I first wrote about doing this back in 2005 or so.? I converted my boat to electric in 2003 .

In 2005 I hauled it out and repaired bottom damage, etc, got it prettied up, then got it out on the river.? Then I did a 90 mile round trip on the Columbia River to the Cathlamet Wooden Boat Show.? With just about 300ah at 36v onboard, there’s no way I could make the trip on shore power alone.? And I didn’t think I’d be able to recharge at Cathlamet or anywhere else on the river.? So I brought some gasoline, a Honda EU2000i genset and 2 chargers.? Going downstream I realized that one of my chargers wasn’t working, so I only had one running (generating just 20amps to the pack) going downstream. ?To make time, I was probably cruising at 40amps.? And so, the pack saw a net loss of 20amps.? By the time we reached the boat show the pack was down about 150ah---and I couldn’t recharge at the docks. ?My wife brought me a spare charger and so, going back upstream I had 40amps of charge current.? If I was using just 40amps, the net current was zero and the pack voltage unchanging. ?But to make it upstream at any rate, I used about 55amps.? After several hours of this, we rolled into a marina for the night (again, no charging available and didn’t want to annoy folks with my genset) at this point maybe 230amp-hours down.? The next morning, things were still not ideal (bad tides) and so initially was still using power despite the genset and chargers.? But things improved and so it eventually was clear I’d make it back, barely---nearly 300ah used from the pack on the trip.? As I recall, the genset/chargers provided about 800ah on the trip.

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Anyway, bottom line is you need to know your pack’s state, what your genset/chargers are capable of and what power levels you’ll need for your trip.? Plan it out and give yourself extra time.? The slower you can run the boat and make progress, generally, the less energy it will take to go the distance.? It’s more complicated with current flow---i.e. with a 2kt current you wouldn’t want to slow your motor to the point that you go 2kts on the water.? Still, do the calcs, bring the fuel, bring spare parts as needed and hope that your genset/charger keeps running. ?Plan for contingencies for the case of those things failing---i.e. keeping enough pack energy to get to the next (or the last) harbor or perhaps having solar or wind power available---or cell phone and a wife who could bring parts J.

I like to power in and out of marinas (or towns) on just electric.? Knowing it’s 4 hours at 3knots vs 3 hours at 4knots, needing to get to the destination in 3 hours dictates the faster rate---at least for the main part of the trip.

It’s fun to watch the Amp gauge.? Start up the genset, plug in the chargers, watch 40amps going into the pack and seeing the bump in pack voltage is nice. ?Then heading out, current drops as you pick up speed until the current direction flips. ?If starting out, your pack is likely already full, so you either let the charger(s) respond to that or you’d want to increase boat speed to draw more current until the net current goes to zero or negative.

It’s all pretty obvious really.

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Enjoy.

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-MT

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Great point.? Also, if you’re like me and don’t necessarily use actual chargers, but instead power supplies used as a 2-or 3-stage charger, consider that as a charger, the power supply needs to be able to handle running in current limit for a long time (most of the charge cycle).? A friend bought a 30amp “charger” for his boat pack but quickly found it would just shut off after long.? I looked into its detail design and the power control chip used and indeed the circuit was doing what it was wired up to do.? In his case, I got this resolved by adding a resistor in one spot that based on the specs of the chip allowed the power supply to run in current limit continuously.? We also found that the subsequent iteration of these “Meanwell” power supply/chargers actual include a switch allowing enabling of 2-stage charging (constant current limit “CI” phase).

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Also when you are cruising (genset running, chargers delivering and motor pushing), if you really need maximum or some minimum amount of steady power from your genset to the pack, be sure that the pack voltage is BELOW the CV set point for your charger/power supplies.? Listen to the genset and if it starts running easier, there’s your clue.? It’s very easy to think you’re still getting full power to the pack only to find that the voltage rose slightly and now one or more of the supplies starts ramping its current output down.? When this happens you can also experience “motor-boating” or a cycling between full-current, then lower, then full again, then lower again as the chargers drift in and out of the CV ramp.? To avoid this, increase the speed of your motor until the charge voltage drops below the start of the CV ramp.

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