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Old 22-09-2019, 07:25   #61
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Re: serious discussion about electric power in large boats

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Originally Posted by LongRange View Post
I very much like the concept of electric power, and my next car will probably be electric, but I cannot envisage getting rid of the diesel anytime soon on my sailboat.

Like most sailing monohulls, we struggle to meet our "house" electrical needs, let alone powered propulsion. Our solar panels generate maybe 250 watts in bright sunlight. Without wholesale conversion to electrical, around 250 W is the most we could possibly invest in propulsion. Many jurisdictions impose a 250 watt limit on motor power in e-bicycles. That is equivalent to a strong adult rider bicycle pedaling hard.

On our sailboat which is 13.75 m LOA and ~12 t loaded, pedaling an exercise bike contraption that drives the prop would probably fail to make a dent unless it is flat calm, when I could achieve maybe a knot if I give it everything I've got. Therefore, my thinking goes, adding a ~250 W electric propulsion unit is a waste of money and time.

The situation is even worse if I commit to getting rid of the diesel engine and fuel tank, and thus go into the kilowatt range. If those 500 kg are replaced by an electric powertrain, and the motor is say 100 kg (wild guess), 400 kg of LFP means just under 3,000 Ah capacity. Disregarding conversion inefficiencies and DoD limits, all that effort and expense would give me six minutes of 30 kW propulsion! Afterwards, I could fire up the exercise bike contraption in the cockpit, if I wanted to continue moving under electrical power

My own conclusion is that any "serious discussion" about electrical power can only arrive at a "NO" answer, at least in the context of a cruising sailing monohull. The limits are imposed by physics. If the energy density of batteries improves by an order of magnitude, it might start to make sense for those who begin and end each day attached to shore power.

You would not use 30kw, normally, unless you usually run your diesel wide open. Also there is no minimum speed or power output level for electric drive. Yes, EP has serious issues when you get into larger boats but it is not as bad as you seem to think.



Probably the ideal setup for a larger boat is to have a diesel AND electric motor. The diesel couples to the prop shaft in the conventional manner, through a marine transmission. The electric motor couples to the shaft via belt and pulley system. With diesel disengaged the electric is free to power the shaft. Or free to produce power from the trailing shaft when sailing at higher speeds. When a boat is pushed to hull speed, there is no speed penalty from increasing drag by loading the motor in regen mode. When sailing at reduced speeds there is a speed penalty from regeneration but it is not a dealbreaker. With the diesel engaged it can turn the prop in the normal manner and depending on where you have set the regen control, either the motor adds a bit of load to the shaft as it produces electricity, or adds virtually no load to the shaft and produces none. What this type of hybrid operation gives you is first of all flexibility. For maneuvering, the electric is superior. For "power tacking" and dodging floating objects and other things, it is a marvel. Instant torque, no minimum idle so no "bumping" in and out of gear. When long legs are needed, the diesel is used. Another advantage is being able to harvest and utilize "free" energy. A big boat maxed out with solar panels can give you a lot of charge. Regen is a big help, too. It is like finding cans of diesel fuel floating around in the sea. The big bank has other uses, of course, besides propulsion.


Such a system is too complex for the typical boater, maybe. That doesn't mean it is not a viable system, and workable for those who are willing to learn more about batteries, electricity, motors and controllers, etc, and who can live with the various tradeoffs.



Am I recommending EP for just anybody with a 40'+ boat? No. Especially not "pure" electric. Serial or parallel hybrid makes more sense for larger boats, and even there, it is definitely not for everyone. In a series hybrid a diesel generator powers the motor electrically, and a battery bank is used for backup or short duration use of the motor but is not an essential part of the power train. The parallel type system gives more flexibility and better performance. The series hybrid has the advantage in simplicity. Neither are more efficient than a straight diesel system unless you also harvest significant "free" energy. A 250w solar panel is not significant in this context and I would say the opening amount of solar would be 1kw.


There are sailors who basically never motor except when docking. For them, pure electric with no diesel might be practical if they do not cruise in any serious definition of the word, and they have easy access to the sea.
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Old 22-09-2019, 07:46   #62
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Re: serious discussion about electric power in large boats

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Originally Posted by danstanford View Post
Sorry if this has been covered elsewhere, but the various unit descriptions make it very hard to make assumptions. Looking at a 6kw Oceanvolt powered boat and wondering what options I would have to increase the range past the 20 nm range published. Is there a hydrogen fuel cell that could provide enough power to run her at 5 knots continuously? how about a portable generator?
The plan would be to only go if I could sail but we all know there are days with no wind and we have to get home....

Currently, hydrogen fuel cells are a non starter. Too many technical issues yet to overcome, but in the future at some point they may become practical.


Generally, e-boaters do not run at such high speeds. Running at half that speed makes an exponential difference in power and range. So the best way to increase range is to slow down. Of course this may not work well when stemming tide, current, or wind/seas. The other and more obvious way is to add another bank.



A 20nm range at 5kt is quite incredible already and I would take those claims with a grain of salt. The EP industry is full of exaggerated or misleading claims. Best to keep your expectations at a somewhat lower level than "as advertised".


The disadvantages seem to be multiplied with larger boats. EP works nicely with boats in the 30' range. Usage patterns can make or break EP practicality. For a day sailer, it is plain stupid to install a diesel when shore power charging of an EP bank is so economical, clean, and convenient. For the guy who basically motors more than he sails, even in a small boat, pure EP would not hack it. The wide gulf between these two extremes is where you just have to weigh pros and cons and make a choice that you will have to live with.
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Old 22-09-2019, 07:59   #63
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Re: serious discussion about electric power in large boats

I wish the OP had told us what he hopes to gain by going electric.

It does NOT help climate change. That’s because charging batteries from shore power is from carbon fuel burning power plants. Because about 30% of utility power is lost in the grid and then more lost in battery charging, a modern diesel in a boat emits less CO2 than the shore power route. And if you pay for electricity by Kwh, electricity is more expensive than buying diesel in most of the country.

As utilities switch to wind and solar this will change - but not really for 10 years+

Using a genset for diesel electric is even worse because it converts energy more times - under Newtons law, energy is lost in each conversion. A diesel propulsion engine is directly connected to the shaft. Energy loss in the transmission is insignificant.

A diesel genset first makes electricity in a fairly inefficient way, then loses part of that in the wires and controllers, then loses more in the motor converting it back into rotational energy to turn the shaft. You will buy more diesel and emit more CO2 with a genset diesel-electric than a direct coupled propulsion engine.

You simply can’t fit enough solar panels on a live aboard cruising sailboat boat to make a meaningful percentage of the energy required for motive power — unless you only run the engine maybe once a week. There’s too much shade from mast and rigging. It’s difficult enough to find space for enough panels to just provide 100% of the hotel loads using solar panels. Little is typically left over for an engine.

If you only run your engine once a week OR only go a mile or two OR have a mast-less flat top power cat totally covered in solar panels — Then solar generated motive power can work.
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Old 22-09-2019, 08:10   #64
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Re: serious discussion about electric power in large boats

Quote:
Originally Posted by danstanford View Post
Sorry if this has been covered elsewhere, but the various unit descriptions make it very hard to make assumptions. Looking at a 6kw Oceanvolt powered boat and wondering what options I would have to increase the range past the 20 nm range published. Is there a hydrogen fuel cell that could provide enough power to run her at 5 knots continuously? how about a portable generator?
The plan would be to only go if I could sail but we all know there are days with no wind and we have to get home....
Youíre looking at it from the wrong angle. To extend range? It is an auxiliary motor, for long range you hoist sails. If you want to power then diesel as primary propulsion direct or as diesel-electric is the answer but now weíre not talking about sailboats anymore.

On maximum power output: this is for emergencies short duration only. For sustained use a small genset powering an electric motor develops enough power to keep moving.
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Old 22-09-2019, 09:06   #65
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Re: serious discussion about electric power in large boats

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Originally Posted by StuM View Post
He said "up to 300 w/hr".

So did he mean that you would see "up to 300 watts" or "up to 300 watt hours" in a specific period of time. Per hour? Per day?.

Assuming "per hour", there is a big difference between the two. If you are getting "up to 300 watts", you can be fairly certain that you will get a lot less than 300 watt hours over an hour. If you get 300 Wh per hour, you will certainly see more than 300 W at times.
My perception of the post was that when that particular boat was sailing at hull speed it could be expected to be able to realize a regenerative output of about 300 watts and of course, the unit of time thence being a factor; just substitute the amount of time sailing at hull speed with the propeller providing the torque power source, rather in similar fashion to be like the time spent charging from shore power at the same wattage input. So if one is on a long passage with a good breeze, one could replenish the batteries at the specific example of 300w/hr rate, such that there could be stored energy for use in propulsion at a later time, e.g., upon need for docking, or short distance of motoring, or motor sailing.

I haven't run the numbers as to the rate of power consumption as it ramps up with boat speed, [obviously very much specific to a given boat design, size and loading] but I suspect it MAY become somewhat similar to the power demand of pumps, blowers and fans, in that the power requirements will increase exponentially with rpm.

For changes in pump speed with a constant impeller size, the affinity laws are:

1. Capacity varies directly with the ratio of the change in rpm.

2. Head varies as the square of the ratio of the change in rpm.

3. Absorbed Power varies as the cube of the ratio of the change in rpm.



That is to say I'm not sure if a boat's power requirement curve follows the cubic curve of the affinity laws. My experience has been in developing electric propulsion motor systems for terrestrial applications, eBuses, eTrucks and eLight Vehicles, and with replacing motors and generators used aboard US Navy ships for various accessory applications and for supplemental ship board power generation. For terrestrial applications windage becomes the major load ramping associate with speed, that and steepness of climb of the roadway, [having to accommodate a 15+% grade with a heavy goods vehicle certainly pushes the torque requirement envelope].

Hmmm, I am now wondering if there is an approximate equivalency of Head and rpm for pumps and a boat's climbing out of is displacement hole as to hull speed. i.e., a square function as to power.

With boats hull speed, climbing out of its own displacement hole in the water is a major added factor which doesn't seem to have an direct equivalent to terrestrial travel, but which must be likely climbing over a steep pitch of roadway until the roadway then levels back out sort of like when the boat then goes on plane instead of remaining in and trying to climb out of its displacement hole.

Need to do some googling to research the math involved.

One of the primary methods of hugely reducing the greenhouse gas emissions of cargo ships is to slow the transit speed drastically and that is what is expected to become mandated as to fleet fuel efficiency standards [most likely a emissions level per unit of cargo weight so as to avail all means and technologies to derive benefit based on a common goal]. The International Maritime Organization, the United Nations and member States are actively discussing how to drastically reduce fuel consumption in the maritime transport sector [and yes there are discussions of including sails on large ships again, albeit most likely rotary sails]. The growing general consensus within the marine sector is that cargo ships will transit at perhaps half or even quarter of their historical average fleet speeds. The physics simply require a low speed of travel. Of course, longer time periods of voyages will put a lot of emphasis and motivation for greater automation and even towards autonomous operation of cargo ships, so as to minimize the on-board crew staffing and related human costs of operation. The likely will come a stage of near autonomous ships wherein their still be engaged a pilot and helmsperson and lookouts and dock line handlers when the ships near port, but may be near crewless in the open seas; crewless but not clueless.

Electrification of transportation is a growing sector, eMarine being considerably more challenging load requirements and self derived power source.
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Old 22-09-2019, 10:13   #66
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Re: serious discussion about electric power in large boats

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I wish the OP had told us what he hopes to gain by going electric.

It does NOT help climate change. Thatís because charging batteries from shore power is from carbon fuel burning power plants. Because about 30% of utility power is lost in the grid and then more lost in battery charging, a modern diesel in a boat emits less CO2 than the shore power route. And if you pay for electricity by Kwh, electricity is more expensive than buying diesel in most of the country.

As utilities switch to wind and solar this will change - but not really for 10 years+

Using a genset for diesel electric is even worse because it converts energy more times - under Newtons law, energy is lost in each conversion. A diesel propulsion engine is directly connected to the shaft. Energy loss in the transmission is insignificant.

A diesel genset first makes electricity in a fairly inefficient way, then loses part of that in the wires and controllers, then loses more in the motor converting it back into rotational energy to turn the shaft. You will buy more diesel and emit more CO2 with a genset diesel-electric than a direct coupled propulsion engine.

You simply canít fit enough solar panels on a live aboard cruising sailboat boat to make a meaningful percentage of the energy required for motive power ó unless you only run the engine maybe once a week. Thereís too much shade from mast and rigging. Itís difficult enough to find space for enough panels to just provide 100% of the hotel loads using solar panels. Little is typically left over for an engine.

If you only run your engine once a week OR only go a mile or two OR have a mast-less flat top power cat totally covered in solar panels ó Then solar generated motive power can work.

Your bias is showing. First of all, large scale power generation is very efficient compared to small marine diesels. Also relatively clean, under current regulations, compared to a small marine diesel. Your diesel has a lot of parasitic load just from turning the engine. At idle, you are still consuming power. And you are usually doing so outside the most economical and efficient power and rpm range. A WELL DESIGNED diesel/electric setup mitigates this a lot. Enough to make it more efficient than straight diesel? Of course not. But not as bad as you seem to think. Also marine transmissions do indeed soak up considerable power. Turn one over by hand some time.



As well, you are ignoring the savings from operating a charging generator at its most efficient power point. Enough to make it more efficient than direct drive? NO. That is, if the diesel, transmisson, prop, and hull are properly designed to work together at peak efficiency and used at the most efficient power point. This does not happen in practice. Practically all sailboats are vastly overpowered. This is done for various reasons, some of them with a logical basis, but the fact remains that you spend an awful lot of time sailing at 3kts and an awful lot of time attempting to break the hull speed barrier with your diesel, if you are like most boaters. Or else you are running it at dead idle, hoping to save fuel, but killing your engine with undertemp underpower underspeed operation and having parasitic loads comprise a higher portion of your power input. An EP system suffers no loss of efficiency running at low speeds. How many boats have you seen where the diesel at IDLE sends the boat downrange at 3.5kts? EP has no minimum idle speed. Parasitic loads are extremely low. Spin the shaft of a large electric motor some time. Try that with a diesel, even with it decompressed or the injectors pulled.



You are very much looking at this thing one sided. In reality, EP is not the best option for the vast majority of larger sailing boats, but neither is it a joke. I will say that it is folly to pull a perfectly good diesel and replace it with electric, but for an old beater boat with no engine or a dead one, a WELL DESIGNED EP setup could be an answer, rather than installing a diesel costing 3x what the boat is worth, or a used engine that was often someone else's problem that they were glad to be rid of.



The worst thing about EP is the unrealistic expectations of stars in the eyes wannabe converts. The second worst thing is the crowd who refuses to look at it objectively and simply distrusts or fears or suspects or hates it due to unfamiliarity with efficient EP design.



My big boat has a long in the tooth Westerbeke/Perkins 4-107. I call it "The Westerbeast". Yeah it oozes a little oil out the rear seal. It smokes a bit until it is warmed up. But it starts in a second and while it is no fuel miser, it doesn't break me to motor out from marina to Lake Pontchartrain, then motor under the bridges and out the Rigolets to the gulf. As long as it continues to serve, I will lovingly care for The Westerbeast. When it dies once and for all and can no longer be rebuilt for whatever reason, I COULD go electric and I know I can make it work for me, from experience. I also know that a Beta diesel is probably the better choice for me, all things considered. Not a fanboy exclusively of either system though both can be engineering marvels.
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Old 22-09-2019, 10:29   #67
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Re: serious discussion about electric power in large boats

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Originally Posted by GrowleyMonster View Post
You would not use 30kw, normally, unless you usually run your diesel wide open. Also there is no minimum speed or power output level for electric drive. Yes, EP has serious issues when you get into larger boats but it is not as bad as you seem to think.



Probably the ideal setup for a larger boat is to have a diesel AND electric motor. The diesel couples to the prop shaft in the conventional manner, through a marine transmission. The electric motor couples to the shaft via belt and pulley system. With diesel disengaged the electric is free to power the shaft. Or free to produce power from the trailing shaft when sailing at higher speeds. When a boat is pushed to hull speed, there is no speed penalty from increasing drag by loading the motor in regen mode. When sailing at reduced speeds there is a speed penalty from regeneration but it is not a dealbreaker. With the diesel engaged it can turn the prop in the normal manner and depending on where you have set the regen control, either the motor adds a bit of load to the shaft as it produces electricity, or adds virtually no load to the shaft and produces none. What this type of hybrid operation gives you is first of all flexibility. For maneuvering, the electric is superior. For "power tacking" and dodging floating objects and other things, it is a marvel. Instant torque, no minimum idle so no "bumping" in and out of gear. When long legs are needed, the diesel is used. Another advantage is being able to harvest and utilize "free" energy. A big boat maxed out with solar panels can give you a lot of charge. Regen is a big help, too. It is like finding cans of diesel fuel floating around in the sea. The big bank has other uses, of course, besides propulsion.


Such a system is too complex for the typical boater, maybe. That doesn't mean it is not a viable system, and workable for those who are willing to learn more about batteries, electricity, motors and controllers, etc, and who can live with the various tradeoffs.



Am I recommending EP for just anybody with a 40'+ boat? No. Especially not "pure" electric. Serial or parallel hybrid makes more sense for larger boats, and even there, it is definitely not for everyone. In a series hybrid a diesel generator powers the motor electrically, and a battery bank is used for backup or short duration use of the motor but is not an essential part of the power train. The parallel type system gives more flexibility and better performance. The series hybrid has the advantage in simplicity. Neither are more efficient than a straight diesel system unless you also harvest significant "free" energy. A 250w solar panel is not significant in this context and I would say the opening amount of solar would be 1kw.


There are sailors who basically never motor except when docking. For them, pure electric with no diesel might be practical if they do not cruise in any serious definition of the word, and they have easy access to the sea.
+1 agree with what you're saying.
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Old 22-09-2019, 10:52   #68
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Re: serious discussion about electric power in large boats

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No, the two phrases only are different in literal terms.

In practice, exactly the same meanings.

An average of 100W yields exactly 100Wh per hour, by definition.

Pedantic, didactic hysteria just drives potentially valuable members away. There are ways to gently correct without insulting.

And for the umpteenth time, not an EE!
They didnít say Wh, or watt hour, or kilowatt hour. They said watt/hour.

I think whatís happening here is that you yourself donít quite understand the meaning of multiplication and division within a numerical unit (but please, trust someone who uses them and whose posts correctly describe them: These operators are critically important for even the *most basic* arithmetic involving units. Correcting such errors is therefore hardly pedantic) Please see my mph and amp hour examples for clarification.
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Old 22-09-2019, 10:55   #69
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Re: serious discussion about electric power in large boats

GrowleyMonster,
as usually, good point.
As for 'dirty ecological' elctricity: My 25ft have a 250W solar panel, 6 kWh (usable) lithium battery and for 5 month in year I able to recharge my battery from zero to full during 5 work days and use EP at weekend. Typically I do not use shore power at all.
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Old 22-09-2019, 11:26   #70
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Re: serious discussion about electric power in large boats

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Originally Posted by SwellGuy View Post
They said watt/hour.
Which everyone agrees is nonsensical. However, in the context, what they meant was either watts, or watt hours per hour, which are equivalent.

Therefore the actual meaning was clear afaic.

A unit of rate like watts or amps "held over a period of time" is not multiplication.

Saying "300 watts **for** one hour", in other words "300 watt hours" involves none of your operators.


> Correcting such errors is therefore hardly pedantic

The **one** member doing so in a gentle and kind manner only **once** is perfectly fine.

That is not what's happened here.

And using such an error to impugn the entire credibility of an experienced poster is IMO really beyond the pale, and counter to the interests of this community.
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Old 22-09-2019, 11:36   #71
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Re: serious discussion about electric power in large boats

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Originally Posted by danstanford View Post
Sorry if this has been covered elsewhere, but the various unit descriptions make it very hard to make assumptions. Looking at a 6kw Oceanvolt powered boat and wondering what options I would have to increase the range past the 20 nm range published. Is there a hydrogen fuel cell that could provide enough power to run her at 5 knots continuously? how about a portable generator?
The plan would be to only go if I could sail but we all know there are days with no wind and we have to get home....
No, without a powerful genset on board, an electric engine will only have a very limited range.

Only suitable for short runtimes getting in and out of your shore slip / mooring.

Basically daytrippers, or sailing-only cruisers with no schedule, i.e. who don't mind waiting days or weeks for solar to deliver another few hours' runtime.
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Old 22-09-2019, 12:00   #72
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Re: serious discussion about electric power in large boats

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Originally Posted by zloitapok View Post
GrowleyMonster,
as usually, good point.
As for 'dirty ecological' elctricity: My 25ft have a 250W solar panel, 6 kWh (usable) lithium battery and for 5 month in year I able to recharge my battery from zero to full during 5 work days and use EP at weekend. Typically I do not use shore power at all.

Nice. I like it. Would be a perfect boat to keep on a mooring ball. Totally self sufficient.
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Old 22-09-2019, 14:44   #73
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Re: serious discussion about electric power in large boats

Just wondering,
Would a large capacity propeller driven Regen system charging under sail create much Heat and Noise?

If noisy, for me that would ruin the joy of sailing.
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Old 22-09-2019, 15:35   #74
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Re: serious discussion about electric power in large boats

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Originally Posted by john61ct View Post
No, the two phrases only are different in literal terms.

In practice, exactly the same meanings.

An average of 100W yields exactly 100Wh per hour, by definition.

That's at least the second time you have equated "average" and "up to". They have very different meanings and consequences.

I repeat "Up to 300W/hr" can be intrepeted in two very different ways. It will not get you 300 Whr/hr if the poster meant 300 W and will require considerably more that 300 W at times if he meant 300Whr/hr



I guess you are one of those who fall for the "Sale - up to 70% off" signs and then can't understand why everything you look at is only marked down by 10% (Hint: You'll find the one item in the store that is actually marked down by 70% in the most hard to get to location.
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Old 22-09-2019, 15:43   #75
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Re: serious discussion about electric power in large boats

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Originally Posted by john61ct View Post
A unit of rate like watts or amps "held over a period of time" is not multiplication.

Saying "300 watts **for** one hour", in other words "300 watt hours" involves none of your operators.

Sigh, I can explain it to you, but I can't understand it for you.



A unit of rate like watts or amps "held over a period of time" IS multiplication.


200 watts **for* two hours is 200 x (multiplied by) 2 = 400 Wh.


Exactly the same as 5 knots for 4 hours IS 5 x 4 = 20 NM.
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