Jak,
It's kind of hard to answer the question without knowing your installation and how you expect to use the boat, but I'll make some broad generalizations. From my perspective, there are few Pros and many Cons.
The most obvious answer is that halving the volts, doubles the amps for any given power. What kind of power are you looking to get from your drive? If you're looking for only 2.5kW, then at 24V your wiring, fuses etc. only need to handle 100 - 120A. But if your boat needs 5kW (7+hp) then your electrical system will need to be sized for at least 225A. Bigger wires are heavier and more expensive. Higher amp loads have a higher potential for voltage drop in the wiring.
If you're planning on using flooded batteries, those kind of amp loads will push you deep into Peukert's losses. Even at lower power settings, you'll find that your battery range will be much less than you expect, higher amp draws (regardless of the voltage) lose energy to heat as a symptom of the battery's internal resistance. You can mitigate this by running a larger battery bank or chosing AGM batteries. AGM batteries have a lower internal resistance than flooded batteries, and Lithium batteries are better still.
Aa far as just the difference of efficiency in the motor itself, you'll find that the same motor at half the voltage will create more heat for the same power setting (double the amps) so you'll need to address supplemental cooling, especially at low rpm where the motor's internal fan is much less effective.
Finally, modern cogged belts, as opposed to common smooth v-belts, are more efficient than you might think. Some products are more than 95% efficient at transmitting power, so your loss would be minimal.
For this type of question, I tend to favor higher voltage and I'm pretty sure that the belted drive will probably outperform the lower votage direct drive with that motor. But I could be wrong.
Fair winds,
Eric
1964 Cheoy Lee Bermuda 30 ketch - Serenity
5.5kW Propulsion Marine drive, 8kWh LiFePO4 battery bank
Marina del Rey, CA
--- In electricboats@yahoogroups.com, "Jak Mang" <jak.mang@...> wrote:
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> I am looking at a Mars motor that turns at a high RPM (2400@48v). The supplier suggests a gear reduction with a belt drive to decrease RPM at the prop. What are the drawbacks of just lowering the voltage to 24 rather than the extra hardware? It seems that there would be some inefficiency from the belt. How does this compare to less than maximum efficiency at 24 volts?
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> Thanks,
> -jak
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