Skip to main content


Go Search

Bill's solar boat blog
Dragonfly 2012 plans
As the Penn State academic year winds down, the crew of the Dragonfly is contemplating summer adventures on the water, exploring the canals and lakes of Upstate New York. Since D'fly came out of the water last fall, we've sanded and repainted the bottom with antifouling paint. On our preimmersion to-do list are the installation of new sacrificial anodes, and a new darker blue color for the hull. The boat's batteries and other systems made it through the winter just fine.
Our summer plans are to travel leisurely and to run the engine only enough to make sure it's happy. For a season on the canal and hops of 20 miles or less, our electric propulsion system does everything we need.
MOG Solar Canal Boat
We heard recently from George McNeir III, the designer of the MOG Canal Boat, pictured above. George's new prototype boat is 40 feet long, solar electric (with an outboard backup), and he's prepping it to do the Great Loop. More at the MOG website:
We knew that the waterways would soon be humming with solar electric boats!
AGNI performance trial on Onondaga Lake
After a year on the water, Dragonfly's hull isn't as smooth as silk, but we decided to generate some real-world data about the performance of her AGNI motor. So on a recent calm day with negligible current, we zig-zagged back and forth across Onondaga Lake and collected data on electrical current draw and the boat's speed.
Speed trial graph
To put this in some perspective, consider the following table, which estimates the number of hours that the boat can be operated with our existing 400 amp hour (48V) battery bank. 
Hrs. operation
Hrs. operation
(solar array off)
(sunny day)
100 (est.)
The table uses some rough assumptions:
  1. We assume that the discharge rate doesn't affect the usable current. (In fact, batteries have greater usable current when they are discharged more slowly).
  2. To preserve battery life, we always stop drawing on the batteries when they are discharged 50%, a practice that is reflected in the two rightmost columns.
  3. For the "sunny day" scenario, we assume a constant rooftop current of 15 amps. In reality, our roof's electrical production ranges from <10 amps (early/late in the day) to about 28 amps (sun directly overhead), and the number of hours of usable sunlight varies with latitude and time of year.
Even with these simplifications, however, some things stand out. First, it takes almost no power to move the boat slowly, and the penalty for going faster is significant. To double the speed from 2 mph to 4 mph requires five times as much current. This is why you can move a 14 ton boat with a 12 hp motor. You can move a 100 ton boat with a 12 hp motor. You just can't move it very fast.
Second, in practical terms, the solar array extends the usable range of the batteries only at speeds under 4 mph. That's because at higher speeds, the electrical demand of the motor is so great that the boat's range is mostly a function of the charge on the battery pack.
Third, for a vessel like ours, water currents matter a lot. On this trip, we have found that on a sunny day with a modest favoring current of 1 mph or so, we can run the boat all day at about 3.5 mph and leave enough charge on the batteries for the next day. If, on the other hand, we face unfavorable currents of, say, 2 mph, our range will be so limited on electric that we are likely to run on diesel.
Winds have some role, but Dragonfly is a heavy, low profile vessel, so wind itself doesn't usually have a big effect on our progress. What wind DOES do, in open waters, is stir up big waves. For safety's sake, when waves are larger than 1 1/2 feet, we generally use the engine.
Hybrid canal boat vs. Toyota Prius
How does Dragonfly, a homebrew hybrid electric vehicle, stack up against the competition? We've been eagerly watching for hybrid electric boats on this trip, and the pickings have been slim.  Boating magazines are full of articles about "green" boats, sporting rooftop solar panels, auxiliary electric propulsion motors, etc., but they appear to be mostly:  1) as-yet unbuilt concept vessels, 2) small boats with limited ranges, or 3) fantastically expensive "green" yachts with gimmicks that don't begin to compensate for the enormous fuel-burning engines that drive the vessels most of the time. (Note: We have encountered a few noteworthy exceptions, like Ted Moores's Sparks:
Prius under sail
Commercially viable hybrid electric boats are on their way, but in the meantime, let's compare Dragonfly with a popular hybrid road vehicle, the Toyota Prius.
Model year
Weight (lbs)
HP (engine)
HP (motor)
Fuel consumption, engine only (mpg)
5-6 mpg
Fuel consumption, engine only (gph)
1 gph
Fuel consumption, engine-motor actual use (mpg) 10 mpg 50 mpg
Fuel consumption, engine-motor actual use (gph) 0.5 gph 1 gph
Fuel storage 100 gal 12 gal
Range (actual use) 1000 mi 600 mi
Bathrooms 2 0
As you can see, the canal boat is clearly the better performer in the category, "Number of bathrooms." The rest is a little harder to compare. After all, we're contrasting a floating 2BR/2BA house with a car. (A nice car, for sure.)
A couple of other carefully selected facts:
  • Every mile of Prius travel is powered, directly or indirectly, by fossil fuels. The energy for the vehicle's electric motor originates in gasoline. (Even the brake regen energy comes--indirectly--from the motive force of gasoline combustion). In contrast, when Dragonfly is running on its electric motor, all of the energy used to move it is solar photovoltaic. (For our Great Loop trip, we had no other way of recharging the propulsion batteries).
  • For full-time cruising boaters, a boat is not just their vehicle; it is also their home. For us in 2010-11, Dragonfly was not just a replacement for our Honda Fit; it was also, from an "ecological footprint" perspective, a replacement for our 4-bedroom house (which was rented to another family, and consequently became part of their ecological footprint).

Coming soon: power curves from sea trials on Onondaga Lake under no-wind/no-current conditions. The results may surprise you.

The Year Between Posts
Observant readers may notice that there's about a year's gap between the post below (June 11, 2010) and the post above (May 31, 2011). That's because Cynthia did most of the heavy lifting blog-wise during that period. Please visit her blog at There's also lots of photos at the SlowBoatCruise Facebook site.
"Are you some kind of engineer?"
Wherever we stop, people inquire about Dragonfly, which is great. Now that we're out of the western Erie Canal (the only place in North America where you're likely to see a steel-hulled packet boat), people typically first comment on the boat's unusual morphology, then on its family resemblance to European canal boats, and then--often much later--"Wow, that's a lot of solar panels." If I explain that the boat is a homemade solar electric/diesel hybrid vehicle, they usually respond, "So, you're an engineer?"
Solar array
As an admirer of engineers, I'm always quick to explain that no, I'm not an "Engineer." There is a profession of Engineering. Membership requires years of study and mastery of a great deal of specialized knowledge. Engineers take a lot more calculus than I did, and many of them actually use it.
Perhaps that's a theme emerging from this project: People don't need to be capital-E Engineers to "do" engineering. Ordinary people can tinker, and do interesting and innovative things to make the world a better place. Call it "little-e engineering." Or "Connecticut Yankee in King Arthur's Court" engineering.
Dragonfly's engine room
This is a view looking down into Dragonfly's engine room. (I like to call this space the "engine room" even though you can't actually stand up in it. You can, however, bang things with wrenches and yell, "I can't hold it together any longer, Cap'n!")
Way over on the left side of the photo there is a green panel with a round electric motor mounted on it. The motor is an AGNI permanent magnet motor, and its diameter is about the same as a dinner plate. The green panel is two pieces of 3/4" hardwood plywood laminated together, painted green (subtle), and given several coats of polyurethane. This motor mount assembly has assorted brackets and plates and bolts securing it together and attaching it to the boat's pre-existing engine stringers, which are two steel rails that straddle the propeller shaft. Most of the motor mount materials came from our local big-box hardware store.
The AGNI electric motor has one moving part. Its only requirement is an input of electricity, and even there it's not too fussy. It's wired to run on 48V, but it can operate at lower and higher voltages without any problem. It delivers near-maximum torque across its entire range, and can function efficiently at any speed in its range. For novice boaters like us, that's nice. Coming into a slip, we can spin the prop at 800 rpms or 1 rpm. Try that with an engine.
To the right of the motor assembly is the gray Yanmar diesel engine that came with the boat. The Yanmar is an extremely reliable engine and this particular Yanmar was well maintained for its first 20 years. I have no doubt that with TLC, it would propel us around the Great Loop safely and economically, and we have already used it to good effect in crossing Lake Ontario. Plus, a diesel engine is lovely to listen to. It's more industrially organic sounding than a gasoline engine.
But it does have hundreds of moving parts. And its complexity virtually guarantees problems. For example, while a car is cooled by dumping heat into the air, a boat is cooled by dumping heat into the water. Raw water is pulled from outside the boat into the boat, heated, then discharged. There are lots of ways of doing this (from fairly simple to very complex), but they all require sucking in water, sending it through your expensive engine or some kind of external heat exchanger, and then discharging it. Now imagine that you're driving your boat from the Mississippi River into the Gulf of Mexico. At best, that water will change from fresh (sort of) to salt (along with barnacle larvae, etc.). But we're now looking at a petrodisaster in the Gulf of Mexico; who knows what will come in with the coolant water? An electric motor doesn't have to deal with this problem. An electric motor doesn't need any stinking coolant water. It doesn't even need much air to stay cool, because it isn't burning stuff.
A marine diesel engine also typically has two sets of filter system to handle dirty fuel. Apparently it is very common for marine diesel to have water in it, which is very bad for engines. So in addition to the standard Yanmar fuel filtering system, almost every marine diesel will have an additional Racor filter system. Works well. Requires maintenance.
The photo below shows the power transmission part of the motor assembly. If you're a gear head, stay tuned for more on that in another post. If you're not a gear head, stick to Cynthia's blog. It's much more interesting!
Power transmission
We're in Mexico!
If you're trying to use the Looper Locator link, it may indicate that we've ventured far inland, which is not the case. Actually, we're on a quiet little river in Mexico, NY, just off Lake Ontario. The Looper Locator website seems to have a rather unconventional way of interpreting latitude and longitude information, mixing together data from different days in some as-yet-undetermined fashion. So it shows us suddenly lurching far off of known waterways. No worries. We'll figure the website out eventually, along with everything else!
We crossed ten miles of open water in Lake Ontario today in seas that were vaguely reminiscent of the TV show, "Deadliest Catch." It was a thrilling experience, in the sense of, "That would be really cool to watch on TV." Dragonfly comported herself admirably. She may not be an ocean trawler, but she has an awesomely large rudder and her prop is way under the boat. That means that she doesn't "catch air" (and run up revs pointlessly) and she listens to directions. And when she chugged into placid Little Salmon River, people came down to the dock and asked, "What's that?" "Is it really electric?" And we graciously answered all of their questions, right after we dashed onto shore and grabbed handfuls of dirt and kissed it.
(I want to thank Cynthia for resisting the urge to blog our daily entries in overly dramatic fashion. A trip like this, for newbies like us, is a mix of much quiet slowness and occasional, "Houston, we have a problem." In consideration of our parents, children, insurance agents, etc., a balance needs to be struck between literary dramatic effect and, well, understatement.)
Tomorrow should be simpler. We would like to cover more miles (up to Henderson's or Sackett's Harbors on the east end of Lake Ontario), but the winds will be from the south (from the land) rather than the north, the forecast is milder, and this part of the lake is less exposed. And there are lots of places to bail out. Most importantly, we have more knowledge about how the boat (and its crew) behaves in open water. We're a good team. It's an interesting blend of us both playing the roles of macho and wimp. If one of us says, "Let's go," the other can say, "No, not a good idea." But if we both always took an overly cautious stance, we'd still be in Macedon.
The people here at Mike's Marina are terrific. The proprietors, Mike and Beth, are gracious, and Fran Talaber generously offered maps, pointers, and enthusiasm for our endeavor, along with a bottle of delicious homemade wine.
Our solar propulsion batteries are fully charged. Let's hear it for fusion!
We're off! (Warning: Technical electrical content, albeit amateur)
Burgee flying
We set sail at 8 a.m. today in a light drizzle and ran for 8 1/2 hours on electric propulsion, thanks to sunshine that emerged in the afternoon and an intentional slow pace on our first day. Everything worked well--knock on wood--the only real worry coming late in the afternoon, when I realized that we had been drawing on the 12v house and bow thruster batteries all day and currently have no way of recharging them without shore power ("shore power" being a landline that you plug into at the end of the day, typically at a marina). This is more than just an academic concern: our 48v propulsion system relies on the boat's legacy 12v system. For example, the main switching relay (which releases high-amp 48v power to the motor) and the motor controller (which regulates the motor, using, for example, the throttle potentiometer) have both low-current 12v components (powered by the house battery) and high-current 48v components (from the solar array and batteries).
In other words, we could be steaming along in bright sunshine, producing electricity in excess of what was being used to turn the propeller, yet deplete the 12v house batteries enough to make the whole system inoperational.
This was a "known issue" during the design phase, left for later resolution. Well, "later" has turned into "now."
Eventual solution: We'll add a switch downstream of the solar power controller, which will allow us to manually switch the photovoltaic output from charging the 48v propulsion batteries to charging the 12v batteries. We may also want to isolate the propulsion system from the legacy electrical system altogether. By stepping down some of the 48v current to 12v, all of the sexy new solar/electric stuff could run off the new batteries. That would require adding some new busses, fuses, wiring, etc. Doable, elegant, sensible, not essential.
Intended interim solution: We plug into shore power at night, and the boat's legacy inverter/charger refreshes the house and bow thruster batteries, which, in turn, service the relays, motor controller, etc.
Problem: It is late in the day, and we don't know whether the free public dock in Clyde has electrical hookups. Further complicating the issue: Depleting a battery, even a deep-cycle battery, significantly decreases its usable life. That's a no-no. Our goal is to never draw down our batteries less than 50%.
Resolution: Two miles from Clyde, I suddenly realized--duh--that the boat's diesel engine can be operated at the same time as the electric propulsion system, as long as the transmission is in neutral, which of course it is when the electric motor is running. So, as the boat is cruising along under electric propulsion (Yanmar diesel in neutral), start the engine. Engine kicks on, dual alterators start charging the legacy batteries. (Okay, it feels a little foolish. We're quietly slipping along a waterway under electromotive propulsion, and running a diesel engine at the same time, which is basically idling. But a few minutes will suffice. Now the legacy battery system is recharged.)
Welcome to Bill's Sunboat Blog

Dragonfly in her new colors, and sporting a solar array

On or about June 1, 2010, we'll be leaving Macedon, New York, on a year-long journey around eastern North America. During the trip (and in the preparations before leaving), we'll be learning about environmental sustainability, community development, natural history, and engineering. With this blog, we'd like to invite you along.

Honeoye in her original colors

The "sunboat" is Dragonfly, a 41' long, 13 ton steel-hulled canal boat that was built in Skaneateles, NY in 1990 by Mid-Lakes Navigation, a family owned company that runs charters and hire boats on the Erie Canal. The Mid-Lakes boats are named after Finger Lakes, and our boat's original name was Honeoye. We'll be relaunching her as Dragonfly in summer 2010. The top picture is her new appearance, which includes a rooftop solar array. The bottom picture shows Honeoye's original color scheme.

Cynthia Berger and Bill Carlsen
State College, PA

A Mastodon in Macedon
An essay on the "natural history" of our boat:

 ‭(Hidden)‬ Admin Links