Replace genset with lithium batteries and a inverter...

[Grateful Escape]

I have a 2006 SD 260, I've owned her for 7 years. I have a genset on-board which I've used a total of 2 times other than running it weekly to ensure she's exercised. It locked up on me last weekend while starting, I haven't had a chance to verify if it's terminal or merely a locked starter/flywheel... either way it's given me pause as to thinking of replacing it with an alternative extended power source. I know removal will drop resale value but that's not a woory for me. I realize that means no AC when off the hook, which is fine with us. Given all the things happening in the van conversion world these days, with reference to extended bonndocking, has anyone seen a similar system [lithium battery-powered, converter, solar/engine charging] that could be used on my 260 in place of the generator. Regardless if my genset is cooked or not, I'm still considering removal so I'll certainly have the space and weight requirements if there is an alternative. Thanks all for your thoughts /comments. Safe boating, all!

 

[hughespat57]

Been considering the same myself, mine never had a generator and adding one is very pricey so thought of same option.
There is a commercial solution (VERY pricey) for high end by Nigel Calder. By the way inverters have relays usually and are not Ignition Protected so it can not be in the engine room.

by me from another thread:
There is two parts to this mostly economics. A new marine generator is going to be $12-15k and while nice, you need to be able to afford it and it will ad some value to the boat but you'll not likely get it back on sale. Used half that as, but you have to find a decent one, then what do you get? Likely high hours already since it is some kind of take out from another boat. And again as mentioned any generator running at anchor in calm air will have a high CO risk. Get CO monitors if not already installed, even the main engines can lead to CO issues.

I have not started yet but my plan is this; for that $6K I can get a good sized inverter/charger 6000W ($1,200) . And a good size LifePo4 Lithium battery bank (48v 200ah) ($1,000) with a battery management system ($250). That will let me run anything I want to. Even the AC for a short period like to cool the cabin a little before turning in at night. So far that's about $3k installed. Zero noise, zero CO. This is where I am going to start.

I don't want solar panels all over the boat. So to augment shore side charging I will add later as a second phase an extra 48v PMA, Permanent Magnet Alternator ($300). PMAs have no internal brushes or regulators just plain wires so no Ignition Protected issues in a gas boat. The PMA will feed into an MPPT (charge controller - $900) next to the Inverter. Whenever my main engine is running it will charge the batteries back up. And/or I can run the AC off the engines before anchoring and really cool the cabin down. So all in I hope to be around $4500.

I plan to start this project this summer and will post how it works.
After having this basic idea my research lead to this where I admittedly got a lot more details. So its being done but I cant see their costs.
https://www.morganscloud.com/2019/02/13/nigel-calders-generator-replacement-machine-part-1-what-you-need-to-know/
https://integrelsolutions.com/

 

[Stee6043]

I think at this size boat not having a generator reduces value, it's not so much that having one increases it, if that makes sense?

At the same time, I don't think having a slick battery/invertor will add value. People generally want a generator to run the air, run the hot water heater and drink some coffee (for extended periods ). Batteries are hard pressed to do any of these reliably, repeatedly?

 

[hughespat57]

I think at this size boat not having a generator reduces value, it's not so much that having one increases it, if that makes sense?

At the same time, I don't think having a slick battery/inverter will add value. People generally want a generator to run the air, run the hot water heater and drink some coffee (for extended periods ). Batteries are hard pressed to do any of these reliably, repeatedly?

With today's systems I think it will be more common. Most large cooking loads are short term 30/45 minutes or less.

It is why I am looking at 48vdc, at 12vdc the current needed is 4x larger. This means huge battery cables and any resistance becomes an issue, cable length to inverter, the inverter internal components, alternator sizing, etc. But at the 48vdc I can get a split phase 240/120 Inverter/Charger at a reasonable price. And the PMA solves the longer term power needs; a solar panel just cant output 3000+ watts without covering the boat (64 sqft). The LifePo4 batteries 48 * 200 is 9.6kw, available at least 8kw.

Now I have made some other upgrades that fit into this plan. 30A 120 shore I upgraded to 50A 240/120.
Stove top is a modern 240 volt two burner. Hot water heater was shot so 6gal is now an 11gal 240v, but engine heats that and it hold well so far. AC will have to see how that works out.

 

[Stee6043]

With today's systems I think it will be more common. Most large cooking loads are short term 30/45 minutes or less.

It is why I am looking at 48vdc, at 12vdc the current needed is 4x larger. This means huge battery cables and any resistance becomes an issue, cable length to inverter, the inverter internal components, alternator sizing, etc. But at the 48vdc I can get a split phase 240/120 Inverter/Charger at a reasonable price. And the PMA solves the longer term power needs; a solar panel just cant output 3000+ watts without covering the boat (64 sqft). The LifePo4 batteries 48 * 200 is 9.6kw, available at least 8kw.

Now I have made some other upgrades that fit into this plan. 30A 120 shore I upgraded to 50A 240/120.
Stove top is a modern 240 volt two burner. Hot water heater was shot so 6gal is now an 11gal 240v, but engine heats that and it hold well so far. AC will have to see how that works out.

When it's 90F, 100% humidity, I want the air on....pretty much non-stop

 

[jmauld]

What is your source for a 48V 200ah battery for $1000?

I am also considering this for when my genset kicks the bucket, but I think your price is too low.

I just purchased a 48V 90Ah battery set and it was significantly more than $1000, but it does have a specific application, and it's UL certified. Which adds value for something that I will be parking in my garage

 

[Doc O Rock]

Watch this. AC and all the power for every luxury. Very interesting.

 

[hughespat57]

What is your source for a 48V 200ah battery for $1000?

I am also considering this for when my genset kicks the bucket, but I think your price is too low.

I just purchased a 48V 90Ah battery set and it was significantly more than $1000, but it does have a specific application, and it's UL certified. Which adds value for something that I will be parking in my garage

slow boat from China Alibaba so we will have to see about the quality...

 

[hughespat57]

Watch this. AC and all the power for every luxury. Very interesting.

yep but there pricing for my load they say is $15k
Their key is just the custom MPPT controller that can calculate the load to adjust it for maximum output without stealing to much horsepower while under way. Everything else is really off the shelf Victron componenets.

 

[ttmott]

Our types of boats don't lend themselves to be without a generator; they are not misers' of electricity even sitting at the dock, including the SR mid sized boats.
I have been planning a conversion to lithium Iron Phosphate batteries for over a year. Below are the electrical sketches for the conversion; these drawings have been in review by a marine electrical engineering company for about a year (the pandemic has delayed progress) and there are some changes needed (save review and comment from @RollerCoastr) as well as the installation drawings to be done but the general configuration is correct. This system has over 1000 amp hours of battery storage with 800 amp hours useable for boat systems and a reserve of 100 amp hours for engine starting which establishes a maximum depth of discharge of 90 percent; this will keep battery life at around 5000 cycles which will yield a minimum 15 years of service. The primary intent is to size the battery bank and inverters to enable the boat's systems (AC and DC) including air conditioning to operate nominally without generator through the night. Even with this size of a system the generator will still be needed more frequently in specific load situations like AC running and making water or hot water heater heater operating; the battery bank will deplete faster than the over night requirement. As you can see the inverters can provide a continuous 10KW which is about what the generator or shorepower supplies nominally as a peak for this boat's summertime loads here in Florida. When the battery bank reaches a depth of discharge of 80 percent (that 100 amp hours still reserved for engine start) I have an Automatic Generator Start system that brings the generator on line to recharge the battery bank then the genset shuts back down. The great thing about the lithium batteries is they can be charged as fast as the charger can pump current to them plus they have virtually no absorption phase so the generator run time is reduced significantly. Typically on a 10 day trip on my boat the generator runs 18 hours per day so that is 180 hours which is about 360 gallons of diesel. Now with the batteries as the primary AC power provider then generator is pretty much there to charge the batteries and it's run time is reduced to provide the 800 amp hours to the batteries which if the boat's systems deplete three times a day that is 2400 amp hours needed from the generator. The system is designed to provide 300 amps of charge current during the charge cycle so consequently the generator needs only to run 8 hours instead of 18 hours and the boat's systems know no difference. That is a savings of 200 gallons of diesel for the 10 day trip not to mention the quite nights of sleep which is the main reason for the modifications. This doesn't include the contribution the boat's engine alternators provide to the charge cycles or when we are at a marina and plugged in; we typically don't stay in any one location for more than a day so the genset actually runs even much less over the 10 day trip.
You may ask how does this provide 240 volts that the AC systems require? These inverters can be setup to operate in split phase; they provide 120 volts 180 degrees out of phase so voltage across the two inverters is the desired 240 volts.
Regarding photo-voltaic solar panels - Our boats simply don't have enough unused acreage to install solar panels that would make a difference in comparison to the demand on the batteries from the boat's systems. The cost trade on my boat showed overwhelmingly no justifiable investment return on the solar panels. It was like peeing in the ocean....
Anyway, the investment and scope to change to a system like this is huge and pretty much every system in the boat requires modifications, large modifications. Just to give you an idea this modification will be between $25K and $30K with me doing the installation..... This is scalable for your boat so you can get an idea of the scope and investment.

 

[dtfeld]

I already have a Magnum inverter installed and have used it for a couple of years now and it does what I designed it to do...run the microwave and coffee make in the morning without the genny waking everybody up. I love it!

I ran it off my starboard house/start bank, but its time to get it it’s own battery source. I’m looking at 8 280Ah prismatic cells to make a 4P2S 560Ah @12V to feed it. These are about $1000 delivered. Google Will Prowse or DIY Solar...I’ve never seen anybody get so excited about batteries...he’s hilarious! He list a couple decent sources.

I’m watching Tom to see how his system works out, but I think you might see more of this in the future, be it retrofits, of new boats from the factory.

If money were no object, I’d get a 24V or 48V Victron Quattro, and enough battery to run the main AC all night. Or convert to DC AC units.

This is doable with enough money and engineering resources!

 

[ttmott]

I already have a Magnum inverter installed and have used it for a couple of years now and it does what I designed it to do...run the microwave and coffee make in the morning without the genny waking everybody up. I love it!

I ran it off my starboard house/start bank, but it time get it it’s own battery source. I’m looking at 8 280Ah prismatic cells to make a 4P2S 560Ah @12V to feed it. These are about $1000 delivered. Google Will Prowse or DIY Solar...I’ve never seen anybody get so excited about batteries...he’s hilarious! He list a couple decent sources.

I’m watching Tom to see how his system works out, but I think you might see more of this in the future, be it retrofits, of new boats from the factory.

If money were no object, I’d get a 24V or 48V Victron Quattro, and enough battery to run the main AC all night. Or convert to DC AC units.

This is doable with enough money and engineering resources!

Dave - the prismatic lithium batteries bring some challenges. First and most important is they do not deal well with shock movement and jostling as we see in boats with any wave action at all; boaters that attempt to use them build reinforcing boxes to put them in. Secondly, they don't dissipate heat well at all and charge rates as well as discharge rates are a fraction of the 18XXX cylindrical LiFePo4 cells. This is why pretty much all high current batteries (Battleborn, Lithonium, Victron, Mastervolt, Testla, etc) do not use prismatic. Just a heads up..
Tom

 

[JC3]

Will Prowse

Google Will Prowse or DIY Solar...I’ve never seen anybody get so excited about batteries...he’s hilarious! He list a couple decent sources.

Most people thinking about solar would benefit immensely from watching Will Prowse! Very nice YOUTUBE channel. JC

 

[dtfeld]

Dave - the prismatic lithium batteries bring some challenges. First and most important is they do not deal well with shock movement and jostling as we see in boats with any wave action at all; boaters that attempt to use them build reinforcing boxes to put them in. Secondly, they don't dissipate heat well at all and charge rates as well as discharge rates are a fraction of the 18XXX cylindrical LiFePo4 cells. This is why pretty much all high current batteries (Battleborn, Lithonium, Victron, Mastervolt, Testla, etc) do not use prismatic. Just a heads up..
Tom

There are a lot of challenges to building these battery cells for sure! I looked at building a DIY 18650 cell as it would be easier to but in an odd shaped dead space on the boat. It’s actually pretty easy to get a small spot welder to put these together. I have a couple books on how to design and build these things. All the components can be readily sourced. Basically a DIY Battleborn.

One of the biggest issue as you mentioned is keeping the charge/discharge rates down, and with a 12 V inverter, it’s tough to do. Either have to upgrade the inverter (Victron Quattro 24V would be my current choice) build multiple battery’s, or limit the current to less than rated for the inverter.

Also getting decent (trustworthy) BMS’s is also an issue...

There is a reason I haven’t pulled the trigger on any of this yet...decisions, decisions.

if I go prismatic, I would need an decent enclosure, and I’m sure this application would take some like out of the cells. I’m on a lake, and we don’t get the heavy pounding...this is “chop” on Lake Lanier.

 

[jmauld]

What about using a 48v lithium battery. Use your inverter to 120v AC and a step down from 48v to the 12v system. I haven’t really started looking at this stuff for a boat yet, but it seems in the residential market 48v systems are more common. I just ordered a 48v, 120ah lithium system for my golf cart. My plan is to pick up an inverter before hurricane season so that I can power the house fridges and some lights/fans overnight without listening to a generator.

 

[dtfeld]

Have to upgrade the inverter. The Quattro is about $2800

The other design criteria is $$$. I only use this system sparingly for microwave/coffee brewing, so I’m not looking to spend too much.

The separate battery for the inverter is mostly driven by wanting to spare my House/Start batteries wear and tear, and the satisfaction of designing and building a system for my own personal education/gratification.

I just replaced my starboard start house bank with 2 new G31 AGM, and I’m going to repurpose the 6 year old set for the inverter bank.

I’ll consider my options until those older batteries die a slow painful death.

 

[ttmott]

There are a lot of challenges to building these battery cells for sure! I looked at building a DIY 18650 cell as it would be easier to but in an odd shaped dead space on the boat. It’s actually pretty easy to get a small spot welder to put these together. I have a couple books on how to design and build these things. All the components can be readily sourced. Basically a DIY Battleborn.

One of the biggest issue as you mentioned is keeping the charge/discharge rates down, and with a 12 V inverter, it’s tough to do. Either have to upgrade the inverter (Victron Quattro 24V would be my current choice) build multiple battery’s, or limit the current to less than rated for the inverter.

Also getting decent (trustworthy) BMS’s is also an issue...

There is a reason I haven’t pulled the trigger on any of this yet...decisions, decisions.

It's probably worth discussing the pitfalls and challenges moving over to Lithium batteries, at least from my engineering and progress to this solution perspective.
"Drop In Batteries" - Sure you can drop in a couple of Battle Born Lithium batteries and use them for engine starting and house loads but existing charging systems will probably significantly shorten the expensive drop-in's life. Lithium require more care and feeding to ensure the Drop In Battery Maintenance System does not interrupt the service. Lithium systems do not like to be stored at full charge and are sensitive to cell / battery unequal voltages; they must remain balanced. This is the finesse of the correct charging system. Another issue is, for example, the engine's alternator is used to charge a lithium battery and that alternator starts to put out high voltage or (not that uncommon) the battery BMS will sense a risk event and immediately disconnect the battery. That disconnect will cause the alternator magnetic field to collapse and the alternator will instantly go very high in voltage (spike). What is at risk and quite possibly be destroyed? About every electronic device connected to the DC power system. It's important to understand that the BMS is there to protect the battery and not the boat.. Secondly, Lithium battery charge profile is different than lead acid in that they can absorb bulk charge current as fast as anything can feed it. Also, Lithium batteries really have no absorption phase in charging; minutes rather than hours so consequently to make best use of the batteries and their potential a charging system setup and designed to accommodate the battery is essential. Back to the engine's alternator; let's say we simply tie a standard internally regulated alternator to the lithium battery. The lithium battery has such low resistance that the alternator will charge at full capacity from start to finish and for the most part overheat and fail. That failure event could also short the diodes and cascade a BMS shut-down which now shuts down all power. It is for these reasons I have external regulators setup for lithium charge profile and thermal monitoring of the alternators to ensure both protection of the batteries as well the alternators. Secondly, I have Sterling APD's (Alternator Protection Devices) installed to absorb that voltage spike should by chance the battery BMS disconnect.
"Dark Event" - Let's say as in my design something in one of the inverters takes the battery bank out of specification and all of the BMS' shut down the entire battery bank. The boat will go dark which is bad, hugely bad. No Nav, no engines, no lights, no nothing.... In my configuration even the generator which is started by a lead acid battery will shut down. Can you imagine being in an inlet and loose all control of the boat? It is a significant risk in my design that needs to be addressed; the engineering firm helping me on the design wants an AGM battery in parallel with the Lithium batteries so should the BMS take out the lithium batteries from the circuit the AGM is still there to pick up the pace. The AGM will not be adversely affected with the lithium charge profile and at most the peak charge voltage needs to be lowered a bit in the lithium profile. What is interesting is the AGM if the system is operating nominally will never go through a discharge cycle because the lithium voltages are flat through most of discharge cycle and consequently when the lithiums require charge the AGM is never in the charge required range. The AGM if the system operates nominally through the lifecycle will be good for 10 to 15 years; it's never gone through a discharge cycle.... I'm still a bit "bullheaded" and challenging the engineers to find another solution to completely move away from lead acid but in reality I'll probably loose that battle....
Battling Alternators - When alternators in a duel engine configuration are combined to charge a single battery they tend to battle for charging and inevitably voltage and current becomes erratic. Individual charge controllers will not solve the situation. If voltage swings become increasing events then the chance to trip a lithium battery BMS increases and back to the Dark Event. To rectify this an alternator balancing device needs to be installed between the charge controllers. Balmar makes exactly that and is called a "Center Fielder". This will be added to my configuration.
Connecting and disconnecting Capacitive and inductive loads - Lithium batteries have the capability to deliver instantaneous extremely high current. When connecting to an inverter for example that connection charges the inverter's capacitors and that event can be thousands of instantaneous amps which not only will probably arc weld the connection but also probably trip the battery BMS. Not good. There has to be a bleed circuit to control the current (like a resistor) as a component of the switching. This needs to be added to my configuration.
Capacity Loss - Let's say one of the Lithium batteries in my system faults and goes off line, how would I know as the system is programmed for a given total capacity? Right now without BMS data output I don't know and this is a real risk situation. The only way I would know is the generator is cycling on and off more frequently. This requires visibility and a solution.
Ambient Temperature - Lithium batteries have parameters in temperature they can be operated. Their live is dependent upon temperature; they really need to be installed in environments less that 120 Deg F - definitely not in the engine room which in Florida routinely sees 140 degrees. Mine will be installed in the Solon under the couch back against the engine room intake plenum. Lithium can be subjected to low temperatures but they cannot be charged at low temperatures and discharge rates must be strictly controlled. So, for installations in freezing climates this is an important consideration.
ABYC; what's happening - ABYC is in the process of establishing requirements for Lithium Batteries on vessels. Things like requiring a BMS and minimum parameters for safe handling are in review. One of the more reaching requirements is to have an external messaging capability to alert of impending BMS shutdown before the shutdown occurs which will require a complex system to implement. Several of the manufacturers already have this in place but many don't like Battle Born. So this needs to be considered for future compliance and insurance impact.

The message here is this is a path of discovery for me to do this right both for reliability and safety. I thought I would pass along some of the more relevant things needed to go down this great technology.

 

[hughespat57]

Our types of boats don't lend themselves to be without a generator; they are not misers' of electricity even sitting at the dock, including the SR mid sized boats.
I have been planning a conversion to lithium Iron Phosphate batteries for over a year. Below are the electrical sketches for the conversion; these drawings have been in review by a marine electrical engineering company for about a year (the pandemic has delayed progress) and there are some changes needed (save review and comment from @RollerCoastr) as well as the installation drawings to be done but the general configuration is correct. This system has over 1000 amp hours of battery storage with 800 amp hours useable for boat systems and a reserve of 100 amp hours for engine starting which establishes a maximum depth of discharge of 90 percent; this will keep battery life at around 5000 cycles which will yield a minimum 15 years of service. The primary intent is to size the battery bank and inverters to enable the boat's systems (AC and DC) including air conditioning to operate nominally without generator through the night. Even with this size of a system the generator will still be needed more frequently in specific load situations like AC running and making water or hot water heater heater operating; the battery bank will deplete faster than the over night requirement. As you can see the inverters can provide a continuous 10KW which is about what the generator or shorepower supplies nominally as a peak for this boat's summertime loads here in Florida. When the battery bank reaches a depth of discharge of 80 percent (that 100 amp hours still reserved for engine start) I have an Automatic Generator Start system that brings the generator on line to recharge the battery bank then the genset shuts back down. The great thing about the lithium batteries is they can be charged as fast as the charger can pump current to them plus they have virtually no absorption phase so the generator run time is reduced significantly. Typically on a 10 day trip on my boat the generator runs 18 hours per day so that is 180 hours which is about 360 gallons of diesel. Now with the batteries as the primary AC power provider then generator is pretty much there to charge the batteries and it's run time is reduced to provide the 800 amp hours to the batteries which if the boat's systems deplete three times a day that is 2400 amp hours needed from the generator. The system is designed to provide 300 amps of charge current during the charge cycle so consequently the generator needs only to run 8 hours instead of 18 hours and the boat's systems know no difference. That is a savings of 200 gallons of diesel for the 10 day trip not to mention the quite nights of sleep which is the main reason for the modifications. This doesn't include the contribution the boat's engine alternators provide to the charge cycles or when we are at a marina and plugged in; we typically don't stay in any one location for more than a day so the genset actually runs even much less over the 10 day trip.
You may ask how does this provide 240 volts that the AC systems require? These inverters can be setup to operate in split phase; they provide 120 volts 180 degrees out of phase so voltage across the two inverters is the desired 240 volts.
Regarding photo-voltaic solar panels - Our boats simply don't have enough unused acreage to install solar panels that would make a difference in comparison to the demand on the batteries from the boat's systems. The cost trade on my boat showed overwhelmingly no justifiable investment return on the solar panels. It was like peeing in the ocean....
Anyway, the investment and scope to change to a system like this is huge and pretty much every system in the boat requires modifications, large modifications. Just to give you an idea this modification will be between $25K and $30K with me doing the installation..... This is scalable for your boat so you can get an idea of the scope and investment.

Sorry for slow response but I cant do a long winded response using my thumbs, had to wait until I had time to get to my desk.
I agree completely with the assumptions about how boat power is utilized and how that does not lend itself to solar based charging. And a very detailed and well thought design obviously. However there are several choices you made that I believe complicate the solution and leads to the additional costs. And that is why I disagree that you need to make any changes to the boats current 12vdc systems.

The first choice was staying with a 12 volt inverter solution and charging using the standard 12v engine alternators.
Any automotive type alternator is not designed for continuous output. They are designed for flooded batteries, that discharge during statrup and then take a high charge for a short period of time and quickly taper off. Standard alternators have the diodes and regulator internal and as they heat up they cut back on output so even a 100A alternator rarely hits full output. This is why your design required Balmer externals to prevent over heating the alternators and burning them out when charging LifePo4 batteries. Also your main disconnect relays isolate the start, alternator & switched loads. This is appropriate for overcharging situations as that is the most damaging to the cells and highest risk of cell thermal runaway. You still have some "un-switched" loads that would not be disconnected on a low voltage disconnect. I assume those would be bilge pumps only. If you have a low or high voltage disconnect you lose all house functions, lights, radios, etc.

Each use case is slightly different as well, and that can drive choices. You have a generator, I never had one. So I am looking at the cost of adding a generator vs battery/inverter. I already changed my FLA battery banks. I have three separate batteries. two marine starting batteries, port independent, starboard engine & emergency bilge pumps, everything else is on a FLA deep cycle Duarcell trolling battery. I already had a three bank AC charger so that was no cost. I added a 1-both-2 battery switch for manual control and a Blue Seas ACR for normal underway charging. I will replace the ACR with a 48v to 12v DC-DC battery charger (Sterling) the manual switch will remain as a backup option if needed. So all my 12vdc systems will stay as they are and have redundant charge capabilities should I have any issues with the LifePo4 batteries/system.

Then as I already described above the inverter is a completely separate system, treated almost like a stand alone generator. The 48v split phase systems are readily available and reduce the size of so many components compared to the high amperage required at 12v. The inverters Mosfets & windings, cables, disconnect switches and relays are all significant smaller, and therefore usually less costly. Then the addition of the PMA/MPPT based charging system is akin to wind or hydro power solutions.

And finally I do plan on prismatic batteries. But have already planned the battery and box arrangement. It will be a bolted pack with separaters of aluminum plates. These plates will be wider than the cells on both sides (fins) The assembly will be inside an aluminum battery box. Ventilation will be included to dissipate heat during charging and to help isolate from engine heat.

Besides Nigel I have also gotten a great deal of marine lithium info form this firm.
http://nordkyndesign.com/category/marine-engineering/electrical/lithium-battery-systems/

 

[ttmott]

Sorry for slow response but I cant do a long winded response using my thumbs, had to wait until I had time to get to my desk.
I agree completely with the assumptions about how boat power is utilized and how that does not lend itself to solar based charging. And a very detailed and well thought design obviously. However there are several choices you made that I believe complicate the solution and leads to the additional costs. And that is why I disagree that you need to make any changes to the boats current 12vdc systems.

The first choice was staying with a 12 volt inverter solution and charging using the standard 12v engine alternators.
Any automotive type alternator is not designed for continuous output. They are designed for flooded batteries, that discharge during statrup and then take a high charge for a short period of time and quickly taper off. Standard alternators have the diodes and regulator internal and as they heat up they cut back on output so even a 100A alternator rarely hits full output. This is why your design required Balmer externals to prevent over heating the alternators and burning them out when charging LifePo4 batteries. Also your main disconnect relays isolate the start, alternator & switched loads. This is appropriate for overcharging situations as that is the most damaging to the cells and highest risk of cell thermal runaway. You still have some "un-switched" loads that would not be disconnected on a low voltage disconnect. I assume those would be bilge pumps only. If you have a low or high voltage disconnect you lose all house functions, lights, radios, etc.

Each use case is slightly different as well, and that can drive choices. You have a generator, I never had one. So I am looking at the cost of adding a generator vs battery/inverter. I already changed my FLA battery banks. I have three separate batteries. two marine starting batteries, port independent, starboard engine & emergency bilge pumps, everything else is on a FLA deep cycle Duarcell trolling battery. I already had a three bank AC charger so that was no cost. I added a 1-both-2 battery switch for manual control and a Blue Seas ACR for normal underway charging. I will replace the ACR with a 48v to 12v DC-DC battery charger (Sterling) the manual switch will remain as a backup option if needed. So all my 12vdc systems will stay as they are and have redundant charge capabilities should I have any issues with the LifePo4 batteries/system.

Then as I already described above the inverter is a completely separate system, treated almost like a stand alone generator. The 48v split phase systems are readily available and reduce the size of so many components compared to the high amperage required at 12v. The inverters Mosfets & windings, cables, disconnect switches and relays are all significant smaller, and therefore usually less costly. Then the addition of the PMA/MPPT based charging system is akin to wind or hydro power solutions.

And finally I do plan on prismatic batteries. But have already planned the battery and box arrangement. It will be a bolted pack with separaters of aluminum plates. These plates will be wider than the cells on both sides (fins) The assembly will be inside an aluminum battery box. Ventilation will be included to dissipate heat during charging and to help isolate from engine heat.

Besides Nigel I have also gotten a great deal of marine lithium info form this firm.
http://nordkyndesign.com/category/marine-engineering/electrical/lithium-battery-systems/

Do not underestimate the 12 volt requirement. In my boat they do not make a marine DC to DC converter large enough to accommodate the loads especially when you factor in the windlass and hungry audio system; I would have to split up the systems and have multiple converters - not realistic for my baseline.... To convert my QSM11's to 24 volts isn't trivial either with Cummins spec DC to DC converters and the starters it became apparent early in the process to stick with 12 volts. So I did consider 24 volt and even 48 volt DC based systems but the trade landed me back on 12 volts. Secondly, there is a loss of redundancy at 24 and 48 volts when you install batteries in series; should one trip on a BMS fault then you loose everything in that serial chain. Where batteries are in parallel a BMS trip event only takes out that battery; this is important to me. So, in my case on this 52DB having larger wiring and components was far less expensive and intrusive than converting to voltages other than 12 volts. Now on a 58DB where the base system is 24 volts then it's a "no brainer".

 

[dtfeld]

For my purposes, I have a stand alone inverter system that is not intended to be charged by the main propulsion engines. All current taken from and returned to the batteries would be via the inverter/charger using AC power from the generator or shore power. Also, this systems is not mission critical.

Here is the article from Battle Born. They used a MS2012 (2000 W) where mine is a 2812 (2800 W), but the general principles apply.

--> https://battlebornbatteries.com/can-use-magnum-ms2012-lifepo4-battery-bank/

I'd need 4 100Ah units to get full rated power out of the inverter and not exceed the BMS limits. The newer 270Ah versions are getting close at a 300A continuous load, but full power on this inverter is 373A. I'd still need 2.

Economics just don't work...yet.