Are electric horses really bigger?

Gas and diesel usually have "advertised" power that is only useful drag racong or in a tractor pull.

Once you find out the REAL 24/7 output of a motor it can easily be less than 1/2 or 1/4 of the advertised.

An electric motor is usually industrial rated 24/7 is the norm.

Will a 3 hp electric motor out pull a 10 hp liquid fueled motor , not a chance.

But the 3hp IS available almost forever.

 

Good points.

 

Not really. Most electric motors are rated at start power consumption for sales purposes. Gas and diesel industrial/commercial engines that are rated at 100% duty are for running 24/7.

 

touche

 

My 3Gm30 engines are rated at 27hp for one hour and 24hp all day everyday. No where near half, and who even wants to run full power all day. How much power does your car have? How often have you used all the power and for how long? The peak power is useful and can be fun, but its not relevant you cant use it 24/7

 

we know there are standards for showing power output of diesel engines, what do the electric motor guys use?

 

It depends on whether you buy an industrial engine from a reputable manufacturer or something with creative specifications.

 

Sure but what iso/sae/ieee etc standards are there?

 

1HP=746J/s Anything else is sales hype.

 

Yer but you still need a standard to measure either unless your joule rating is coming from electrical consumption therefore your hp is a calculation from that and hence meaningless to compare to braked hp of engines

 

If it comes from energy consumption, then it is what they sometimes use to inflate the power rating for sales purposes. An engine or motor power rating is for output. Otherwise, if you use input, a really badly tuned engine would have a higher power rating than one that runs well.

 

"My 3Gm30 engines are rated at 27hp for one hour and 24hp all day everyday. No where near half"

It was designed as a boat engine , not a car or small truck marinization.
\
Different advertising requirements.

 

Sorta.

An electric motor can make maximum torque regardless of rpm.
An electric motor can make static torque, torque with no rpm.
Electric motors are rated in horsepower which is 1HP = 746watts based on input/draw. The output is then rated by how efficient the motor is in percentage. A 10Hp electric motor that is 80% efficient will have an output of 8Hp.

Successful applications of electric motors used in a loco-motive type arrangement are trains, hybrid cars, very large dump trucks.
The train engine and dump trucks benefit by having no clutch type of mechanism when applying power which would be disasterous.
None of the 3 use full power all of the time, just getting started/moving mostly, then as the load lessens the power requirement does too.

A planing hull might could benefit or an air entrapment tunnel/cat since the load goes down once underway. A displacement hull doesn't really get over a load "hump" does it, the power requirement is constant or increases as speed increases, no? I don't think a steady state power requirement arrangement would see the benefits as much.

 

Re 1) Efficiency is a method of qualitatively comparing one set of conditions/output to another and is unitless. There are perhaps 5 or more efficiencies that can be used in discuusing engine performance. Thermal efficiency - the amount of energy available from the fuel input if all the energy is extracted compared to the actual work out put
Volumetric efficiency- the amount of theoretical swept volume flow rate compared to the actual flow rate throuhgh the engine
Heat absorption efficiency - the amount of heat produced due during combustion compared to the amount of heat coming out the exhaust,
Compression efficiency- theoretical compression at one compression stroke compared to actual cylinder pressures at different rpm.
Carnot efficiency- cannot remember the relationship at this time

All of these change at different rpm and load

I expect you are referring to fuel efficiency but you need a base point and the actual consumption to be accurate

Fuel efficiency could be in this case the amount of of fuel burned per unit time to produce 100 hp then compare it to the amount of fuel burned to produce the same 100 hp at a different rpm

Or
Fuel efficiency could the amount of distance you will get out of one gallon of fuel at different speeds
Ie. At 20 mph burning 10 gal/ hour The base is 2 mpg. Compare this to the boat going 30 mph and burning 20 gal/hour and getting 1.5 mpg
The comment of the result would then be " it is 33% more efficient to run the boat at 20 mph"

To just say that an engine is most efficient at 50% of rated horsepower is vague

 

Re 3) if you hook a tow line onto a boat and pull it at a given speed you can determine the horsepower requirement for the hull. Say your expression "bucking a headwind" requires 100 hp

If we were to take a 50 hp motor and gear it to 2000lbft of torque, it will not move this boat at the same speed
Torque is the amount of a sustained twist that an engine can put into a shaft and is used to determine horsepower at a given rpm.

It is not a matter of torque