My new boat, bought for $5,000 from a man who told us only after we’d paid that we had two days
to move the boat before he was kicked out of his slip, puttered out of the Alameda Channel and into San Francisco Bay. A 1974 Tartan 34C, "No Bubbles" fulfilled the promise of its name. At full throttle, the 14-hp Johnson outboard motor I’d lashed to the transom moved us wakelessly toward the Oyster Point Marina, ten miles across the bay. It would take six hours to get there.
| Story by Ian McNanie |
When I bought No Bubbles, I knew it needed work. The previous owner had taken the engine out to do repairs and left it in a dock cart for months, where it rusted into oblivion. And that was a problem I could actually see. But I wasn’t deterred. I work as an intern with former MythBuster Jamie Hyneman, who offered unlimited tools and advice. His shop has everything you need to build anything, and he spent years sailing a dive boat in the Caribbean. I also work at a robotics company. Between the two, I knew I could handle the project—especially since I’d decided to completely replace the shot motor with an electric one. Here’s how I did it.
At my electronics job, we were working with brushless 30-kilowatt scaled-up permanent magnet drone motors, which are much smaller and more powerful than similarly sized induction motors.
The motors are designed for DIY projects like airplanes and cars, and after writing custom firmware for one and troubleshooting the powertrain, I decided to order a 27-kV version for my sailboat. “KV” is a constant that approximates the rpm the motor will spin per volt applied to it. If I multiply kV (rpm/v) by my target voltage (80 v), I can predict that, unloaded, the motor will spin at about 2,160 rpm. Loaded, this puts it in a similar range to the boat’s original Atomic 4 engine. To control it, I added a 500-amp electronic speed controller (ESC) from Alien Power System hooked up to an RC transmitter.
One benefit presented itself before I even hit the water: The Tartan was designed with the motor right in the middle of the cabin. It takes up a lot of room. To walk through, you have to squeeze around the engine cover. But with the new tiny motor, which is only six inches in diameter and three inches thick, I could replace the engine cover with a small step and regain all of that floor space.
Jamie helped me attach the motor to the prop shaft. We figured it would probably have enough torque to start moving the prop, so I made it direct drive for now, with no gear reduction. But if the bilge filled up and the bilge pump failed, that would leave the motor submerged. The salt water would destroy the bearings instantly. To avoid that, I built a small plexiglass box around the motor to keep the water out.
The motor runs on six 12-v 66-Ah deep-cycle batteries in series. On a calm day, it draws about 30 amps at about 3 knots. To make the boat go faster, I’ll eventually need to change the prop, up the voltage, and get a new ESC that can handle it.
I also found eighteen solar panels on Craigslist for only 20 cents/watt. Jamie and I welded an aluminum frame in an arch above the companionway, where we mounted five of the panels—power supply and an awesome rain shield. During peak sun, the panels can provide 375 watts. That’s fine for charging my house pack, which runs the basic electrical components of the boat, but the motor batteries still need to connect to shore power. Eventually I’ll cover the boat in the remaining panels and add a 3,500-watt Harbor Freight inverter generator. That should provide enough power to run the boat most of the time.
Chainplates are metal supports that poke through the deck for the rigging wires to clip to. They’re bolted to pieces of wood attached to the hull. The compartment surrounding the starboard knee was completely filled with water. Once I cut out the fiberglass around it, the plywood was so rotted I could scoop it out with my hands. I cut a new piece of wood, and Jamie gave me some fiberglass, epoxy, and filler to seal it back in. My biggest mistake was forgetting gloves. Getting the bits of epoxy out of my arm hair afterward might have been the hardest part of getting No Bubbles back on the water.
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Source : Popular Mechanics