Are electric horses really bigger?

For the last 20 years or so all gas outboards must be rated at their shaft output. You could have a 200hp motor, but if only 5hp gets to the shaft then if you advertise it as anything other than a 5hp motor you will get Stephen on by the FTC and the USCG.

Electric motors can be rated any way they want, or just make it up, which far to many of them do.

The reality is that if an electric motor claims to be the same as a 5hp, then it really should be rated as 5hp at the shaft just like the gas one is.

 

What are you using for batteries? Battery capacity? What speeds are you operating at? Wouldn't your range be tied to battery capacity instead of motor kW?

 

Input power is from Voltage*Current. Shaft power is from RPM and Torque.

 

How you calculate power is irrelevant.

 

What do you mean?

Say an electric motor is advertised at 2kw, but its power at the shaft is only 1kw due to power label only measuring input power on a cheap electric motor. Which is the sort of scam you see in this industry.

Gasoline outboards have regulation as mentioned so a 2kw outboard has 2kw as the shaft.

Both are labeled 2kw but the electric has half the real world power of the gasoline. The regulators need to hold the electric outboard manufactures to the same standard as other outboards. So it seems the way its calculated is relevant.

 

So how can you support your comment that an electric motor is not rated at the shaft? Nema has specifications for applying a horsepower rating and it is usually based on the continuous duty service horsepower that the motor will provide at its designed rpm.

So if you are hooking say a hydraulic pump up to an electric motor, and the pump requires 2 hp input at 3600 or 1800 rpm, then you purchase the applicable motor.

But it is a 2hp electric motor (at a specified rpm).

Unless you are speaking of unscrupulous electric motor vendors, but it is unlikely that many could exist if they are taking input horsepower, ie kw and calling the equivalent input kw input the same as output??

 

We are talking about unscrupulous vendors. look at some of the sales material!

 

Yes, as long as it means propeller shaft power...

 

"Optimized propulsive power design, achieves 65% efficiency, equivalents to 7HP gasoline outboards"

Same page:

"A: Hi，max amperage draw is 87.5A， wattage is 2100 wat。"

https://www.amazon.com/Caroute-N300-24V-Brushless-Electric-Saltwater/dp/B00WF521

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Caroute Motor, care to elaborate how is it not lying to claim comparable or better output than 7hp (5.2kW) from 2.1kW input draw (1.7kW ouput mentioned above)?

 

I don't know. It seems that all electric or trolling motor sales material copy each others material. If they lie, I can lie. It's the same with the old and famous manufacturer Elco too (http://www.elcomotoryachts.com/ep-99-outboard.shtml) 4.3 kW in, 9.9 HP out. They are all perpetual-motion machines by brochures. Trolling motor horses are Shetland's ponies. Nothing wrong with ponies, they are just smaller.

Anyway, Caroute did publish their test results and efficiency. Who else of the trolling motor manufacturers?

 

Yeah I don't mean to single out caroute as this is a wide speead problem. My guess is that It stems from using thrust at really low or no speed. This was done probably so that they didn't have to try selling 0.15hp motors. 20lb sounds better. Then as props are optimized for really lpw speed these motors can beat bigger ones in bollard pull - this has given the opportunity to claim equivalent to this and this gas hp motor -philosophy. Even if it means more thrust in very limited usage parameters.

 

Sounds plausible.

 

The federal regulations do not cover electric motors, so they can call their motors anything they want. There is probably a consumer fraud issue that keeps them from completely making stuff up, but they are not required to rate their motors at the shaft like gas motors are.

So a 2kw electric motor could be
1) 2kw at the shaft continually
2) 2kw peak maximum burst draw
3) 2kw peak motor draw with a 1kw peak controller
4) 2kw rated wires

And probably all sorts of other things I haven thought of.

Sadly you are wrong, all of the electric outboards I have seen I think are rating the motors as 2kw motors if they draw 2kw maximum.

But then they sell the 2kw draw as a 75hp gas equivilant by some weird electric hp>gas hp Formula that has never been explained to me.

Just as an example, Torquedo has a motor called the Torquedo 10, that has a maximum peak draw of 12kw and a continuious draw of 10kw. Ok, good on them for spending the current draw not the peak. But then they mention it has a propulsive force of 5.6kw. WTF so this is a 5.6kw motor not a 10kw motor.

Worse they say is will replace a 25hp gas motor. NO IT WON'T. That gas motor was rated at the shaft, so they are suggesting a 5.6kw shaft output is the same as a 25hp shaft output. It's just a fricking lie. They have to know it's a lie, I mean I am an attorney with a philosophy degree and I know it, one of their engineers has to have mentioned it before.

http://www.torqeedo.com/us/en-us/pr...xnd6wEd_i-_tl8nDcYyGR3AI4c3dlFc01MaAhXk8P8HAQ

If they really wanted to prove to me that the Torquedo 10 was the same as a 25hp outboard it would be simple, take two identicle boats put one motor of each type on the back, and go race them. If the electric wins great, but they never will.

 

The first motor I bought for my project was definitely over rated. Every time I'd ask the vendor questions the continuous duty rating kept getting lower and lower. The price was right and it preformed ok, also gave me the data I needed to find the right motor, but it definitely wasn't what it was advertised as.

I found the amazon listing for the caroute motor, it says to use 4 12v 150ah batteries. If anyone else was wondering.

I would love to see a torqueedo 10 vs 25hp outboard race!

 

The 5.6 kW given by Torqeedo is NOT shaft power, It's propulsive power. And they claim that it is equal to 20 hp OB's propulsive power.

I can buy the 5.6 kW propulsive power and it is actually very good for 10 kW electric input power. If it's true, it's more honest way than giving shaft power. Although it will not be the same for different kind of boats so they should also give boundary conditions for that.

Then they claim that OB's have very poor propulsion efficiency. Despite much higher shaft power they produde the same or even less propulsive power. That may be true for some very extreme case, but in that extreme case Torqeedo is not going to have 56% total efficiency.