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Old 01-12-2019, 03:59   #1
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Gemini 105mc conversion Diesel to EV?

Hello All,

I am curious if anyone has converted a Gemini 105 to EV yet? I am asking because yesterday I went and walked 1996 Gemini 105 that needs a bit of work, but within the price we talked about is looking to be a decent starting point. I know there are many videos of people scraping the diesel engine in favor of a gas outboard, but with my background of building electric bicycles for fun and owning a tesla model 3, the idea popped in my head of going the EV route. While looking at the boat, the owner was able to start the diesel engine, but it ran very poor and shook pretty violently and while looking at it i noticed there was a leak coming from the side of the engine block and closer inspection appears to be a hairline crack in the block of the engine near the head, so the engine is shot basically. After talking to the owner about that and a few other things i noticed, he threw out the price of 35k on the purchase and i told him i would get back with him after giving it some thought and also told him i gotta talk it over with the other half (don't have a other half at the moment, so a bit of a fib), but just wanted to buy time to think this over.

So the idea i was thinking was pulling the diesel engine, but leave the prop head and attach the electric motor to it for propulsion instead of re-inventing the wheel completely. I also looked into the company i buy my electric bike motors from and they offer a 96v 50kw max/25kw continous Motor/Controller kit for $2400, which could be combined with 4s x Tesla Model S battery modules for bare minimum battery pack for $3600.
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Old 01-12-2019, 04:05   #2
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Re: Gemini 105mc conversion Diesel to EV?

Hi,

take a look at some yt channels like Sailing Uma, Rigging doctor or Beau and Brandy sailing. They all converted sailboats to electric. Beau and Brandy used the batteries of a Chevy Volt in a 48V config.
Sounds interessting, please keep us updated.
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Old 01-12-2019, 04:36   #3
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Re: Gemini 105mc conversion Diesel to EV?

Quote:
Originally Posted by harlem24 View Post
Hi,

take a look at some yt channels like Sailing Uma, Rigging doctor or Beau and Brandy sailing. They all converted sailboats to electric. Beau and Brandy used the batteries of a Chevy Volt in a 48V config.
Sounds interessting, please keep us updated.
I will check those out, the chevy volt cells are very cheap, but extremely heavy compared to tesla cells and i would imagine on a boat, weight is KING....

I guess i was more or less curious whats a good target amount of kw of power needed for power cruising if not sailing... The owner told me in the past he would only cruise @ 50% throttle and based on that knowledge and the diesel engine maxing at 20kw output, in a "oh ****" situation i was thinking around 20kw continous would be needed to hopely get out of danger...
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Old 01-12-2019, 04:40   #4
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Re: Gemini 105mc conversion Diesel to EV?

Not sure, but if you check the electric beke vids of sailing Uma, they test their electric motor somewhere in a channel in Florida and afair they needed 20-30A with a 48V system to go around 4-5kn.
They have a 36ft 70s mono.
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Old 01-12-2019, 05:05   #5
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Re: Gemini 105mc conversion Diesel to EV?

I am thinking a 50kw max/ 25 kw continuous is a very nice size to push that boat. Evaluating propeller sizing and the impact of the transmission system is warranted, given the electrical motor may be quite happy turning at lower rpm than the diesel.
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Old 01-12-2019, 05:22   #6
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Re: Gemini 105mc conversion Diesel to EV?

Have a look at this, some interessting insigts.

https://www.sailinguma.com/the-motor
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Old 01-12-2019, 05:26   #7
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Re: Gemini 105mc conversion Diesel to EV?

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Originally Posted by harlem24 View Post
Not sure, but if you check the electric beke vids of sailing Uma, they test their electric motor somewhere in a channel in Florida and afair they needed 20-30A with a 48V system to go around 4-5kn.
They have a 36ft 70s mono.
That seems very low... thats only about 1.5 to 2.0kw output if those numbers are real.. thats very low power usage to do 4-5knots.

Since the origional drivetrain is designed for low rpm engine, a DC based motor would benefit in this case, since DC motors are more effecient at low rpms and produce more torque vs AC motors, which are more effecient at higher rpms, thus why electric cars are AC based or some sort of dual DC/AC based like the Tesla, which uses DC for low-end and low speeds on the Model S and AC side of the motor for higher speeds.
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Old 01-12-2019, 05:31   #8
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Re: Gemini 105mc conversion Diesel to EV?

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Originally Posted by harlem24 View Post
Have a look at this, some interessting insigts.

https://www.sailinguma.com/the-motor
Ah, i see... they went with an old forklift motor.. very very old technology, but very reliable due to how tuff they build them to withstand high amp spikes... That motor maxes at only 4.8kw, which is far less power than i expected to do 4-5 knots...

The motor kit im looking at is from a china based electric 2 seater car with max speed of 75kmh. Maybe something smaller could do the job based on the Uma setup results.
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Old 01-12-2019, 05:36   #9
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Re: Gemini 105mc conversion Diesel to EV?

Just looked at their website: Electric yachts says that they need 5.7kW to go 5.6kn.
With a 7,5to 36ft boat.
And they actually have now a 4.8kW motor with direct transmission.
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Old 01-12-2019, 05:38   #10
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Re: Gemini 105mc conversion Diesel to EV?

And most of the time they sail, cos it's a sailboat...
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Old 01-12-2019, 06:00   #11
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Re: Gemini 105mc conversion Diesel to EV?

Another option is something like this... if that little of power is really only needed for propulsion... these kits can be had for around $3k... but I kinda like the inboard motor route better...

https://youtu.be/QsH6QKBuz1g
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Old 01-12-2019, 06:11   #12
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Re: Gemini 105mc conversion Diesel to EV?

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Originally Posted by harlem24 View Post
Just looked at their website: Electric yachts says that they need 5.7kW to go 5.6kn.
With a 7,5to 36ft boat.
And they actually have now a 4.8kW motor with direct transmission.
hmm, if that is the case, then its probably a 10 to 15kw motor, because 5.7kw continuous is typically a 1/3rd to 1/2 of the max power on most motors I see...
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Old 01-12-2019, 06:25   #13
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Re: Gemini 105mc conversion Diesel to EV?

Electric yachts proposed a 20kW motor for their boat.
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Old 01-12-2019, 08:02   #14
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Re: Gemini 105mc conversion Diesel to EV?

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Originally Posted by storx View Post
I guess i was more or less curious whats a good target amount of kw of power needed for power cruising if not sailing... The owner told me in the past he would only cruise @ 50% throttle and based on that knowledge and the diesel engine maxing at 20kw output, in a "oh ****" situation i was thinking around 20kw continous would be needed to hopely get out of danger...

"power cruising"? What sort of range do you want? How are you going to recharge your batteries? Battery bank size and energy sources are the major constraints with EP. You need to clarify your use case.
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Old 01-12-2019, 08:28   #15
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Re: Gemini 105mc conversion Diesel to EV?

I would think your system would need to be similar in size to this boat.

https://www.youtube.com/channel/UCj0...XZzyKqZz4cu-yg


He is estimating 11 hour run time at 3 knots. No feasible way to recharge while cruising that I can see.
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