Thoughts on a viable and MARKETABLE Electric Drive Train

[valhalla360]

Originally Posted by Emoyeni

Valhalla, I’d buy this boat. And I’m about to go electric on my C&c 30. A lot of posts thus far are about the engineering side of this equation and I think while important it misses the main selling point of electric: quietness and lack of smell of the drivetrains. If I wanted to motor for 20 hours, I’d buy a motorboat. Sailing is a sensory experience and that’s true even at 3kt.

I'm not buying the noise issue. With a 25hp 4 stroke, we could easily hold a normal conversation from opposite sides of the cockpit while under way. We also had a diesel Catalac catamran of similar size with diesel inboards...again, noise wasn't an issue.

Of course, I'm saying no one really motors for 20hrs straight, so it's not necessary to build a drivetrain that can provide it. What you won't be able to sell is a boat that can only motor at 3kts if you want to go more than 10 miles.

So find the sweet spot that covers 95% of users and market a boat that can meet their needs.

[Ericson38]

Originally Posted by Ericson38

100 gallons of diesel has just over 4 million Watt hours of energy. With a 25% overall efficiency (thermal & mechanical) that 100 gallons has 1 million Watt hours. That's for 322 kg of mass. So the net extractable energy density in Watt hours/kg = 3105.

The best EV batteries are in the 260-270 range in 2020.

So that means diesel is 11 times as energy dense currently.

Over 10K engine hours, at 1.5 gal/per hour cruising at 6kts, you would consume 6667 gallons of fuel and motor 60K nautical miles. At $3.00 a gallon, you would spend $20K.

If you look at this table for generator ratings and fuel consumption, at the 1000 kW mark (1 million watts), this level of output can be maintained for 1 hour using 71.1 gallons. This is much better than I estimated using 25% efficiency, which required 100 gallons.

https://www.generatorsource.com/Dies...nsumption.aspx

[Adelie]

Originally Posted by valhalla360

I'm not buying the noise issue. With a 25hp 4 stroke, we could easily hold a normal conversation from opposite sides of the cockpit while under way. We also had a diesel Catalac catamran of similar size with diesel inboards...again, noise wasn't an issue.

Of course, I'm saying no one really motors for 20hrs straight, so it's not necessary to build a drivetrain that can provide it. What you won't be able to sell is a boat that can only motor at 3kts if you want to go more than 10 miles.

So find the sweet spot that covers 95% of users and market a boat that can meet their needs.

Plenty of folks motor 20hr straight.
Crossing the doldrums
Running from Olympia, WA up Desolation Sound in Canada.
NYC up to Maine.
As a percentage of users, the number that do so is small, but the percentage that think they might and want a boat that can do it is somewhat higher.

[Adelie]

Originally Posted by Ericson38

1 hp= 746 watts. Not sure where you got the 18 hp for 1 hour value. That depends on turbo or not, for one thing.

On my Universal Model 32 (Ericson 38) I would get 6.6 kts at just under 0.8 gallon per hour all day long. This is in the 28 hp range (boat was 16K lbs). Getting about 7 mpg.

With the 75 hp Yanmar 4JH2-HTE at 2800 rpm (into the turbo) at 7 kts, I estimate power at 55 hp and was using still under 2 gallons per hour. This is the 49 foot Taswell at 40K lbs. Getting about 3.5 mpg.

I couldn't find the specs for the 4JH2-HTE, I did find them for:

4JH4-TE. 75 hp turbo
That shows 2gal/hr @ 2600, which shows 38hp at the prop. --> 19hp-hr/gal
https://www.yanmar.com/marine/product/engines/4jh4-te/

4JH45 45hp natural
2gal/hr @ 2750rpm ---> 25kW = 34hp --> 17 hp-hr/gal.
https://www.yanmar.com/marine/product/engines/4jh45/

4JH3-DTE 125hp, turbo intercooler
4gph @3125 rpm --> 73hp --> 18.25 hp-hr/gal
https://www.yanmar.com/marine/product/engines/4jh3-dte/

All 3 of these Yanmars are about 122ci displacement.

These guys say 20hp-hr/gal is a high end estimate for turbo diesels at peak torque but that boats should not be propped so they can reach peak torque so something less than 20 that is more likely in real life.
and 12hp-hr/gal for large naturally aspirated gasoline engines
https://www.sbmar.com/articles/fuel-and-horsepower/

I looked into potential economy improvements for turbo over naturally aspirated.
The best info I found is that turbo in cars is might be a bit under 3% more efficient. This data I believe is mostly from gasoline vehicles. It's not clear whether there was an apples to apples comparison of the same engine with and without a turbo or if it was just the same model car but not necessarily the same engine.
https://www.caranddriver.com/feature...-economy-bust/

All the the discussions I found about the advantages of turbo-diesel is that it widens the power band and increases HP for a given weight engine. The narrow power band is why diesel semis tend to have a lot of gears. Nobody talks about an economy advantage. It seems like there might be a small advantage from the above link but it is minor enough in real usage that it's not something people tout.

[Adelie]

Originally Posted by Ken Fry

I think you know this, but 1hp is 746 watts, (.746kW. ) not the .746 W you quoted above.

The resistance curve for displacement sailboats gets very very steep at around hull speed. If a sailor motored a 46 foot displacement sailboat at 5 knots (well below hull speed) their fuel burn per NM could be on the order of half that of the Trawler, or lower. But that depends upon the actual boat and numerous other things.

Yep, I got that wrong. Good catch.

[carstendenmark]

Seems that all are so nitty about the cost of good quality LiFePO4 batteries...

At no less than 330K US$ for a new Gemini, I think it may be an option just to put in a huge power bank, that can run the two pure electric engines to make you pass the doldrums at 3 knots.
The feeling of going 3 knots, instead of lying flat dead for days, is good !
(Adding enough detachable solar panels to flip out in daytime, should provide you the 3 knots, even when charging for the nights.)
So we have an electric world cruiser. With a big power bank, the speed can be much higher for a few hours, if needed.

The noise - well, did you ever TRY an electric yacht ?
Then you will hear the remarkable difference.

Maintenance - a good quality battery bank is supposed to let you go for at least 10 years hazzle free. No oil changes, no filters, no clogging of injectors, no water in the diesel tanks, no storage procedures when put on the hard, and NO smell. Wow !
valhalla360, did you ask Gemini if they are interested ?


Turbo's are the way to go, if you want mechanical trouble.
I've had two gasoline cars with turbo. VERY expensive to repair. Required higher octane fuel. Never again !
Better to have a bigger engine, that runs smoothly.

[Ken Fry]

Originally Posted by Ken Fry

So... My caution is that it might not sell as planned. (Or it might sell better than planned.) In either case, solid market planning can help avoid a painful experience.

I did not realize (until reading one of your early posts that I'd missed) that you, Valhalla, don't intend to build this. Therefore none of my cautions regarding market research apply. Musing is not painful.

Your basic idea will work, of course. Those of us who have built electric and hybrid cars and boats can confirm that. History can too: electric boats have been around for longer than ICE boats.

Like you, I am awaiting the engineering explanation for how a 1 hp electric motor matches a 4 hp ICE. (There is no explanation for that based upon valid Newtonian physics.) Ditto for claims of significant advantages for direct drive, when good engineering practice and efficiency numbers cannot support the benefits in most applications.

It is possible, for a driver with considerable skill to drive a 5 speed car around in 5th gear from a stop and until the first hill. But why would anyone want that? Acceleration is terrible, hill climbing is terrible, because tractive force is terrible.

The motors like the Thunderstruck one can be hooked directly to the prop shaft with no reduction, but then they cannot produce their full hp, because the torque required at low rpm exceeds the motor's maximum current rating. Could a person instead use a bigger, heavier more expensive motor? Of course, but then the system is heavier and more costly than the original motor/reduction combo. There are applications, like driving a lightly loaded fan, where direct drive makes sense. There are others where it makes no sense at all.

There is nothing required for a boat like you envision that is has not been proven to work in zillions of applications. How many people want such a boat is a a matter for market research. My guess would be about 1%-2% of the sailing market, given very good promotion. In the sailing biz that would be a hit.

[Ericson38]

Originally Posted by Adelie

I couldn't find the specs for the 4JH2-HTE, I did find them for:

4JH4-TE. 75 hp turbo
That shows 2gal/hr @ 2600, which shows 38hp at the prop. --> 19hp-hr/gal
https://www.yanmar.com/marine/product/engines/4jh4-te/

4JH45 45hp natural
2gal/hr @ 2750rpm ---> 25kW = 34hp --> 17 hp-hr/gal.
https://www.yanmar.com/marine/product/engines/4jh45/

4JH3-DTE 125hp, turbo intercooler
4gph @3125 rpm --> 73hp --> 18.25 hp-hr/gal
https://www.yanmar.com/marine/product/engines/4jh3-dte/

All 3 of these Yanmars are about 122ci displacement.

These guys say 20hp-hr/gal is a high end estimate for turbo diesels at peak torque but that boats should not be propped so they can reach peak torque so something less than 20 that is more likely in real life.
and 12hp-hr/gal for large naturally aspirated gasoline engines
https://www.sbmar.com/articles/fuel-and-horsepower/

I looked into potential economy improvements for turbo over naturally aspirated.
The best info I found is that turbo in cars is might be a bit under 3% more efficient. This data I believe is mostly from gasoline vehicles. It's not clear whether there was an apples to apples comparison of the same engine with and without a turbo or if it was just the same model car but not necessarily the same engine.
https://www.caranddriver.com/feature...-economy-bust/

All the the discussions I found about the advantages of turbo-diesel is that it widens the power band and increases HP for a given weight engine. The narrow power band is why diesel semis tend to have a lot of gears. Nobody talks about an economy advantage. It seems like there might be a small advantage from the above link but it is minor enough in real usage that it's not something people tout.

I don't find the data you summarized. Graphs are clearly marked. Also, I have had mine for 5 years and know what it consumes, and know that about 55 hp in my case gets the boat to 7 kts. This is a 40K boat, 49 feet overall, Taswell 49.

From the graph- the 4JH4-TE consumes 2 gallons per hour at 2600 RPM and shows 68 hp developed at the prop (output flange of the KM4A transmission), not 38 HP that you mentioned. It is also a 2 liter engine. Max power is 75 marine HP at 3200 rpm at 4 gallons per hour. I never run mine at full throttle, only at the 3/4 point. You can see from the torque curve that the engine is most efficient within the 1800-2600 rpm range.

If you look at the 4JH4-HTE (water cooled turbo version verses non-cooled TE model), the power developed at the 2 gallons per hour point (2200 rpm for this engine) is 82, versus 68 for the non cooled turbo engine. Both are turbo charged, while the HTE turbo housing is water cooled to make the air denser, even after turbo compression before it enters the cylinder on downstroke.

[Adelie]

Originally Posted by Ericson38

I don't find the data you summarized. Graphs are clearly marked. Also, I have had mine for 5 years and know what it consumes, and know that about 55 hp in my case gets the boat to 7 kts. This is a 40K boat, 49 feet overall, Taswell 49.

From the graph- the 4JH4-TE consumes 2 gallons per hour at 2600 RPM and shows 68 hp developed at the prop (output flange of the KM4A transmission), not 38 HP that you mentioned. It is also a 2 liter engine. Max power is 75 marine HP at 3200 rpm at 4 gallons per hour. I never run mine at full throttle, only at the 3/4 point. You can see from the torque curve that the engine is most efficient within the 1800-2600 rpm range.

If you look at the 4JH4-HTE (water cooled turbo version verses non-cooled TE model), the power developed at the 2 gallons per hour point (2200 rpm for this engine) is 82, versus 68 for the non cooled turbo engine. Both are turbo charged, while the HTE turbo housing is water cooled to make the air denser, even after turbo compression before it enters the cylinder on downstroke.

The 4JH4-HTE is a 110hp motor. At 2600rpm it uses just under 3gal/hr using the "ideal" propeller. At 2600 it can make about 100hp.
https://www.yanmar.com/marine/product/engines/4jh4-hte/


You indicated your engine was a 75hp turbo pulling 2gal/hr at 2600rpm so I looked for the closest thing Yanmar is currently making. That's how I got to the 4JH4-TE, 75hp turbo, 2gal/hr at 2600rpm using the "ideal" propeller.
https://www.yanmar.com/marine/product/engines/4jh4-te/

For this engine, it CAN make 68hp at 2600rpm, as shown by the upper 2 curves as you indicate above. The problem is that the propeller can't absorb that much power. What the "ideal" prop will use at a given RPM is shown in the bottom curve. At 2600, 39hp is how much the prop will use. If the prop is spinning at 2600 and you apply 68hp, the prop will accelerate to 3100 or so rpm. The upper 2 curves are the maximum that the motor can deliver at those RPMs on a dynomometer or with various other loads.

Notice that the fuel usage curve and the prop power curve are similar. This supports my argument that the prop power curve is what the engine is producing at any give rpm. If the upper 2 curves were what the engine was producing then the fuel usage curve would look similar to them. The prop and fuel curve are similar to the drag curves as a function of boat speed for a displacement hull too. I may dig that up if I have time later.

RPM, fuel usage and speed are straightforward to measure, so I am have no quibbles your reporting of those data points. You indicate that your engine was using 55hp at 2600 burning 2gal/hr, but unless you had a dynomometer in your system I don't see how you could directly measure that. It seems to me that you likely obtained that info by reading the power curve chart for your engine, specifically one of the 2 top curves. Is there another way you determined actual horsepower used that I missed or haven't learned of?

Then there is the issue of the "ideal" prop that Yanmar designs to. Is that the prop on your boat? Probably not. They make various assumptions about boat size, max speed, prop size, prop pitch, number of blades,..... The prop on your boat is probably similar to the ideal one, and the power and fuel curves are also probably similar. Or maybe, coincidentally your prop matches the "ideal" prop that yanmar shows data for. Probably they pick an ideal prop to be slightly conservative so most buyers are pleasantly surprised by fuel usage and speed made.

If you want to read up on engine vs prop power curves, pg 3-5 in Gerr's Propeller Handbook. Not everything I argued above is there, but much of it is.

.I marked up the 2 charts for the 4JH4-TE in the graphic below, plus a 3rd graphic where the prop power curve was changed to Green and the Fuel curve overlaid on it so the similarity in shape can be seen clearly.

[Ericson38]

Recall my original observations-

On my Universal Model 32 (Ericson 38) I would get 6.6 kts at just under 0.8 gallon per hour all day long. This is in the 28 hp range (boat was 16K lbs). Getting about 7 mpg.

With the 75 hp Yanmar 4JH2-HTE at 2800 rpm (into the turbo) at 7 kts, I estimate power at 55 hp and was using still under 2 gallons per hour. This is the 49 foot Taswell at 40K lbs. Getting about 3.5 mpg.

Both of these data points are locatable on the power and fuel use curve for the 4JH4-HTE. Only the RPMs are different, but the power developed and gallons per hour are the close to the same.

For the Universal engine's points, look at 1400 rpm on the 4JH4-HTE. That's about 28 hp at about .5 gallons per hour. My engine was consuming .7-.8 gallons per hour, but was not a Turbo with the water cooled housing. So new Yanmar is better than older normally aspirated Kubota block (4 cylinder-32 hp) by 10% or so.

For my 4JH2-HTE, look at the 2000 rpm point on the 4JH4-HTS graph. Power is 55 HP, and fuel rate is 1.5 gallons per hour, maybe a little better than what I measure from real life experience. Again about 10% better use of fuel than what I had.

[valhalla360]

Originally Posted by Adelie

Plenty of folks motor 20hr straight.
Crossing the doldrums
Running from Olympia, WA up Desolation Sound in Canada.
NYC up to Maine.
As a percentage of users, the number that do so is small, but the percentage that think they might and want a boat that can do it is somewhat higher.

The use case was coastal cruisers, so crossing the doldrums is not relevant. Though in that case, you hear many people talking about motoring at little more than idle speed. They basically just want to make some headway to get out...well, throttle way back and the range on this hybrid goes way up.

Running up to Maine or the Inside Passage, can and is typically broken up into multiple runs. Those making a fast dash, usually will head offshore and sail.

[valhalla360]

Originally Posted by carstendenmark

Seems that all are so nitty about the cost of good quality LiFePO4 batteries...

At no less than 330K US$ for a new Gemini, I think it may be an option just to put in a huge power bank, that can run the two pure electric engines to make you pass the doldrums at 3 knots.
The feeling of going 3 knots, instead of lying flat dead for days, is good !
(Adding enough detachable solar panels to flip out in daytime, should provide you the 3 knots, even when charging for the nights.)
So we have an electric world cruiser. With a big power bank, the speed can be much higher for a few hours, if needed.

The noise - well, did you ever TRY an electric yacht ?
Then you will hear the remarkable difference.

Maintenance - a good quality battery bank is supposed to let you go for at least 10 years hazzle free. No oil changes, no filters, no clogging of injectors, no water in the diesel tanks, no storage procedures when put on the hard, and NO smell. Wow !
valhalla360, did you ask Gemini if they are interested ?


Turbo's are the way to go, if you want mechanical trouble.
I've had two gasoline cars with turbo. VERY expensive to repair. Required higher octane fuel. Never again !
Better to have a bigger engine, that runs smoothly.

Have the Gemini gotten that expensive? (I haven't looked at new prices lately) I would much prefer the single central engine as it keeps the systems simpler. Never suggested a turbo.

But yeah, given the overall price, a moderate size battery bank is not a deal breaker in terms of cost. But the whole doldrums thing is not part of the use case. Coastal cruising 3kts is a marketing deal breaker.

I've been on a couple electric boats and no there wasn't some magical difference. Similar with EV cars. Heck, I almost got ran down by a big diesel motorhome last week when I didn't hear it roll up behind me in a parking lot. Modern ICE don't make a ton of noise (and my hearing is just fine). Now if you are looking at a 60yr old 2 stroke...that's a different ballgame.

[Ericson38]

Originally Posted by valhalla360

The use case was coastal cruisers, so crossing the doldrums is not relevant. Though in that case, you hear many people talking about motoring at little more than idle speed. They basically just want to make some headway to get out...well, throttle way back and the range on this hybrid goes way up.

Running up to Maine or the Inside Passage, can and is typically broken up into multiple runs. Those making a fast dash, usually will head offshore and sail.

Coastal cruising in the Chesapeake is mostly about motoring around, with the AC running, and getting to the next marina by sundown. Then there are the ICW migrations to and fro.

Our boat has a 1000 amp hour battery bank (12kW/hr. capacity). My max dockside charge rate is 130 amps for the 13 Volt bank. So that's about 1700 watts for 4-5 hours at a 50-60% depth of discharge. Out of the 50 amp 120 volt marina service, I'm using 15 amps to get back to 100%, leaving 35 amps for AC and such. Can just run 1 unit AC and fridge with that remainder of the 120 V 50 amp service.

An electric propulsion boat in the Chesapeake is going to need to recharge a bank about 4-5 times the size of the one we have for house batteries, right ? Not sure what size bank folks are considering, based on their cruising needs.

But at the next marina, right? With the 50 amp service, or maybe two of them in parallel. Even then, at 100 amps and 120V dockside service, we are talking about 7-8 hours recharge from full depletion, with a 5000 amp hour 12 V bank.

With a 50 amp service and 50% depth of discharge, and the aforementioned 60kW hour bank, that is 5 hours at 50 amps. Nothing left for AC, so maybe 20 for batts and 30 amps for house AC while dockside. This raises it to 12.5 hours to replace 30KWhours from the electric engine's battery bank.

[valhalla360]

Originally Posted by Ericson38

Coastal cruising in the Chesapeake is mostly about motoring around, with the AC running, and getting to the next marina by sundown. Then there are the ICW migrations to and fro.

Our boat has a 1000 amp hour battery bank (12kW/hr. capacity). My max dockside charge rate is 130 amps for the 13 Volt bank. So that's about 1700 watts for 4-5 hours at a 50-60% depth of discharge. Out of the 50 amp 120 volt marina service, I'm using 15 amps to get back to 100%, leaving 35 amps for AC and such. Can just run 1 unit AC and fridge with that remainder of the 120 V 50 amp service.

An electric propulsion boat in the Chesapeake is going to need to recharge a bank about 4-5 times the size of the one we have for house batteries, right ? Not sure what size bank folks are considering, based on their cruising needs.

But at the next marina, right? With the 50 amp service, or maybe two of them in parallel. Even then, at 100 amps and 120V dockside service, we are talking about 7-8 hours recharge from full depletion, with a 5000 amp hour 12 V bank.

With a 50 amp service and 50% depth of discharge, and the aforementioned 60kW hour bank, that is 5 hours at 50 amps. Nothing left for AC, so maybe 20 for batts and 30 amps for house AC while dockside. This raises it to 12.5 hours to replace 30KWhours from the electric engine's battery bank.

Exactly, Chesapeake or ICW, lots of people making short day hops. A very common use pattern all along the east coast, great lakes, gulf coat along with many other areas.

As far as 4-5 times your 12kwh capacity...my original suggestion was 40kwh based on 4hr at 10kw output to maintain 6.5kt on a Gemini catamaran and later upped a bit (45kwh) to make sure the user isn't dragging the bank down to 0%. You can argue the exact amount but very much consistent with my original idea.

Sure it will take several hours to recharge but if you get in around 5pm and don't leave the next day until around 10am, that gives you 17hrs, so you only need to pull around 2.3kw to fully charge 40kwh for the next day's travels. Even a single 30amp can do that if you aren't running the air/con. With a 50amp, you won't even notice it with heavy house loads on a 34ft cat, since a 50amp can put out a steady 8-9kw (this would allow if you were operating a larger boat that required more power for propulsion with a proportionally larger battery bank).