Switch to 24V or 12/24V Hybrid Electrical System

The only item that is a power hog on most boats is the refrigeration system.

Sure boaters in the south ma require air cond 24/7 , but they mostly accept the need for a couple of gensets , and not much battery power.

A boat with a propane reefer and freezer , and range only requires minor electric for anchored out weeks or months. WE DO IT!

Why bother with multiple electric systems , thousands of pounds and dollars of aging batt sets ?

Any big juice eater like a water maker can operate when the laundry is being done.

Larger FW tanks and no watermaker to buy/install/maintain/repair.

Why the need? What lifestyle is the Desirement????

Absolutely. Sometimes I am in total agreement with FF, and this is one of them...

Agree, that's the bottom line, what is this boat going to be used for and where?

I see so many newbies spending a lot of time and money getting the boat to match what they think it should have based on reading and dreaming and other people's opinions (which are based, at best, on how they happen to use their boat, and/or their budget.).

I was a little bit like that when we got the Hatt, but I had a clear view of what we were going to do and basically needed to do that. My extraneous enthusiasm was tempered by the guy who owned the yard where I was getting to know and outfit the boat, a process he was profiting nicely from. At one point he said, look, you've got your basics done, cruise the boat for awhile and then you'll know what "nice to haves" you really want. Seven years later, about half the stuff on the original list never got done and most of that was off the list completely.

The way to get a feel for what does and does not come in 24 v is to browse a comprehensive marine catalog and check on the descriptions of the products. On our boat there may be a half dozen things that we had to convert to 12v. Sound system- alarm -gauges etc. Also remember that motors and their peripherals have to be tuned in to the 24v.

Just an engineering tidbit: The reason you see 24v in larger boats is that for big engines, a 12v starter is physically too big to fit next to the engine block and catch the flywheel. 24v starters use thinner windings and so can make more torque out of a smaller machine. So big boats with big engines usually get 24v. If they could have managed with 12v, they probably would.

So once the engine has to have a 24v start bank, what to do with the rest of the boat? Wire it for 24v and get boxed in with limited supply of 24v doo-dads, or have a separate bank of 12v and an endless supply of doo-dads? Some go one way, some the other.

My preference for big engines that require 24v to start is to have a bank for just that purpose, and 12v for the rest of the boat. Some engines can easily handle a second alternator and that makes it easy.

Once you get into really big house banks with the goal of avoiding an AC generator, you are entering the realm of electrical engineering and this system really needs to be designed. Not just gathering bits of knowledge from the net.

Peter B said:

why did the US persist with 120vAC for the domestic reticulation, when the rest of the world largely uses 240vAC..?

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Had to look up reticulation . Not sure what you're saying here, I think you made my point. The US made an incorrect decision using 120vac, the ROW uses it because it is more efficient and provides the same amount of work for half the current. Reduces losses all around. Why our long transmission lines are in the 100,000vac or some such area. Maybe because our government thought we weren't smart enough to handle 240vac safely. The US has made other decisions like this, sealed beam headlamps vs H4s come to mind. Our government is not infallible by any means.

Peter B said:

Also, why is 12v DC the norm for almost all non-AC purposes..? I suspect it is the ease of building 12v batteries, and the fact there are so many non-marine 12v appliances, (e.g. all/most recreational road vehicles), such that it is much more expensive to produce 24v appliances for relatively minor gains.

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Yes, the norm issue. And it might very well be the reason why I don't go to 24v--not enough availability of hardware and appliances. The manufacturers don't go into 24v items big-time because there isn't enough demand for them; there isn't enough demand for them because they aren't mass produced at more attractive prices by the manufacturers. And it very well could be that there aren't enough efficiency and power gains to make the switch to 24v for smaller boats worthwhile. There was a time when 6v was the norm, everything DC manufactured was 6v. 12v was upsetting the apple cart. Perhaps we are at that stage for 12v now, perhaps 12v will remain the norm for smaller boats well into the future. That is what I am in the process of feeling out.

Peter B said:

Finally, we, like you, wanted to avoid AC on the boat, so the only AC we use is for at-berth charging and to pre-heat the hot water before cast-off. The rest is off-engine charging, solar panels, and Airbreeze wind to augment that when the sun is down/obscured. We cook with propane, and have LED lights, and a small inverter for e.g., laptop charging. We are therefore very self-sufficient at anchor - virtually indefinitely. It means we don't have aircon, and we don't run washing machines or dishwashers, but with only two of us, it works for us.

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That is where we are headed too. The heavy power consumers we will have on the hook are the washing machine and refrigeration, no AirCon.

How do you handle your refrigeration needs while on the hook?

Peter B said:

I certainly feel you could achieve all you want without the complication & cost of adding in the 24v side of things, but the DC diesel charger makes sense if you want to run much AC off an inverter. Solar and air power would struggle to cope with that.

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It very well might be the case that I stick with 12v, it's what the boat has now, and it works. The small DC water-cooled diesel engine genset, a couple more batteries, and another inverter if required (there's one on the boat now) will be the first major change I make, if I do anything at all. Then a wind generator and solar cells, the roof of a KK42 pilothouse is a nice space for it. Might not be enough space to make much difference though, even with the better solar panels coming out now.

FF said:

The only item that is a power hog on most boats is the refrigeration system.
Sure boaters in the south ma require air cond 24/7 , but they mostly accept the need for a couple of gensets, and not much battery power.
A boat with a propane reefer and freezer, and range only requires minor electric for anchored out weeks or months. WE DO IT!
Why bother with multiple electric systems, thousands of pounds and dollars of aging batt sets?
Any big juice eater like a water maker can operate when the laundry is being done.
Larger FW tanks and no watermaker to buy/install/maintain/repair.
Why the need? What lifestyle is the Desirement????

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Absolutely agreed also. That is what I started out wanting for our boat's refrigeration--one of the Absorption Cycle types. We used to have a kerosene fridge when I was a kid. It worked, but not very well. I don't know of any Absorption Cycle marine refrigerators.

I'd guess your propane refrigerator and freezer are RV models, are you genuinely happy with their performance? If so, what make/models did you settle on? Is rolling while underway an issue?
How about an Icemaker--now there's an invention, an Absorption Cycle icemaker.

eyschulman said:

The way to get a feel for what does and does not come in 24 v is to browse a comprehensive marine catalog and check on the descriptions of the products. On our boat there may be a half dozen things that we had to convert to 12v. Sound system- alarm -gauges etc. Also remember that motors and their peripherals have to be tuned in to the 24v.

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Excellent points. Proposal: 24v for the heavier power consumers--refrigeration, anchor winch, etc., 12v for the rest. More complication, maybe not worth the performance gains. Especially if I could find good models of absorption cycle fridges & freezers. Now that would be cool (oy vey).

Wil said:

Absolutely agreed also. That is what I started out wanting for our boat's refrigeration--one of the Absorption Cycle types. We used to have a kerosene fridge when I was a kid. It worked, but not very well. I don't know of any Absorption Cycle marine refrigerators.

I'd guess your propane refrigerator and freezer are RV models, are you genuinely happy with their performance? If so, what make/models did you settle on? Is rolling while underway an issue?
How about an Icemaker--now there's an invention, an Absorption Cycle icemaker.

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Watch or read "Mosquito Coast"!!!!

Ski in NC said:

Just an engineering tidbit: The reason you see 24v in larger boats is that for big engines, a 12v starter is physically too big to fit next to the engine block and catch the flywheel. 24v starters use thinner windings and so can make more torque out of a smaller machine. So big boats with big engines usually get 24v. If they could have managed with 12v, they probably would.

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Exactly. Thinner windings and more torque out of smaller motors. One of the advantages of 24v. They would have stayed with 12v anchor winches and whatever other heavy duty equipment they use, despite being able to get the same power out of smaller and I suspect more reliable (half the current, so cooler running) 24v motors? A larger diameter flywheel would have solved the larger 12v starter motor issue, but 24v was used due to "thinner windings and so can make more torque out of a smaller machine". Two advantages in one--smaller size for the same power, uses half the current.

Ski in NC said:

So once the engine has to have a 24v start bank, what to do with the rest of the boat? Wire it for 24v and get boxed in with limited supply of 24v doo-dads, or have a separate bank of 12v and an endless supply of doo-dads? Some go one way, some the other.

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That's the crux of the issue--the lack of availability of the more commonly required 12v items. It's an unfortunate paradox: the manufacturers won't make the 24v items due to lack of demand; consumers don't demand them due to lack of supply.

Ski in NC said:

My preference for big engines that require 24v to start is to have a bank for just that purpose, and 12v for the rest of the boat. Some engines can easily handle a second alternator and that makes it easy.

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That is one nice way out of the 12/24v charging issue.

Ski in NC said:

Once you get into really big house banks with the goal of avoiding an AC generator, you are entering the realm of electrical engineering and this system really needs to be designed. Not just gathering bits of knowledge from the net.

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I have no further interest in burning my boat down than you. Of course it would be a very professionally thought out system, if undertaken.

Ski in NC said:

Watch or read "Mosquito Coast"!!!!

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Thanks for the tip, will do!!!

psneeld said:

yes..yes...I think most here understand basic electricity...

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Basic question: do you think 6vdc is as 'good' at performing work efficiently as 12vdc?

Wil said:

Basic question: do you think 6vdc is as 'good' at performing work efficiently as 12vdc?

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Just the question alone speaks you are missing most of our points.

Sure higher voltage, smaller gear and smaller losses...

Go for it...

but first...re-read this about a million times...caltexflanc posted it in post #33

I see so many newbies spending a lot of time and money getting the boat to match what they think it should have based on reading and dreaming and other people's opinions (which are based, at best, on how they happen to use their boat, and/or their budget.).


probably after rereading it only 500,000 times...you may see what many of us. and if not certainly 2 of us, are saying....

psneeld said:

Just the question alone speaks you are missing most of our points.

Sure higher voltage, smaller gear and smaller losses...

Go for it...

but first...re-read this about a million times...caltexflanc posted it in post #33

I see so many newbies spending a lot of time and money getting the boat to match what they think it should have based on reading and dreaming and other people's opinions (which are based, at best, on how they happen to use their boat, and/or their budget.).


probably after rereading it only 500,000 times...you may see what many of us. and if not certainly 2 of us, are saying....

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Absolutely couldn't agree more with caltexflanc, you, and all others about newbies (and maybe some oldies even) getting caught up in their own dreams and other people's opinions/positions, thus wasting alot of money. What I don't seem to be able to get across is that This Is A Thought Exercise. Sure, I advocate for 24v heartily--but am I actually going to do anything about it? That is why I started this really good give-and-take conversation in the first place.

I want to know the actual reasons behind the 'norm' and 'convention', especially when there seems to be a better alternative that a lot of other boats are already using. I knew from the beginning that it would be an expensive pita, but I want to know just exactly why. What I've come up with so far is that the availability of a lot of the 12v items will be very spotty in 24v, so that goes a long way towards ruling out pure 24v (but what do the bigger boats do?). That having a 12/24v system would be unnecessarily complex. Good reasons those, and that might be why I don't do it. Hope that clarifies things.

Wil said:

Absolutely couldn't agree more with caltexflanc, you, and all others about newbies (and maybe some oldies even) getting caught up in their own dreams and other people's opinions/positions, thus wasting alot of money. What I don't seem to be able to get across is that This Is A Thought Exercise. Sure, I advocate for 24v heartily--but am I actually going to do anything about it? That is why I started this really good give-and-take conversation in the first place.:lol:

I want to know the actual reasons behind the 'norm' and 'convention', especially when there seems to be a better alternative that a lot of other boats are already using. I knew from the beginning that it would be an expensive pita, but I want to know just exactly why. What I've come up with so far is that the availability of a lot of the 12v items will be very spotty in 24v, so that goes a long way towards ruling out pure 24v (but what do the bigger boats do?). That having a 12/24v system would be unnecessarily complex. Good reasons those, and that might be why I don't do it. Hope that clarifies things.

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Maybe because the "better" is so slight...no one else cares....

but maybe if you keep looking...someone might be able to point to real world numbers why a total 24V system would be better...but I've never seen any (other than for a specific piece of equipment like a thruster)...till then talking theory and reality is a fun mental exercise...so how many so far have thought a changeover was good?

Maybe I live in an alternative reality, but I simply just do not get this "scarcity of 24 volt" stuff. It is all very available on my planet. As I said before, I have had no problem getting 32 volt stuff either. What am I missing here? 24-12 converters (or 32 - 12 for that matter) are easy to source if you need them.

psneeld said:
...so how many so far have thought a changeover was good?
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..... and how many are on 'pure' 24v or higher (just the DC side) boats? Is there such a thing? Are they all 12/24v+ combos with a very substantial amount (half or more?) of the electrical items being 12v?

caltexflanc said:

Maybe I live in an alternative reality, but I simply just do not get this "scarcity of 24 volt" stuff. It is all very available on my planet. As I said before, I have had no problem getting 32 volt stuff either. What am I missing here? 24-12 converters (or 32 - 12 for that matter) are easy to source if you need them.

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it's all available and not THAT hard to get...but like twinkies over organic lettuce...

every 7-11 and Little General has twinkies...not organic lettuce...

pull into any decent port and 24V stuff and service is certainly available...

I agree having 2 different voltage systems on a boat is no big deal...but not only 24V or switching to it if you only want to add a 24V appliance or 2....

FF said:

The only item that is a power hog on most boats is the refrigeration system.
A boat with a propane reefer and freezer, and range only requires minor electric for anchored out weeks or months. WE DO IT!

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What make/model of fridge and freezer do you have?

???

I read this and get befuddled. Some comments seem to suggest that going to a higher voltage either in DC or AC reduces work. Wattage is the electrical definition of work and the load dictates wattage thus the work. Granted electrical current reduces with higher voltage given the same wattage. However the work remains the same. 24 volts and 12 volts will run the same temp if the wiring is sized accordingly. One is not more efficient than the other given proper wire sizing. Work is work and nothing is free and you can not create nor destroy energy. Physics are Physics!

Cathy and David said:

Work is work and nothing is free and you can not create nor destroy energy. Physics are Physics!

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Agreed. Why do bigger boats go to higher DC voltages?

Wil said:

Agreed. Why do bigger boats go to higher DC voltages?

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Because of the starters!!! Covered that already.

Ski in NC said:

Because of the starters!!! Covered that already.

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That is just too simplistic thinking. I said that larger flywheel diameters would solve your issue about a 'large 12v starter diameter'. There are other reasons why large boats go to 24v and higher.

Wil said:

That is just too simplistic thinking. I said that larger flywheel diameters would solve your issue about a 'large 12v starter diameter'. There are other reasons why large boats go to 24v and higher.

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Maybe the answer is as simple as them wanting to save weight and cost of heavier gauge wiring, Wil, of which there is plenty on the large vessels. It seems to go up exponentially, the larger the boat, more of everything along with the volume and displacement. Maybe too simple, but it is a serious suggestion. Otherwise there appears to be so little in it re efficiency as to not make it worth it to change. There are davit and winch systems out there with plenty of power, so grunt appears not to be an issue. You just need the heavy duty wiring to those items. Maybe 24v is better than 12v, but the reason why we stick with what we have now is probably, in the end, as mundane as the same reason the US does not plan to go 240vAC. That is too much already out there including plant and stock existing in the present format. So too expensive to make the change. So you sort of answered your own question, right there.

As to why 24v has not bumped 12v like 12v did to 6v, well, same reason as above, and the only car I remember with a 6v system was early VW beetles, and they had huge issues getting bright enough lights, so gave in to 12v in the end mainly for that reason I think. Maybe if they had had LEDs back then..?

Often the simple answers are the correct ones.

Dreams aren't born in facts usually......but reality is.

Wil said:

Ok, let me try to do that with specific examples. Inverters with 24v vs. 12v inputs run cooler & more efficiently, refrigeration compressors with 24v vs. 12v inputs run cooler and more efficiently, 24v anchor winches are more powerful than 12v winches with smaller wire runs. Using less current and more voltage is intrinsically more efficient and powerful. By its own definition, 24v is a more efficient and cooler-running system than 12v. Of course there's a limitation on how high one can go in DC voltage, but that isn't something I've researched. By the same logic, do you think a 6v system would be just as good as a 12v system? If not, that is exactly the same reason why I think 24v is better than 12v.

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ASSUMING all of your assumptions are correct in the above statement the issue you are ignoring is the tremendous infrastructure out there to support 12v things (thank you cars).

So yes, while 24v systems may be inherently more efficient, because of economies of scale, 12v things will cost less than half the price for any given thing.

So, while you save 2-3% in electricity use and transmission, you are losing at least 50% in item costs.

People spending a few million $$ for a 65' boat, probably don't car that a replacement alternator costs a few thousand.

I do.

As an aside, the best change I made on my boat was switcihing my 120v fridge and freezer for 12v and adding four 110w solar panels to my pilot house roof. Yes, within the week, I will post the details)

Wil said:

That is just too simplistic thinking. I said that larger flywheel diameters would solve your issue about a 'large 12v starter diameter'. There are other reasons why large boats go to 24v and higher.

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Might be simplistic, but pretty accurate.

Flywheels are built to SAE standards, so things being driven can be standardized. If you build a bigger fw to accomodate the wider engine block and wider starter, you just boxed your engine company out of many driven components (like marine gears, generators, pumps, automotive transmissions), or forced the need for machined adapters.

It is cheaper to bolt on a 24v starter than to redesign to a larger fw size.

Regarding US power engineering and 120v vs 220v elsewhere: US power engineers are not idiots. Yes we use 120v for small household loads. But we also use 240v for larger power loads. And go into any industrial plant and you see three phase, which is significantly more efficient than any of the above. Get into decent sized motors and volts go up: 240v3ph for little stuff. 10hp up or so- 480v, 300hp up or so- 4kV. Base load generators- around 30kV into the switchyard, around 250 to 500kV out of the yard. Well understood and practiced the concept of selecting voltages to minimize resistance losses.

But as in boats, you have to apply costs to the analysis. There is little benefit in designing a 480v3ph toaster. Duty cycle, line losses and cost of mfg would make that a stupid decision.

Calculate the cost of all the line losses in your proposed boat for its entire life cycle using 12v. Repeat using 24v. Write the numbers down. Now estimate the cost of specifying and maintaining a 24v system vs 12v. Write that number down. Compare numbers. That is why small boats stick with 12v. Like the toaster example.

Ski in NC said:

Might be simplistic, but pretty accurate.

Flywheels are built to SAE standards, so things being driven can be standardized. If you build a bigger fw to accomodate the wider engine block and wider starter, you just boxed your engine company out of many driven components (like marine gears, generators, pumps, automotive transmissions), or forced the need for machined adapters.

It is cheaper to bolt on a 24v starter than to redesign to a larger fw size.

Regarding US power engineering and 120v vs 220v elsewhere: US power engineers are not idiots. Yes we use 120v for small household loads. But we also use 240v for larger power loads. And go into any industrial plant and you see three phase, which is significantly more efficient than any of the above. Get into decent sized motors and volts go up: 240v3ph for little stuff. 10hp up or so- 480v, 300hp up or so- 4kV. Base load generators- around 30kV into the switchyard, around 250 to 500kV out of the yard. Well understood and practiced the concept of selecting voltages to minimize resistance losses.

But as in boats, you have to apply costs to the analysis. There is little benefit in designing a 480v3ph toaster. Duty cycle, line losses and cost of mfg would make that a stupid decision.

Calculate the cost of all the line losses in your proposed boat for its entire life cycle using 12v. Repeat using 24v. Write the numbers down. Now estimate the cost of specifying and maintaining a 24v system vs 12v. Write that number down. Compare numbers. That is why small boats stick with 12v. Like the toaster example.

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Great answer with excellent detail and reasoning. Thank you. I got it, understand what you propose, and agree that's what I should do. I don't have the skills--yet--to do the analysis you speak of, that's what I was hoping someone on TF might have already done. It's along the lines of why I asked if anyone had already done a 24v conversion and what was the result.

Wil said:

Great answer with excellent detail and reasoning. Thank you. I got it, understand what you propose, and agree that's what I should do. I don't have the skills--yet--to do the analysis you speak of, that's what I was hoping someone on TF might have already done. It's along the lines of why I asked if anyone had already done a 24v conversion and what was the result.

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Oh, I thought we were explaining why that person doesn't exist, so don't hold your breath waiting.