Understanding battery consumption on mooring/anchor

[Woodland Hills]

I have a 20kw Onan and a 12kw Northern Lights and I run each around 3hrs a day, the 20kw in the morning when the inverter bank is depleted, this translates to roughly 6 gallons a day maybe a bit more. Our last fill up was at $1.83 a gallon so about $11 a day for fall usage. In the summer we cool the boat from 7am until 9pm for about 14 hours a day, also alternating generators for about $25 a day in fuel.

We air condition from April/May until August/September depending on how far north we get and how soon we get out of Florida! We are currently in Long Island Sound and haven’t run the a/c for weeks. We have 5 a/c units on board, but only run the salon all the time. The galley gets run when cooking and the master stateroom runs for a couple of hours before bedtime to cool it down to around 67 for sleeping. Unless the boat is opened up for thru-ventilation we also have two 70liter/day dehumidifiers we run whenever the generators are on.

To that you have to add the cost of oil changes every 100hrs, the filters I buy in bulk for $10 and the oil in 5 gallon pails from NAPA for $45 a pail. An oil change takes just over a gallon: 5 liters and 1/2 an hour. I suck the old oil out the dipstick and have a hand pump on the pail to refill. A quick back of the envelope calculation gives about $2.00 an hour out of pocket cost with today’s cheap fuel.

We carry 1075 gallons of fuel on board in two centerline tanks. I do not have flo-scans on the generators so I am just guesstimating at their burn, but this is in line with what others with the same boat have reported.

I hope this helps....

[Group9]

We have 540 watts of solar, and we can keep our refrigerator/freezer running at anchor and that's about it. Anything else, especially the AC, hot water heater, or oven range, needs the generator.

On a cloudy day, we can't even keep the fridge running without seriously pulling down the batteries.

[SV__Grace]

Wouldn’t it be better to run AC with the generator than to use battery cycles?

Small example- when my wife blow dries her hair I run the generator for the 5 minutes it takes to do so, where it would take an hour of generator time to put that much energy back into the batteries.

[Simi 60]

Them some big gensets you have there, I suspect they have bugger all load on them for most of their running time.

To the op if this helps

We have 8 x 220ah agm batteries linked as 24v giving 880ah
9 x 250w solar panels
1 x 7.5 kva genset 6 kw
A victron 5000/120 inverter charger
A midnite classic 150 mppt for the solar panels

From that we run
800 litres/30 cubic feet of fridge freezer across 4 x 240v household units
A household 180 litre/47 gallon 240v hot water system turned on manually.
40 inch and 32 inch TV on 240v
Multiple computers and 23 inch monitors on 240v
240v microwave, pressure cooker, 4 slice toaster and multiple other short run items.
Most lighting is 24v
24v and 240v pumps
No a/c even though we live on the same latitudes as Florida to Cuba (well ventilated boat)

Batteries rarely get below 85%
If its a sunny summer day we are 100% solar
Winter may require a 30 minute head start on genset in the morning with hot water system on as well.
Rainy day needs 1.5 hours to charge batteries and do hot water system

We have not been on a marina in 4 years

[Woodland Hills]

Originally Posted by Simi 60

Them some big gensets you have there, I suspect they have bugger all load on them for most of their running time.

To the op if this helps

We have 8 x 220ah agm batteries linked as 24v giving 880ah
9 x 250w solar panels
1 x 7.5 kva genset 6 kw
A victron 5000/120 inverter charger
A midnite classic 150 mppt for the solar panels

From that we run
800 litres/30 cubic feet of fridge freezer across 4 x 240v household units
A household 180 litre/47 gallon 240v hot water system turned on manually.
40 inch and 32 inch TV on 240v
Multiple computers and 23 inch monitors on 240v
240v microwave, pressure cooker, 4 slice toaster and multiple other short run items.
Most lighting is 24v
24v and 240v pumps
No a/c even though we live on the same latitudes as Florida to Cuba (well ventilated boat)

Batteries rarely get below 85%
If its a sunny summer day we are 100% solar
Winter may require a 30 minute head start on genset in the morning with hot water system on as well.
Rainy day needs 1.5 hours to charge batteries and do hot water system

We have not been on a marina in 4 years

They are not what I would have specified. I am guessing that they are sized for all 5 a/c or heat units to run 24/7 with everything including the watermaker and the stove and oven turned on! Remember that I don’t have a trawler or a long range cruiser, I have a planing hull motoryacht designed for short term weekend trips or marina usage as an apartment. I have just done my best to make it usable as a cruiser.

[Simi 60]

Originally Posted by Woodland Hills

They are not what I would have specified. I am guessing that they are sized for all 5 a/c or heat units to run 24/7 with everything including the watermaker and the stove and oven turned on! Remember that I don’t have a trawler or a long range cruiser, I have a planing hull motoryacht designed for short term weekend trips or marina usage as an apartment. I have just done my best to make it usable as a cruiser.

Wasn't having a go at you, I was just surprised at their size.

When ours was a working prawn trawler she would have had hefty gensets onboard as well, lucky for us they were taken out when she was reconfigured but, if they had been left in I wouldn't be changing them out until I had to either.

[ranger58sb]

Originally Posted by nmcafee

So, am trying to understand what life on the mooring, or anchor will look like on our future boat. Am targeting either a ~55 foot Hatteras or a Sea Ray 550 Sedan Bridge. I love the sedan bridge helm but prefer a standup engine room you can find on the Hatteras.

Question is......If I have a 17kW generator and a battery bank. Want refrig and lights and power for computer to be always available. Want AC to be available at night. The generator charges the batteries, how much life do I have on the batteries? Will the generator be running all night if I am running the AC?

I am budgeting 1g of fuel per hour of generator, I just don't have a clue how many hours it will need to run per day. 1g of fuel x 24 hours gets to be real money pretty quick.

Have tried to google but just must not be using the right terms.

Nathan

Nathan, where are you... and/or where do you see yourself doing most of your boating... and/or how often or for how long a duration do you anticipate anchoring?

You can see many have commented on AC being a big driver in your calculations.

FWIW, we almost never needed the AC at night on anchor; only in marinas where there's very little breeze.

Which in turn meant we could usually easily get by for a couple weeks at anchor running the genset for a couple hours each morning and each evening... while we charged batteries, cooked meals, and heated water. The rest of the time, we used the inverter powered by batteries.

There are several related issues in all that. More inverter use needs a better battery capacity. "Better" can take several different paths. Also, the charging regime I described only works for a while, depending on battery types, and then afterwards a full charge to 100% -- usually on shorepower -- become necessary.

Anyway, if you provide a bit more info, folks may be able to home in on better ideas for you.

-Chris

[a64pilot]

A rather scientific answer to the question of how long does it take to charge an AGM battery
https://marinehowto.com/how-fast-can...ry-be-charged/

Ref the suitcase generator on a larger motor yacht, I’ve not seen it either, but then I have never seen a larger motor yacht actually living at anchor.
I’ve seen a few derelicts, but I don’t think that’s what we are talking about here.
I’ve seen a few that spend a few days, maybe even weeks at anchor in the Bahama’s moving from one Marina to another, but in truth I have never seen one actually long term on the hook. Suitcase generators will recharge batteries, and are cheap and disposable, but will last longer than you think, about half as long as a “real” generator, if the oil is changed weekly.
Many if not most MY’s are designed to run off AC power, not much except the lights are DC and even then many really have more AC lighting than DC.
So that pretty much means large generator running most all of the time.

So let’s run some numbers. First to begin with the 100 hour oil change is smart, I know some will jump in and say my generator specs 250 hour oil changes, but if you want the thing to really last a long time, 100 hour oil changes will pay off.

So assume only 10 hours a day generator, which will return your batteries to a full 100% charge by the way, but that’s of course 70 hours a week, an oil change every ten days or three a month.
That’s also about 3600 hours a year if I do the math correctly, so how many years will a generator last? Maybe three on the outside? What does a big generator cost?
$20,000? If so then that’s pretty much $7,000 a year amortized out.
Fuel cost is honestly pretty much irrelevant, but from a generator life and oil change aggravation etc you can see how it may make more sense to just buy a Marina slip.

[theDangerz]

I feel like the important discussion here should be about the use of A/C than anything related to batteries.

Most boats can be completely self-sustaining on solar alone if you plan correctly (without running A/C all night).
Very few A/C units will run for more than a hour or two on 12V batteries alone, and most aren't even setup to run without the genset as it's simply that inefficient.

The truth is that life on the boat is different than what you're accustomed to back home and chances are you won't need the A/C all night (or at all most nights). Most of us find that the prevailing winds/breezes we get at anchor are more than enough for a comfortable night's sleep.

The small handful of times in our 2 years out here that we've run our A/C were during rainstorms where we had to close up the boat or when we're in a marina (very rare for us) for repairs.