Estimating Electric Consumption

I think the "why" was about why would electric be any different here. Slow turning prop on a diesel setup is also more efficient.

Often the most efficient prop is not practical due to many other factors.

 

Nonsense. The fact that there is a clutch allows for slipping at an avoiding stalling. Diesel can be geared to spin exactly the same prop. The fact that very big wheels are not used is not beacuse of stalling. That is a bogus argument.

 

and some people think a kW or kWh would be different depending on the motor type. The largest difference is that the diesel will create 2-3x as much heat as shaft power.
However propeller doesn't care about the engine's cooling needs.

edit: for clarity's sake it is good to note that Captain Canuck removed several posts of his.

 

So at what actual hp could I run a typical 40hp outboarder as an example, reasonably without excessive engine fatigue or fuel use?

I'm curious if these claims of increased overall propulsion power efficiency (e.g. torqeedo claims 2kW can be equivalent to 5HP) are just BS or due to practical considerations in real life. Like it's just not practical or cost effective to match the motor torque and rpm to a gear box and propeller for typical outboarders.

If you had one specific outboarder could it actually deliver the max HP with different propellers? Or would different boat resistance and propellers lead to the motor not being able to use all it's HP? Simply because of mismatch of RPM / Torque and propeller.

It's clear in the ideal case there is no difference, but it would seem to me that in practice electric motors should have more flexibility to match for max propulsive power output while maintaining energy efficiency.

I'd love to hear your results Captain Canuck! I "want to believe" too

 

Torqeedo claims are totally BS. It has been shown in many tests that 2 kW Torqeedo is not even close to any 4-5 hp outboard in performance. It is outperformed by 2.5-3.5 hp models as well.

Torqeedo does have as high bollard pull as 5-6 hp, but boats move and bollard pull has no value for most of us.

40 hp outboard is designed to be used in a planing boat and will have high efficiency in that use. Typical propeller efficiency is about 70%.

If it is installed to a displacement boat, it will have rather poor performance due to very high prop rpm (typically about 3000 rpm) and propeller size optimized to thar.

 

You can run it at 40HP. If that is using too much fuel, you can use a smaller engine and go slower.