Power budget

In my ongoing search for a quality Trawler/liveaboard/cruiser; There doesn't seem to be much consistency in generator sizes. I've seen everything from 3.5 KW to over 10KW on the same size vessels. It seems to me that AC and immersion type water heaters are the main power criminals. I've researched fuel burn for various size generators.
At approx. 75% load the fuel burn for:
8KW- .67 gph
7KW- .59 gph
6KW- .50 gph
5KW- .42 gph
4KW- .33 gph
3KW- .25 gph

Any real life experience with genny sizes and fuel burn costs would help me build my budget.

Where are you planning on boating, and during what seasons? What sort of conveniences and creature comforts do you want? Gas or electric cooking?

How much fuel you burn running your generator is much more dependant on how much power your particular boat, and your particular lifestyle than the generator.

That's because within reason the small generators we find on our boats will generally come in fairly close to each other in terms of fuel used per kilowatt hour produced.

Yes, there will be some exceptions to that general rule. Newer design engines are typically more fuel efficient than older design engines. Running a particular engine at a particular loading produce somewhat better results than the norm.

So, in terms of power budget, we burn around 10 gallons per day on the hook in our boat. We have a 47' power hungry boat and we do not try to conserve.

That fuel burn is not an exact number and nobody probably has one, and it wont apply to your boat anyway. The 10 gallon per day number is an estimate based on differences between flowscan readings and actual fuel taken on. It is also skewed by my actual use of the same size generator in home and industrial settings, so it is an educated guess.

All good questions and ones I've thoroughly dwelled upon. I plan on cruising for a few years. I'm from Pa. so cold weather is something I'm familiar and comfortable with. I plan on following the seasons; Great Loop style more or less, leaving the Great Lakes later in the season. I prefer open screened windows to AC at home. I sleep with a window cracked in the winter time. It's the southern US that concerns me as I get grumpy when I'm hot. I'll be cruising alone, with an old dog that also gets grumpy when he's hot. Propane stove. I take fast showers, luke-warm showers suffice. I was an active Marine for 6 years, I still consider a shower a luxury.

ksanders said:

How much fuel you burn running your generator is much more dependant on how much power your particular boat, and your particular lifestyle than the generator.

That's because within reason the small generators we find on our boats will generally come in fairly close to each other in terms of fuel used per kilowatt hour produced.

Yes, there will be some exceptions to that general rule. Newer design engines are typically more fuel efficient than older design engines. Running a particular engine at a particular loading produce somewhat better results than the norm.

So, in terms of power budget, we burn around 10 gallons per day on the hook in our boat. We have a 47' power hungry boat and we do not try to conserve.

That fuel burn is not an exact number and nobody probably has one, and it wont apply to your boat anyway. The 10 gallon per day number is an estimate based on differences between flowscan readings and actual fuel taken on. It is also skewed by my actual use of the same size generator in home and industrial settings, so it is an educated guess.

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That's exactly the number I came up with when I averaged all of my consumption calculations (mostly AC) based on 5-6 KW units.

Don't forget to add refrigeration as a power consumer. In a 24 period, it's a big energy user, that runs year round.

Without giving my reasons or boring you with data I will give you what I feel is correct for a 35-45ft. Powerboat with an owner who wants to be cool when it is hot, take a hot shower, keep food cold, and cook a meal and make coffee. A minimum of 7KW generator, a propane stove, a 2500W Inverter/Charger, a water heater with both electric and engine heat exchanger and a house battery bank that can handle a typical days drain for 3 days before being charged. And if any of this stuff is over 10 years old enough money designated to replace it.

Larry M said:

Don't forget to add refrigeration as a power consumer. In a 24 period, it's a big energy user, that runs year round.

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I've calculated 3.0 to 4.0 amps DC on a 12v system. Half of that on a 24v DC system. Less than the trolling motor on my bass boat. I would think an adequate house battery system should keep my food preseved.

Billyfeet said:

Without giving my reasons or boring you with data I will give you what I feel is correct for a 35-45ft. Powerboat with an owner who wants to be cool when it is hot, take a hot shower, keep food cold, and cook a meal and make coffee. A minimum of 7KW generator, a propane stove, a 2500W Inverter/Charger, a water heater with both electric and engine heat exchanger and a house battery bank that can handle a typical days drain for 3 days before being charged. And if any of this stuff is over 10 years old enough money designated to replace it.

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I'm a retired airline mechanic, please bore me with data.

I have a 38' light and narrow boat with the following: 12kbtu/hr ac/heat, 6.5kbtu/hr ac/heat, 1500w water heater, 140w fridge, and lots of little loads. The 5kW handles all this at around 75% load. To turn on the dive compressor, water heater must be off. That's about the only load management I need to do. And since dive compressor is not regularly used, it is not an issue.

A 5kW suits my needs very well. I think most trawlers could run on a 5 unless you start getting into bigger boats with the larger airs. I could probably run a 16 in the salon and still use the same gennie.

The 5kW with fridge and AC's cycling on and off all night averages about one gal in three hours. Probably averages about 1/3 to 1/2 load.

When not using ac's, a 1000w inverter runs fridge, coffeepot, laptop, etc, and gennie is off.

Very pleased with the system design.

Ski in NC said:

I have a 38' light and narrow boat with the following: 12kbtu/hr ac/heat, 6.5kbtu/hr ac/heat, 1500w water heater, 140w fridge, and lots of little loads. The 5kW handles all this at around 75% load. To turn on the dive compressor, water heater must be off. That's about the only load management I need to do. And since dive compressor is not regularly used, it is not an issue.

A 5kW suits my needs very well. I think most trawlers could run on a 5 unless you start getting into bigger boats with the larger airs. I could probably run a 16 in the salon and still use the same gennie.

The 5kW with fridge and AC's cycling on and off all night averages about one gal in three hours. Probably averages about 1/3 to 1/2 load.


When not using ac's, a 1000w inverter runs fridge, coffeepot, laptop, etc, and gennie is off.

Very pleased with the system design.

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Worst case scenario; 100• and 90% humidity somewhere on the TennTom. 50 bucks a day in fuel to be comfortable.

I find when actually traveling, even a hot muggy day the boat is comfortable enough with windows, doors and hatches open. The killer is trying to sleep on such a night, that is when the gennie is used. But even then, run gennie and ac's for a couple hours, cool and dry out boat and usually can turn it off and sleep fine. Easily can stay comfortable on summer days for a gallon a day for gennie.

Most of my gennie hours actually come from winter running. When cruising, the "bus heater" keeps cabin warm using coolant from the main engine. Sleeping, though, the boat gets cold fast and gennie stays on all night running the ac's in reverse mode for heat.

Ski in NC said:

I find when actually traveling, even a hot muggy day the boat is comfortable enough with windows, doors and hatches open. The killer is trying to sleep on such a night, that is when the gennie is used. But even then, run gennie and ac's for a couple hours, cool and dry out boat and usually can turn it off and sleep fine. Easily can stay comfortable on summer days for a gallon a day for gennie.

Most of my gennie hours actually come from winter running. When cruising, the "bus heater" keeps cabin warm using coolant from the main engine. Sleeping, though, the boat gets cold fast and gennie stays on all night running the ac's in reverse mode for heat.

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Ahh. Yes. Nights. Like a camper when it's cold.

My worst case scenario includes having guests aboard. Most likely my 80 year old parents (fit and healthy) for a week or so at a time. Many of my friends are retired airline and can cruise between one airport and another. Does my $50.00 per day "worst case" budget need adjusted downwards? I have a fairly reliable and effective method of predicting the "use cost" of something: I call it ECAD. Estimate Closely And Double.

Gen fuel really inconsequential. Main engines eat the most. Figure a 80mile day at 2nmpg and that is 40gal per day. Most trawlers do better, mine is close to 4nmpg at 7kts. Depends on what you end up buying. Most 40 to 44' call it 2nmpg for estimating purposes. Fits your ECAD model, which I like!!

So main engine eats 40gal/day, that's $160.
Gennie eats 2gal/day in minimize mode, that's $8.
Run gennie all day, figure 10gal, that's $40.

Budget $200/day worst case in fuel. Could be better, but prepare for that.

Most older folks can handle the heat as long as there is a breeze, especially outside of cabin in the shade.

Ski in NC said:

Gen fuel really inconsequential. Main engines eat the most. Figure a 80mile day at 2nmpg and that is 40gal per day. Most trawlers do better, mine is close to 4nmpg at 7kts. Depends on what you end up buying. Most 40 to 44' call it 2nmpg for estimating purposes. Fits your ECAD model, which I like!!

So main engine eats 40gal/day, that's $160.
Gennie eats 2gal/day in minimize mode, that's $8.
Run gennie all day, figure 10gal, that's $40.

Budget $200/day worst case in fuel. Could be better, but prepare for that.

Most older folks can handle the heat as long as there is a breeze, especially outside of cabin in the shade.

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Thanks. That's very helpful. I've guesstimated various fuel burn rates for the size and style Trawler I want and their various propulsion systems. Because 10,000 is a nice round number and 24 months is another nice round number I know my avg. daily miles is 13.8. That's the magic number (and the cost of Diesel) when it comes to estimating use cost for engine fuel.

When cruising in my 40, in December where I use a diesel heater (about 1 gal/day), and go the distance from NJ to Ft Pierce, FL and back....only anchoring occasionally...I spend about $1000/week for EVERYTHING from toothpicks to eating out to fuel. That's for 2 and a large dog.

When I find free dockage, anchor out more and stay at a place that's inexpensive for a monthly rate....I knock that back to around $750/week for the 4 month trip average (16-18 weeks). There are weeks that we only spend a couple hundred...but then we tend to splurge a little more some place else.

That's not a lot of dining out or other entertainment...just plain old living aboard a boat on the go.

I have an 8kW Genset...that I use when it's needed...but I also have a 1000W Honda that I use just to top off batteries 2X a day in some situations where I really don't need the 8kW.

Ski is right on the mark as usual. We have anchored out in June/July for the last few summers. Where you drop your hook makes a world of difference. The outer banks has a lot of great locations. The closer you are to the ocean, the better comfort. Cape look out, Ocracoke to name a few are great spots to open all hatches and let the breeze blow though the boat. BTW, I hate sleeping hot !!!! and I slept great. BUT if you drop your hook near the marsh or creeks inland you will not have a breeze and the bugs will eat you alive. You will need to run your genny all night. So why not just go into a small town and plug into electricity and do some sight seeing. Stay the whole month and get a better deal. If I'm anchoring out for extended periods of time I usually run my genny 1.5 hrs in the am and 1.5 in the pm to keep the batteries charged. Of course you need to use power management to run systems because they all wont run at the same time. It never has been a problem. Lets see here, bulk charging the batteries, running both A/C's, while you are making coffee and baking cookies also washing and drying clothes. Nope, not gonna pull the load. It took a while to convince the wife this was normal.

>I've calculated 3.0 to 4.0 amps DC on a 12v system. Half of that on a 24v DC system. Less than the trolling motor on my bass boat. I would think an adequate house battery system should keep my food preseved.<

4 amps DC for 12 hours or more probably 16 hours a day is 48 to 64 AH , so one 120AH deep cycle battery will be down to 50% each day.

The house bank size will decide how many days you can anchor with no noisemaker.

The quality of the charging system will decide if 5 hours or 10 hours is required to get mostly recharged.

I usually figure a noisemaker all up cost is about $10.00 per hour.

But that includes fuel, maint , repairs and a kitty for the new one when the installed one dies.

Therefore the first question should always be , how can I have a great lifestyle with NO noisemaker.

IF Air cond is required you can only go to the power pole if cost is a concer.

If AC is not required , there are many ways to live just fine , quietly , but not for Free!

We have a 12KW NL genny we run everywhere we go. We average ~1GPH

I call it ECAD. Estimate Closely And Double.

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Excellent system for boat budgeting, just to remember to round up generously after you double. And anything you don't spend, put into the reserve fund for stuff you never thought of or thought would never happen. I always felt the reserve fund should initially be the cost of an engine blowing up. This approach cuts down the financial anxiety level to zero.

Get a generator that will power everything running full blast at once, the price difference is very little and as others have pointed out the cost per kilowatthour is virtually the same at any given level. The whole "loading it right" stuff is mostly urban legend, as long as periods with no load are avoided.

Ski in NC touched on the increased "start up" demand of electrical equipment, it can be 2-3 times more than the specified draw. When we replaced the compressor unit for the eutectics, the frig guy said have nothing else drawing on the 6.5KW Onan when starting the compressor.

All electric boat...Our 7.5 Kohler runs 1 hr +/- am / 1.5hr +/- pm. All needs on board stay well supplied. Figure we use approx 1.75 gal gasoline per day. Have AC - don't need it. I do lots of evening BBQ and love cooking that way.

When needed in colder weather (SF Delta seldom goes below + 35 f) we heat with "HeatMate" non pressurized alcohol heater. Super easy to use and very safe. Can be used to heat pot of coffee water too.

Heatmate 5200 Portable Non Pressurized Alcohol Heater Stove Steve | eBay

Any unvented fuel burning heater will dump water into the air.

Alcohol or propane the walls may run with water depending on the Delta T.

FF said:

Any unvented fuel burning heater will dump water into the air.

Alcohol or propane the walls may run with water depending on the Delta T.

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None of that noticed using HeatMate. Of course, we don't need to let it run wild. During day, it's not on for more than three to six hour intervals and not always on high. Then off for hour or two. Never leave it on while sleeping. The moderate climate on water in in SF Delta offers reduced need for heat (winter day usually 35 to 50 f /night 30 to 38). Also leave couple windows cracked while heater is on.

HeatMate sold in 2000's is the same exact heater (I do mean exact) that my family used on boat in NY during the 60's

Happy Boat Heating Daze! - Art

Interesting that those numbers all work out to about .083 GPH per KW

Hi,

I'm moving from 50+ years of sailing to a Trawler, currently looking at a Ranger 29. My question is about total power usage:

She is equipped with a 16kBtu/hr and a 10 kBtu/hr reverse cycle, electric stove, microwave, hot water, and small electric space heater. This is far more power consumption than the two 30 Amp power cords or the 5kW genset will supply.

It seems that to cook on a hot day, I have to cool the boat, turn off the a/c and hot water, cook the food, and turn the a/c back on.

Is this typical of the drill?

Seems strange coming from an all-solar sailboat with propane heat, hot water, and cooking.

Should I covert to propane, pass on this boat, or eat cold food?

Thanks

StuartBell said:

Hi,

I'm moving from 50+ years of sailing to a Trawler, currently looking at a Ranger 29. My question is about total power usage:

She is equipped with a 16kBtu/hr and a 10 kBtu/hr reverse cycle, electric stove, microwave, hot water, and small electric space heater. This is far more power consumption than the two 30 Amp power cords or the 5kW genset will supply.

It seems that to cook on a hot day, I have to cool the boat, turn off the a/c and hot water, cook the food, and turn the a/c back on.

Is this typical of the drill?

Seems strange coming from an all-solar sailboat with propane heat, hot water, and cooking.

Should I covert to propane, pass on this boat, or eat cold food?

Thanks

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Yes.....juggling electric loads seems to be a lot of people's hobby as they think I am crazy for upgrading to a 50A 125/250 cord which allows me to run 2 more electrical appliances than 2-30A cords and is heavier duty for constant live aboard/cruising use.

I also converted to propane yet kept one of my really nice electric hotplates as it comes in handy for the odd times of not opening up the burnertop.

Ultimately if you are a non-marina type cruiser...I see the advantage of working as many systems as possible towards 12 or 24V...especially as more and more marinas charge outrageous prices for electrical service. But having the service available and convenient doesn't mean it was a waste if you use it sometimes. (Though expensive to upgrade...better do easy the original install).

Have you talked with Ranger about this? If a used boat, did a PO add some of these things (the little space heater, probably) Have you confirmed how many watts each of those is? Actually the two 30s, with a total of 7200 watts, should come fairly close, but that's a totally blind guess. A properly designed boat should have shore power and genset capacity to each power the whole thing. If not, makes you wonder what else they skimped on. Personally I wouldn't buy such a boat.

As our control panel is easily accessible in salon, next to pilot station; I find no problem to jockey breakers on and off for limiting load on entire system; whether on shore or gen set power. Jockeying breakers for use sequences is only wise... I've seen what can happen when a boat's electric system gets way overloaded and its main breaker unexpectedly malfunctions (i.e. it actually melted - not supposed to, but it did!)... can we spell F-I-R-E!! Boat and house electrical systems are not the same animals; IMHO, both should be given the respect each deserves.

Not that it is needed; system could withstand greater load. However, for sanity and safety sake I keep our load at or below 25 amps. Once water is hot it stays as such for fair piece of time. Elect stove/oven can be but does not need to be used at same time as microwave. Fridge/freezer stays cold for up to hours so turn off at breaker for a while poses no problem. Not too many electric lights needed on at same time. C-phone/computer charge is little draw and batt-bank charger draws little too. Luckily our climate requires limited need for air conditioner or heaters. And, for long duration need of heat while on hook I have a fool proof alcohol heater that can also be used to heat coffee water or even cook on if desired...

http://store.hamiltonmarine.com/bro...4,39661.html?gclid=CJ2b1Mnj6MECFRFlfgodSUoA9Q

Soooo - On hook (which we luv to be) gen set need not often run for long period. I see no need for inverter. We manage fine with batt 12v set up and ac power availabilities. Also, have solar panel that keeps gen set starter batt up. And, I keep a brand new starter/deep-cell combo batt isolated and fully charged in its own batt box... just in case emergency might arise for extra 12v power.

We B Happy!!