Gemini 105mc conversion Diesel to EV?

[bouncycastle]

[QUOTE=harlem24;3031017
SNIP

What I don't get is, what are you talking about engergy conversion? An electric motor has an efficency of over 95%. If you lose 5% in transmission, then there is 90% usable power at the prop. Compared to about 25-30% you get out of an ICE...

[/QUOTE]

Unfortunately this planet consists of the laws of Physics and the sales reps selling you an idea

A boat with either sails or ICE or Electric will have parts and components and modules that have maxim efficiency of some sort and non of them will be 100% efficiency. If one component has 50% efficiency and pass that to another part that has 80% efficiency the sum of the components is something like 40%

In a electric system the battery will have from 50% efficiency to 95% depending types and temperatures and other factors

Lithium types like LiFE and LiPo tend to be able to give back 90% to 95% of this power that was given to them in the charging in IDEAL conditions and temperatures and there are leakage of charge over time a few % daily or monthly depending on factors

Lead acid types tend to only give back 70% of the power that was given to them and then leakage and temperature can easily send this south of 50%.

So if we take a lead acid battery with 50% of the original charge available then the electric motors 90%efficiency is gonna be something like 40% efficiency in this drive train

Most electric motors will get their power from a battery which will pass the power through a Speed controller and heavy duty wires and there will be losses often about 25% before getting to electric motor. That will tend to mean the Elric more will give at best 90% return of this 75% power and often its more like 80% depending temperatures work loads RPM etc . So a simple drive train to the engine can look like 60% returns after the battery and speed controller and electric more have done their things

Then there are the factors like shaft to props which suffer friction losses and the propellers which are often at best 60% efficient

So taking total energy in versus total energy out we often find that ICE solutions tend to be from 3% to 8% global efficient with their fuels

Electric combinations when all factors are combined we tend to find that Global efficiency vary more depending the quality of equipment from figures of 5% for lead acid solutions to highs of top end state of the art Tesla type lithium solution returning north of 25% but average real world stuff with lower power density LiFePO4 is more like 10 to 12%

In most drive chains each component will be at its best efficiency at some exact speed or RPM or workload

Often in drive chains each components best. efficiency is not the same as the other requirement to suit the other components so these other components will reduce the global. efficiency.

Then the other factor that impacts electric solutions is the cycle life of a battery which means we have to factor in the costs per charge in electrical costs and battery replacement costs and those number tend to expose electric power chains costing 5 times as much per mile than diesel fuel solutions

Hope that helps

[bouncycastle]

Originally Posted by mikedefieslife

My cat is 4.500kg fully loaded so similar to Gemini. I have a 29hp Yanmar and a 16/14 prop. In 30knts on the nose the boat will do about 3.5-4 knts. In lesser winds 5knts isn't a problem. The issue is more the waves. Even as low as 16knt winds can produce waves the boat crashes into and drops from over 5 knts to 2.8knts speed, then accelerates, then hits the next one hard enough to try to rip fixtures off the walls.

Excluding those events, fuel economy is roughly 2.5l per hour. The tank is 125l but you can only get 100l in there, giving a range of 200nm miles.

If went electric, I would want a minimum of two 15kw motors, for rougher weather, and would want to run them at close to full speed. At that rate I'd need 10 times the LFP bank I already have to run the motors for an hour.

That would weigh 200kg plus cables. My current engine weighs 141kg and the fuel 60kg.

Thank you this reply of your supplies Lots of useful data to show the real story


I shall start with two ICE powered mono hulls of similar length about 28 feet

The first one is 3 ton 27 foot long fairly wide 1970 3/4 keel in calm conditions with 9HP SAAB uses 1/3rd Uk gallon per hour ~1/55 litres per hour and does 5.5 knots 100% flat out

The second craft is 4 ton 30 feet long pretty narrow 1968 boat 3/4 keel in calm condition with Yanmar 18 HP at 1800 rpm about 60% throttle doing about 5 knots uses 1 liter per hour

Using the fudge number 0.4 laters per ton per hour the heavier craft comes out ahead than the lighter craft . The engines and props are the factors . The bigger engine running at 60% gas giving about 8 HP uses less fuel than the smaller engine flat out giving about 8.5 HP .

The narrower hull has less skin friction
The bigger boats water line speed is marginally greater
The bigger boat goes a tad slower saving fuel

If we wanted to figure out the power required to push these boat we could tow them and using a spring on the tow line that showed the KG force r on the tow rope we can figure it all out

The Kilogram weight the sting reins at different speeds will show how many watts of drag the boat create at different speeds .

The graph would be EXPONENTIAL TYPE and show something like 2 kilowatt required to tow both types at boats at close to their maxim water line speeds of ~6.5 knots say ~95% speed and ~8 kilowatts to tow them at speeds of ~7 knots the near 100 % speed .

However at middle of the water line speed like ~3 knots we would find that 25% % the power is needed or about 500 watts . As we go slower such as 2 knots 200 watts would be required

These are all NET amounts and show speed is not LINEAR


So a 9 HP engine with 5% global efficiency delivers 500 watts NET
So a 9 HP engine with 10% global efficiency delivers 1000 watts NET

We can Probaly assume the 8HP boat at 5.5 knots is probably global efficiency of ~9 % due to good BIG non Folder twin bladed prop high reduction box low RPM prop .

Because the 18HP engine boat is producing only the same 8.5 HP but using slower speeds and has longer water line and more narrow hull its global efficiency is higher probably ~12% also with non folder big two bladed prop.


Modern very wide cruising boats with larger skin drag can expect the global efficiency to be less

Modern inline diesels engines with multi injection can expect efficiency global efficiency

The fuel used and required is component of DRAG from hull Drag from wind Weight and Hydrodynamic shapes boat trim etc ,

However towing boats is hard work so we can with computer programs calculate the forces and power requirements with often a ~98% accurate results for calm water results .

These computer programs start to fail with rough water predictions

Taking your cat some 4 tons we can say it really two very narrow boats with 15 HP engines each hull has weight of 2 tons

Runing the numbers 5 knots and 2,5 later per hour divide by 2 we find the the ratio 0,4 liters per ton has been exceeded by some factor
The flaw here is the single leg prop is large prop close to surface and instead to return the good 60% prop effecientcy it is probably less than that . The drag from the egg also creates extra drag similar to a a extra half of a hull in skin drag
A s Prop of this size is very big in prop terms and would return best efficiency at slower speeds probably 3 to 4 knots
Putting a smaller prop might help improve fuel figures at five knots but the impact against head winds would be more dramatic
All props are compromise much like the gears in a car
High gears in car good fuel MPG low gears bad MPG
However steep hill high gears bad results so gear down
Same with boats strong head winds require prop that has more push like low gears have

A better prop under one hull can return better fuel figures but risks to be damaged on ground strike and worse add lots of drag when not working unless it is folder prop . Often the folder props will not be so efficiency thereby removing the advantage to put prop under the boat to deeper water

Hope that helps

[mikedefieslife]

Originally Posted by harlem24

Posted some YT channel who are 100% electric, but all monos.
Sailing Uma, rigging doctor, Beau and Brandy sailing.
Uma and rigging doctor both crossed the atlantic without problems.

What has crossing the Atlantic go to do with electric motors though when on a sailing vessel? Pretty much all sailing vessels sail across the Atlantic both ways, unless they have unforeseen issues. Uma's recent crossing only saw the electric motor ran when they needed to tack, and when they were testing the new throttle.

Of course saying that, I do know of a Lagoon that motorsailed the whole way and suprised a few people in the ARC when it turned up first. Until they checked the engine hours that way

I would be more concerned about costal sailing and island hopping. I do love the idea of electric, though especially on a larger boat with a big diesel generator for when things get gnarly. Of course, it could be said if you have to burn diesel might as well burn it for propulsion instead, but having the generator would just be more of a back up/failsafe.

I still maintain though on a gemini you could have both an ICE and electric motor happily living side by side.

[harlem24]

Originally Posted by bouncycastle

Then the other factor that impacts electric solutions is the cycle life of a battery which means we have to factor in the costs per charge in electrical costs and battery replacement costs and those number tend to expose electric power chains costing 5 times as much per mile than diesel fuel solutions

Hope that helps

When I take a look at what maintenance is to be done on an ICE on a boat and what can go wrong/break, I am not so sure about the costs.
But hey...

[StuM]

Originally Posted by bouncycastle

Anyway 36 USA gallons converted to kilos to KWatts energy and estimate 5% of that power makes some 55 KWatts useful power to the boat
2x12 KW electric packs makes 24 kilowatts and with energy conversion estimate 10% makes 2 .5 kw useful, power to the boat .

You are VERY confused. You can't just mix power and energy like that.
And you can't take "total lifetime efficiency" and apply it to a single part of the life cycle.

To take it to more practical terms:


Using the common rules of thumb for marine auxiliary diesel engines of 1 gal per hour per 20 HP

36 USG of diesel will provide roughly 700 HP hours. or 500 kWh of propulsion energy.

2 x 12 kWh batteries will provide 24kWh. Assuming a realistic 90% efficiency in converting that to propulsion energy, that's about 21 kWh of propulsion energy .

[StuM]

Originally Posted by bouncycastle

So a 9 HP engine with 5% global efficiency delivers 500 watts NET
So a 9 HP engine with 10% global efficiency delivers 1000 watts NET

Once again, you can't just do that.


9HP is the rating of the engine, not what it is generating at a specific RPM in specific circumstances.


A 9HP engine at WOT will generate around 9HP of propulsive thrust (what you would have to call nearly 100% efficiency). That's why it's call a 9HP engine.



Running at 50% of max RPM, it will probably deliver about 1 HP ( what you would call 10% efficiency).


DO you really get 10 times the efficiency running flat out?

[bouncycastle]

Originally Posted by StuM

You are VERY confused. You can't just mix power and energy like that.
And you can't take "total lifetime efficiency" and apply it to a single part of the life cycle.

To take it to more practical terms:


Using the common rules of thumb for marine auxiliary diesel engines of 1 gal per hour per 20 HP

36 USG of diesel will provide roughly 700 HP hours. or 500 kWh of propulsion energy.

2 x 12 kWh batteries will provide 24kWh. Assuming a realistic 90% efficiency in converting that to propulsion energy, that's about 21 kWh of propulsion energy .

Yes you can mix power and energy like that more info below
Yes you can take total life time efficiency and apply it to single part of the life cycle more info below

Confusion reins supreme in the world of rules of thumb whos thumb is the measure

The rule 1 usa gallon per hour for each 20 HP
On a need to know basis it works for average cruising boats cruising in reasonable weather

There is no real data from this rule of thumb on weather boat types speeds all sorts of factors that can make the rule fall apart

Many rules of thumb are iffy at best

In a hurricane going against 50 knot head wind and boats cruising speeds are knocked to close to zero knots often means you might need more like 100 gallons to 20HP so the rule falls apart

In a hurricane going with a 50 knot tail wind cruising speeds are exceeded and engine has hardly any RPM means you might only need more like 1 gallon to 200 HP so again the rule fell part

All energy can be measured very very exactly given all the data speed weight time etc
If the data is not exact examples like plus or minus 50% then the results will risk to be close to useless

So most energy is measured in egg head world laboratory in terms of JOULES and then converted into other energy forms like Watts amps horsepower newton kilos etc

So it is possible to convert Diesel fuel into watts but its not normally done to turn it into volts and amps even though volts multiplied amps makes watts

Electric power from battery can be turned into watts and volts and amps and horsepower but not so easy to turn it into fluid onzes or gallons or kilo newton force equivalents.

As a example There exists ( mtoe ) metric ton oil equivalent to replace electric power generated by coal or gas or hydroelectric power or nuclear power .
Yes we can measure watts power from any source compared to oil or coal or solar power


However most every type of energy can be converted to JOULES but then if I do that in this forum I could lose the people reading the thread because most sailors would not know a JOULE from a dead fish that fell onto their head from the sky

That means when I convert battery watts to horse power I can use the simplex systems 750 watts equals one horsepower instead to convert everything into JOULES

If your not used to converting energy then comparing electric watts power to horse power is gonna be problem.

Example
One boat goes with 35% efficient diesel engine in calm waters top speed full throtle at 10 knots and the global efficiency of the fuel burn to distance covered is 5%
The same boat another day goes the same journey with 35% efficient diesel engine into strong head winds full speed full throtle but can only get 5 knots forward speed and the global efficiency of the fuel burn to distance covered is 2.5% because the same boat had to use twice the time and twice the fuel to go the same distance as the first journey .
The same boat another day goes the same journey with 35% efficient diesel engine with strong tail winds full speed full throtle but can get 20 knots forward speed and the global efficiency of the fuel burn to distance covered is 7.5% because the same boat had to use the half the time and half the fuel to go the same distance as the first journey.

We can infer a rule of thumb this diesel engine is always 35% efficient when it goes flat out top speed but we don't know it's horse power or its tourgue and its efficiency at a Lowwer RPM and worse we know nothing about the boat it is attached too

Therefore this data above is of marginal to possibly no benefit to us .

The above data allows us from three journeys to infer a rule of thumb that the certain type of boat with that certain type of engine has a average global efficiency of 5% but its suspect information with only three journey data base used

If we did 3000 journeys and the average global efficiency of fuel use global efficiency was 5% we would then be more able to infer that most results of this boat with this type of engine will be global efficiency of 5% plus or minus 50% (so global efficiency maximum is 7.5% and minimum is 2.5% )

We still don't know the Horse power or type of boat or distance traveled or energy of fuel or force of wind in knots but the important detail we do know the global efficiency if that information is needed .

We know more than the information the engine is 35% efficient
which is not a lot of useful information as all journeys including running the engine at zero speed the engine is always 35%

Many experts over time have accumulated lots of useful data on marine engines coupled to many types of boats in many sea conditions.

These experts vary in their rules of thumbs on the subject of global efficiency of boats with marine diesel engine but most would agree it is some where between 2.5 % to 10% for most small boats and higher for larger ships due to economy of scale .

Sales reps selling you a marine engine need a useful number for them to sell so they will look the highest efficiency number they can find and if it is 37% for a modern diesel engine versus typical petrol engine 25% that sells it is a no brainer diesel is so much better

A sales rep could maybe tell you the global efficiency of the petrol engine version on that boat is 4.5% costing $ 50000 versus the
Diesel engine version higher global efficiency of 5.5% costing $ 60000

Now you can figure out how many hours of engine use over so many years will it take to break even and be ahead of the game if you buy the Diesel engine version costing $10000 extra with a minor better global efficiency rate


As sales reps prefer a easy life it is more easy to give you a near useless number diesel 37% versus petrol 25% and get you to fork out the extra cash with Mumbo-Jumbo numbers called dales pitch numbers

Its also with life cycle for resale more easy for sales rep to show the idea the diesel engine version of the same boat retains its resale price better but you got to pay more to get more

This resale factor is sales pitch on cycle life. How true this data is again suspect


Batteries have various important factors cycle life, amp or Joule storage , real use able power , safety, recharging times, recharge efficiency , discharge efficiency , cost per unit cist per power unit to charge and discharge, robustness to misuse and temperature to big to cover here all these facts today

All chemical batteries types suffer one big flaw if you demand continuous high work loads versus their capacity in amps their efficiency tends to be seriously reduced
Light loads on most battery types will often return the highest efficiency.

A typical LiFe type battery will have maybe 95% return of the power in efficiency with light loads and can drop to lower than 90% with high workload demands
Cycle life of the battery will go from as high ad , 4000 cycles if the cycles are shallow like 50% DOD depth of discharge . Continuous 100% DOD the cycle life will be greatly reduced often to less than 1000 cycles
We can calculate the cost ratio benefit buying larger capacity battery so as to increase cycle cost ratio

A typical lead acid battery when we factor in all the above data for these types we find that often the lead acid types cycle costs per cycle are four times larger than the LiFe types even though the lead acid types costs are often four times cheaper per amp equivalent than LiFe

So yes we can measure individual cycles versus life cycles for batteries

2 times 12 kW battery will equal 24 kW of power to start with.
If the specifications of the battery shows at the normal work load discharge rate that it can deliver ,90% the power the a maxim of 90% of the battery power is available to be used much the same as we can say a 90% full gas tank has the potential to deliver that much fuel energy .
This is merely the measuring of the battery one component and not the entire drive system .
This would be a typical sales rep sales number

This electric power from battery now ,90% will go through wires and suffer losses from heat and Resistance .We would expect 5% losses

Then the power now 90% reduced by 5% will go through speed controllers and suffer losses often from MOSFET duty cycle issues . Typical losses are 5%

Then the power now 90% reduced by ,,,,5% reduced by another 5% will through electric motor and suffer losses best vibration etc. Losses of 15% tend to be the real expected losses

Then the power now 90 %. Reduced by 5% then reduced by 5% then reduced by 15% will go though shafts to propeller and suffer losses . losses from craft with water seals resistance make 5% losses the normal

Then the final drive of the propeller will duffer losses often more than 40%

So when we figure the total losses we find that final global efficiency can be as low as 5% and rarely can attain more than 40%.
Lower cost simplex electric power systems will tend to return global efficiency of about 10% and higher cost versions would expect to return global efficiency number closer to ,20%

So we could say many 24 kilowatt electric power units will at ,10% global efficiency return 2.4 kilowatts of final power in the real world

The sales rep will be stuck on the upstream number 22 kilowatts

[Matt Johnson]

Originally Posted by bouncycastle

Boat3








The rule 1 usa gallon per hour for each 20 HP
On a need to know basis it works for average cruising boats cruising in reasonable weather

There is no real data from this rule of thumb on weather boat types speeds all sorts of factors that can make the rule fall apart

Many rules of thumb are iffy at best

In a hurricane going against 50 knot head wind and boats cruising speeds are knocked to close to zero knots often means you might need more like 100 gallons to 20HP so the rule falls apart

Nowhere in his quote did he state a speed of the boat. His statement was that a diesel engine consumes 1 US gallon to make 20 hp for an hour. How the 20 hp is used doesn't matter or change what he said. The engine could be in a car, spaceship, log splitter or boat.

If a 40hp engine is loaded and spinning at an RPM that produces 20hp, it's roughly using 1 gallon an hour.

Matt

[StuM]

Originally Posted by bouncycastle

In a hurricane going against 50 knot head wind and boats cruising speeds are knocked to close to zero knots often means you might need more like 100 gallons to 20HP so the rule falls apart

In a hurricane going with a 50 knot tail wind cruising speeds are exceeded and engine has hardly any RPM means you might only need more like 1 gallon to 200 HP so again the rule fell part

That's not even just wrong.

You clearly don't understand the concepts of power and energy, nor how a ICE works.

If you are just sustaining position against very strong winds, you will be putting out the maximum HP your engine can make. To make that HP requires the same fuel input regardless of whether you are using it hold against the wind or to motor at your top speed in calm conditions. In either case, You will still use roughly 1 gallon per 20 HP per hour (maybe 30% more because you are outside of the efficient operating range of the engine - but certainly not two orders of magnitude greater).

If you have hardly any RPM, you are generating hardly any HP, but whatever HP you are generating still requires roughly the same amount of energy (fuel) input per HP hour.

All energy can be measured very very exactly given all the data speed weight time etc
If the data is not exact examples like plus or minus 50% then the results will risk to be close to useless

So most energy is measured in egg head world laboratory in terms of JOULES and then converted into other energy forms like Watts amps horsepower newton kilos etc

Again, your lack of knowledge is revealed.

Let me put it into terms you may be able too understand:
To quote Ernie from Sesame Street: One of these things is not like the other things.

Watts amps horsepower newton kilos are not energy forms. (
(And they are not all the "same things" either)

So it is possible to convert Diesel fuel into watts but its not normally done to turn it into volts and amps even though volts multiplied amps makes watts

No, it is not possible to covert "diesel fuel" into watts.

Conversion of 1 liter of diesel fuel to energy can result in anything from 1 milliwatt or 1 megawatt of power.
(It's the difference between burning it all at once and drip feeding it to a burner)


Actually diesel is frequently used to generate power specified in volts and amps (That's how a 2KVA generator for example is specified).

Electric power from battery can be turned into watts and volts and amps and horsepower but not so easy to turn it into fluid onzes or gallons or kilo newton force equivalents.

If you mean "measured in" rather than "turned into", I agree. They are fundamentally different types of units.

As a example There exists ( mtoe ) metric ton oil equivalent to replace electric power generated by coal or gas or hydroelectric power or nuclear power .
Yes we can measure watts power from any source compared to oil or coal or solar power

No you can't. But you can measure watt hours of energy.

See above. 1 mtoe can generate ANY number of watts, depending on what time period you consume the energy over.

However most every type of energy can be converted to JOULES but then if I do that in this forum I could lose the people reading the thread because most sailors would not know a JOULE from a dead fish that fell onto their head from the sky

Actually, EVERY type of energy can be measured in (not converted into) Joules since that is the international standard unit of energy.

That means when I convert battery watts to horse power I can use the simplex systems 750 watts equals one horsepower instead to convert everything into JOULES

You can convert battery Watts to HP because they are both units of power. Again, you can't convert either to Joules because a Joule is a unit of energy, not of power.

And once again "battery watts" (or amps or volts) tell you nothing about how much energy is stored in a battery, it just tells you how quickly you are drawing energy from the battery.

If your not used to converting energy then comparing electric watts power to horse power is gonna be problem.

Since you clearly can't grasp the difference between energy and power, there is already a problem.

Example
One boat goes with 35% efficient diesel engine in calm waters top speed full throtle at 10 knots and the global efficiency of the fuel burn to distance covered is 5%
<snip>

Sorry, that makes no sense at all. 5% of what?

We can infer a rule of thumb this diesel engine is always 35% efficient when it goes flat out top speed but we don't know it's horse power or its tourgue and its efficiency at a Lowwer RPM

You are revealing your lack of knowledge again.

I have that data from my engines and for engines on many other boats.

Just about every marine auxiliary diesel engine manufacturer produces Power/torque/fuel burn data for the rated RPM range of their engines. Include HP at the prop for a suitably propped vessel.

and worse we know nothing about the boat it is attached too
Therefore this data above is of marginal to possibly no benefit to us .

I use that data every time I plan a delivery passage on a different boat.
For any particular boat it's not that hard to estimate HP requirements under various conditions based on LWL, displacement and a few basic design factors.

The above data allows us from three journeys to infer a rule of thumb that the certain type of boat with that certain type of engine has a average global efficiency of 5% but its suspect information with only three journey data base used
<snip>

More of this strange "global efficiency". Please explain in simple terms what you actually mean by it.

We still don't know the Horse power or type of boat or distance traveled or energy of fuel or force of wind in knots but the important detail we do know the global efficiency if that information is needed .
We know more than the information the engine is 35% efficient
which is not a lot of useful information as all journeys including running the engine at zero speed the engine is always 35%

If the engine is "running at zero speed", it must be 100% efficient since it will not be consuming energy"

[quote]
<snipped more rambling about these various "efficiencies">

Batteries have various important factors cycle life, amp or Joule storage , real use able power , safety, recharging times, recharge efficiency , discharge efficiency , cost per unit cist per power unit to charge and discharge, robustness to misuse and temperature to big to cover here all these facts today

Still the confusion between power and energy.
Yes, they store Joules.
No they don't "store' amps.
"real use able power" is largely irrelevant in a deep cycle marine battery. It is only important for very high draw situations, where it is usually specified in "cranking amps".
There is no such thing as a fixed "cost per power unit". Cost of charging (energy units, not power units) is solely dependent on the energy source you use to charge the battery.

[bouncycastle]

Originally Posted by StuM

Once again, you can't just do that.

You seem to have lost the real meaning of the statement so i will outline the logic again below this sentence

Originally Posted by StuM

9HP is the rating of the engine, not what it is generating at a specific RPM in specific circumstances.

A 9 HP engine rating means the maximum power of that engine at some maximum RPM is going to give you 9 hp

if you run the engine at any other RPM than the maximum RPM you will get less HP than 9 HP

A 9 hp single cylinder diesel engine will normally have a maximum RPM of 3700 RPM
The same engine will have a idle power minimum RPM of 700 RPM

Engines like this often come with a manual that often shows a HP power curve.

A typical power curve graph would show this 9 HP engine going from a low of 1 HP at 700 RPM to a maximum of 9 HP at 3700 RPM

At the mid throttle (not 3700 \2 equals 1950 RPM ) instead 3700 minus 700 equals 3000 RPM now devided by 2 that equals 1500 RPM mid gas we would expect to get half the HP being produced which is 4.5 HP .
However the power curve is not linear it is often curved and we might find that at 1500 RPM the mid gas position the engine makes 6 HP not the expected 4.5 HP .
Engines for many reasons tend to produce power curves rather than linear power graph lines.

When a 9 HP engine is switched off it produces zero HP

Therefore the term 9 HP engine cannot mean it makes 9 HP all day long even when it is switched off

Rating of a 9 HP engine is a loose guide term sales agents make to give you some idea what purpose you can put this engine too .
You can choose if your boat needs only 4 HP to choose to get the 9 HP engine and only use it at some lesser gas position to get the required 4 HP probably found at near to 1200 RPM

Originally Posted by StuM

A 9HP engine at WOT will generate around 9HP of propulsive thrust (what you would have to call nearly 100% efficiency). That's why it's call a 9HP engine.

Not exactly . Most diesel engine will never exceed 37% efficiency.
That means they waste some 63% of the diesel fuel energy as heat vibration noise etc .
A 9 HP engine is called a 9 HP engine because at its output shaft a measuring device has seen that the engine at WOT top speed top RPM produced 9 HP .
Often in the engine manual this is called shaft HP .

Originally Posted by StuM

Running at 50% of max RPM, it will probably deliver about 1 HP ( what you would call 10% efficiency).

Again this might be some mix up in terms
If a 9 HP engine is at 50% of the maximum RPM we from the power curve manual would probably find this equals about 6 HP .
Engines differ some might show closer to 5 HP at 50% RPM and others might show closer to 7 HP as all makes of engines differ in power outputs.
Some diesel engines might produce maximum HP of 9 HP at closer to 3000 RPM and other produce 9 HP at closer to 4000 RPM .

Diesel engines often come with a efficiency curve graph
Often the graph is some type of fairly flattened out type bell curve .
For example the engine might show at mid gas 1500 rpm the engine has peak efficiency of 30% .
However as the RPM increases or decreases the effiency curve might go down to 20% at slow idle RPM of 700 RPM and 23% at maximum 3700 RPM

Clearly the Most efficient use of fuel will be to run this engine at 1500 producing 6 HP which is ~ 63% of rated power of ,9 HP

However at 30% effiency that is only for the engine not the entire drive train .

If the global efficiency was 10% after all losses we would say that from the 6 HP the engine produced only 0.6 HP of power arrived to do the work to push the boat

In another example I did this one HP you refer to might be the global efficiency power that arrived from larger engine after all losses are calculated

Hope that clears it up for you

Originally Posted by StuM

DO you really get 10 times the efficiency running flat out?

Again I think there is some mix up in terms here

Power curve tables will generaly show most engines will produce the best efficiency around the 50% to 70% gas positions and flat out WOT will often produce less efficiency often up to 30% drop in efficiency in WOT use .

This does not mean a peak effiency of 30% at 50% gas position will mean zero % efficiency at WOT .

It means that there will be drop of ,30% on the peak efficiency of 30% which would drop the final efficiency to 20%.

From that info above we can see that if some engine says it is 37% efficient that does not mean it is always 37% efficient at every RPM . You need to check the efficiency curve graph to see what RPM will give peak efficiency of 37%

Hope that helps

[StuM]

Originally Posted by bouncycastle

Clearly the Most efficient use of fuel will be to run this engine at 1500 producing 6 HP which is ~ 63% of rated power of ,9 HP

However at 30% effiency that is only for the engine not the entire drive train .

If the global efficiency was 10% after all losses we would say that from the 6 HP the engine produced only 0.6 HP of power arrived to do the work to push the boat

Sigh.


The engine will be producing 6HP AT THE PROP SHAFT under your scenario.

Again I think there is some mix up in terms here

Ain't that the truth!

From that info above we can see that if some engine says it is 37% efficient that does not mean it is always 37% efficient at every RPM . You need to check the efficiency curve graph to see what RPM will give peak efficiency of 37%

Hope that helps

Doesn't help at all. Please post one of these mythical "efficiency curve" graphs and any engine data quoting a "37% efficiency".




Meanwhile, back in the real world. Here's the specs for one 9HP engine runniing at max 3600 RPM and producing 9HP of "propeller output power". At 1800 RPM it is producing about 1 HP of "propeller output power"


At a comfortable cruising RPM of around 75% Max RPM (2700), it's generating just under 4HP of that same propeller output power.







Meanwhile on the fuel consumption front, it's only burning about .1 gph at 1800 RPM compared to the 0.6 gph at 9HP

At 2700, it's burning a bit less than 0.3 gph/




To summarise those figures:


That little engine is getting around 10-15 HP per gallon per hour. But no way does efficiency in terms of power to rate of fuel burn vary by orders of magnitude over its operating range.



Not as efficient as the larger more common 30-50 HP found in a lot of cruising boats where the 1:20 figure is a better fit.

[valhalla360]

Originally Posted by bouncycastle

Yes you can mix power and energy like that more info below

.........

The sales rep will be stuck on the upstream number 22 kilowatts

Please take this in a positive way that it's intended...seriously consider brevity in your posts.

I haven't read your last few posts as they simply go on too long. Sometimes you need 4-5 paragraphs to get an idea across but in a forum setting a 4 page post...I tend to ignore and I'm sure most others do also.

[bouncycastle]

Boats 4

Originally Posted by StuM

Sigh.


The engine will be producing 6HP AT THE PROP SHAFT under your scenario.
Ain't that the truth!

Doesn't help at all. Please post one of these mythical "efficiency curve" graphs and any engine data quoting a "37% efficiency".




Meanwhile, back in the real world. Here's the specs for one 9HP engine runniing at max 3600 RPM and producing 9HP of "propeller output power". At 1800 RPM it is producing about 1 HP of "propeller output power"


At a comfortable cruising RPM of around 75% Max RPM (2700), it's generating just under 4HP of that same propeller output power.







Meanwhile on the fuel consumption front, it's only burning about .1 gph at 1800 RPM compared to the 0.6 gph at 9HP

At 2700, it's burning a bit less than 0.3 gph/




To summarise those figures:


That little engine is getting around 10-15 HP per gallon per hour. But no way does efficiency in terms of power to rate of fuel burn vary by orders of magnitude over its operating range.



Not as efficient as the larger more common 30-50 HP found in a lot of cruising boats where the 1:20 figure is a better fit.

The point of the thread is to expose the problems or advantages of converting a large cat with inboard to electric power

To show this it requires a fuller understanding of where rules of thumb come from and the risks to get it very wrong if you try to use the wrong logic .
Petrol heads have great ability to overestimate the ICE systems and spark heads equally suffer from blind spot over estimation of the power systems.

If the thread was ICE fuel consumption there is umpteen threads out there better able to cover this issue here is one with lots of rules of thumbs

https://www.boatingmag.com/calculati...suXV9uAfYU.03*



The above graphs supplied in post no #71 supply enough data to make your own fuel efficiency graph
We know the amount of fuel going into system at What RPM and the outputted power in watts or HP .

The engine alone graph is flattish and there is a drop off after about 3000 rpm but engines never work without to do work

There fore the marine gear curve is more useful and the best ratios look to be around the 2600 RPM for this engine using that size prop and gear box

From that graph we can work out the ratio s to show what amount of fuel gives the biggest bang in Hp for the buck spent on fuel

We can work out the % of fuel wasted as heat vibration noise etc and the thermal efficiency of the engine

Alternatively contact the manufacturer and ask them to twesk the graphs on their data sheets to give us these results

Alternatively put all the data points into a spread sheet and figure it out

What matters from these graphs is there is a peak efficiency probably at 50% point like 2500 RPM

However to get a real world result we need to attach this engine to a typical real boat such as a 3 ton 3/4 lenth keel skeg rudder 1970 era narrow sail boat

Then we need to in calm conditions measure the speed versus RPM and that will expose all the real data

If we assume that this 27 foot boat flat out WOT 9 hp does 6 knots the graphs when we run the numbers will tell us this boats global Efficiency is about ~4 % at WOT

The sum is simple total fuel in WOT is 0.6 gallons per hour convert its fuel energy in watts joules inputed versus work accomplished result three tons moved at 6 knots some 6 nautical miles

This tells me if I put a electric power solution that has global efficiency of 10% I need less power probably 4 HP or ~ 3 kilowatts to get the same speed 6 knots .

For all sorts of technical reasons this class of boat would perform cheaper and better with less power probably 1 kilowatt and less speeds like 2.5 knots using a electric power solution .

For all sorts of technical reasons this same boat would preform better for fuel consumption efficiency use using a 18 HP diesel engine at half gas position doing about 5 knots

All this can be figured out using computer calculators that have the right data

However as battery technology and solar cells etc improves we can with graphs predict that electric power solutions will most likely displace diesel engine solutions by ~2035 maybe sooner .


Getting back to this cat the best result for electric will probably be for large prop under one hull to push the boat at 2 knots.
One large prop is often more efficient than two small props.
Slow speeds return more efficiency than fast speeds and can often double the range of the typical battery pack solutions for modern boats .
Cover the boat in as many solar cells as possible to give more free power in day time and extend the range further

Carry a E teck outboard or some fuel efficient outboard for entering harbours where speed and power is needed for short range use

If going 200 miles plus at 6 knots is needed then for now it is probably best to get a suitable inboard solution either to replace the broken engine or to work alongside some non battery solar cell electric engine solution

Just my two cents

[harlem24]

Why the F would one go 200 miles with 6kn on motor?
We are still talking sailboats, aren't we?

[skipmac]

Originally Posted by harlem24

Why the F would one go 200 miles with 6kn on motor?
We are still talking sailboats, aren't we?

1. Traveling the ICW on the US east coast. Bad weather you can stay inside and still make time but you have to motor. I usually go inside around Hatteras since it seems like every time I pass that area a nasty front hits.

2. Long ocean passage, hit a large calm. You can sit in the middle of it for a day or three or more or crank up, motor away from the calm and get back to sailing. Can cut transit time in half on a long passage or you can hand out in the boat rolling in the swells waiting for the wind.