Jimmy Cornell goes Electric, with a Cat

[Joh.Ghurt]

Originally Posted by David Ess

Its NOT hypocritical because his electric boat will have LESS emissions than one with diesel.

I want a nuclear powered aircraft carrier! No emissions either for propulsion and electricity. Even the steam powered catapults are emission free.

[wingssail]

Originally Posted by Adelie

...Whatever comes next for cruising is going to be a significant change from what we have now. ..

One thing that will be different is that the dominant feature of tomorrow's cruising boats will likely be their solar array.

Using BigBeakie's numbers:

Originally Posted by BigBeakie

Lwl 15 meters
Boa 8 meters
Lwl:Bh 12.25:1
Cruising displacement 13.5 T...
We carry 4.3 kW of solar PV charging 14 kW of LFP propulsion bank...

his solar array is larger in area than my mainsail.

These will be more "floating solar farms" than they are sailboats.

And they probably won't be monohulls.

[David Ess]

Originally Posted by Joh.Ghurt

I want a nuclear powered aircraft carrier! No emissions either for propulsion and electricity. Even the steam powered catapults are emission free.

In fact, I've heard the catapults are going electric too.

[double u]

"... range extending battery charging as a backup..."

& there go the "zero emissions"...
(a dugout canoe paddled by a person subsisting on vegan foods...-could possibly be "Zero" emissions, everything else...

[double u]

Originally Posted by David Ess

Its NOT hypocritical because his electric boat will have LESS emissions than one with diesel.

surely true! as 98 is less than 100.
So far nobody has taken the TOTAL footprint of the boat into account-
once with ice & once with electric/no fossile fuels.
As the footprint of the boat before any propulsion imho is huge compared to the propulsion (cost is a good guide...), the type of propulsion will make very little difference

[Dave_S]

Originally Posted by BigBeakie

Dave:

Our figures for our cat are as are as follows:

Lwl 15 meters
Boa 8 meters
Lwl:Bh 12.25:1
Cruising displacement 13.5 T

At 3 knots motoring, hull resistance is 315 Newtons with 1.25 kW drawn from battery
At 6.5 knots motoring, hull resistance is 2,832 Newtons with 18.36 kW drawn from battery

For comparison to show you the importance of knowing your efficiency curves. at 5.5 knots motoring, our resistance is 1,378 N and battery used is 7.8kW. That's only 1 knot slower but look at the difference in battery consumption!

At WOT our projected top speed is 9 knots, but power required to do that is over 60 kW, so it ain't gunna happen.

We carry 4.3 kW of solar PV charging 14 kW of LFP propulsion bank, so when becalmed we can motor in balance with the solar output alone and not draw on the battery storage at somewhere between 3 and 4 knots during daytime, then motor at night on battery down to 20% DOD when the 16kW genset comes on automatically & recharges batteries to 95% ( never to 100% ) in 45 minutes, & then motor in silence for another 4 hours. Repeat as necessary.

Solar is the key to EP cruising, without a doubt. Do whatever it takes to get as much solar production as possible.

Nigel Calder has carefully calculated (repeatedly) the total cost of charging batteries using diesel at between USD$15 to $20 per Kilowatt of battery storage. Do the math over a season of cruising on that basis, and then see what your diesel is really costing you. And you think EP is expensive???

And conversely, what savings are had with EP with good solar array and regen. Our regen will be about 1 kW so on passage that would be 24 hrs x $20 DCP* = $480 saving/day.

* Diesel Charging Penalty

Great information, thank you 🙂

[catsketcher]

Efficiency of props

I was wondering if anyone had anything on prop efficiency at typical diesel revs. If electric motors are more efficient it may be because they have spin slower than diesels.

I notice a similar effect with my four stroke outboards. We use more fuel than a similar cats with diesels when motoring in calms. Too much more to be due to the better fuel economy of a diesel engine. But my props spin at about 1500rpm when cruising and are 12 inch in diameter and my friends have larger props.

The prop effect is interesting. To move a boat you have to move water aft - it is a change in momentum concept. Momentum = mass x velocity. If my prop is half the area (I have a 12 inch prop and my figurative friend has a 17 inch prop) then I have to push the water twice as fast to get the same change in momentum.

But pushing things fast is inefficient, as shown by Big Beakie's data. To move something you must increase its kinetic energy. KE = 1/2mv^2. So to push my prop wash twice as fast will take 4 times the energy.

This means my smaller prop is about half as efficient as the larger prop turning slow. Electric motors can put out huge torque at any speed so they don't need to be in a torque band to start producing useful thrust. I would think the designers know of this phenomenon and use it to get the props to be more efficient than diesel props at slower speeds.

All power to Big Beakie and other early adopters. They get to forge a path so that we can come along later and learn secondhand about the utility of the system.

I have been looking into electric for ages and have never made the jump. But with the price of Lithium plummeting and the choice of having a smaller ICE for long distance, I am certainly not against the idea of replacing my twins with electric sometime in the future. It would be great to never fuel up again for using my boat as it is mostly used - for sailing around the lake until we go cruising again.

[mcarthur]

Originally Posted by JustMurph

But, IMO in a blue water cruising boat, you need that full power ability for emergency situations, e.g. motoring off a lee shore in storm conditions. In a day sailer, maybe not.

JM, not picking on you, but I've heard this often - "what about the emergency time?"
If that's how we should be sizing and deciding propulsion, why don't we all have 1000hp jet engines ready for the "emergency"? Because it's not viable (though would look cool!). Even hauling around bigger engines that you ever need is the same - not viable for the small chance and time they may be needed, even if the sales and marketing department do get an inordinate say.

Everyone has their own "OMG I need X for situation Y". There's a difference though between getting yourself out of a not uncommon situation and doing the same in high luxury: having the 200hp ready on a sailing boat for that OMG I'm on a lee shore and I've lost all ability to sail (note "sailing boat") is a luxury - you'll definitely get off that lee shore once in 10 years you need to, but you are lugging that weight and problem of larger engine around for the other 9.98 years.

How about having an engine that can get you off the lee shore (once in the blue moon), but not at 50knots speed, more like 3 knots of speed - still gets you away from that situation, but you don't need a huge engine to do so. That's what propulsion sizing (diesel or electric) is about - the ability to move the vessel in whatever level of adverse condition you want to pay the price for. I'd be happy with moving out of harms way at a couple of knots - don't need 50kn boat speed. I'll bet BigB can do that with the electric only, no need for the diesel!

There are situations when boat speed is more important - going over a bar when you can't (not won't: can't) wait for example. I'd choose the ability to pickup speed to match the needs then! But then most small to mid-size sailing vessels already fail here too, as do small-mid displacement motor vessels: being limited to 6-7kn means they'll never be able to come through the big bars that are crashing around! Yet somehow they often do! I'm sure they'd be happier, in that one situation in 10 years, being in a faster or bigger or longer or...just somewhere else .

So some people may want to "get away from the cyclone that's 3 days away, at 30knots". I'm happy they have the money and boat to do that! For the rest of us, propulsion from electric motors that are correctly sized seems sensible (backed where needed by lots of solar, and possibly diesel genset or alternator).

[Adelie]

Originally Posted by double u

surely true! as 98 is less than 100.
So far nobody has taken the TOTAL footprint of the boat into account-
once with ice & once with electric/no fossile fuels.
As the footprint of the boat before any propulsion imho is huge compared to the propulsion (cost is a good guide...), the type of propulsion will make very little difference

EVs get about 3mi/kWhr at somewhere near 60mph.
Building an EV creates more emissions than to build a ICE vehicle.
But the EV is some much more efficient using it's energy to propel itself that even using coal generated electricity, it will create less than half the emissions over it's life time.
Comparing a Tesla-3 to a Rav-4, they break even on emissions at about 21,000mi.
https://www.wsj.com/graphics/are-ele...e-environment/

The Cal 34 I want would get about 1mi/kWhr at 6kt. That means it takes significantly fewer miles to break even with a gas or diesel powered version of the same even if all the power came from coal fired shore power from a marina. If all the power is coming from on board solar panels.....

For a boat with a dead ICE that needs to be replaced, I would expect that the emission from manufacturing a new ICE are the same or greater than for a new electric motor and batteries, especially if the batteries are Lead acid (LA). For Lithium batteries, the ICE would probably be the same or less. Why? Because 95-98% of the material in LA batteries is recycled.

[Adelie]

Originally Posted by catsketcher

Efficiency of props

I was wondering if anyone had anything on prop efficiency at typical diesel revs. If electric motors are more efficient it may be because they have spin slower than diesels.

I notice a similar effect with my four stroke outboards. We use more fuel than a similar cats with diesels when motoring in calms. Too much more to be due to the better fuel economy of a diesel engine. But my props spin at about 1500rpm when cruising and are 12 inch in diameter and my friends have larger props.

The prop effect is interesting. To move a boat you have to move water aft - it is a change in momentum concept. Momentum = mass x velocity. If my prop is half the area (I have a 12 inch prop and my figurative friend has a 17 inch prop) then I have to push the water twice as fast to get the same change in momentum.

But pushing things fast is inefficient, as shown by Big Beakie's data. To move something you must increase its kinetic energy. KE = 1/2mv^2. So to push my prop wash twice as fast will take 4 times the energy.

This means my smaller prop is about half as efficient as the larger prop turning slow. Electric motors can put out huge torque at any speed so they don't need to be in a torque band to start producing useful thrust. I would think the designers know of this phenomenon and use it to get the props to be more efficient than diesel props at slower speeds.

All power to Big Beakie and other early adopters. They get to forge a path so that we can come along later and learn secondhand about the utility of the system.

I have been looking into electric for ages and have never made the jump. But with the price of Lithium plummeting and the choice of having a smaller ICE for long distance, I am certainly not against the idea of replacing my twins with electric sometime in the future. It would be great to never fuel up again for using my boat as it is mostly used - for sailing around the lake until we go cruising again.

Gas outboard vs diesel inboard has several things going on.

In terms of hp/gal/hr diesel has about a 9:5 or 9:6 advantage over gasoline.
Outboards use smaller, fast props which are not as efficient as larger slower ones. If you got a high thrust prop for your motor you could probably get an extra 5-20% better fuel economy, at the cost of top end speed. Given that it is an outboard geared for planing, the speed loss will probably be minimal, hard to say.

I don't understand the efficiency tradeoffs of electric propulsion nearly as well so I won't comment.

[JustMurph]

Originally Posted by wingssail

his solar array is larger in area than my mainsail.

You must have a very small main!

Originally Posted by catsketcher

Efficiency of props

I was wondering if anyone had anything on prop efficiency at typical diesel revs. If electric motors are more efficient it may be because they have spin slower than diesels.

As Adelie mentioned above, larger props are more efficient. E.g. if you over prop a diesel, you will slightly reduce top end but will gain a decent chunk of efficiency.

Regarding the efficiency of electric setups, they are generally specified for a lower top speed/peak power than diesels typically would be, thus the power/speed duty point that the prop is specified for is quite close to your cruising speed (and hence more efficient). On the other hand diesels will be cruising at 50% or less of their rated power, so the props are also further from their specified duty.

Originally Posted by mcarthur

JM, not picking on you, but I've heard this often - "what about the emergency time?"
If that's how we should be sizing and deciding propulsion, why don't we all have 1000hp jet engines ready for the "emergency"? Because it's not viable (though would look cool!). Even hauling around bigger engines that you ever need is the same - not viable for the small chance and time they may be needed, even if the sales and marketing department do get an inordinate say. .....

Ahh, you're way off the mark there mate. The standard diesel setups in most boats are sized for "just enough power to get out of harms way in an emergency". Most are not overpowered by any means. Many are already border line underpowered. Pulling even more power out of them with electric setup will absolutely come with compromise. Whether you can live with that is up to the individual and their use case. Day sailer, give me some little electrics. 100%. Blue water cruiser, there's no way I'm reducing HP.

E.g. A few years back I was sailing on a Lagoon 421 and we had to get directly upwind in 30 knots and short sharp chop. Seeing as that thing couldn't have sailed to windward to save its life, we chose to motor. With the pair of 30s pegged at WOT we barely hit 4 knots. If you believe the marketing and electric horses are bigger than diesel horses, a pair of 10kw electric motors should be "functionally equivalent".

Who here honestly believes that that Lagoon 421 with 20kw of electric propulsive power instead of 44kw from the diesels, would have still been doing 4 knots, let alone moving at all?

[Adelie]

Originally Posted by JustMurph

.....
Ahh, you're way off the mark there mate. The standard diesel setups in most boats are sized for "just enough power to get out of harms way in an emergency". Most are not overpowered by any means. Many are already border line underpowered. Pulling even more power out of them with electric setup will absolutely come with compromise. Whether you can live with that is up to the individual and their use case. Day sailer, give me some little electrics. 100%. Blue water cruiser, there's no way I'm reducing HP.
The old standard was an engine big enough to go directly up wind against 20kt wind with a 2nm fetch at 2kt boat speed if I recall.

E.g. A few years back I was sailing on a Lagoon 421 and we had to get directly upwind in 30 knots and short sharp chop. Seeing as that thing couldn't have sailed to windward to save its life, we chose to motor. With the pair of 30s pegged at WOT we barely hit 4 knots. If you believe the marketing and electric horses are bigger than diesel horses, a pair of 10kw electric motors should be "functionally equivalent".
That sounds like a boat problem not an engine problem. Why would you go offshore in a boat that could not go upwind in 30kt of breeze?

Who here honestly believes that that Lagoon 421 with 20kw of electric propulsive power instead of 44kw from the diesels, would have still been doing 4 knots, let alone moving at all?

The Lagoon 421 is a charter condo meant to remain in the marina when those kinds of winds are coming from where you want to go.
Electric propulsion is not meant to remediate the shortcomings of the boa, so, as you say diesel is the way to go for a boat like that.

[seandepagnier]

Originally Posted by catsketcher

Efficiency of props
12 inch prop and my figurative friend has a 17 inch prop) then I have to push the water twice as fast to get the same change in momentum.

This is exactly correct. I have a 32 inch prop. I would even consider going larger. The larger propeller will always be more efficient. Fish and dolphins are very efficient and their tails to body are proportionate. This should give you an idea of what size propeller you need, typically it is between half the beam to the full beam of the boat.

Originally Posted by JustMurph

Regarding the efficiency of electric setups, they are generally specified for a lower top speed/peak power than diesels typically would be, thus the power/speed duty point that the prop is specified for is quite close to your cruising speed (and hence more efficient). On the other hand diesels will be cruising at 50% or less of their rated power, so the props are also further from their specified duty.

This is just the pitch and camber. The propeller itself is sized to fit in the inboard location which basically means the efficiency is terrible because it is an 18 inch propeller when it should be a 48 - 60 inch one.

Ahh, you're way off the mark there mate. The standard diesel setups in most boats are sized for "just enough power to get out of harms way in an emergency". Most are not overpowered by any means. Many are already border line underpowered. Pulling even more power out of them with electric setup will absolutely come with compromise. Whether you can live with that is up to the individual and their use case. Day sailer, give me some little electrics. 100%. Blue water cruiser, there's no way I'm reducing HP.

The thing is, you don't need any HP to begin with. In these "emergency" situations you should generally be able to use the sails. This always worked for me I am not sure what the hesitancy is about this.

Secondly, the electric motor can output huge amounts of power. I have a $45 electric motor rated for 60 volts 60 amps. This weighs under 2lb. so a 20lb motor could do 36kw. If the electric motor is watercooled it can do even more power for its weight. Consider drone motors power to weight. So really you can easily have much more power available. It won't be as efficient pushing the motor as it will get hot, but for short duration, the electric motor can have the power and reliability that nothing else can match.

The reality is when you break it down the truth is people want to motor against strong winds for hours and hours. This is not something that is any good to do yet it is the only real argument for the diesel and yes batteries ultimately limit the energy storage making this absurd scenario unrealistic on electric power.

E.g. A few years back I was sailing on a Lagoon 421 and we had to get directly upwind in 30 knots and short sharp chop. Seeing as that thing couldn'it have sailed to windward to save its life, we chose to motor. With the pair of 30s pegged at WOT we barely hit 4 knots.

If you can't sail upwind in 30 knots there is something wrong with the hull and rig: this has nothing to do with electric power.

[smj]

Originally Posted by seandepagnier

This is exactly correct. I have a 32 inch prop. I would even consider going larger. The larger propeller will always be more efficient. Fish and dolphins are very efficient and their tails to body are proportionate. This should give you an idea of what size propeller you need, typically it is between half the beam to the full beam of the boat.

This is just the pitch and camber. The propeller itself is sized to fit in the inboard location which basically means the efficiency is terrible because it is an 18 inch propeller when it should be a 48 - 60 inch one.

The thing is, you don't need any HP to begin with. In these "emergency" situations you should generally be able to use the sails. This always worked for me I am not sure what the hesitancy is about this.

Secondly, the electric motor can output huge amounts of power. I have a $45 electric motor rated for 60 volts 60 amps. This weighs under 2lb. so a 20lb motor could do 36kw. If the electric motor is watercooled it can do even more power for its weight. Consider drone motors power to weight. So really you can easily have much more power available. It won't be as efficient pushing the motor as it will get hot, but for short duration, the electric motor can have the power and reliability that nothing else can match.

The reality is when you break it down the truth is people want to motor against strong winds for hours and hours. This is not something that is any good to do yet it is the only real argument for the diesel and yes batteries ultimately limit the energy storage making this absurd scenario unrealistic on electric power.

If you can't sail upwind in 30 knots there is something wrong with the hull and rig: this has nothing to do with electric power.

How can one sail with a 32” prop? That’s like towing a large drogue. We are talking sailboats, and in this thread catamarans?

[catsketcher]

Originally Posted by Adelie

Gas outboard vs diesel inboard has several things going on.

In terms of hp/gal/hr diesel has about a 9:5 or 9:6 advantage over gasoline.
Outboards use smaller, fast props which are not as efficient as larger slower ones. If you got a high thrust prop for your motor you could probably get an extra 5-20% better fuel economy, at the cost of top end speed. Given that it is an outboard geared for planing, the speed loss will probably be minimal, hard to say.

I think it is the 9:5 ratio that causes the difference because my engines are the slow turning 3:1 gearbox large diameter prop motors.