Jimmy Cornell goes Electric, with a Cat

[BigBeakie]

Originally Posted by Tupaia

Generator fuel consumption will also vary with the state of charge of the batteries. If it can keep up with the demand then the fuel consumption will remain fairly constant or reduce as the batteries reach full. If it can't keep up then then it will increase as the batteries discharge until it reaches maximum output then it should remain constant as the batteries continue to discharge.


Hope you are good at spreadsheets.

It would be cheating to have the motor using the bank + genset output. It has to be just the kW from the genset, so as per my other post, I'll do my best to balance kW in from genset vs kW out to motor.

But, luckily if it comes to that, the Admiral is a whiz at spreadsheet skills. You should see our project plan and Bill of Materials planning

[jmh2002]

Originally Posted by jmh2002

Other times in light air they have also found (electric) motor sailing to be a very efficient option too: "We often just assisted with about 1 KW of power to get a couple of knots of speed to assist the sails"

Here's an interesting thought...

Electric motorsailing with one electric motor, but having the other electric motor in regen.

Maybe on a light performance Cat the increase in apparent wind that is created from electric motorsailing can allow the sails to increase boatspeed sufficiently more that the regen can also perform some charging too, without the whole exercise being self defeating?

I don't think the Gunboat 60 that I quoted earlier tested this type of scenario because I think they mentioned that they preferred not to create extra drag by using regen in light air, in order that they could sail (or electric motorsail) as fast as possible towards their destination instead.

I'm not trying to suggest perpetual motion in any way, rather just 'helping to offset the loss from the batteries'. Solar would be helping too hopefully.

So really more in terms of extending range (and reducing genset runtime / fuel consumption) for long light air passages across oceans, instead of necessarily being the fastest or most efficient option, ie: you will get there slower but you will have conserved diesel, which might be necessary or helpful in some situations.

I can imagine some light air electric motorsailing scenarios where this might work, but of course it's only just that - imagining.

But the apparent wind that can quickly and exponentially be developed on a performance Cat is a powerful advantage, so I'm interested in thoughts and comments about this

[Joli]

Originally Posted by seandepagnier

I tacked the entire c&d with 15-20 knots on the nose, doing 99 tacks. Was really great experience and lots of people who witnessed cheered me along. Sounds like you didn't learn anything about sailing, when I still learn more each time.

https://www.soundingsonline.com/feat...-dos-and-donts

[JustMurph]

jmh2002: Pretty sure that is a perpetual motion scenario.
You'd find that the force vector from the engine providing regen will be subtracted from the engine providing propulsion. You could just reduce the power from the propulsion motor and save more power than what you would have gained with the regen (because of the inefficiencies in the energy conversions).

[jmh2002]

Originally Posted by JustMurph

jmh2002: Pretty sure that is a perpetual motion scenario.
You'd find that the force vector of engine providing propulsion would be cancelled out, or reduced by the one providing regen. Or you could just reduce the power from the propulsion motor and save more power than what you would have gained with the regen (because of the inefficiencies in the energy conversions).

Well maybe you're right, I'm simply not sure. That's why it's interesting.

But I don't think the force vectors would necessarily cancel each other out. The drag from some Regen is not at the same level as the thrust from some propulsion, and both can also be varied.

And what your points don't cover is the somewhat exponential increase possible via apparent wind speed. I'm not explaining myself well, but performance Cat sailors know what I mean - with a bit of a push all of a sudden the boat is making it's own wind and now going much faster than it otherwise normally could.

"you could just reduce the power from the propulsion motor and save more power than what you would have gained with the regen"

You are not wrong with that statement. As I made clear I'm not suggesting that it would be possible to 'gain more power than used' via this scenario, instead only offset some of the loss.

Using one motor to electric motorsail may get the boat up into a speed range where it's now sailing efficiently and generating it's own apparent wind.

And the loss from some regen may be less than the overall gain from electric motorsailing, thereby extending range.

So yes, still an overall loss of course (no perpetual motion), but at a slower rate.

There's kind of 3 scenarios for this comparison in very light air (and I'll throw some imaginary boatspeed numbers there just for explanatory purposes):

Sailing only: very slow or maybe almost no progress at all, boatspeed 3kn (or less?)

Electric Motorsailing only: faster, but continous battery drain, boatspeed 6kn

Electric Motorsailing + Regen: faster than Sailing only, slower than Electric Motorsailing only, but slower battery drain too, boatspeed 4-5kn

So basically some of the force generated by the sails would go towards boatspeed, and some towards regen.

No regen and reducing the power from the propulsion motor wouldn't generate the same apparent wind speed, so there would be nothing 'extra'.

But I agree that at this 'reduced propulsion power' the boat may now be at that same 4-5kn boatspeed anyway - but the battery is being drained at a faster rate, right? (so less overall range).

I guess it really depends how much more apparent wind (and therefore boatspeed) can be generated via electric motorsailing, as to whether the numbers work or not.


I think it would be an interesting experiment.

Thanks for your thoughts

[JustMurph]

It's a good thought experiment and I see what you mean.

What you might be able to do is use some propulsion to get the boat going, generating more apparent, then back it off. And maybe even in that state you could have a little bit of regen. But using regen while also propelling the boat on the other engine will use more power. The drag force will directly take away from the propulsive force. Because the prop is less efficient in regen than it is in propulsion, you have to lose power.

[jmh2002]

Originally Posted by JustMurph

It's a good thought experiment and I see what you mean.

What you might be able to do is use some propulsion to get the boat going, generating more apparent, then back it off. And maybe even in that state you could have a little bit of regen

Yes, that is the kind of situation I meant

[jmh2002]

Just to give a more real world example:

I'm sure you can imagine a situation in light air where the sails will barely set and boatspeed is minimal (especially since motion keeps shaking what wind there is out of the sails too), but with a bit of a push from propulsion a big light reacher will fill and set consistently and light cat might then do 8kn without too much trouble now.

That 'bit of a push' can create a lot more apparent wind generated boatspeed on a Cat.

So it would take A LOT of propulsion to motor at that same 8kn, but perhaps very little to motorsail.

Part of that is not so much the amount of propulsion, but just that consistent little push, preventing the boat from slowing down, and therfore keeping the apparent up.

[BigBeakie]

Originally Posted by jmh2002

Just to give a more real world example:

I'm sure you can imagine a situation in light air where the sails will barely set and boatspeed is minimal (especially since motion keeps shaking what wind there is out of the sails too), but with a bit of a push from propulsion a big light reacher will fill and set consistently and light cat might then do 8kn without too much trouble now.

That 'bit of a push' can create a lot more apparent wind generated boatspeed on a Cat.

So it would take A LOT of propulsion to motor at that same 8kn, but perhaps very little to motorsail.

Part of that is not so much the amount of propulsion, but just that consistent little push, preventing the boat from slowing down, and therfore keeping the apparent up.

JMH,

You're not the only one to wonder about this, I have as well. I think you're on the right track. It will depend on size of light air sail, point of sail and AWA, and it would assume an efficient hull shape/displacement ratio.

In some months I'll be able to answer the question. Intuitively ( meaning no data whatsoever to support a hypothesis) I think you'd need the Servoprop to be the regen source because it is far and away the highest regen system available. And you'd want the highest regen at the lowest speed, which is the Servoprop strength, as well as the least drag, ditto the Servoprop.

Sails produce so much more power compared to regen drag that there is a differential here to consider and exploit, as you have proposed.

So in case you're wondering why didn't I go with the Servoprop rather than the AXC series motor?

I think having large solar production is a much more cost effective way to get energy. I believe the AXC, while producing less regen at slower boatspeeds ( ie below 8 knots), is a more "industrial" solution. Less complicated, less prone to prop damage & fouling, more serviceable by third party technicians, much more & easily scalable ( from 10kW up to 40kW), shaftdrive vs saildrive advantages, and cost.

[jmh2002]

Originally Posted by BigBeakie

Sails produce so much more power compared to regen drag that there is a differential here to consider and exploit, as you have proposed.

'Differential' is a good word to describe what I was thinking and imagining - thanks

[double u]

"...about 100 watts of efficient electric propulsion (70-80%), or 1hp of engine...."

"...Electric motorsailing with one electric motor, but having the other electric motor in regen.
..."
no further commentary necessary...I rest my case!

[Dave_S]

Not directly related but I don't understand why they would tax electric cars by the kilometres....

https://www.abc.net.au/news/2021-10-...-tax/100576568

[Sand crab]

Originally Posted by Dave_S

Not directly related but I don't understand why they would tax electric cars by the kilometres....

https://www.abc.net.au/news/2021-10-...-tax/100576568

It's not that crazy. The fuel tax pays for roads so e-cars should kick in their fair share.

[goboatingnow]

Originally Posted by Dave_S

Not directly related but I don't understand why they would tax electric cars by the kilometres....

https://www.abc.net.au/news/2021-10-...-tax/100576568

Road pricing is generally seen as the way to replace fuel taxes as EVs dominate private transport. It’s a fair approach too though I think it should weighted by car cost

[JustMurph]

About half of what we pay for fuel in australia is tax.