Replacing diesel with electric

[keith4001r]

Emergency: sails won't cut it.
I think many here are missing the part where I will have a gas generator "for charging the batteries ".
Freak hurricane blows in- I'm screwed.
Big hole in the boat- I'm screwed.
Jaws bites off the transom- I'm screwed.
But screwed or not, the batteries will be up.

[GrowleyMonster]

Originally Posted by Dockhead

I think it's actually pretty easy to summarize the mass of discussion.

* Electric propulsion fairly expensive, but might work just fine for light usage -- principally getting in and out of marinas in reasonable weather and otherwise doing everything else under sail.

* No substitute for diesel if you expect to motor any kind of distances in calms or motor against the wind in strong weather.

* Hybrid electric propulsion -- trying to get the range and power of mechanical drive diesel propulsion by pairing an electric motor with a diesel generator -- doesn't really work at the scale we have and technology which presently exists. Because the generator has to be so big, and efficiency losses converting to electricity and back, and all the weight and volume of so many systems.



I think you will get it more or less right if you think of electric propulsion as an enhancement to the functionality of an engine-less boat, rather than as a substitute for diesel propulsion.

A diesel auxiliary engine -- they way they have been specified for the last few decades -- turns a cruising sailboat into a truly dual propulsion vessel, which can either sail or motor, or motorsail. If you use your boat like this, you will be disappointed in electric propulsion.

However, if you are experienced sailing engineless boats (I am, for example), and don't mind using your boat that way most of the time (I do mind, but YMMV), then you might be delighted with the advantages of electric propulsion -- silent, clean, simple, no fuel, etc., etc. This remark of yours: "I only want mechanical propulsion to get in and out of a slip and for an emergency." -- sounds like you might be a good candidate.

Much of what you say there has a strong core, at least, of truth. However, electric propulsion is only expensive if you let it be expensive. My repower, including a 10.56kw/hr bank. cost me less than $2500, and if I knew then what I know now, I could have done it even cheaper. The cheapest new marine diesel out there is I believe about $8k in the crate, diy install. Electric is not ideal for everybody, no. Anyone who has researched the topic thoroughly and still has doubts, should probably not go for it. But cost should never be an issue. Even turnkey systems can come in well under the cost of a diesel.

[keith4001r]

Originally Posted by Jim Cate

I'm struck by the "emergency" part of the statement myself. Many "emergencies" are situations where the minimum power present in the proposed electric system would be sadly lacking. Other "emergency" scenarios would over tax the range limitations.

I'd say that only the "in and out of a marina berth" application is well suited to the electric drive as described.

Jim

Thanks, Jim. I think you get the idea.

[keith4001r]

Originally Posted by Dave_S

You have probably seen this but these guys did this for US$1400. It's worth a look if you haven't seen it.

Sailing Uma— Electro-Beke

Thanks, and I have. This may be what got me thinking about it in the first place.

[keith4001r]

Originally Posted by GrowleyMonster

Much of what you say there has a strong core, at least, of truth. However, electric propulsion is only expensive if you let it be expensive. My repower, including a 10.56kw/hr bank. cost me less than $2500, and if I knew then what I know now, I could have done it even cheaper. The cheapest new marine diesel out there is I believe about $8k in the crate, diy install. Electric is not ideal for everybody, no. Anyone who has researched the topic thoroughly and still has doubts, should probably not go for it. But cost should never be an issue. Even turnkey systems can come in well under the cost of a diesel.

Growley, I'd be interested in knowing what you would do to trim the budget. I'm working on a pretty tight budget myself.
Thanks for your input.

[GrowleyMonster]

Originally Posted by valhalla360

Actually the worst of both worlds:
- Heavier
- More Complex
- More cost
- Less efficient

There really is nothing it does better. It isn't even good for running house electrical loads as a generator sized for propulsion is massive overkill for house loads.

Not sure what you are implying about torque. Assuming the generator is matched to the engine, torque isn't an issue.

The voltage isn't a big concern if you are OK with running a 110v or 220v system. Yes, it needs respect and proper installation but no more dangerous than your Mr. Coffee.

Indeed. But "proper installation" can be the deal killer for higher voltages. Higher voltage systems actually offer greater efficiency due to lower current and exponentially smaller copper losses. However the electrical standards are somewhat different when you go over 50V. A nice big 48v bank is actually kind of a sweet spot. If you go over that voltage you may as well go to 144v or higher. A 110vac inverter should run more efficiently at higher voltages, btw.

A hybrid system is indeed going to cost more, of course, add weight, and be more complex. However it doesn't have to be particularly inefficient. Case in point... piggybacking an electric motor over the prop shaft with belt and pulleys. You can simply ignore the electric motor when it is not needed. Or you can adjust the regen and use the turning shaft to spin the motor and produce electricity at about 92% efficiency, not far behind what you get from a marine alternator. Or if you sail fast enough, (most boats under 30 feet won't) you can generate power by the prop freewheeling. (The transmission must be able to sustain freewheeling of the output shaft, and not all of them can.) Or leave the transmission in neutral and use the electric drive for quiet operation or low speed precision maneuvering, or instant on demand propulsion for tacking, etc. Some boats are a PITA to tack, especially single handed, and being able to simply twist a knob and get a burst of go can be pretty handy. A straight diesel electric setup where a diesel generator powers an electric motor has some advantages in some applications, but this IS very inefficient.

I will say this. I considered going hybrid, but discarded the idea due to lack of space in my engine compartment and the desire to cut my dependence on fossil fuel to minimum, and on infernal combustion engines to zero. It does look better on paper than it does in reality, for most users, but for someone willing to deal with the extra complexity and expense, hybrid can offer great flexibility, especially if you add a respectably sized solar array to the mix.

Another caveat... it is possible to add so much stuff to a boat that it becomes more stuff than boat. Some boats simply should not be considered proper homes for a hybrid propulsion system. If you can't figure out where you will put 4 8D or 8 GC2 batteries, your boat needs to have diesel or electric but not both, IMHO.

[GrowleyMonster]

Originally Posted by hafa

One thing I've not seen nor heard of is a prop shaft that can be directly driven by either an electric motor or a diesel engine. Did I just miss it?

Old idea, has been implemented quite a bit and even mentioned in this thread. People who are not tinkerers or technically inclined usually end up not liking it. Some folks can't even be bothered to maintain their diesel engine, let alone monitor a more complex system. And it is not the answer to world hunger or the ozone hole. If you think you might benefit from such a system after doing your research, then by all means, build it. All you need is a few inches of exposed prop shaft that you can secure a pulley to, some basic tool skills, some angle iron and plate, pulleys, belts, motor and controller, cable and wire, and a 48v battery bank. And your existing diesel. You could even use a pump clutch to completely isolate the motor from the shaft when desired, though spinning it with no load won't hurt a thing and your diesel won't even notice the resistance. Or you can release belt tension and remove the belt. Whatever. To drive the prop with the diesel, just start it up and put it in gear. To drive it with the e-motor, take the engine out of gear and run the motor. To charge batteries from the trailing shaft, just turn up the regen with the engine out of gear. To charge batteries with the diesel, start the diesel, put it in gear, turn on the regen. This will turn the prop as well, but you can install a second clutch on the shaft if you want to disengage the prop and charge with the diesel. If this seems too complicated, you might want to forget about it.

A straight electric drive comes with a fairly small weight penalty since you are getting rid of fuel tanks and a presumably dead diesel or gas engine, and associated systems. The electric motor weight is trivial, as is the controller weight, but the batteries of a large bank can be heavy. Typpically a simple electric repower adds about 300lbs to the boat. A hybrid system adds battery weight, but keeps the diesel and fuel tank. The weight penalty then, is substantial. And we havent even considered 600w or so of solar panels. In a displacement sailboat, a few hundred extra pounds is no biggie, maybe. Maybe not. In a small boat, space is an issue. Not every boat is a good candidate for a hybrid drive, nor is every owner or skipper. You would need to ask yourself exactly why you want a hybrid system in the first place. Like I said, its not for everyone.

[GrowleyMonster]

Originally Posted by keith4001r

Growley, I'd be interested in knowing what you would do to trim the budget. I'm working on a pretty tight budget myself.
Thanks for your input.

Well, I am already bottomed out on the batteries. 8 6v GC2 Eveready golf cart batteries, 220ah, from Sams Club, bought 3 years ago for $85/ea. It is really hard to get any cheaper, and these batts are holding up surprisingly well. Having experimented with direct drive, I now see potential for increased efficiency by ditching the reduction gear in favor of a simple thrust bearing, sizing the prop accordingly. That idea is still in the works, not to save money but to save killawatts. But its a fact, you can easily save $400 or so if you can get by without a reduction gear. Finally, there is the motor and controller. I went with a BLDC (or PMAC if you insist) 5kw motor made by motenergy, and it was cheap enough that I bought a spare. The controller originally was a square wave controller from Kelly, and I have since upgraded to sine wave. Slightly less efficient but much cheaper would be a salvaged motor and controller from an old golf cart or forklift. Figure $800 for a BLDC motor and 300a controller. Salvaged brushed DC motor and controller might go for $100 to $400. Maybe even FREE, if you are a good scavenger. Thats about it. I am using 2/0 welding cable for phase wires and battery connections. Switching to 1/0 would not save me much. I might do what one enterprising fellow down in Panama does, though, and make my own terminal lugs out of copper pipe. They can be pricey. Oh, and charger. I bought a 4 bank 12v charger from Worst Marine and it works pretty good, except it doesn't equalize, of course, and I have to connect each pair of leads to TWO of the 6v batteries anyway. So I found a surplus Variac, a rectifier from an old stick welder, meters and cable, and made a fully manual charger that I can charge the whole bank in series, or each battery individually, with correct and proper equalizing capability. I would not bother with the smart charger. I would use the variac rig for general charging, and build a small float charger for automatic maintenance. Be advised, a manual charger requires vigilant monitoring while charging. Also with no isolation transformer, certain precautions are necessary. But it is extremely flexible and not expensive, and I need it anyway to equalize, so really the 4 bank smart charger is not justified, for me. YMMV. Some folks NEED a smart charger.

Oh, remember with a brushed motor, propane or gasoline accessories onboard are a no-no. Well, I cook with diesel anyway.

[ranger58sb]

Originally Posted by keith4001r

Emergency: sails won't cut it.
I think many here are missing the part where I will have a gas generator "for charging the batteries ".
Freak hurricane blows in- I'm screwed.
Big hole in the boat- I'm screwed.
Jaws bites off the transom- I'm screwed.
But screwed or not, the batteries will be up.

Eyes wide open!



FWIW, I've read that using the portable gen to run a battery charger works faster than charging batteries directly from the portable gen. Just maybe something to examine, if you haven't already.

Originally Posted by GrowleyMonster

My repower, including a 10.56kw/hr bank. cost me less than $2500, and if I knew then what I know now, I could have done it even cheaper. The cheapest new marine diesel out there is I believe about $8k in the crate, diy install.

How long before you have to replace the electric bank? I'd guess the life of that new diesel would be somewhere between 30-50 years? How many bank replacements would be needed over that kind of lifespan?

(I realize it's not a perfect comparison, since the electric system includes both mechanicals and "fuel"...)

-Chris

[valhalla360]

Originally Posted by keith4001r

Emergency: sails won't cut it.
I think many here are missing the part where I will have a gas generator "for charging the batteries ".
Freak hurricane blows in- I'm screwed.
Big hole in the boat- I'm screwed.
Jaws bites off the transom- I'm screwed.
But screwed or not, the batteries will be up.

If you put in a generator that matches the HP requirements, a backup generator will service the "emergency" aspect.

You don't say what your boat and current power is so let's assume a 35' mono with a 25kw diesel.

If you put in a 25kw electric motor with a 30kw generator (to account for losses), you have roughly the same emergency capability but you have an expensive heavy system that is much heavier. You could even cut back a bit on the generator if your willing to accept slightly less capability. Say you put in a 15kw generator with 10kwh of batteries (a large heavy bank). Assuming 100% full batteries, that will give you about 1/2hr of full power before risk of damaging the batteries, then another 20-25min before power starts to drop off dramatically. (Of course, if you aren't at 100%, it could be dramatically less time at full power)

Now from your description, it was more likely a 2-3kw portable generator which are actually rated at 1.6-2kw of continuous output (in the prior examples, I was assuming the 30kw & 15kw generators were continuous output). Assuming the batteries are almost empty that leaves you 2kw you can apply to the prop shaft, 2kw might get you 2kts in calm conditions without wind (my 5hp dingy motor would get our 34' cat up to 3kts in those conditions). Against any headwind, you will be lucky to hold position let alone make headway. I've used all of my 25hp (~20kw) to make 3kts against a 30-35kt headwind. With 1/10th that we would have been going backwards. (in one example it was a 50' wide channel, so no tacking up the channel).

So realistically, you have negligible emergency capability.

[keith4001r]

30' mono, non running 16hp diesel.

Again,
I'll check weather for wind before leaving the dock,
If it's sunny, solar will charge batteries.
If insufficient sun, gas generator will charge batteries.

Not interested in hybrid, strictly electric for propulsion with a generator for charging only when necessary.

Thanks

[valhalla360]

One option where it could be viable is a catamaran:

Put a standard diesel in one hull, slightly larger than normal (if the boat normally gets a pair of 25kw engines, put in a 40kw engine).

In the other hull put in an electric motor and generator sized for house loads...say a 5-10kw generator and 10kw electric motor. You could even add a modest battery bank...say 5kwh.

Around the docks, you would have to get used to the difference in response but you still have the twin engine docking advantages.

Many catamaran owners run on one engine for normal cruising anyway, so that still works for longer runs, you can run on the big diesel.

In an emergency, you can run both sides at full output as long as the fuel holds out and the total output will be roughly equal to the twin diesels.

If the big diesel goes down, you have a limp mode with generator/electric motor.

5-10kw generator is nicely sized to match house loads on a 40-45' cat.

If you just want to tool around the harbor at slow speed, you can turn off the big diesel and run on battery for a while (or if it's a mile or two from the marina to open water).

[Kenomac]

Originally Posted by StuM

Depending on what sort of emergency you are anticipating.

I suppose NIGHT TIME would be considered an emergency if one was 100% dependent on the sun for propulsion.

Wouldn't NIGHT TIME also be the other half of the day when there's little to no wind available? Good luck getting anywhere quick using a portable generator to power your battery charger during the NIGHT TIME hours.

[double u]

Kenomac, the wheel just BEGS to be reinvented...continuously...! (electric: heavy, short range, expensive, less environmental-friendly - but so ...IN!)

[valhalla360]

Originally Posted by keith4001r

30' mono, non running 16hp diesel.

Again,
I'll check weather for wind before leaving the dock,Good thing weathermen are never wrong
If it's sunny, solar will charge batteries.on a 30' sailing mono,
you will be lucky to get 500w unless you pull the mast and cover the entire deck. That's about 2/3hp. If you cover the entire deck, you may get the equivilent of 2-3hp. Typicaly assumption is you get the equivalent of the rated wattage for 4-5hrs per day. It's not 100% efficent charging battery banks, so it's going to be a long time to save up enough power to do anything. Of course, this assumes nice sunny days...get a rainy overcast week at it could be drastically less.
If insufficient sun, gas generator will charge batteries. Tell us what size generator and how you will mount it on a 30' boat. We used a 2400w yamaha at anchor but it got stowed safely when under way as it won't take a dousing with water & survive and securing it would be difficult in rough conditions in it's operating position.

Not interested in hybrid, strictly electric for propulsion with a generator for charging only when necessary. Adding a generator is by definition a hybrid.

Thanks

Realistically, the existing motor is putting out 8-10hp for normal cruise speed (non-emergency).

So assuming 500w and 4hr of charge, that's 2kwh per day. Assuming you are OK with slower speed and throttle back to 6kw of output, you get about 20min of run time per day of solar charging (probably less with inefficiency factored in). Of course that assumes you have a battery bank capable of storing the energy. Let's say you want a very modest 3hr range at 6kw output, that's 18kwh of energy. Lead acid batteries are typically assumed to have 30-50% of their rating as usable without damage. (lithium are around 80-90% but at much higher up front cost). That translates to around 3000amp-hr of battery at 50% usable on a small 30' boat.