Hi,
Maybe you are right re Mars/Motoenergy cooling, but not with the Lynch which I suggest has better mechanical cooling properties for an open framed air cooled motor.
Also I'd like to take issue with your comment re "tried and true system".
If anything falls into that category it is the Lynch design. Here's why. John Fiorenza of Mars/Moto Energy worked for Briggs & Stratton I understand, and they built the Etek under an agreement with Lynch, albeit at much less power than the Lynch without infringing patents. John then went on to the motors you refer to, designed in US and built in China I believe.
Lynch motors are in all walks of life and go back over 20 years. I suspect there are more out there than Mars motors but as this list is US centric you'll see more about the Motoenergy I suspect. Great motors and good value I have to say though. But....
Here (if your boat is the right size) is why direct drive is better and more efficient than a geared system for some of us. First if you are replacing an IC engine of around 12hp with a Lynch and an efficient system/prop etc then you can do so with a direct drive 24V system.
The point I think many miss is that once they gear say at 2:1 and run at 48V is that they now need to run at around twice the current of a 24V system to maintain the motor at its peak 90% efficiency. In other words my system is designed to run at peak motor efficiency at cruise speed not at higher boat speeds as most 48V systems do. The only real reason for going to higher voltage systems is to get more power, but if you don't need the power then it is better to stick with a more efficient system. If I needed more power I'd go to 36 or 48V and gear at the cost of motor peak efficiency at cruise speed and therefore a cost in range. I'm well aware of IR squared losses and the pros and cons of a 24V string versus a 48V series string and V=IR etc.
Also the moment you gear and run motors at higher speeds you have higher frictional losses and therefore reduced efficiency. The ideal motor would be insulated and 100% efficient. Really we don't want to cool but we have to as we are not spending money on superconductors etc.
Say you run a motor at 80% efficiency at 1 kW then there are 200 watts of wasted heat. If however I run at my cruise speed of 4 knots at 90% efficiency I'm only losing 100 watts of waste heat that I could recover and say heat water for a shower with. As the whole propulsion system is a serial efficiency equation then I'd prefer to have efficient overall propulsion power than a shower ;)
Have a look at performance charts and voltages and efficiencies here and you'll see what I mean http://www.agnimotors.com/site/index.php/technical-data/143-series
Cedric Lynch now works with AGNI out of interest.
So many choices and variables eh, but what is right for one may not be right for another, however it is good to be aware of why we make certain choices when designing a system.
John
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