, optimize the transfer of energy from the solar array using a peak-power tracking algorithm, calculate how much “free energy” is left over after all other needs are satisfied, then set that as maximum thrust at full throttle. It’s thus easy to crank the throttle to full speed ahead and cruise on solar power alone, knowing that precious amps will be rationed in a way that won’t deplete the batteries.

(Naturally, there’s an emergency override switch that applies full power to the thruster – if a freighter suddenly materializes on a collision course, the future status of the battery is no longer as interesting!)

And no, pedal, solar, and sail speeds do NOT add linearly... boats don’t work that way. But it is nice to have options. Incidentally, we considered the seemingly obvious approach of integrating pedal and electric modes into a single system, but there is no good way to do it that does not involve jackshafts, clutches, speed reducers, and nonstandard hardware. Though it may seem redundant, having separate electric and pedal thrusters adds a lot of reliability and simplicity to the design. The combination of three propulsion modes gives the Microships maximum flexibility under a wide range of conditions without having to pollute the water, carry stinky fuels, and generate nasty noises.