tell me if this is a bad idea

I trust the collective braintrust here than most of the sailing forums I am.

I am planning on moving aboard a 37foot sailboat in the next couple of years and leaving land live (mostly) behind. In my quest to make things simple, yet still pleasant enough aboard, I am contemplating getting rid of the diesel engine and the diesel generator and going for a diesel electric hybrid (Motor drives the prop.. generator supplies power to it and the boat)

THe Boat will be mostly kept 12v.. but some things do not work so well on at the voltage.. like hot water heaters and the like.. but I do not want to fire up the generator everytime I want to use something that uses 120v.

I was considering adding 10 batteries in series to take some of the load off of the generator for transient 120v usage (laptop, microwave, stuff of that nature) but I find myself worried not of the voltage, but the amperage. I am a decent stage electrician, and while I often deal with 400amp service, I do not have to design these systems out.

So.. how many amps does 10 batteries.. say at 1000ccas, in series, put out at the end of the wire?

If you would look into the diesel electric hybrid system for sailboats it would give you dock side propulsion as well as able to run your hot water system.

You could also do a propane/natural gas system.

propane scares me. I have seen too many boats blown up from gas and propane. Usually one a summer down here at the shore.

But yes, that is the system I am looking at. I was just thinking batteries for light and transient loads so I do not have to power up the generator if I wanted to run a laptop all night or nuke a bag of popcorn and watch a movie

Diesel, battery array, inverter(s), controller. Generator charges batteries - no direct power. When the battery gets over-drawn the diesel kicks on ala a UPS with generator backup at a data center.

If you live on the boat you will be parked at a marina with actual power 99% of the time, no? So this is only "at sea" we are discussing?

at the dock during the spring,summer, and fall.. but I am intending on some long cruises and spending winter in the keys or caribbean.. so when on a mooring or at anchor, it is a bit hard to find shore power.

The only thing that worries me about my idea of 10 batteries in series.. I know the voltage should be around 120.. but what is the amperage going to be?

Depends on the batteries. Most alternate energy house systems run 10 little batteries like the ones found in computer UPS or kid's power wheels. Depending on the size, these will give you about 10 amps.

I'm no expert on this, but look into the DIY wind/solar energy sites for a proper answer on doing this the simple way.

good idea.. I never considered the DIY wind and solar people.

This is why I come to you guys for most things

10 batteries in series won't give any more amps than 1 battery, just more voltage.

amiright?

Wait, don't you need 120v AC? 12 batteries in series would still give you DC current. Match the number of batteries to your wattage demands, then run an inverter.

yea.. I was just reading on that Tom.. I was working from a vastly simplified worldview today it seems.

Too much research in too little time.

I will probably run about 4 or 5 patteries in parallel and run an inverter. I knew there was a reason nobody else was doing this

Yes, 120v AC (actually 110v) is a root-mean-square (RMS) value from the sine wave, very different from 10 12v DC batteries in series. You want an inverter, and you also want to make sure it's a true sine wave inverter, not an "approximate sine wave".

You also don't want to look at CCAs. Cold Cranking Amps is a rating for lead-acid starter batteries (the kind you put in traditional cars), which are constructed to optimize for giving a large amount of current for a short period of time (turning the starter motor). For this kind of application, you're going to want standby/deep cycle batteries, that are optimized for delivering a larger part of their total energy charge over a longer period of time at a lower current level. The two designs are very different, and a battery that's good for one is not good for the other.

^This. Look at reserve watt hours to compare batteries to each other.

Looks like this was a zombie thread, but a fun thought exercise. Would a trolling motor work? I doubt it with that keel, but I'll float it out there.

• Get a 36v (3 battery) and a 112lb thrust motor. Might be good enough? Probably would be slow as a dog though, no where near your hull speed if it could move it at all.
  • If it isn't enough thrust, you could run two of them, 6 batteries total
  • If it isn't enough capacity, but it is enough thrust, you could run 6 batteries in series/parallel for double the capacity