Sunday, August 16, 2015

Buiding confidence

My two strong heroes: Charles and Andrew

First connection tests with the controller. Notice the snacks ;)
My boat is not the same that it was 6 weeks ago, when I sailed it down to Helsinki. First I started experimenting with the idea of an electric motor inside of a traditional combustion outboard motor. I first bought a 1966 6hp Evinrude. The motor didn't quite fit inside of the hood, but otherwise it worked great. Only downside was the small size and pitch of the propeller. I know that my electric motor's max amp power is 100A, but at max voltage(24V) it was only using 40A to get the max speed(3,5kt). There was still 60% of torque left. So the next week I bought another "shell": 70's 15hp Terhi(Valmet) Finnish made outboard. This one had already bigger and steeper prob and the possibility to add even bigger. I had some difficulties with adjusting the shaft coupling, but got it working. Now I could also fit the motor inside without modifying the hood. This bigger outboard added some speed and power to my boat, but the main problem with converting outboards to electric ones was still there: revolutions per minute. Basic outboard engines run around 4000-6000rpm(that's what I've heard, cos the first time I opened an outboard was the first one I converted 4 weeks ago ;) and my electric motor runs only around 2000rpm. It has the torque, but not the speed. The only way to rev it up was to double the voltage. So I made a test by putting two of my three battery pairs to series and make 48V for the motor. This doubles the rpm to 4000+ and gives the max power of around 4kW. With this configuration I got the speed up to 5 knots, but the cost of consuming more than twice the amps than going 4 knots. I haven't done yet more throughout tests about the consumption versus speed, but I know when it's calm I can go 3 knots with only 30 amps of power. That speed gets me twice the hours than going 4 kts. The 48V mode is only for emergency situations, when I need the speed and power to go upwind or against harsh conditions.
Andrew was the firstborn. With him I also introduced the
new 220Ah battery banks to the boat.
The positive surprise is to notice that the efficiency of my geared solution is pretty good if I compare it to the cheap 1.1kW outboard that I had last year that was giving me just about 3 knots of speed at full power and using around 30-40 amps. So I've began to think that this electric motor style is gonna be the one that take me around and now that I have two working shells, I will keep the smaller one(Evinrude) with me as a spare, if something happens to the shaft, gear of prop. I haven't got the regeneration to work yet, cos my main goal was to make a working electric propulsion motor first, then if I can get it to charge my batteries, that will be just a bonus :)
I'm happy about what I've archived so far with the boat. Trust is something that you have to earn. You cannot buy it, nor get for free. On trust you can build something that makes you confident. That's how I've been starting to feel about my boat and my plans. And that feels good ;)