# Electric motors in boats



## [email protected] (Mar 21, 2012)

Hi
I know this is an EV car forum and I am asking a sailing electric motor question but to be honest the sailing forums I am on tend to be populated with the majority of people who dont think an electric powered sailing boat is feasible. I think it is and there are a number of examples of boats happly sailng and motoring with electric hybrid power. Having a hybrid car means I have put my money where my mouth is when it comes to hybrids.

So if I can indulge your time for a moment I will explain where I am heading with this.

The catamaran I am building is 55 foot long and 12.5 tonnes in weight. The designer has specified two 50 hp diesel motors to drive it. I intend to swap the diesel for electric motors. The question I am getting to is around what type of motor I should use...DC or AC...brushed or brushless. But before I go into that let me just say that the power will be made available through a bank of batteries which will be fed from wind, sun and a genset. So I will return in other threads to these topics, but for now just think of a large battery bank and inverter supplying whatever power is needed to the electric motors.

So let me run my current thinking past you...
The power requirements is 50hp diesel each side and also the power will be needed in three specific situations. 
*Gentle:-* leaving or arriving at a dock on a relatively calm day where we will use the motors to manuover the boat, gentle trottle use no big deal, using very little power. The battery pack will easly support this use;
*Medium:-* We are sailing along and the wind is coming from the wrong direction and we need to make up time. We will turn on the motors and provide additional push to the boat upwind with or without the sails. This would take about 50~75% of the power/thrust of the diesel motors depending on how much of a hurry. This could last two ot three hours. The batteries will need to be topped up as we go but the genny etc will keep the batteries powering along. 
*Heavy or Emergency:-* This is where we are in trouble with a storm chasing us or having to run into a heavey wind to get to a save place. Generally speaking this will require full power for a 3~4 hour period or maybe longer, 8 hours. This situation will be rare (hopefully) but when it happens it happens. In this scenario I believe that th egenerator will need to continuously supply power directly to the motors or something like that...dont know. But it will require something special to get us out of danger.
One final thing I have just thought of...when sailing...majority of mobile time I will want the props to regen if possible. Generally speaking people turn the prop slowly to reduce drag and then when the boat gets sailing, allows the prop to counter rotate to regen.

So there you have it. My question is ...does a Brushless, 3 phase AC motor of about 35KW make sense to you, given the info above.
Any comments critical, positive, anything is gladly accepted.

Many thanks

Mick

PS...if you would like more info I have started a build thread here


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## jddcircuit (Mar 18, 2010)

[email protected] said:


> Hi
> I know this is an EV car forum and I am asking a sailing electric motor question but to be honest the sailing forums I am on tend to be populated with the majority of people who dont think an electric powered sailing boat is feasible. I think it is and there are a number of examples of boats happly sailng and motoring with electric hybrid power. Having a hybrid car means I have put my money where my mouth is when it comes to hybrids.
> 
> So if I can indulge your time for a moment I will explain where I am heading with this.
> ...



I have a similar dream that is somewhere down the road for me. I am approaching the dream from a slightly different angle. I am trying to get my motor and battery control working before I get a boat. I live on the water and had a large twin inboard gasoline sport fisherman that was fun but didn't satisfy my boating needs and not to mention strained my budget.

The motor that I am starting with is a 30kw permanent magnet synchronous motor (3 phase brushless dc). It is from a junkyard Toyota Prius hybrid. In the Prius the electric motor is integrated with the transmission that provides a 4 to 1 gear reduction to the axle shaft. The motor and transmission are in a single aluminium casing with transmission fluid lubricating and cooling throughout both. It looks perfect for salt water environment to me.

Everything I have read shows lower kw motors replacing higher hp engines without sacrificing performance. I can't recite all the reasons why but the low end torque is a big part of it.

I am using a small electric car project as a test bed for developing and testing my charging and drive electronics to ultimately be used for a large twin screw displacement boat hull.

Good luck and please keep posting your progress.

Jeff


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## major (Apr 4, 2008)

[email protected] said:


> My question is ...does a Brushless, 3 phase AC motor of about 35KW make sense to you, given the info above.


Hi Mick,

Sure. Either PMAC or induction motor. I would not even screw around with brushed DC.

Regards,

major


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## tomofreno (Mar 3, 2009)

I assume you intend to use TWO PMAC motors, since they are replacing two 50 HP diesels. Should work. If you need them to output 50 HP continuously in a storm for 8 hrs that is about 298kWh. A 180Ah LiFePO4 cell is about 12.3 lb and 0.576 kWh, or 0.047kWh/lb, other Ah sizes vary a bit. I would guess you would want to keep the battery pack total weight less than say 500 lb? That would be 23.5kWh, so yes the generator (maybe two smaller ones for redundancy) will have to supply full power for most of the 8 hours. There are some other threads around here on boats.


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## glaurung (Nov 11, 2009)

Hi,

There is one electric catamaran in Finland that could be inspirational.
I was there in summer and got a tour after telling that i have build an electric Range Rover.It has two ac motors to drive and one bolted to diesel generator. Lithium batteries.They made their own motors and controllers. Even batteries are from Finland.Very fine ship.
http://venenetti.fi/uutiset/inari-iii-ylitti-odotukset
http://venenetti.fi/jutut/inari-iii-lipuu-sahkoisesti-pohjoisessa

Full steam ahead!

Regards, Harri


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## [email protected] (Mar 21, 2012)

omofreno;294113]I assume you intend to use TWO PMAC motors, since they are replacing two 50 HP diesels. Should work. If you need them to output 50 HP continuously in a storm for 8 hrs that is about 298kWh. A 180Ah LiFePO4 cell is about 12.3 lb and 0.576 kWh, or 0.047kWh/lb, other Ah sizes vary a bit. I would guess you would want to keep the battery pack total weight less than say 500 lb? That would be 23.5kWh, so yes the generator (maybe two smaller ones for redundancy) will have to supply full power for most of the 8 hours. There are some other threads around here on boats.[/QUOTE]

Thanks guys.
Tom Yes I will be using two motors. Re the batteries I am expecting a fair weight of batteries regardless, expecting at least 500lbs, more like 750+lbs. The genny will need to continuously top up the batteries as we motor if heavily weather is the go. I need to do the calcs but hoping if i can match in and out I can keep a steady state. But more work to be done on that. I'm currently looking at two of these kits... http://www.electric-cars-are-for-girls.com/electric-vehicle-motor.html. The HPEVS system looks great.


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## [email protected] (Mar 21, 2012)

omofreno;294113]I assume you intend to use TWO PMAC motors, since they are replacing two 50 HP diesels. Should work. If you need them to output 50 HP continuously in a storm for 8 hrs that is about 298kWh. A 180Ah LiFePO4 cell is about 12.3 lb and 0.576 kWh, or 0.047kWh/lb, other Ah sizes vary a bit. I would guess you would want to keep the battery pack total weight less than say 500 lb? That would be 23.5kWh, so yes the generator (maybe two smaller ones for redundancy) will have to supply full power for most of the 8 hours. There are some other threads around here on boats.[/QUOTE]

Thanks guys.
Tom Yes I will be using two motors. Re the batteries I am expecting a fair weight of batteries regardless, expecting at least 500lbs, more like 750+lbs. The genny will need to continuously top up the batteries as we motor if heavily weather is the go. I need to do the calcs but hoping if i can match in and out I can keep a steady state. But more work to be done on that. I'm currently looking at two of these kits... http://www.electric-cars-are-for-girls.com/electric-vehicle-motor.html. The HPEVS system looks great.


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## major (Apr 4, 2008)

[email protected] said:


> The HPEVS system looks great.


Yeah, it's a nice motor/controller package. But won't do that 35kW continuously. If you're going to need that much power for 4 to 8 hours, you'll need a bigger motor/controller, possibly liquid cooled.


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## tomofreno (Mar 3, 2009)

Yes, sealed and water cooled. Maybe something like this:
http://shop.electro-vehicles.eu/shop/details.asp?prodid=1101040&cat=0&path=1100,1101
Don't know much about these guys, but they claim that marine applications is one of their main interests.


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## ddmcse (Oct 9, 2008)

Mick, check these guys out.
http://www.propulsionmarine.com/electric/10kw-water-cooled-electric-drive


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## boekel (Nov 10, 2010)

I'd go for standard industrial parts, like I did:

http://www.youtube.com/watch?v=_z8ALiBgUZM

http://www.youtube.com/watch?v=dPGMGF9LKis

Those parts are virtually bulletprove, watercooled is possible but way more expensive.

I'm investigating the use of a smaller gen-set of about 30 kW plus a battery so I can use 30 kW forever and about 120 kW (max of my vfd) for shorter runs. Also of course to use battery-only-mode.

Is it going to be a lightweight ship? if not lead-acid is still a very good option, 2v traction cells last a long time and are very forgiving, no need for bms...


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## Arlo (Dec 27, 2009)

Im excited to see how this thread progresses.


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