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Old 28-08-2017, 15:00   #1
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How feasible is 100% renewable electric cruising right now?

I've been very impressed with how much juice I can get from the sun to run all sorts of things on my boat without ever plugging in or running the motor - my wife's 2000 watt 110v hair dryer being the thing I'm probably most proud of.

I have a Pearson 424 (22,000lb disp). Some folks in my owner's group are re-powering with Electric Yacht's Quiet Torque 20 motor with supposedly great results. I'm not sure if they're doing hybrid (diesel generator) or all electric. There will probably come a day where I too will have to replace my good old W58 motor. Our boat lives on a mooring, and when we cruise we either anchor or pick up a mooring - so we never plug in.

If I remove the motor and diesel tank, I now have a massive empty engine bay - roughly 5'x4'x4' and the space where an 80 gal diesel tank was (about 5'x4'x3') behind that. The electric yacht QT 20 will supposedly fit where my old V-drive was under the cabin sole. So, I have a ton of space for batteries. I imagine weight would likely be my limiting factor for batteries, not space.

For experiment's sake, let's say on average I have to motor my boat for 2 hours every day at 6 knots with the Electric Yacht QT 20. Let's also say I'm in a sunny, windy place at low latitude - say Curacao.

Assuming these things, how much solar, hydro-generator, and wind charging wattage do I need to be a completely "off the grid" yacht?
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Old 28-08-2017, 15:08   #2
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Re: How feasible is 100% renewable electric cruising right now?

Sounds like you need a diesel generator to charge your batteries and run your electric motor.
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Old 28-08-2017, 15:12   #3
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Re: How feasible is 100% renewable electric cruising right now?

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Sounds like you need a diesel generator to charge your batteries and run your electric motor.
Well... that's precisely what I'm asking. Do I?
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Old 28-08-2017, 15:27   #4
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Re: How feasible is 100% renewable electric cruising right now?

Was just reminded of my favorite Grandpa Simpson quote: "I used to be with it! Then they changed what "it" was. Now what I'm with isn't it. And what's "it" seems weird and scary to me. It'll happen to you someday!"

Anyhow, obviously this technology is developing rapidly and what I'm proposing is not far off. My question is - is this feasible now?
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Old 28-08-2017, 15:30   #5
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Re: How feasible is 100% renewable electric cruising right now?

What is the voltage & amperage at 6kt using that motor? Can you ask your cohorts?

My guess is that if you mounted 2000-2500w of solar on the boat you could do 3.5-4kt for 3hr per day.

Speed really costs.

Mounting that much is probably unrealistic. Probably you can mount 1000w on the Bimini and dodger.

If you have arch you can get another 250w. Swing out panels on the cockpit lifelines would get you another 200w-ish.

Before I did the swing out panels I would buy a set of semi-rigid panels to store below and bring out for motoring.
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Old 28-08-2017, 15:34   #6
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Re: How feasible is 100% renewable electric cruising right now?

Hi Peregrine,

The answer will depend on a few variables. The biggest one, motoring at 6 kts under what conditions? Motoring at 6 kts in smooth water, no wind or waves takes a LOT less power than motoring at 6 kts into a 15 kt headwind with 2-3' seas.

The other variables will be what other electric loads will you be running on a daily basis? Do you have a large fridge and freezer? On a passage using an autopilot? These are also large power draws though much less than the motor.

I've looked into electric power on my 422 and the limiting factor is always range under power. Without doing detailed math (pointless without more data anyway) here's some very approximate numbers. The W58 is about 45 kW. Cruising in calm conditions at low rpm might use 10-12 kW. So 2 hours motoring might use 20 kW hours. I doubt you could easily fit 1000 Watts worth of solar panels. Assuming clear, sunny, ideal conditions optimistically you'll get maybe 5-6 hours of good charging and a couple more partial charging. So you might get 6-7 kW hours charge back into the batteries and that's ignoring the charging inefficiencies.

Bottom line, i don't think you can get there from here, at least with solar. Every time I did the math the answer came out, buy a LARGE diesel generator and a LARGE charging system.
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Old 28-08-2017, 15:40   #7
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Re: How feasible is 100% renewable electric cruising right now?

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Hi Peregrine,

The answer will depend on a few variables. The biggest one, motoring at 6 kts under what conditions? Motoring at 6 kts in smooth water, no wind or waves takes a LOT less power than motoring at 6 kts into a 15 kt headwind with 2-3' seas.

The other variables will be what other electric loads will you be running on a daily basis? Do you have a large fridge and freezer? On a passage using an autopilot? These are also large power draws though much less than the motor.

I've looked into electric power on my 422 and the limiting factor is always range under power. Without doing detailed math (pointless without more data anyway) here's some very approximate numbers. The W58 is about 45 kW. Cruising in calm conditions at low rpm might use 10-12 kW. So 2 hours motoring might use 20 kW hours. I doubt you could easily fit 1000 Watts worth of solar panels. Assuming clear, sunny, ideal conditions optimistically you'll get maybe 5-6 hours of good charging and a couple more partial charging. So you might get 6-7 kW hours charge back into the batteries and that's ignoring the charging inefficiencies.

Bottom line, i don't think you can get there from here, at least with solar. Every time I did the math the answer came out, buy a LARGE diesel generator and a LARGE charging system.
Got it. Thanks Skipmac. You have the same hull as I do, I believe. Sounds like it doesn't make sense using just solar. Are you still running your W58? The idea for me would be to get rid of the diesel not just swap it out for a diesel genny.
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Old 28-08-2017, 15:40   #8
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Re: How feasible is 100% renewable electric cruising right now?

Pearson 424? Call it 10 ton displacement.
EY Quiet Torque 20? 20kW, 48V system. (20 kW = 26 HP).

Sounds like you are actually planning on putting appropriate sized electric propulsion for your boat. Well done, it's rare.

It's hard to say how much power it will take to drive your boat at 6 knots in good conditions, but let's say 50% or 10 kW.

So for 2 hours motoring, you'd need 20kWh.

Based on 5 hours per day full sun equivalent, that means that you need at least 4000 Watts of solar panels to supply the energy. At 200W per square metre, thats 20 square metres, 215 square feet of panels.

Wind generator? Hope for an average of maybe 200 Watts. So that's 4.8kWh per day. Which means that you will need at least 5 wind generators.

Hydro generator? Possibly same sort of output as wind generator - but only when you are sailing at a decent speed.

Assuming LiFePo and you are using 80% of capacity, that means you need 25kWh or storage
(about twenty 12V, 100Ah batteries).
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Old 28-08-2017, 15:45   #9
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Re: How feasible is 100% renewable electric cruising right now?

Quote:
Originally Posted by Adelie View Post
What is the voltage & amperage at 6kt using that motor? Can you ask your cohorts?

My guess is that if you mounted 2000-2500w of solar on the boat you could do 3.5-4kt for 3hr per day.

Speed really costs.

Mounting that much is probably unrealistic. Probably you can mount 1000w on the Bimini and dodger.

If you have arch you can get another 250w. Swing out panels on the cockpit lifelines would get you another 200w-ish.

Before I did the swing out panels I would buy a set of semi-rigid panels to store below and bring out for motoring.

A customer testimonial for this motor from their website has a 22,000lb yacht and says "With my current 440 AH bank, I have motored for 24 hours at 2.5-3 knots in 3-4 foot seas before depleting the power, impressive in my humble opinion." - Gulfstar Sailmaster 39 - ElectricYacht

He's also talking about getting some re-gen from the motor as it spins during sailing.
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Old 28-08-2017, 15:55   #10
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Re: How feasible is 100% renewable electric cruising right now?

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Originally Posted by Peregrine1983 View Post
A customer testimonial for this motor from their website has a 22,000lb yacht and says "With my current 440 AH bank, I have motored for 24 hours at 2.5-3 knots in 3-4 foot seas before depleting the power, impressive in my humble opinion." - Gulfstar Sailmaster 39 - ElectricYacht

He's also talking about getting some re-gen from the motor as it spins during sailing.
440Ah? That's a 48V motor, so presumably he is talking about 20kWh of storage.
(Sounds about the same as identified above call it 600lbs and $20,000+ worth of batteries)

If that lasted for 24 hours, then he's running at about 1HP. I can believe that if he is doing 2.5-3 knots running with those 3-4 foot seas, but certainly not heading into them.

(There's almost always a subtle gotcha in advertising/testimonials)
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Old 28-08-2017, 15:56   #11
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Re: How feasible is 100% renewable electric cruising right now?

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Pearson 424? Call it 10 ton displacement.
EY Quiet Torque 20? 20kW, 48V system. (20 kW = 26 HP).

Sounds like you are actually planning on putting appropriate sized electric propulsion for your boat. Well done, it's rare.

It's hard to say how much power it will take to drive your boat at 6 knots in good conditions, but let's say 50% or 10 kW.

So for 2 hours motoring, you'd need 20kWh.

Based on 5 hours per day full sun equivalent, that means that you need at least 4000 Watts of solar panels to supply the energy. At 200W per square metre, thats 20 square metres, 215 square feet of panels.

Wind generator? Hope for an average of maybe 200 Watts. So that's 4.8kWh per day. Which means that you will need at least 5 wind generators.

Hydro generator? Possibly same sort of output as wind generator - but only when you are sailing at a decent speed.

Assuming LiFePo and you are using 80% of capacity, that means you need 25kWh or storage
(about twenty 12V, 100Ah batteries).

Sounds like the boat would have to look like a wind/solar farm. Not sure if you're being facetious about the appropriate size motor - that was my other question as 20kw seems massively under powered. Are you being facetious or is there something about electric motor power ratings that I'm missing?
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Old 28-08-2017, 16:24   #12
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Re: How feasible is 100% renewable electric cruising right now?

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Sounds like the boat would have to look like a wind/solar farm. Not sure if you're being facetious about the appropriate size motor - that was my other question as 20kw seems massively under powered. Are you being facetious or is there something about electric motor power ratings that I'm missing?
Not being facetious at all.

20kW = 26 HP.
A common rule of thumb for an auxiliary engine is 2 - 4 HP per ton. 26 HP for a 10 ton vessel is reasonable and certainly not "massively under powered":

Or did you actually mean to type "over powered"?

There is a lot of hype about EP motors, thrust and "equivalent horsepower" where the EP proponents claim that somehow EP is different and because of the torque curve of EP somehow 1HP of EP provides the same propulsive power as much more powerful diesel engines under typical sailboat auxiliary conditions.

A typical example would be Torqueedo, who claim things like:
"10kW continuous output – powerful propulsion comparable to a 20 HP combustion engine"

or OceanVolt
"Q: WHY IS THE 15KW OCEANVOLT MOTOR EQUIVALENT TO A 45HP DIESEL ENGINE?
A: The torque of Oceanvolt electric motors is significantly higher than that of a diesel engine - and they both have the same propeller.

and elsewhere:
" A 10kW Oceanvolt electric motor easily outperforms and is more powerful than a 30hp diesel engine.

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Old 28-08-2017, 16:24   #13
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Re: How feasible is 100% renewable electric cruising right now?

I build solar systems for a living. Most of our off grid systems keep a small diesel generator as a backup. That's pretty much what you have now. I'd stick with that until a lot of progress has been made with storage systems.
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Old 28-08-2017, 16:49   #14
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Re: How feasible is 100% renewable electric cruising right now?

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Not being facetious at all.

20kW = 26 HP.
A common rule of thumb for an auxiliary engine is 2 - 4 HP per ton. 26 HP for a 10 ton vessel is reasonable and certainly not "massively under powered":

Or did you actually mean to type "over powered"?

There is a lot of hype about EP motors, thrust and "equivalent horsepower" where the EP proponents claim that somehow EP is different and because of the torque curve of EP somehow 1HP of EP provides the same propulsive power as much more powerful diesel engines under typical sailboat auxiliary conditions.

A typical example would be Torqueedo, who claim things like:
"10kW continuous output – powerful propulsion comparable to a 20 HP combustion engine"

or OceanVolt
"Q: WHY IS THE 15KW OCEANVOLT MOTOR EQUIVALENT TO A 45HP DIESEL ENGINE?
A: The torque of Oceanvolt electric motors is significantly higher than that of a diesel engine - and they both have the same propeller.

and elsewhere:
" A 10kW Oceanvolt electric motor easily outperforms and is more powerful than a 30hp diesel engine.

Interesting. Thanks Stu. So with that calculation though my boat is currently "massively overpowered" at 58hp.
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Old 28-08-2017, 17:21   #15
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Re: How feasible is 100% renewable electric cruising right now?

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Got it. Thanks Skipmac. You have the same hull as I do, I believe. Sounds like it doesn't make sense using just solar. Are you still running your W58? The idea for me would be to get rid of the diesel not just swap it out for a diesel genny.
Yep, same hull and I'm still running the W58. In case you haven't found this out, the W58 is the exact same engine as the Perkins 4.154 series 200 and the Perkins parts are A LOT cheaper than the Westerbekes.

The 422s also have the same rig dimensions as the comparable 424s. Of course the 422 is center cockpit but there are some other subtle differences. The engine is a little more forward in the 422 and no drive shaft to the V-drive. Fuel tanks are under the settees in the main cabin so very accessible and the water tank is in the hollow place in the keel.
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