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Offline mokamo

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Mokai - Electric powered motor
« on: October 01, 2018, 06:18:15 PM »
Greg from Ohio who bought my Mokai will replace the gas motor to an electric motor which can go around 20 mph according to him. I think equivalent to 11HP. Battery according to their initial calculation will 7 hours.. Anyone tried this kind of conversion? He's hoping to conplete his project before spring...and will share to us if he succeeds..
Wow if he succeed, i will need to buy a used one again..7 hours play time is good enough and just buy few more batteries to extend runtime..
Greg has a friend from Energizer who will help him in this conversion. Greg has a background in engineering so hopefully they succeed..as this will give old model owners another option to enjoy their boat..no need to buy the latest..
« Last Edit: October 01, 2018, 06:25:02 PM by mokamo »

Offline Painlesstom

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Re: Mokai - Electric powered motor
« Reply #1 on: October 01, 2018, 10:10:49 PM »
The technology to power the boat electrically is available, but highly doubt it would be going 20 mph or lasting 7 hours unless it was driven remotely with no passenger on board. Not even sure if the old hull intake tunnel is able to flow enough water to let the boat go that fast, the pump would have to spin up past 5000 rpm to stand a chance of coming close. 7 hour run time (if even remotely possible) would require several heavy batteries, combined with the motor would weigh much more than the gas engine it was replacing. Electric cars don't go faster or farther than their gas counterparts, the Mokai would be no exception. Will be interesting to see what they come up with though, but I wouldn't hold my breath.
Tom

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Offline Maritimer

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Re: Mokai - Electric powered motor
« Reply #2 on: October 02, 2018, 07:39:53 AM »
Would running an electric motor "backwards" give you a decent reverse? Surely it would clear weeds out of the intake grate! And it would be much quieter, right? I hope I live long enough to see battery technology evolve to make this practical!

Offline Painlesstom

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Re: Mokai - Electric powered motor
« Reply #3 on: October 02, 2018, 07:46:18 AM »
Running the pump in reverse could serve to clear the grate, but it probably wouldn't function as reverse very well. Hard to say for sure without trying it, would be interesting to watch.

Tom

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Offline mokamo

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Re: Mokai - Electric powered motor
« Reply #4 on: October 02, 2018, 09:07:53 AM »
I think Greg is a member here but might not be checking this forum regularly as he has a construction business. So share your comments here so they know the challenges ahead of them..For me Mokai running 15 mph for 7 hrs is good enough using lithium batteries...and hopefully easy to remove so you can swap gas powered motor and battery powered motor.

Offline happul3

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Re: Mokai - Electric powered motor
« Reply #5 on: October 02, 2018, 09:15:59 AM »
Greg from Ohio who bought my Mokai will replace the gas motor to an electric motor which can go around 20 mph according to him. I think equivalent to 11HP. Battery according to their initial calculation will 7 hours..

Let's look at some numbers. 11HP => 8.2 KW electric power. Assuming 90% motor/controller/wiring efficiency, the target is 9.1 kW the battery system must supply continuously. Using 36V/4.4Ah/2lbs battery pack as building block (last time I looked that was excellent lithium pack in terms of weight, capacity and pricing) , will need 58 such packs (9121/36/4.4=58) to run for 1 hour and 402 packs to run for 7 hours.  Battery weight will be close to 120 lbs for 1 hour setup. Price tag above $2K without controller, which will cost nontrivial amount too. I suppose the weight can be reduced somewhat using individual, higher capacity cells, but cost will go up considerably. Slice it any way you like, but the 1hour power system will be >100 lbs weight and >$2K (that's without motor).  Relative to stock mokai, it'll be at least 80 lbs added weight. No way it will go 20 mph with just 11hp, just as Tom pointed out earlier. And our imaginary 7 h version will just sink because of added weight.   

Offline Painlesstom

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Re: Mokai - Electric powered motor
« Reply #6 on: October 02, 2018, 12:29:27 PM »
Thanks for the numbers, I knew it was unrealistic and outrageously expensive but didn't feel like taking the time to work it out. Glad you did, thanks.  \./8
Tom

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Offline niteshft

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Re: Mokai - Electric powered motor
« Reply #7 on: October 02, 2018, 01:29:25 PM »
I can't quite remember the name of the magazine but it had an article of someone converting a 17' open boat to electric drive, I looked around but can't find it. He used a 24v motor for drive.

 As far as a mokai going 20 mph, the prop would have to spin up quite high and may cause cavitation issues.

Offline Painlesstom

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Re: Mokai - Electric powered motor
« Reply #8 on: October 02, 2018, 02:05:14 PM »
It took a 40hp Kawasaki jet ski motor to spin the pump to 7000 rpm and got 32 mph out of a "new hull" model that originally came with the Subaru. So I'm going to guess that if there is any chance of the old hull with the smaller intake tunnel hitting 20 mph, the pump would have to hit at least 6000 rpm. Guessing again, that would take at least 20-25 hp and no cavitation.

Powering a boat by batteries, and keeping the weight equal to the gas engine, you would lose speed and have a fraction of the run time. It's still in the novelty stages, would be cool to see where the technology goes though. Maybe we should all send emails to Elon Musk, maybe he could make a Mo-Tesla. LOL  :D
Tom

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Offline happul3

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Re: Mokai - Electric powered motor
« Reply #9 on: October 02, 2018, 02:17:08 PM »
I can't quite remember the name of the magazine but it had an article of someone converting a 17' open boat to electric drive, I looked around but can't find it. He used a 24v motor for drive.

I can't imagine 24V drive going faster than trolling. Current required to go at a "normal" boating speed (15mph? 20mph?) would be unreasonably high. For reference, here is a similarly sized electric boat: Bolt 18 by Mylne 18ft, 1650lbs; 100kw / 135bhp Electric ; 24kwh Lithium battery; Cruising speed  20 knots for 30+ minutes. Going back to 24V battery, 100 kW would translate into 4,000A. What kind of wire could carry that? 1 inch, 2 inch? That's why whenever people build high power electrical contraptions they increase voltage...