Electric Cruiser

No.

Best answer.
Keep in mind, when comparing electric motor output to diesel engine output, the power curves are completely different and an electric motor that puts out 220hp would destroy a diesel for power and acceleration to the prop. I couldn't say what the conversion would be, but you shouldn't need nearly as much power in electric.

-Will (Dragonfly)

 

Oh, that I'm aware of. It's a bit frustrating, frankly (though understandable), that electric drive manufacturers list their motors in "diesel equivalent values" and sometimes entirely obfuscate the kW draw for them.

 

It's really simple if you ask me and it revolvs around money. A control system for a 80kWh battery is going to cost you, there is no cheap DIY solution. Motors and controllers are cheap enough and available even sh. Chargers, dc-dc converters, etc. are all available. Implementing a hybrid system is going to take some tought but is entirely doable.
What remains is that the finished article is going to have a lot more weight than a normal diesel configuration, and you must live with that.
Charging at a public marina is possible even if it's going to take 24h to fully charge the batteries.

 

Not true, you need exactly the same power, physics don't change. You can play around with torque and vary the rpm but the net result is only a change in prop size and pitch. The prop does not care where the kW's come from, only that they are there. In IC engines you use more or less fuel to adapt power, electric motors vary amps or volts to adapt. But the hull needs x kW to the prop for a certain speed under certain conditions.

 

It's not a question of the power available overall, but at a given RPM, which is why Will said "power curves". Electric motors have full torque available at zero RPM, which means you can have a large propeller and not worry about it dogging the engine at low speeds, so you don't worry (as much) about how much power they develop as you run RPMs up.

 

Yes I know, and while true it does not translate like that into real life. How big a propeller you can fit is limited by the hull you put it under. Then there is prop efficiency, a fixed prop is optimised for a certain boat speed, at all others it is mismatched (that's why CPP's were invented). So while it is true that you can have a very flat torque curve with full torque at 0rpm most of the time it does bring nothing. Slow manouvers with electric drive benefit mostly from the fact that the motors response is very linear and immediatly controllable, but that's about it. The rest of the time you have the same problems as with a IC engine, and there is no "electric horses are bigger". If you optimise the prop for 8kn at 1000rpm then always run 4kn at 400rpm you have the wrong prop for the speed.

 

Very true.

 

I have, I even made a list of all the solar powered boats and experiments I could find. But the Silent Yacht is WAY too heavy. I think to be energy efficient isn't high up on the list of yacht designers, because fuel is so dirt cheap, just to be fast and cost efficient. Which is fine for yachts but I believe much more is possible. I'm looking more at the Harryproa's that Rob Denney designs, they are sailboats but they are engineered to be very light. That's what you need if you don't want to escalate since more weight requires more structure to hold it together, more batteries, heavier motors and more weight etc. I should say I have zero experience yet with boat building, I'm just dreaming and trying to learn, but I (want to) believe a reasonably large electric boat could be build around 4-5t and that would drastically reduce the power and energy requirements.

PS: But again, I haven't found such a boat or a building plan. But this is why I'm leaning towards somehting like a 50ft+ ILAN (incredibly long and narrow) type trimaran. Lots of empty hull, all the weight in a central hull, amas need little structure weight and add little drag. For limited range electric motorboat or an electric motorsailer this isn't necessary, but I think for pure solar panel driven cruising boat you need to use quite different designs. But for berthing this would be a disadvantage.

 

What they don't say is how big the battery is and how long it lasts at 7.5kt and how fast you go at 6-8 hours a day on battery. The way they overcharge for 4x150 solar panels their batteries are probably similar priced. But like Rumar says there are no turnkey solutions so it's expensive for them to do.

I've attached my utterly naive and amateur numbers for my project. This would be for a 50ft / 15m long and narrow slender monohull/trimaran with 4t displacement, power required for a certain speed and how long the energy lasts. (50% assumed efficiency from battery to actual propulsive power, naive hull form, weight is probably too optimistic). Resistance and power required for speed from prelimina.com.



Even with that hypothetical boat if you want to travel 6-8 hours at 9knots (5.6kW @ 7.8kts) you need about 40kWh batteries. I'd consider 6knots the cruising speed (2.0kW @ 5.8kt), then you can go all day long. I'm hoping to get by with 20kWh DIY batteries and low power hardware.

For a shorter and heavier monohull like the northman you probably need double or triple that. So it's possible but it's going to cost way too much. My guess is that their 6-8h cruising is on 4 or 5 knots. Maybe that is good enough especially with a generator, but I'd get the numbers and do my own calculations.

Maybe a solution could be to take an old 50ft sailing trimaran and take off / sell the mast, sail and motor and have an electric motor and battery retrofitted?

 

Overall, diesel electric is not the most economic system. For what you pay for the used batteries, electric motor, generator, controllers, etc. you can install a diesel engine and cruise for two decades. However, if you plan is to use Tesla used stuff, might as well take the motor and controller off the car too and stop half assing the design.

 

There's an argument for that, certainly, but the Tesla motors are way over powered for the needs of a boat, and there are many motors (or the complete pod drive assemblies like the one I mentioned above) that are purpose-designed.

I'm fully aware that series-hybrid diesel-solar-electric is not the most cost efficient, and that a simple straight-diesel setup would be very inexpensive to run. My main driving requirement, however, is that 95% of the time driving the boat, the propulsive power would be from either shore-power-derived or solar-derived energy, with the diesel as an occasional-use range extender or an emergency backup. I want to reduce my dependency on fossil fuels to as near zero as possible. With a genset that burns SVO, it would be zero.

Goals aren't always about making something the lowest cost possible. I don't have a lot of money, but I don't have to have the cheapest boat available either.

Cheers.

JD

 

Where are you getting the vegetable oil for free? If you get used oil from a frier cleaning it costs more than diesel.

 

Re-read my comment: "I want to reduce my dependency on fossil fuels to as near zero as possible. With a genset that burns SVO, it would be zero."

 

JDR,

In my humble opinion, it's not feasible on your budget.
It may not even be feasible on a huge budget.
A stabilized monohull with a zillion solar panels has been tried.

But you could put light weight panels on your kayak and go like stink all day-light long with no battery.

 

That's an interesting conclusion you have. I've done a bunch of research and don't agree with you.