Probably the number one question I get asked about Eleccentricity, my electric lobster boat, is, “How far will it go before you have to stop and recharge?” Until now, I only had a vague idea. It’s like driving a car with a broken gas gauge. You develop a feel for when it’s time to stop for gas, but with an electric boat, you don’t even know how many “gallons” you put in. Now all that has changed with my latest semi-expensive gizmo, the Trimetric 2025 battery meter.
Batteries are rated by amp hour capacity, and that rating depends on how quickly they are discharged. My batteries are rated at 180-220 amp hours, fast discharge to slow discharge. Since I have six batteries that’s about 200 amp hours at 36 volts, or 7200 watt hours. So that’s 100 watts for 72 hours or 1000 watts for 7.2 hours. There is no way to poke or prod a battery to find out how many amp hours are left. True, the rest voltage drops as the batteries are depleted, but once the batteries are put to work, voltage measurements no longer work as a measure of remaining capacity unless left undisturbed for a while. Inconvenient. The Trimetric solves this by keeping track of every amp used and how long, and maintaining a running total, starting at zero after a full charge. So if I go for three days without a charge (I normally charge once a week) I can instantly read what percentage of my battery bank still remains, based on the numbers I programmed into the meter unique to my system.
This brings up an important point about batteries (and you thought the complexity was over?), that you can’t drain the battery bank 100% without it shortening the life of the battery. The life of a battery is defined by the number of discharge/charge cycles it can go through, and if you discharge it below 50% on a regular basis you will be buying a new battery bank in a few years. I like to draw down no more than 30%, which should allow me 2000 cycles or 10 years. The new gizmo will help me with this.
Now that I have completed sea trials I can accurately answer the range question. The thing about electric propulsion is that slow is better. Double the speed and you will triple or even quadruple the power required. At low speeds the range is great: 200 miles at 1 MPH. With a modest 30% battery drawdown that range is 70 miles, not bad. Even at 3 MPH the range is around 28 miles, but with electric power it’s not like you stop abruptly after 28 miles, remember, you can always slow down a little and extend your range and even increase the discharge to 40% or 50%.
Things get interesting when we add solar panels (virtually, at this point). The new roof I added has the capacity to hold about 400 watts of solar. This alone has the ability to push the boat at around 4 MPH, giving infinite range at this speed…as long as the sun shines. By the usual standards of figuring solar gain, this would happen between 4 to 5 hours per day. It also means greater range at higher speeds, and the chance to recharge when at rest. But that’s another big chunk of change, not one I’m quite willing to part with at this time.
So why go electric? You can easily put an outboard on your boat and be like everyone else. I spent a little more and got a quiet ride, a recharged battery bank for less than a buck and smoke-free boating no matter which way the wind blows. And soon, my range will be extended…as long as the sun shines.
8/10 Update: I can now report that one circuit of hauling my 5 traps took 3 amp hours of battery reserve. That’s 1.5% of my total battery capacity, 5% of my drawdown goal of 30%, and 3 amp hours X 36 volts = 108 watt hours. If we assume a charge efficiency of 93% then it will take 116 watt hours of utility power, which sells for about $0.18 per kilowatt hour. So the fuel for this 5 trap haul (round trip) cost .116 X .18=2¢