Wattage Usage on a 30' sailboat

[barnakiel]

It all depends on the gadgets like fridges, APs and radars mostly. Other than that you do not need a lot of juice.

If you run a fridge, an AP, or use your radar a lot, the solars will not be enough. Alternator is the answer in such cases in any small boat.

On an overcast day your solar production may may drop by 80% or more. Two dark days and you are cooked.

b.

[SURV69]

Originally Posted by Stu Jackson

Rubbish. 45 homers would be in one season. NOT one game, and certainly NOT lifetime. Geez....

Please, please, please, listen to what we're trying to tell you and stop arguing with the great input you're getting.

well Stu ... uh ... like ... yeh it's pretty dogone obvious that it would be a year ... but evidently you didn't understand the statement or what it was trying to say.

If I say my Frigoboat draws 3 amps, anyone with any common sense "knows", that a Frigoboat fridge would not ever draw 3 amps in 10 minutes, or for matter 3 amps in a day. Same goes for a 7" TV drawing less than 1A.

If the numbers being bounced around actually had values that could be misconstrued into actually meaning something different, then yes, we STUPID PEOPLE(me), would obviously HAVE to use A, Ah, W, Wh, voltage and wire type and size and all this stuff ... in PROPER TERMS.

I'm not saying your wrong ... I'm saying that you should know darn well what the "mislabled" values are because generally speaking .... especially for a 30' sailboat ... no other assumption even makes sense.

I say spend less time berating, attacking and criticizing others who don't speak at your electronically elevated level.

In my business(Surveyor for 40 years), I never berated or attacked what you would term as "Stupid", clients ... I always tried to understand what made sense and how what they were saying might sense, when I figured out the facts. Very often, the "wrong things", they were saying made perfect sense.

As I said, if you really cannot ascertain what someone means when they say 3A, instead 3Ah, then you are really being stupid in your own way.

[kmacdonald]

^Still doesn't get it.

[StuM]

Originally Posted by SURV69

If I say my Frigoboat draws 3 amps, anyone with any common sense "knows", that a Frigoboat fridge would not ever draw 3 amps in 10 minutes, or for matter 3 amps in a day. Same goes for a 7" TV drawing less than 1A.

You still don't get it. Your fridge will draw 3 Amps all the time it is running, whether for 1 second or for 10 days.
(3 amps in 10 minutes and 3 amps in a day are both meaningless expressions)

Without knowing how long it runs each day, you don't know how many Amp hours per day you need. It will be 72 Amp hours if it runs continuously but it will be 3 Amp hours if it runs for 2.5 minutes an hour.

If the numbers being bounced around actually had values that could be misconstrued into actually meaning something different, then yes, we STUPID PEOPLE(me), would obviously HAVE to use A, Ah, W, Wh, voltage and wire type and size and all this stuff ... in PROPER TERMS.

We've seen far too many situations here where people do what you do - mangle the correct terms, and consequently come up with entirely wrong conclusions. If you get into the habit of using the correct terms, such confusion disappears.

[fryewe]

Originally Posted by SURV69

If I say my Frigoboat draws 3 amps, anyone with any common sense "knows", that a Frigoboat fridge would not ever draw 3 amps in 10 minutes, or for matter 3 amps in a day. Same goes for a 7" TV drawing less than 1A..
[snip]
As I said, if you really cannot ascertain what someone means when they say 3A, instead 3Ah, then you are really being stupid in your own way.

If you say to me that your Frigoboat draws 3 amps, I take it to mean that it is drawing 3A right now...and can do so for a second, or a minute, or an hour, or a day....

And if you know how long it ran, drawing 3A all the while, then you can calculate how much ENERGY, the fridge used. And that's the important thing. Amp hours is a measure of that energy...limited energy stored in your battery...delivered at a rate that is measured in amps, normally.

You seem to understand that, and that's good.

The energy delivered by your battery can also be discussed as being delivered at a rate expressed in watts...and the energy can be calculated in watt hours.

The difference between amp hours and watt hours as measures of energy is that the watts (and thus watt hours) includes the voltage as well...because watts are current times voltage.

Current and power (amps and watts) are measures of the rate the energy is being used...or delivered back to the battery.

Monitoring battery state with amps and amp hours vs. watts and watt hours needs simpler circuitry and reasoning if the concepts are understood.

The total energy in a battery system, as designed and delivered, is commonly expressed in terms of amp hours. It's important to understand that current is the rate at which the energy is being used...and that if you can approximate the rates and times at those rates, you can calculate how much energy was used...and thus know how much energy is remaining in the system.

This understanding also allows judging the rate at which a charging system is delivering energy...again in amp hours determined by how long the energy was delivered at the rate in amps called charging current.

Hope this helps.

[StuM]

Originally Posted by SURV69

In my business(Surveyor for 40 years), I never berated or attacked what you would term as "Stupid", clients ... I always tried to understand what made sense and how what they were saying might sense, when I figured out the facts. Very often, the "wrong things", they were saying made perfect sense.

My block of land is 1500 metres. I want to fence it.

Damn, I've just paid for 1500 metres of fencing.
I meant 1500 square metres and I only needed 160 metres of fencing.

[leftbrainstuff]

Lets clarify you're units.

You need to specify your daily budget in terms of amp hours. This reflects both your current draw and duty cycle.

Then you can work backwards to determine what wattage of solar panels will meet your daily needs.

For FLA you assume only 30% is useable. Solar performance is mostly latitude dependent. 5 hrs of good solar performance is a typical practical metric.

Power (Watts) = V (Volt) x Current (Amp) is our simple formula to crank the numbers.

Sent from my SM-N900T using Cruisers Sailing Forum mobile app

[Stu Jackson]

Originally Posted by SURV69

well Stu ... uh ... like ... yeh it's pretty dogone obvious that it would be a year ... but evidently you didn't understand the statement or what it was trying to say.

In my business(Surveyor for 40 years), I never berated or attacked what you would term as "Stupid", clients ... I always tried to understand what made sense and how what they were saying might sense, when I figured out the facts. Very often, the "wrong things", they were saying made perfect sense.

As I said, if you really cannot ascertain what someone means when they say 3A, instead 3Ah, then you are really being stupid in your own way.

For someone who didn't know Mr. Aaron's accomplishments, then they wouldn't know. Duane Kuiper had a nice career. He hit all of one, ONE HR. Is that per year, per game or lifetime?

I've had some stupid clients. My approach was always to TEACH them, and almost all of them learned. You seem to be one of the few who resists.

As for your last para, it's still nonsense, and the rest of the respondents have politely explained just why.

Please, listen up. It DOES make a difference, regardless of the size of your boat.

And, BTW, I didn't call you stupid. I said anyone who refuses to learn is stupid if they get the info and still argue about it. Different things.

[boatpoker]

Originally Posted by SURV69

As I said, if you really cannot ascertain what someone means when they say 3A, instead 3Ah, then you are really being stupid in your own way.

I would think as a surveyor you would recognize the value of accurate, specific terminology. I believe this is especially important when dealing with someone as inexperienced as the OP.

[valhalla360]

Originally Posted by SURV69

well Stu ... uh ... like ... yeh it's pretty dogone obvious that it would be a year ... but evidently you didn't understand the statement or what it was trying to say.

It could be 45 home runs for the entire season or 45 home runs so far in the ongoing season. You haven't given us enough information.

If I say my Frigoboat draws 3 amps, anyone with any common sense "knows", that a Frigoboat fridge would not ever draw 3 amps in 10 minutes, or for matter 3 amps in a day. Same goes for a 7" TV drawing less than 1A.

It may draw 3 amps but how many hours per day is it drawing those 3 amps. Example: If your engine starter draws 600 amps but typically starts in 2 seconds, it's only going to use approx. 0.33 amp-hrs.

If the numbers being bounced around actually had values that could be misconstrued into actually meaning something different, then yes, we STUPID PEOPLE(me), would obviously HAVE to use A, Ah, W, Wh, voltage and wire type and size and all this stuff ... in PROPER TERMS.

Since we have shown you clear ways they could be misconstrued, using the proper terms is important.

I'm not saying your wrong ... I'm saying that you should know darn well what the "mislabled" values are because generally speaking .... especially for a 30' sailboat ... no other assumption even makes sense.

I went back and re-read your first post. The numbers and units are all over the place and I can see several places where I could reasonably assume two or more possibilities.

I say spend less time berating, attacking and criticizing others who don't speak at your electronically elevated level.

It's not meant as an attack. If you use correct terminology, it's easier to help answer your question.

In my business(Surveyor for 40 years), I never berated or attacked what you would term as "Stupid", clients ... I always tried to understand what made sense and how what they were saying might sense, when I figured out the facts. Very often, the "wrong things", they were saying made perfect sense.

In my business, people who make assumptions with clients who don't understand what they are talking about, have it come back to bite them almost every time when they make incorrect assumptions. If the client is saying something illogical, you clarify what they actually mean, you don't assume.

As I said, if you really cannot ascertain what someone means when they say 3A, instead 3Ah, then you are really being stupid in your own way.

I can ascertain the meaning of the terms perfectly well. I'm not a mind reader though, so if that makes me "stupid" I will lay claim to that title.

No one is trying to criticize or berate you for initially using the incorrect terms. If you had simply went back and clarified your terminology, we would have all moved on. It's your insistence that there is no difference or we should understand what you meant that is causing the push back.

Below is a good example of what you are suggesting we do with your initial post:

[Cap Bill Des]

SURV69- We spend 5 months each winter on our Ericson 33 in the Caribbean. We installed all the cruising equipment on our boat before we left New York 4 years ago and we're pleased with how it's working.

We have two 85 Watt panels, 170 watt total. Two Grp 27 flooded deep cycle house batteries, 210 ah total, plus a starting battery. A Xantrex battery monitor, which is critical to monitor and understand the system. Two separate 15 amp MPPT panel controllers. 60 amp alternator on the engine.

Our loads are Isotherm holding plate fridge ( no freezer), autopliot, radar, 7" chartplotter, laptop computer, phones, fans, instruments, stereo, propane solenoid, and lights ( ALL LED), pressure water pump, bilge pump, windlass.

At anchor on a sunny day the batteries are fully charged back up by Noon. ( the maximum current we have ever seen is about 11 amps net into the batteries (at that moment the only load was the 0.1 amp monitor)). Typically the battery monitor will read -35 ah when I get up, it gets back up to zero by lunch, integrates positive ah during the afternoon, then resets to zero and starts integrating negative ah as the sun sets.

So at anchor we never have to run the engine unless we get two very cloudy days in a row.

At the other extreme, an overnight sail with the autopilot and just about everything turned on does require running the engine for about an hour.

I think our system works because we installed all new, efficient equipment.

The evidence of success this year is that we have cruised since January 4 without once touching a dock. No use of shore power at all. And our grand total diesel consumption is just under 30 gallons, or about 60 hrs engine time total.

We were considering larger solar panels, but given how we can replenish batteries so fast on a sunny day I think our next step, if we can find ghe space, will be another house battery. That might let us sail overnight without ever starting the engine.

I hope this is the kind of information you were looking for.

[Pete7]

Originally Posted by Stu Jackson

Please, please, please, listen to what we're trying to tell you and stop arguing with the great input you're getting.

Really? like tablets using 10AH and depth sounders 7AH, or needing to spend 5 - 7k on solar, wind etc.

[Cheechako]

Originally Posted by laika

Can;t add much to the other responses already, just ancedotal. I'm in the caribbean sun right now with 7 36W panels (250W) on a 27ft. With full midday sun I see 13A coming thru sometimes. A good day will be just north of 80Ah (just over 1Kwh). I power a tiny little engel fridge which takes about 1.8A on average (say 2A x 24hr = 50Ah). That already most of I get even on a good day. That along with lights, fans and possibly an autopilot / chartplotter, I'm lucky to come out ahead. No way with a computer! It would be great to have another panel or two, or, even better, a windgenerator to compliment the panels.

Your energy production will not go as far as you think it will, but whatever you got is better than nothing.

Far more useful than all the bru haha about units! In the Caribe, not summer, I found a small 1.5 cu ft 12V fridge needed at least 80 amp hours replaced daily. I'm not aware that any normal sized 12v unit is remarkably better at electrical usage than another..?

[Mystic38]

there is much good advice in this thread about changing your mindset to aH for electrical calculations, however the shortform answer to your original question of "is 120W of solar enough" is yes, PROVIDED that you have a MPPT charge controller...(a MPPT controller allows for the use of the full wattage of the panel)

I have a sabre 38 with a single refrigeration unit.. this accounts for 90%+ of all electrical consumption at anchor (about50aH/day) and a 130W solar panel plus MPPT charger that in full sun charges at 9A (vs about 6.5A for non MPPT) and so will generally recover to full charge by 2-3pm

Originally Posted by SURV69

I have just bought 4 30 watt/12 volts panels and a 20A controller for my Bristol 29, which I plan on living in and cruising full-time. I chose the 30 watt panels because I didn't want to spend a lot of time installing my first choice(2x100watt). I also have 2 690AH starting batteries and a 800+ AH battery(left it at home) ... all wetcell batteries. I might add another large house battery later(along with 2 40-80 watt panels) My alternator delivers 40 amps when the engine runs.

I cook on an alcohol stove, use minimal lighting and am operating on a 2A notebook computer. My fridge is a Frigoboat which draws 3A per hour of running, which is about 15 minutes per hour(daytime), and about 5-10 minutes each hour at night. Beginning last years I've learned to "enjoy", heat and tolerate cold. My 7"TV draws about 1/2A and my mp3 player(with speaker), draws about 1/6A.

My computed amperage, daily is expected to be about 35 or so amps on average.

For summer, I expect the 120 watts should suffice and deliver about 40+ amps daily.

I'm figuring that rainy/cloudy days will reduce wattage, but these days might also reduce fridge running time and hopefully keep me covered.

I know there are lots of sailors with hundreds of wattage, and with wind vanes to boot, but I'd like to hear from those who have operated in the 100W to 200W range ... and hear what they think of their system setups.

[Bill Seal]

If my engine uses 1 gph, how far can I go?

I think the confusion comes because gallons of fuel are like Amp-hrs. but Amps are like gallons per hour.