Solar panel

Brushless Outrunners can not produce the power of an Inrunner because the only way heat can escape is thur the shaft. Inrunners have the winding coils up against the outside of the case and can be cooled very easily.
I have been racing brushless boats for years, 7.5 HP from 33 volt lipo and 92 mph around a 1/4 mile oval for 6 laps in a 19lb. Hyro.

 

and for OP - "small boat" is too vague. It can mean 10' to some or 25' for another person.

Lost of people have small <15' rowboats and trolling motors charged by a solar panel. Panel on shore though - no point carrying it with you. This application is sensible on vacation homes etc. More details needed to know what makes sense - or doesn't.

 

Bert,
I said I don't know because none of the manufacturers give any data. The 20% came from the Torquedo site I listed -I didn't 'suggest' it, it is the ONLY efficiency number I have seen. I would love to see someone challenge it and their claim of 2.5 times more efficient. If you are a serious customer I am sure they would be happy to prove it to you.

 

That sounds wild! Are the races in Cleveland? Where can I read up on this interesting sport?

 

That is actual not completely correct. All mine brushless outrunners have the shaft mounted to the magnets, and the stationary coils can be mounted to a surface which can easily be cooled. Your outrunner may have been different to the 4 different types I have here. Bert

 

My wife always says, she can juggle all figures to let you hear what you want to hear. I agree with you that too many companies are throwing vague statements around, without actual saying something exact. Like the best shipping line in the world, 20% better than the competition, what is better. So , the marketing division of Torquedo is no different than others. I agree with you, unless specifics specified, it is meaningless. I don't give a hood how good or how bad the efficiency is, as long it works for the application , as long a person has the pleasure from it and he can afford it, that counts for me.

 

My guess would be that your inrunner is being run at very high power/low efficiency, generating tremendous heat for your goal of highest speed/short range of 1.5 miles. Seems an equivalent outrunner would need special cooling/heat sinks, if it works at all. Force cooled pancake motors might be the way to go for electric boat drag racing, because no iron armature provides quick acceleration.
http://articles.sae.org/10599/

Non racing boats seem to have a goal of maximum range at maximum efficient speed, where less heat is generated and the torque of outrunners excels.

Porta

 

Jim may be right that an inrunner can be cooled easier. But the magnets are closer to the center of the shaft, whereby the torque is lower than the outrunner of the same size. Outrunners are often used on aeroplanes whereby the cooling is provided by the 9000 - 10.000 rpm of the propeller. I am experimenting in cooling the outrunner for my 5,4 meter boat in a liquid way, running at way below the maximum power rating. I don't need the maximum power rating as I have at my age, all the time in the world.

Thank you, it gives me the confidence that I am on the right track for my boat.
I wish that manufacturers produce larger diameter outrunners at 75 kv for up to 36 Volt boat applications. But I haven't found any. Bert

 

Indeed, I had a look at the Torqeedo pdf file and they are making a statement that they are up at overall 44 - 56 % efficiency and a petrol engine between 5 and 15% . According to that statement, my electric boat creation is anything between 18 and 35%. Like my wife said, she can prove that a petrol engine does between 50 and 60% and Torqeedo between 10 and 20%. It just depends what is left out and what is in the comparison. Bert

 

Hope this helps, Bert.

Porta

 

More info here http://forums.offshoreelectrics.com/forum.php
Yes this is a NUE 1530/1Y racing motor with a 300 amp Swordfish ESC. My Eagletree data logger shows 90 to 92% eff. at 180 amp draw in the boat while racing.

No secrets to cooling, the shortest path with the most surface area wins.

 

thanks Porta, I have made provision for 3 Brushless motors to be mounted in the engine compartment and running parallel, should the battery technology improve and affordable larger power packs (25 kwh) becomes available. At present I have only 1 outrunner of 130Kv and up to 72 Volt. However, I have designed my system with not more than 36 Volt. i.e. 4680 rpm.
I have a down gearing to 1100 rpm. My prop is 46 cm. The lower revolutions per minute allows the ESC to perform better. Even Rick was impressed with the low noise it made. That link to HobbyKing had a too high Kv to my likings and they are running at such a high rpm, that wear and tear will start becoming an issue. Also vibrations. Bert

 

Hi Porta,
Something I forgot to ask. What would you do , when you are in my shoes. Would you design it with 3 ESC's for those 3 motors, or would you have all three just the coils connected to each other, of which one has the 3 sensors, but using only one ESC. The ESC I designed and made, can handle up to 8 Mosfets parallel x 6. Also it can handle up to 400 Ampere over current sensing, although with 3 motors at 36 Volt, I would only draw maximum 150 Ampere.
How would you design it?
Bert

 

That 90+% of the motor + ESC? is incredible if it is average for the circuit, Jim! It takes one minute to go 1.5 miles at 92mph, so I guess 92 is peak speed.... You clearly know what you are doing, and must be winning- good for you! Peukert effect must be bad on the batteries if they go to empty on one run...

I guess breeze cooling suffices for the motor at those high speeds...

Porta

 

FWIW comments above.

Porta