This Yellowtail system is in fact what I use and have done so successfully for seven years:
Now let's put this direct drive vs gear reduction discussion to bed once and for all. There is nothing wrong with direct drive, but like all engineering design there are pros and cons. I'll come to that in a moment, but suffice to say that for most leisure boats/yachts discussed on this list the most common system is a 48V DC motor with a reduction drive.
Here's some pros and cons of DC direct drive.
Pros
- As long as the power requirement is not too high you get a quieter as efficient system and more cost effective system compared to a 48V geared one.
- Depending on displacement/power and range required you can run at 24V, therefore needing less batteries if using typical large AGM ones or Lithium. If you need more you can run at 36V or 48V in series but will not be able to use the full voltage due to a higher shaft RPM, limited Prop choice, but you will get more power than 24V and naturally more range at cruise speed.
- Less weight and more compact.
Cons
- You are more restricted in prop choice and shaft RPM as to make a DC direct drive as efficient as possible (with just air cooling) you need to choose the lowest Torque/amp you can and consequently (as it's directly related) you get a lower RPM/Volt. The shaft RPM will then govern the prop choice, controller voltage to get the power required. Consequently peak shaft RPM will tend to be higher than geared with a more optimised prop.
- If you don't have a hull attached Plummer Block/Thrust bearing you can't remove the drive with boat in the water.
- Shaft alignment is trickier.
- You have to match the prop and optimise it to get the right balance of motor voltage vs amps to maintain the best efficiency at cruise speed. That's much easier with 48V geared.
John R.
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