Viability of electric only propulsion in 2018 - is there a good option after all?

[StuM]

Originally Posted by BigBeakie

KTP,

What is the C rating of your batteries? This is quite important as LA technology often cannot give the motors the kW rating they need, particularly at full power. Even some Lithium batts do not have a high enough C rating for EP, surprisingly.

C rating for LA???
No one bothers with them.
FWIW, the Maximum Continuous Discharge rating for a Lifeline 125Ah AGM is 950 Amps

[BigBeakie]

Yes, but in what time period? No sense having a 10kW motor and your batteries cannot deliver enough power to run it at nominal power rating. Hence the C rating issue. In other words, his 10 kWh bank needs to be able give that energy up in one hour if he wants to run at full power.


Sent from my iPad using Cruisers Sailing Forum

[CharlieJ]

And then there is this production boat by the founder of OV:

http://tinyurl.com/ycdjeggp

[skipmac]

Originally Posted by StuM

I'd like to publicly thank Growley Monster for his contributions to this and other threads on EP.
It's great to see someone who is actually walking the talk honestly putting forward both the pros and cons of EP without any hype or hyperbole.

He is a voice of sanity in what are often insane discussions.

[john61ct]

Originally Posted by StuM

FWIW, the Maximum Continuous Discharge rating for a Lifeline 125Ah AGM is 950 Amps

Originally Posted by BigBeakie

Yes, but in what time period? No sense having a 10kW motor and your batteries cannot deliver enough power to run it at nominal power rating. Hence the C rating issue. In other words, his 10 kWh bank needs to be able give that energy up in one hour if he wants to run at full power.


Sent from my iPad using Cruisers Sailing Forum

950 ÷ 125 = their Discharge C rating

[valhalla360]

Originally Posted by CharlieJ

And then there is this production boat by the founder of OV:

http://tinyurl.com/ycdjeggp

Its actually an interesting boat and if all you need is a low speed harbor launch, it's quite viable. I don't have a use for a harbor launch but I've seen ads for electric launches for quite some time (duffy comes to mind).

30' LOA 7' beam and 3200lb displacement (admittedly much larger engines but a 30' cigarette boat will weigh in at least double the displacement for reference), it doesn't appear to have much in the way of cruising amenities but appears to be designed primarily to make electric viable. I would be curious what the design load limits are and what impact that has on performance and range given the extreme light weight.

If you back calculate it out, 9kts is about 6.4kw draw to get the 42mile range claimed. (Interesting when others have claimed 7kts at 7kw on a 50' boat several times the displacement.)

For reference, a 25hp diesel with a 5 gal tank should match the extended range version in performance when run at a similar 6.4kw output.

They don't list the price so can't say if it competes financially but if your need is a low speed harbor launch, it looks viable.

[StuM]

Originally Posted by BigBeakie

Yes, but in what time period?

What part of "continuous" and "Amps" don't you understand?

[KTP]

What are people's opinions of the Battle Born 12V drop in LiFePO4 batteries?

12V 100AH in a case with BMS, 100A continuous, 200A for 30 sec discharge rates. Charge with AGM or Gel profile (14.4 to 14.6V)

$950 from various sources with free shipping.

Eight of those would give you ~50V at 200AH, 90% discharge 180AH (about 9kWh) with a 200A continuous discharge rate. Would cost $7600 and weigh 232 pounds.

Twelve Lifeline 12V 125AH would give you ~48V at 375AH, 50% discharge 187.5AH (about 9kWh). Would cost $4800 and weigh 864 pounds.

The advantage on the Lifeline, other than lower cost and length of time in business (many years) is you do have the option of taking them down to full discharge in an emergency situation, which would give you probably another 7 to 8kWh (accounting for sag below 12V). The lithium bank is only going to have 10% left, or about 1.2kWh before it is totally drained. So while it is a fair comparison above for normal recommended use, the Lifelines would give you that bit of emergency reserve that you would not have with the lithium bank. Obviously though if money is not an option, you could have 3x the lithium for weight and have your emergency reserve there but we are comparing capacity and cost here for normal use.

At 50% discharge the Lifeline charts give you about 1000 cycles. The Battle Born are supposed to be 3000 cycles. In reality a sailboat is not likely to hit either of these points before age has degraded both battery types (the lithiums lose capacity per year even if not used). I would guess typically one might use 100 cycles per year. Both battery types are going to be toast after 10 years...consider it a fuel cost.

It is a tough decision. Which one to go with?

[CatNewBee]

All electric works since the 60es. Look at submarines, a big battery bank and a small thermo-nuclear reactor keeps them for decades crossing oceans all-electric.

[GrowleyMonster]

Originally Posted by CatNewBee

All electric works since the 60es. Look at submarines, a big battery bank and a small thermo-nuclear reactor keeps them for decades crossing oceans all-electric.

Subs relied on electric power from flooded cell batteries for much much longer than that. The first diesel subs ran on batteries when not on the surface.

[GrowleyMonster]

Originally Posted by KTP

What are people's opinions of the Battle Born 12V drop in LiFePO4 batteries?

12V 100AH in a case with BMS, 100A continuous, 200A for 30 sec discharge rates. Charge with AGM or Gel profile (14.4 to 14.6V)

$950 from various sources with free shipping.

Eight of those would give you ~50V at 200AH, 90% discharge 180AH (about 9kWh) with a 200A continuous discharge rate. Would cost $7600 and weigh 232 pounds.

Twelve Lifeline 12V 125AH would give you ~48V at 375AH, 50% discharge 187.5AH (about 9kWh). Would cost $4800 and weigh 864 pounds.

The advantage on the Lifeline, other than lower cost and length of time in business (many years) is you do have the option of taking them down to full discharge in an emergency situation, which would give you probably another 7 to 8kWh (accounting for sag below 12V). The lithium bank is only going to have 10% left, or about 1.2kWh before it is totally drained. So while it is a fair comparison above for normal recommended use, the Lifelines would give you that bit of emergency reserve that you would not have with the lithium bank. Obviously though if money is not an option, you could have 3x the lithium for weight and have your emergency reserve there but we are comparing capacity and cost here for normal use.

At 50% discharge the Lifeline charts give you about 1000 cycles. The Battle Born are supposed to be 3000 cycles. In reality a sailboat is not likely to hit either of these points before age has degraded both battery types (the lithiums lose capacity per year even if not used). I would guess typically one might use 100 cycles per year. Both battery types are going to be toast after 10 years...consider it a fuel cost.

It is a tough decision. Which one to go with?

Me? Just what I got. 220ah 6v golf cart batteries, $85/each. I'll let you do the math. Mine are 4 yers old and kickin it just fine, still. Best bang for the buck. The only catch is you have to actually maintain them a little or they are only good for a couple of years.

[skipmac]

Originally Posted by CatNewBee

All electric works since the 60es. Look at submarines, a big battery bank and a small thermo-nuclear reactor keeps them for decades crossing oceans all-electric.

In this case the power all comes from the reactor. There's enough battery power for a buffer and to get by when the reactor needs to shut down or scale back.

With a current cost of $1-2 billion each for a nuclear sub this probably isn't a viable option for a sailboat anyway, even if a reactor could be made small enough to fit.

[StuM]

Originally Posted by CatNewBee

All electric works since the 60es. Look at submarines, a big battery bank and a small thermo-nuclear reactor keeps them for decades crossing oceans all-electric.

Question: Why do submarines have a big battery bank with a reactor on board?

Answer: As very termporary backup if they shut the reactor down - not for propulsion. They also have a diesel generator.



Nuclear subs don't use EP for propulsion, they use steam generated by the heat of the nuclear reaction to drive turbines.

[KTP]

Originally Posted by GrowleyMonster

Me? Just what I got. 220ah 6v golf cart batteries, $85/each. I'll let you do the math. Mine are 4 yers old and kickin it just fine, still. Best bang for the buck. The only catch is you have to actually maintain them a little or they are only good for a couple of years.

I would rather have the non-spillable, set and forget Lifeline even though they are about 3x the cost of the FLA.

Actually when looking at the lifetime vs discharge curves for Lifeline I am seeing above 500 cycle life even at 80% discharge.

So one might decide that they are probably only going to have 50 to 100 80% discharges per year and decide that 5 to 10 years is plenty of life for one set of batteries....treat them more like replaceables (like having to service your diesel engine once every 5 years instead of once a season).

At the 25AH rate for a GPL-31XT 125AH battery you get 920 watt-hr from each battery at 80% discharge. So twelve would give you a bit over 11kWh and last for 5 to 10 years.

11kWh puttering around at 3kW gives you over 3 hours of motoring at an estimated 5 knots in smooth water. Plenty of time to get out to the sailing areas. (I am guessing here, because 6kW equivalent diesel power (1/2 gallon per hour) moved us at 6.6 knots.)

[StuM]

Originally Posted by GrowleyMonster

Subs relied on electric power from flooded cell batteries for much much longer than that. The first diesel subs ran on batteries when not on the surface.

But not for long and not for any major distance. WW2 U boats did about 24 hours and 80 miles or so at slow speed. A lot less if they needed to do more than about 4 knots. Beyond that, they had to run diesels on the surface.