Electric inboard motor, my journey to find proper motor

As I plan to build a solar Catamaran, I had to find a reliable, powerful and affordable inboard motor who work at voltage around 48Vdc. Well, two motors.
The challenge is to have proper RPM who match propeller. Or to install the max diameter propeller who fit the boat and match the motor RPM in order to have best efficiency.
I first thought about PMAC motor available at thunderstruck-ev or electricmotorsport as other motor brand who can be find on plugboat are WAY to expensive (Bellmarine, Torqeedo, Epropulsion, Oceanvolt and so...).
I put my hand on a used Motenergy ME1507 air cooled motor and then start:

Plan #1: Motenergy ME1507 + reduction ratio.
This motor is the same used on many Zero electric motorcycle and can output over 60 kW peak.
But continuous output power at 48V is low at around 8 kW. This motor also exist in liquid cooled version call ME1616 and can output roughly 12 kW continuous at 48V.
The RPM at 48V is around 2000 rpm and I ask on another forum if direct drive in an option with smaller propeller instead of large propeller with a reduction ratio. Everyone tell me reduction ratio is a must (pic 1).
Based on this, I had the choice between belt and pulley or build a gearbox. Gearbox look the best solution to me and I start to look at Toyota Prius transmission to stole planetary gear to build a gearbox.
Then, my mind take a break and think about trying to find a planetary gearbox. I found one use who fit the need (3:1 ratio) on ebay for less than 200$.
That look promising (pic 2-3).
The thing is with an output rpm drop at around 666 rpm the boat would need a very large propeller.
It's still doable as those motor can spin faster than their based RPM with some FOC (field oriented control).
All this was over many weeks and, recently, a night my mind has an sparky idea: Is an electric vehicle (EV) motor could still work at 48V?

Plan #2: EV motor direct drive.
Most EV motor are design to work at 300-400V (depend of the state of charge (SOC) of the traction battery).
So, is it will work at 48V? I look over the web, ask friends with more knowledge than me and... it should work. But I have to test it because the RPM will be much slower.
And I has to choose the good motor because not EV motor are create equally. Many EV motor are integrated to their gearbox and are a single unit. I explore and find that Nissan Leaf, Kia Niro/Soul, Huyndai Kona, Smart EV and Mitsubishi Imiev have their motor separable from their gearbox.
I test a Smart motor with my tiny ASI BAC controller and it work. And sensorless, not even need to read encoder (pic 4).
The big advantage of those motor is they are rudge, water cooled, lightweight, design to last and often really affordable at scrapyard. Oh, they also can output a lot of torque. 395 Nm (291 lbs-ft) for the Kona EV motor I plan to use.
So, low RPM + lot of torque = I plan to integrated those in a direct drive application with proper propeller.
More to come

 

Hi Everybody . First post here.
EV at the first glance look as affordable source of powerplant . But high voltage in salt water does not sound well for me . Even 48V saltwater enviroment cut be dangerous . If fresh water only ok. Why the motor must be inboard ?

 

Those motor have really good efficiency at around 96-97%.
But in my case, as it will spin around 6 time slower cause of the lower voltage, I think the efficiency will be in the blue circle area, so around 85-95%.
Any thought?

 

Yeap, I've read story about electrical shock with 12V battery in salt water.
But between those who successfully use 360V battery in electric/hybrid boat and those scare with 12V system in salt water, I think 48V is a good compromise (power / dangerosity).

Simplicity, reliability, protection. In fact, why not inboard?

 

Simplicity ok, reiability , protection ,it depend.

 

where are the piston rings
Isopack: 2013 (Second Generation) Nissan Leaf Drive Unit Teardown https://isopack.blogspot.com/2017/10/2013-second-generation-nissan-leaf.html

 

I suppose the shown motor diagram is the one based on the design voltage of some hundred volts.
If so, it will not be helpful to extract from this diagram data for this motor to use under 48 V input.
Not only the rpm at 48 V will be far lesser, also the power will (and the efficiency, and, and ...).

 

Yabert,

For your consideration:

The Live Rudder

I drove one of these for a summer as a tour boat.
The live rudder swings a full 180 degrees.
The maneuverability is unmatched.

Mounting the motors in your two rudders,
water cooled, high voltage, tilt-up, huge
diameter props may be a consideration.

 

I'm fully ok with the first points, but I'm really interest to know why the efficiency will be lower.
I mean, lower than the 85-95% I'm talking about post #3.

 

Thank to share. The power rudder is an interesting concept, but it completely destroy the concept of Keep It Simple Stupide.
It's a more complex assembly who imply bevel gears, multiple shaft, seals and bearings. So I still think, at the moment, that our plan of strait shaft direct drive is nice.

 

Planetary gears have lots of gear tooth friction from the smaller multiple gears spinning on the disc platform, Plus viscosity losses associated with lubrication, compared to single small to large gear reductions or maybe even single belt drive.

Depending on design, inboards can have front water disturbance and shading to the prop losses from the hull immediately in front.

It might be a good idea to have the motor efficiency for torque, rpm, PMW, prop, V, etc. curves Peak at the cruising speed or the speed where it will be used the most, or at least where the various factors line up for best efficiency.

"Simplicity, reliability, protection. In fact, why not inboard?"
Asian style trailing shaft Motors are much better at all of these compared to inboard, and some have been designed for very large boats. No seals that leak into engine room; much shorter downtime for prop, shaft hull damage and the shaft swings up when collisions occur; no dry dock or underwater diver needed to free prop entanglement or damage; fast to switch out with a spare motor, Etc.

Just my humble observations, may not work for everyone!

 

I've read about this. Belt can reach 98% efficiency when maintain properly. The Alpha drive single stage gearbox I found is rated at 97% or more efficiency.
That look super acceptable to me considering the reliability and the lack of maintenance involve compare to belt an pulley.

Yes, I will try to find the best efficiency to cruise at 6-7 knot.
Can you explain me what do you mean by: PMW, prop, V,

 

Sorry, I'm not able to explain the complex things about your question "why".
Electrical motors are designed to work at a specific operating point. As I understand the graphic in #3 is derived from a test at DC voltage of 345 V.
This Voltage with an appropriate current is "fed" in a part of the virtual motor called inverter which gives an AC output to the actual motor with frequency, voltage and current unknown (at least to me).
I don't think the inverter would like your 48 V DC input or do anything meaningful with it, e. g. causing the motor to rotate at desired rpm and torque.

 

Yes, the OEM inverter will not work at 48V. Generally those EV inverter work at voltage from 250V to a bit over 400V.
My plan is to use EV motor with proper 48V inverter. I did some 48V tests with ASI BAC 2000 inverter.
I plan to use ASI BAC 8000 inverter or EZKontrol EZ-C481200. If anyone have other suggestion, please let me know.

 

I guess you didn't understand my last paragraph ( above ).
No bevel gears, no multiple shafts, no added seals and bearings.
You also may have missed the benefits:
water cooled, higher voltage possible, tilt-up option, and large diameter prop capacity.

Best of luck with your project.