Viability of electric only propulsion in 2018 - is there a good option after all?

[GrowleyMonster]

I would like a nuclear reactor for my boat, too, please.

[seandepagnier]

So everyone wants nuclear power.

I'm going prefer an anti-matter drive since it has orders of magnitude more energy density so much more capable rendering nuclear power, boring, obsolete, inadequate. The fact that a single malfunction could have catastrophic consequences for all is inconsequential.

With small nuclear reactors everywhere it is a straightforward progression to power killer robots with machine learning that destroy us. This is no longer science fiction. If a drone has this power source, a single submarine drone could sink thousands of boats, wiping out several marinas every day. A single flying drone can destroy power grid beyond repair. There are many things that can be done for relatively little cost. Or maybe just use it to spread radiation around by accident. But everyone wants it? Or everyone wants it for themselves but no one else?

With diesel power over time it will change the chemical composition of our air and sea spoiling it for humans in the future. This is a slower threat but the result is as bad or worse.

With electric power, the situation seems not as bad (provided generators, or grid power is not used for charging), but lithium and lead are both very toxic and cause a lot of suffering in the places they are mined and recycled. There is still significant energy consumption, but not as wasteful. It's questionable if this approach has a long term future.

With sails and oars, the impacts are minimal by comparison. These have proven over time to have minimal negative effects. So get with it I say, just use sails and oars and you are ok.

[RaymondR]

Originally Posted by Dockhead

I think nuclear power on cruising boat scale could be made quite safe, and the tiny volumes of waste involved can be disposed of (after 20 years) down salt mines. If you care about global warming (and acid rain, and . . . ) nuclear has got to be a better option.


Nuclear power would be a dream. Unlimited electrical power -- motor right around the world if you want. Ultimate autonomy, which would be just what we need, especially those of us who cruise in distant, remote places.



Unfortunately we will not get that in our lifetimes, methinks. . . .

Radioisotope heat source and Stirling cycle engine??

[Dockhead]

Originally Posted by Jim Cate

DH, as a physicist, I'm kinda surprised at this statement. Of course, having been retired for over 30 years, I'm not current with developments, but your claim is pretty far from my idea of reality.

So, please explain how you propose to make a small reactor or whatever other nuclear power source you have in mind. I'd like one, please... if feasible, but I'm not holding my breath!

Jim

Well, I never "proposed to make" one! I'm not a physicist nor a nuclear power engineer (my uncle was, though). I don't know whether it's really feasible or not, or how much it could cost.


However,



The Soviets, way back in the 1970's, built a 5kW thermionic reactor weighing only 300kg


https://en.wikipedia.org/wiki/TOPAZ_nuclear_reactor


Here is one the size of a garbage can:
https://www.defenseone.com/ideas/201...-power/151434/


which produces 1 megawatt -- yowza!


I believe most satellites and space probes have small nuclear reactors of one kind or another.



There is plenty of technology available to make a nuclear reactor which could power a cruising yacht. Whether it could be made cost-effective or not, or whether we would even ever be allowed to possess such devices is probably doubtful. But while we're dreaming anyway, as we have been since the beginning of the thread . . . .

[Dockhead]

Originally Posted by boat_alexandra

. . . With small nuclear reactors everywhere it is a straightforward progression to power killer robots with machine learning that destroy us. This is no longer science fiction. If a drone has this power source, a single submarine drone could sink thousands of boats, wiping out several marinas every day. A single flying drone can destroy power grid beyond repair. There are many things that can be done for relatively little cost. . . . .

Welcome to the 21st century!


There will be many such challenges, one of which might wipe out the human race or turn the earth into some kind of post apocalyptic hell. Nuclear power not required at all.



Better cut the dock lines now and get in as much cruising as we can in the meantime!



I'm not entirely joking.

[Dockhead]

Originally Posted by saghost

I don't have a handy 30 kW example to work with; unfortunately Polar Power stops at 20 kW right now, and the big synchronous AC generators are a horse of a different color entirely.

But take a typical modern small charter/liveaboard cat, like a Leopard 40 or Bali 4.0. They've got three smallish diesels onboard - two ~30 hp engines pushing saildrives, and a 6 kW diesel generator.

Yanmar 3YM30AE plus SD25 on each side, 346 pounds per side. Northern lights 6kW generator, 377 pounds without the sound enclosure.

Electric yacht 20SD 20 kW sail drives are 177 pounds each. If you're willing to lose a knot of top speed, Torqeedo Cruise 10 FP SD is a 10 kW motor pod on a sail drive mount that's only 83 pounds.

A Polar Power 8340-VP40 20 kW DC diesel generator is 396 pounds. An AIMS 5kW pure sine inverter is 34 pounds.

So an electric system with all the same functions can have 285 pounds of battery and still be the same weight, or 475 pounds of batteries if the cruise pods are good enough.

Torqeedo's 5kWh 48V sealed battery packs weigh 82 pounds each - meaning 15 kWh is still lighter with the big motors, or 40 kWh with the smaller ones.

This doesn't even include the two starter batteries you'd eliminate or downsizing the now largely redundant house battery pack (it also doesn't include the 48V-12V converter to charge the house pack from the main pack or a 48V charger for shore power, but I don't expect either of those to be very heavy.)

Real numbers -- that's useful.


But I don't see saving weight or complexity here. The system you propose will weigh the same, but will have half of the power production ability (which is probably OK, since you can peak shave from the batteries when you need full power). It will have far less redundancy, with many single points of failure introduced, which did not exist with the conventional system. It will be rather more complex.


And what do you get in return?

[Dockhead]

Originally Posted by RaymondR

Radioisotope heat source and Stirling cycle engine??

DoD are using exactly this for very small generators

[atoll]

you are looking at this all wrong!
with the proliferation of plastic waste in the oceans,and the proposed launch of numerous floating waste collection booms,these booms would make ideal platforms for solar and wind powered energy stations where electric boats could plug in and recharge every 20 miles or so...........

[Dockhead]

Originally Posted by saghost

Yes and no. Yes, you're certainly correct that the conversion to electricity, charging the battery, and then converting energy back to motion in the electric motor are losses the simple propeller doesn't have.

However, a simple fixed propeller keeps the engine from ever running at the most efficient points (unless a more aggressive propeller pitch is selected that won't allow the engine to reach full rpms and produce full power.)

The generator, on the other hand, can be set to run at only the most efficient points. Starting with better engine efficiency, the overall efficiency should be similar or better for modern permanent magnet motors and generators.

Combining the power output and fuel consumption charts Yanmar publishes for the 3YM30AE, I came up with between 25% and 30% efficiency for the entire speed range. By contrast, Polar Power promises 35% efficiency to electricity (so including half the conversion losses) using a similar Volvo Penta engine. It's not hard to find a PMAC motor that's ~87% efficient or better for most of the operating range...

It's all in the numbers. But I surely doubt Polar Power's numbers -- combined losses of both the IC engine AND the alternator are only 65%? What makes the Volvo capable of more than 40% efficiency when the Yanmar with exactly the same technology can't do better than 30%? Somewhere in that Yanmar speed reach is its own "most efficient point", isn't it?


And why do you think that the generator is going to be operating at its "most efficient point"? Making 20kW, it will be running at 2900 RPM, which is not indeed its most efficient speed. It will on the contrary be operating to produce maximum output, not greatest efficiency. You have to modulate the power of the generator just like you modulate power of the conventional diesels, so you won't be always at torque peak, which is the "most efficient point". On the contrary, since you've replace two 20kW diesels with one 20kW generator, you will more often be operating the generator flat out, which is not the most efficient speed. Nor is that the regime most conducive to engine life.


It seems to me that this setup has one use case where it really makes sense -- that is when you can plug in overnight and power yourself in and out of the marina with power produced not by you on board, but by the electrical power grid. Now that is a really significant gain in efficiency, and cost. I figure it costs me about £1 per kW/h to generate electrical power on board my boat when you consider amortization of the genset, fuel, and maintenance. You are saving a lot of money if you can substitute electrical power grid power, for that. But for cruising off grid -- I don't see any advantages.



Another configuration which could be really intriguing for a catamaran -- suggested by someone above -- would be to have ONE of these systems in one hull, and a conventional diesel in the other. Motoring long distances, you just use the conventional diesel, which notwithstanding the numbers proposed above, must be more efficient than hybrid, and simpler, with less to go wrong. Maneuvering in harbor, you add electric from the other hull. And you have a mongo generator and storage system for domestic power, replacing the genset and house bank with far more capable systems.


And you also get the ability to plug in and drive the boat for a couple of hours on power grid power, and you get the ability to store a lot of solar and drive the boat with that if you want -- if you are in a sunny anchorage for long enough between motoring.


But other than those two situations -- you'd be even better off by having two conventional diesels but substitute the separate genset with large alternators on the propulsion engines. We had some discussions on that recently.

[CatNewBee]

... just catch 2 whales, put a harness on them let them pull you - Like horses on land. They feed themseves on the way.

[ranger58sb]

Originally Posted by boat_alexandra

I realized sculling oar is free and better.

My sails are free. I don't paint. Rigging is free, repairs replacements free.

cook and heat with wood, which is also free.

It turns out everything you need to go cruising is free.

Sculling can be an elegant solution -- for someone physically capable. You must be; many aren't.

Other stuff is only "free" if you don't count your own scrounging and fabricating time... and presumably you don't sew or crimp with your teeth, so maybe there's some equipment and tooling costs in there someplace, too.

-Chris

[atoll]

Originally Posted by CatNewBee

... just catch 2 whales, put a harness on them let them pull you - Like horses on land. They feed themseves on the way.

might want to put a winch drum on the bow as well....whales dive to 600m or so every few hours

also an improved guidance system,using a squid on a stick in front of the whale

[Matt Johnson]

A similar suggestion to the catamaran 'one in each hull' option would be a Toyota Prius Power Split Device. If the monohull design called for a 30 hp engine, install a 10kw motor and a 15hp diesel driving the same prop shaft.

If peak power is needed, use both the engine and motor to provide 30hp combined.
If you need to charge the bank, have the diesel act as a generator and charge the battery bank.
If you have no charge to battery bank or a failure, the diesel can power the boat with its 15 hp.
If you want just electric, just run off the bank until charge depletes.
I'm sure the regenerative braking could also be controlled to act as a tow generator.

It seems that, unlike the separate generator and just electric drive, you'd have redundancy of being able to propel the boat under electric, diesel, or a combination of both.

The planetary gear set that makes up the power split device is extremely reliable. Plus, you get to eliminate the transmission and starter from the diesel. And since we'd want to manually control if the engine or motor is running, you eliminate the complex Prius electronics.

Matt

[saghost]

Originally Posted by Dockhead

Real numbers -- that's useful.


But I don't see saving weight or complexity here. The system you propose will weigh the same, but will have half of the power production ability (which is probably OK, since you can peak shave from the batteries when you need full power). It will have far less redundancy, with many single points of failure introduced, which did not exist with the conventional system. It will be rather more complex.


And what do you get in return?

What did you gain? A lot of flexibility in when or if you run the diesel. All of the undock/raise anchor, motor to a safe distance, turn into the wind and raise sail events and the 'crap I need to drop/reef that sail now' events can be done without an engine start.

For boats that are mostly sailed and don't use much AC, that might be 90% of engine starts and associated wear.

Low speed handling is better because the motors respond instantly and are perfectly happy spinning at low rpms.

I also gain the ability to use AC power without the generator, including large amounts for shorter periods. Microwave? Coffee Maker? Induction cooktop, which gets a lot of heat out of the salon, removes a logistic headache, and takes away one of the more dangerous things onboard.

It's also about things you don't have - two-thirds of the engine maintenance and the associated thru hulls are gone. No clutches in the transmission/saildrives, which not only reduces maintenance and improves reliability but should make the seals more reliable since the heating and cooling of the oil isn't happening.

You're saying it increases single point failures, but it looks to me like it decreases them. Power for the main pack can come from solar, wind, hydro, dock, or diesel. Yes, there's only or diesel engine if you commit to a long motoring event, but you don't lose all power if that engine dies. The pack as proposed is several modules in parallel, so if you have a problem with one you can disconnect it and use the others. The electric yacht drive motors are actually twinned 10 kW units, so even if something falls there (which should be much less common than a diesel problem,) you can probably continue using just the other motor in that side.

[saghost]

Originally Posted by Dockhead

It's all in the numbers. But I surely doubt Polar Power's numbers -- combined losses of both the IC engine AND the alternator are only 65%? What makes the Volvo capable of more than 40% efficiency when the Yanmar with exactly the same technology can't do better than 30%? Somewhere in that Yanmar speed reach is its own "most efficient point", isn't it?


And why do you think that the generator is going to be operating at its "most efficient point"? Making 20kW, it will be running at 2900 RPM, which is not indeed its most efficient speed. It will on the contrary be operating to produce maximum output, not greatest efficiency. You have to modulate the power of the generator just like you modulate power of the conventional diesels, so you won't be always at torque peak, which is the "most efficient point". On the contrary, since you've replace two 20kW diesels with one 20kW generator, you will more often be operating the generator flat out, which is not the most efficient speed.

I don't think Volvo/Perkins technology is substantially better than Yanmar technology. Nevertheless, I believe both quotes are correct. That's because no, in a single speed transmission fixed propeller environment the Yanmar doesn't ever get close to ideal operating conditions.

I'm doing this on a smartphone, so I'll try to do it without links. The thing is, for almost every engine the best efficiency is set almost maximum throttle in the low to mid rpm range - getting the most out of the air pumped in at speeds where the volumetric efficiency is high and frictional losses aren't too painful.

But if you set up a propeller aggressive enough to get there, the engine doesn't have enough extra torque to force that to higher speeds for the maximum power output. So instead, the propellers are sized to match the maximum output at high rpm, and the engine goes through that mid range at one quarter throttle or less - all the propeller can absorb. Yanmar includes a nice chart with max engine power and propeller curves in the 3YM30AE data sheets that Google can easily find pdfs of.

Unless you have a continuous requirement of 20 kW or more, which doesn't match what I've read for people's motoring trips, how fast/hard you run the generator is a matter of chosen strategy, and while it probably won't get max efficiency at that high rpm max output setting, it can get close to it while putting out almost that much power.