A diet for the boat

May 2024

By Christopher Birch

We just put our boat on Ozempic. It had to happen. For many years my wife Alex and I occasionally indulged in a shameful pleasure: We ran our engine when we were at anchor just to charge the batteries. We knew it was a bad habit, but it was just so satisfying to watch those amps flow and to see the joy in our batteries’ eyes as they thrilled over the feeding frenzy.

Every diesel pro will tell you that running an engine at idle is horrible for its health. Fuel pumps and injectors get gummed up, and the engine innards frost over with a nasty coating of carbon in spots. It’s best to “run ’em hard and run ’em hot,” they say. The needless and regrettable fuel consumption and carbon emissions compound the sin of idling. Maybe most importantly, running the engine destroys the peace and quiet of the anchorage for us and all our neighbors. It’s a rude and unhealthy practice.

We needed to be better but we just didn’t know how to stop idling. Then the new diet drug Ozempic came along and injected us with inspiration. If a medicine could help people lose their appetite for food, maybe we could rejigger our boat to help us lose our appetite for engine-charging. I figured that if we permanently disconnected the engine alternator charging wire from our boat’s house battery bank, idling would be no fun at all and we would finally stop our bad habit. So that’s what we’ve done. And it works!

A little boat project got us started. Like many sailors, we’ve recently switched our onboard house bank over to lithium. It’s easy to pull power out of a lithium battery, but it’s a little trickier to put power back into one. Most alternators that come as original equipment on a diesel engine produce too much electrical noise for lithium, and their charging profile isn’t compatible. So when switching up to the new battery technology, the standard solution is to replace the alternator that came with the engine with a high-capacity alternator designed for lithium. These big, expensive alternators throw out a ton of power and lithium will happily soak up every watt of it.

Here’s where two problems creep in: First, the engine isn’t designed to run that big-hipped new alternator, and it struggles with the work. The overload causes excessive belt wear and engine wear. Second, unless the batteries happen to sit less than 12 inches away from the alternator, the required wiring run will be massive in diameter and impractical to install. Technicians do their best, but wiring inevitably remains undersized and the systems run hot as a result. Sometimes dangerously hot. All the problems with lithium that I’ve seen have nothing to do with the batteries themselves and everything to do with poorly engineered engine-charging systems.

The solution is to stick with the alternator that came with the engine and task it with only charging its own AGM start battery. For the lithium house battery bank, we need to find another charging source of power. Options include shore power, genset, wind, solar, hydro, and DC to DC charging.

Alex and I live on our boat and are out voyaging full-time. We prefer life on the anchor and rarely go to the dock. In our first 10 years with the boat, we plugged into shore power exactly once. I finally offloaded the charger and the big yellow cord in an effort to lighten the boat. Shore power just isn’t our thing.

Other choices have drawbacks, too: An auxiliary genset combines all the downsides of running the main engine with the complexity and expense of an additional system – no thanks. Wind generators are too noisy. Instead, we went with the remaining options: solar, hydro and DC to DC.

The plan is simple: Fire up the diesel for moving the boat when it’s not practical to sail. (I’ll have that argument with Larry Pardey in the afterlife.) And rely on solar, primarily, for charging house batteries.

The wiring aboard our boat enforces this doctrine. Like a good diet pill, our charging system takes away all the fun from gluttony. Our little DC to DC charger passes a pathetic 30 amp drip of power from the engine start battery over to the house battery when the engine is running. It’s simple and easy and the power it puts out is free of electrical noise, but it’s a nearly inconsequential amount of power and fuels none of our appetites for sin. It’s just boring watching a measly 30 amps trickle across the boat so we shut down the diesel when we aren’t motoring somewhere. With the lazy man’s solution off the table, we’re forced to make better choices in our life. Like less power consumption and more solar power input.

The screenshot at right shows the production from one of the seven independently regulated 100-watt panels aboard our boat. Installing solar power is like signing up for a gym membership; it’s healthy and makes you feel good about yourself. Free, silent, solar power does all the heavy lifting in our energy budget. I also think it’s just shy of miraculous that the hot sun makes my beer cold – a party trick that never gets old! At night, and when the sun is behind clouds, our hydro-generator takes over power production while making a quiet hum in our wake.

We have many modern, power-hungry cruising amenities aboard our boat, things like refrigeration, Starlink, and a watermaker. We enjoy these luxuries but we also make every effort to economize and try to be smart about our power usage. Opting to make water and charge tool batteries when the house batteries are at 100% and overflowing in the sun’s bounty is one of many examples of how we’re actively working to optimize the balance between power production and consumption onboard. All the while, we leave the diesel in the tank.

Bad dietary habits and bad boat habits have a lot in common. Doctors yammer on about cholesterol and we know that a big slab of beef isn’t good for our health. (Or the cow’s health.) But it just tastes so darn good to eat steak while I idle my engine! Watching those amps fly while bovine blood dribbles down my chin is heaven and oh-so-hard to resist. Sometimes it’s helpful to have safeguards in place to save us from our worst selves.

Christopher Birch is the founder of Birch Marine Inc. on Long Wharf, Boston. He is now out cruising full-time with his wife, Alex, aboard their 36-foot Morris Justine. Follow their voyage at EagleSevenSailing.com.

 

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