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Old 15-04-2019, 21:58   #1
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Electric motor conversion

Does anyone have experience with this company and or kit?

https://www.electricmotorsport.com/m...ve-system.html

It won't be quite the 50hp motor that she has in her now but with my diesel generator and a nice battery bank i'll be able to do continuous hull speed when not under sail.
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Old 15-04-2019, 22:35   #2
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Re: Electric motor conversion

Roughly 13kw (180*72) motor, around 16 HP. Ballpark, this will propel a 4 ton boat to hull speed.
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Old 15-04-2019, 23:09   #3
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Re: Electric motor conversion

Does it actually work out to replace a diesel engine with an electric one, battery bank and generator?
Shouldn't you have a big number of solar panels to make it work?
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Old 15-04-2019, 23:16   #4
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Re: Electric motor conversion

Hull speed is based on a combination of length at waterline, hull design and weight. Not simply weight.

Iím more than happy with a 5kt motoring speed with electric.

Sized properly you can get continuous operation of an electric motor and battery bank setup with a generator. I have an 8kw which is more than enough for the small setup iím installing.

I have added 200 watts of solar but those are currently only for my house bank. I can add solar for the propultion bank as well but not too terribly worried about that as I tend to like running a generator for ac etc when iím away from the dock.

My house bank solar is primarily to keep her charged up when shes sitting on the hook and iím either not onbord or just not running the generator.
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Old 15-04-2019, 23:35   #5
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Re: Electric motor conversion

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Originally Posted by cgm12mgc View Post

Iím more than happy with a 5kt motoring speed with electric.
Until you have to motor into the wind.
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Old 15-04-2019, 23:38   #6
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Re: Electric motor conversion

Push forward on the throttle and lean on the generator to recharge the battery bank. Right back at 5kts
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Old 16-04-2019, 20:35   #7
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Re: Electric motor conversion

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Originally Posted by cgm12mgc View Post
Push forward on the throttle and lean on the generator to recharge the battery bank. Right back at 5kts
It appears to be a 13kw motor. With an 8kw generator, full speed will completely deplete 1000ah of batteries in 2 hours even with the generator running. An 8kw generator is only good for a 10.7 HP motor assuming no electrical or drive train losses.
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Old 16-04-2019, 21:06   #8
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Re: Electric motor conversion

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Originally Posted by NPCampbell View Post
It appears to be a 13kw motor. With an 8kw generator, full speed will completely deplete 1000ah of batteries in 2 hours even with the generator running. An 8kw generator is only good for a 10.7 HP motor assuming no electrical or drive train losses.
sounds like if the sun, moon and winds align depleting me of juice that i'll have to go old school and anchor while I recharge. I'll keep the rum stocked!
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Old 16-04-2019, 22:14   #9
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Re: Electric motor conversion

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sounds like if the sun, moon and winds align depleting me of juice that i'll have to go old school and anchor while I recharge. I'll keep the rum stocked!
It's not that uncommon to need full throttle for significant periods of time.

If you are willing to live with significant performance reduction, that's fine but no, an 8-10hp generator isn't going to be able to match a 50hp diesel even if you can squeeze a little extra out of the battery bank.

The first question should be: Why are you looking at this change? A standard diesel will be more efficient and cheaper. If you don't need the performance, you can retrofit a smaller diesel.
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Old 16-04-2019, 22:36   #10
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Re: Electric motor conversion

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Originally Posted by NPCampbell View Post
It appears to be a 13kw motor. With an 8kw generator, full speed will completely deplete 1000ah of batteries in 2 hours even with the generator running. An 8kw generator is only good for a 10.7 HP motor assuming no electrical or drive train losses.
Ease off to 90% of full speed and (nearly) double your time.
Ease off to 80% of full speed and quadruple your time.

People with a 45'/14t cat can motor 4.5-5kn with solar alone - that's people out there doing it, not charging their armchairs.

I'm still charging an armchair too right now, but figures we've received are that, since our nominal hullspeed would be near 9kn, so
nominal hullspeed = 124kW (let's pretend that is 100%)
90% hullspeed = 83kW (59% of max amperage)
80% hullspeed = 30kW (21% of max amperage)
70% hullspeed = 22kW (16%)
60% hullspeed = 11kW (8%)
50% hullspeed = 6kW (4%)
Now your numbers will be different, but the idea is to look at the progression as your go slower.

If you travel at maximum, you won't last long on batteries alone (the comment on only getting 2 hours with the genset running is purely a case of poor choice of matching speed-motor-genset-batteries and not inherent to electric motors!).
BUT, if you're will to come down a little in speed, then there's a lot of possibilities for matching ok speed with distance under batteries alone, or under batteries with genset (maybe solar input too).
So at nominal hullspeed, if the OP had 2 hours of battery draw available at my figures above (an HUGE amount at that speed, but the importance isn't the 100% value it's how much it increases with speed), then the use on batteries alone is:
Nominal hullspeed = 2hrs
90% hullspeed = 3.4hrs
80% hullspeed = 9.3hrs
70% hullspeed = 12.7hrs
60% hullspeed = 25hrs
50% hullspeed = 47hrs
WITHOUT genset!

There's more and more doing it and it works.

In our reality, we see a sweet spot at 60% of hullspeed or about 5.5kn using 11kW total. An 18kW DC genset would work fine giving continuous motoring as long as the diesel lasts (and much quieter and a bit more efficient than diesel only propulsion). We could decide to go 1kn slower, and use about half the power meaning running on batteries-only for short time/distances between endpoints is feasible. Want longer battery-only without genset, then just buy more of them...
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Old 16-04-2019, 22:40   #11
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Re: Electric motor conversion

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It's not that uncommon to need full throttle for significant periods of time.
My diesels aren't rated for continuous duty at full throttle. I would hazzard that there are very few who are like you and have that capability. Most would be limited to minutes (not hours) of full throttle according to the manufacturer.

So while I agree it's nice to have the oomph to hit a high speed when needed, for most people/boats that high speed is very time limited. And...well you can do the same with electric motors as they usually have a peak capability far beyond the continuous rating.
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Old 17-04-2019, 05:12   #12
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Re: Electric motor conversion

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My diesels aren't rated for continuous duty at full throttle. I would hazzard that there are very few who are like you and have that capability. Most would be limited to minutes (not hours) of full throttle according to the manufacturer.

So while I agree it's nice to have the oomph to hit a high speed when needed, for most people/boats that high speed is very time limited. And...well you can do the same with electric motors as they usually have a peak capability far beyond the continuous rating.
They may or may not be rated for full throttle but when the poo hits the fan, you can typically firewall the throttle for several hours without damage.

A lot of it is about warranty coverage...do it on a daily basis and you might wear out the engine prematurely. Do it every 3-6 months and it's unlikely to have any noticeable impact on longevity.

With an undersized battery/generator setup, once the battery is dead, it doesn't matter what the electric motor is rated for. Also is the generator spec'd to allow continuous full throttle? Suddenly that undersized generator looks even worse.

Heck, look at outboards, most bass boats are idle speed for firewalled and it's common to see 20-30yr old outboards still in good working shape.
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Old 17-04-2019, 08:17   #13
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Re: Electric motor conversion

We get it, youíre no fan of electric motors. You can stick to diesel... I do in my other boats. People survived for thousands of years without a motor in their boat and as I have stated, mine is to get out of the marinas and under bridges etc. donít like it? Donít do it.


Same concept as what youíre saying, I can run my 61í sportfish wide open throttle for a few hours but iím up shi*ts creek when I run out of diesel at a burn rate of 120 gallons an hour... atleast with electric I can refill while on anchor 👍🏻
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Old 17-04-2019, 08:32   #14
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Re: Electric motor conversion

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Until you have to motor into the wind.


If I need to go upwind thatís what sails are for.
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Old 17-04-2019, 11:40   #15
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Re: Electric motor conversion

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nominal hullspeed = 124kW (let's pretend that is 100%)
90% hullspeed = 83kW (59% of max amperage)
80% hullspeed = 30kW (21% of max amperage)
70% hullspeed = 22kW (16%)
60% hullspeed = 11kW (8%)
50% hullspeed = 6kW (4%)
I'm curious where these numbers come from. As long as you are below hull speed, shaft HP generally increases with the cube of speed. So 50% hull speed should generally equal HP/8 at 100% hull speed. 50% hull speed should require 15.5kW if 124kW is req'd at 100% hull speed. Shaft HP is independent of the method of propulsion. (i.e. HP req'd = disp pounds / (10.665 / SL ratio) ^ 3)

Solar: 50% hull speed or 15.5kW would require around 1000 sq ft of solar operating at 100% efficiency. 1000 sq ft is larger than the footprint of a 45' catamaran.

Battery: 15.5kW would last less than 45 minutes taking 1000 AH of batteries to 100% DOD without running the genset.
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