# House Boat Conversion



## remy_martian (Feb 4, 2019)

You need to go do some math (or mine is wrong)

Cruise at 96kW (one engine at power) at 6 MPH will get you 3 miles of range with the ten 48V 100Ah batteries you have planned...


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## MattsAwesomeStuff (Aug 10, 2017)

You don't seem to have too limited a budget, but, I would not spend the money on an AC51. Just reuse something already out there.

Likewise I would not buy new batteries, I would reuse OEM EV batteries. And lots, and lots of them, up to your whole budget.

Boat duty is pretty severe compared to car duty. With most cars we can say "Meh, yeah, this 15hp motor can put out 150hp anytime you'll ever actually do that", because outside of motosport, you're pulling like, 20hp at highway speed, and you'll reach highway speed in a few seconds, so who cares about overdriving the motor. But on a boat, none of that is true. You'll actually be using 130hp constantly to maintain even a slow speed. That's not just hard on the motor (meaning, it'll actually have to be sized appropriately), it means you're going to bleed batteries badly.

Talk a little bit about your range and travel expectations.


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## kennybobby (Aug 10, 2012)

For a boat application you need high torque more than high speed since the prop RPM is cavitation-limited.

The great thing about electric motors is that full torque is available at low rpm right off the start.

If you could use a different gearbox ratio then it would reduce the battery pack current draw.

The hard part of sizing this system is knowing the required torque and rpm at the prop to meet your goals. If you could find a dyno chart for the volvo engines then it might help understand some of the factors to consider. i'm sure there are online calculators to determine power requirements for boats based upon weight and speed, etc.

i don't know if boekel is still active on this forum but he has a wealth of experience with large boats, see Measured power consumption of a boat (70T barge)










i like to look at electric motor charts with torque on the X axis since that is controlled by current, and the speed is the resultant depending upon the load, such as this for the AC-51. Notice how linear the current ramps up at full torque in the low-rpm region.


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## remy_martian (Feb 4, 2019)

Full torque might be available but the horsepower is zero. A gearbox multiplies torque and new props cost a fortune.

The 2:1 drives are close to optimal, so can double the torque to the props at low speed, yet still make speed at 5000 motor RPM.

Horsepower, not torque makes speed. There's no magic, despite a flat torque curve. And, unless you have bags of money, the drives and the props should be reused as is.


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## chc911 (8 mo ago)

@remy_martian Thank you for your input. I was going to make a case similar to what @kennybobby did before he graciously shared his input. 
I would agree with you whole heartedly if I were trying to make a ski boat surpass theoretical hull speed and plane out. However the closest real world comparison I can make to my application is a sail boat which is routinely powered by 30-40Hp diesels with similar weights to my boat and similar speed (7-8mph cruise). The torque is what powers these boats with the correct prop as you said. I replaced my props 3 years ago for about $700 so to me that would be a reasonable investment for an upgrade to some "high torque" props. You are correct in that I do not want to replace my outdrives.

I found this online calculator that should help with the discussion 





Vicprop - Prop calculator for Displacement and semi-displacement hulls


Vicprop, marine propeller specialists.



vicprop.com





I entered data based on continuous power and torque charts of the HPEVS AC-51 (We can discuss if this is the best option once we better under stand what is needed.)








Here are the power results:









@MattsAwesomeStuff While I am capable of "hacking" together a system I would like something that is fairly plug and play. I do not want to put hundreds of hours into figuring out the particulars of some random CANBUS system. With that in mind what would you recommend? I am not locked into any of the hardware I have recommended, it is just where I am starting the research from.

Travel expectations: 
Max Range 29 miles / ~4 hrs at ~7mph

How can I use the AC-51 charts to determine estimated power consumption to maintain that speed? The peak and continuous charts are quite different. Currently I can maintain ~7mph on one engine at 2250RPM

I can not find any charts for the current volvo B230 engines but they are ~130hp new. Keep in mind they are very old and despite my best efforts are not running at their optimum specs.


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## kennybobby (Aug 10, 2012)

Did you make a typo on the form--mean to enter 64 instead of 34 for the max rated HP?

The B230F engine seems to be rated as 114 HP on various websites, and the B230E at 131. Those are likely peak numbers at some high RPM. One fellow swapped out the cam for performance mod:


> had the car on a dyno at one point...peak of 117.9lb-ft torque, but the important part was the 100+lb-ft from 1900 to 4000rpm


So it might be reasonable to assume 90 ft-lbs at 2250 rpm, which makes your single engine cruising power ~39 HP. Two engines can give you quicker acceleration, but you said can cruise just fine on one.

The AC motor looks to easily exceed the ICE, at 2300 rpm it is capable of 137 ft-lbs at 64 HP.

Now comes the hard part--how to provide the energy needed to run 4 hrs at cruise speed.

Back of the Envelope:
Assume it takes 100 ft-lbs before the gearbox, so the motor will need 450 Amps to make that torque and cruise with the present propeller. That's about 43kW and for 1 hr, 43kWh at 96V.

So ignoring losses it would take about a 180 kWh pack--two Tesla 90 packs. That would be 2000 A-Hr capacity at 96 V to run 4 Hrs. Most early EV packs other than Tesla were only good for about an hour of driving, but they are much higher voltage ~360-400 and the gear ratio is much higher at around 8:1.

With a high voltage motor, higher gear ratio and the right prop, then you might do it with a 500 A-hr pack at 400VDC.

You might do a 3-hour cruise with 375 A-hr at 400VDC. Still very large format cells.


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## remy_martian (Feb 4, 2019)

The calculator does not agree with observed speeds on ICE. He's seeing nowhere near 10.4mph, even on two engines he sees 6.5mph.


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## chc911 (8 mo ago)

@remy_martian I did not get the same calculations. When I entered my current motor values it came out very similar to actual. I have seen a little over 12mph full throttle on both engines. 
Image of ICE values and results attached below. 
(I did change my hull to better reflect my boat. I put 1.5 feet but my actual hull draft may only be ~1ft. My outdrives are ~2ft. I have attached an image of my boat below also.)

@kennybobby


kennybobby said:


> Did you make a typo on the form--mean to enter 64 instead of 34 for the max rated HP?


I used the max continuous horsepower shown in the continuous graph for the motor specs. I am assuming this is max horsepower available for cruising and cruising speed is what I used also.


https://www.hpevs.com/Site/images/torque-curves/ac-51/96%20volt/Imperial%20pdf%20graphs/AC51%2096%20volt%20650%20amp/Continuous%20graphs/ac51%2096%20volt%20650%20amp%20imperial%20continuous%20graph%20FC.pdf





kennybobby said:


> Now comes the hard part--how to provide the energy needed to run 4 hrs at cruise speed.


And this is where I knew it would get interesting and destroy my plans and budget. For discussion sake lets work backwards from what I planned above. I am making a lot of assumptions that I know what I am talking about next so please correct me so that I can learn.

I adjusted the motor hp on the calculator until max speed equaled 7 knots. That equaled 60ftlbs at shaft. According to how I looked at the graph that would be about 275amps.
Please let me know if you do not agree.

275 amps at 96 volts = 26.4 kwh
(96 volts works well because it allows me to have two 48v house banks for the inverters. This is a cost saving over not having to have separate chargers, batteries, etc. for the house and propulsion)

Attempt to go max distance at 7mph:
10 batteries specified above @ 5.12KWH ea. = 51.2KWH. 
Assume I can use as much as 80% of that capacity = 40.96KWH
Supplement with 12kwh from generator = 52.96kwh
(240v split phase/50amp each leg)
House load = 3.6kwh
Available for propulsion = 49.36KWH
That would be almost 2 hours of runtime with generator? 1.4hr of all battery?

Cost
Batteries $14,990
Motors $10,000
Chargers/Inverters $2598
Adapters $2000
Additional wiring $1000
Shipping $1000
Total $31,588
I do not achieve my goal of budget or range. There are benefits to electrical that offset the cost and I plan on installing a house bank anyway.
I would accept this range if I could get closer to my budget. Sitting on the lake waiting for the generator to provide some charge is not a bad thing!!

Another negative is with this battery bank both motors can only pull a max of 500 amps together or independent. I assume I can limit max amp from each motor through the controller. I need the continuous duty of the larger motors more than the peak hp/torque. I have never had to use full power, even in heavy winds, to control the boat.

Any ideas on doing it cheaper?


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## kennybobby (Aug 10, 2012)

i hadn't seen the limited performance due to motor heating up--may need to consider a motor with liquid cooling, like a leaf motor, or seimens motors from the Ford etransit vans, that would lower cost too.

Nice looking boat, takes a big rig to haul it. Where are you putting in, at Lake Lanier or do you have a river route?


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## chc911 (8 mo ago)

@kennybobby They offer water cooling plates for the AC-51 and the controller.

I had considered the leaf motors because they have nearly identical numbers to the ICE motors. However I would really like to keep this from being a time suck of disassembling a car, figuring out all the buss stuff,etc. I have not looked at the etransit vans. If someone had a clean install kit I would be interested in it.

I currently have the boat at lake Hartwell in the upstate of SC. Will probably leave it here.

Thanks for all your help and if you come across anything that may help me out please let me know.


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## remy_martian (Feb 4, 2019)

So, you're converting a boat to electric, but will have the racket of an ICE generator running the whole time vs merely upping the battery capacity by 12kWh?

🤪


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## brian_ (Feb 7, 2017)

chc911 said:


> The torque is what powers these boats with the correct prop as you said.


No, power is what powers any vessel. The combination of torque and speed to produce that power is determined by the speed through the water and the propeller choice. If you are using the original prop then the combination of electric motor and any added reduction gearing will need to produce the same torque at the same speed as the original engine for matching performance.


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## brian_ (Feb 7, 2017)

chc911 said:


> They offer water cooling plates for the AC-51 and the controller.


A cooling plate for the controller makes sense; a controller plate for the motor does not. If you want a liquid-cooled motor, get a liquid-cooled motor. HPEVS does offer AC Electric Oil-Cooled Drive Systems for Marine Applications.


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## brian_ (Feb 7, 2017)

chc911 said:


> How can I use the AC-51 charts to determine estimated power consumption to maintain that speed?


If you know the power output required and you want the electrical power consumption, all you need is the efficiency: power output divided by efficiency is power input. That's on the charts, but only for various speeds at full power; efficiency will not be the same at the actual operating power, but you could use the value for full power at the relevant speed as an approximation.


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## kennybobby (Aug 10, 2012)

Electric motors don't make power, they make torque--and it is proportional to the current. At a given current the resulting speed that it turns depends upon the load on the shaft. That's why i like to plot torque on the X axis.

On an EV the size of the battery pack determines possible performance. Size the pack first based on vehicle weight, range, acceleration requirements, then pick the motor.


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## remy_martian (Feb 4, 2019)

Power makes speed. Horsepower, kW. Torque can only be converted to force, not speed...there's no time component in torque.

Yes, you can back out torque at a given speed, which gives current needed to maintain that speed, but if a motor does not make the horsepower number, what you get at zero RPM for torque is irrelevant.

Electric motors only make torque, and _deliver_ no power, when stalled. Meanwhile, you're pushing your 500 amps at it, waiting for magic. 

A gearbox, in this case ignoring losses, transmits all of the power through it and trades speed for torque. Max motor torque operating point does not deliver max power at a given prop/tire RPM.

The power required for a boat is at the prop, not the motor. For a car, it's where the rubber meets the road. Both of those levers,that convert torque to force, have to be turning to be useful in converting that force to speed. The force balances the load. The load varies with the square of speed, usually....it's not constant.

Motor power can continue to go up if the torque drops. By your twisted reasoning, you'd look for the peak motor torque and operate the gearbox at that motor RPM point, when you should be operating the gearbox at max delivered motor power which will deliver more power to the prop/tire at a given RPM of the prop/tire.

Figure out peak HP or kW for the motor as RPM, determine the RPM you need at the tire or prop (for a tractor or boat, this is easy), ratio your drivetrain accordingly. Conversely, if your drivetrain has a fixed ratio, you need to have a prop made that turns at half the RPM (for this boat) of the peak HP RPM of the motor curve, not its peak torque RPM.


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## kennybobby (Aug 10, 2012)

Looks like we will just have to disagree about how electric motors really work and how to select one for the task. 

My point of view comes about from working the past 40 yrs in the design and development of controllers and electric motor actuators, including testing hundreds of electric motors on various dynamometers. 

For anyone still reading all this and needing to pick a motor, i would recommend to get a second technical opinion from some of the top tier motor designers and manufacturers such as Inland Motors aka Kollmorgen, etc. Most of them have motor selection handbooks or guides to help you calculate your torque requirements and size the motor to do the job.


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## UglyCarFan (8 mo ago)

OP: I'd also consider looking at the DIY Solar Power forum if you have not already done so. Are you planning a nice solar panel array for your houseboat? I would.....

If so, you might factor that into your plans. Victron makes great equipment for applications such as yours.


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## chc911 (8 mo ago)

Thanks to everyone who has contributed to this thread. All the information is valuable and I believe will be a resource to others looking to do something similar.

Update:
I took the boat out this past weekend on 1 ICE and found that cruising at 5 knots accomplished my goals nicely. I recalculated my expected usage and achieved the below assumptions.

I adjusted the motor hp on the calculator until max speed equaled 5 knots. That equaled 41ftlbs at shaft. According to how I looked at the graph that would be about 125amps.
Please let me know if you do not agree.

125 amps at 96 volts = 12 kwh 

Attempt to go max distance at 5.5mph:
10 batteries specified above @ 5.12KWH ea. = 51.2KWH.
Assume I can use as much as 80% of that capacity = 40.96KWH
Supplement with 12kwh from generator = 52.96kwh
(240v split phase/50amp each leg)
House load = 3.6kwh
Available for propulsion = 49.36KWH
That would be 4 hours of runtime with generator? 3hr of all battery?

How far off am I on these assumptions? @kennybobby @remy_martian @brian_ 




brian_ said:


> No, power is what powers any vessel. The combination of torque and speed to produce that power is determined by the speed through the water and the propeller choice. If you are using the original prop then the combination of electric motor and any added reduction gearing will need to produce the same torque at the same speed as the original engine for matching performance.


 @brian_ . My point here was that if I changed props to utilize the electric torque then I could achieve the same speed with fewer RPM. I see where that was confusing.



remy_martian said:


> So, you're converting a boat to electric, but will have the racket of an ICE generator running the whole time vs merely upping the battery capacity by 12kWh?
> 
> 🤪


@remy_martian An additional 12kWh of battery capacity is ~$3000 and runs out when it runs out. The generator will produce that hour after hour as long as there is fuel. There are multiple reasons to keep the generator. One of which is that I can stay out all weekend as I am this weekend. I am also decreasing maintenance from 3 ICE to 1 so there is still benefit to going electric.



UglyCarFan said:


> OP: I'd also consider looking at the DIY Solar Power forum if you have not already done so. Are you planning a nice solar panel array for your houseboat? I would.....
> 
> If so, you might factor that into your plans. Victron makes great equipment for applications such as yours.


@UglyCarFan I do plan on supplementing with solar in the future. That is a big reason I chose the inverter/chargers described in the original post. Of course I am not set on any equipment yet and know that Victron does make nice equipment.


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## remy_martian (Feb 4, 2019)

Get a fuel flow meter and determine fuel flow at 5kt. That should get you a HP number. 

You can back out the torque needed with the RPM you measured at that fuel flow.

For the money about to be spent, I would collect real data vs correlating a calculator.


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## aktxyz (6 mo ago)

I have used that same vicprop calculator for some stuff I am working on.

Any chance you are considering motors way larger than you actually need? When I put your hull spec numbers into vicprop and choose 5 or 6 knots as the target speed, the HP required at the prop is much lower than what you are looking at ... making the AC-51 look like overkill (or am I missing something). Only the hull spec info is used in figuring out HP required for a certain speed. The number of engines, rpm, engine hp, bearings, etc ... don't get used in the "hp required for speed" calc. Change those values wildly and this hp-for-speed number stays the same.

HP required at propeller(s) for desired 5 knots speed: 14 HP
HP required at propeller(s) for desired 6 knots speed: 24 HP

The vicprop calc is quite generalized, so makes some assumptions. A brick shaped boat and an FPB style boat with same length/beam/draft/disp would obviously have different results, but the calc would show the same result. My guess is that a houseboat shape is probably on the underestimate side of the power requirements.

Have you checked out what this tolly guy has been doing? using 10kw lynch motors






Also for super-turnkey and budget blowing, this is this fairly new solution (this saietta company has some historical relation to the original lynch shop ... also reading about this lynch guy is fairly interesting/entertaining)









Propel D1 - Launch Edition


10 kW (25 hp equivalent) marine inboard Automotive spec controller with vector control Various lithium battery pack & charger options The Propel D1 is a 10 kW (25 hp equivalent) marine inboard based on a highly efficient Saietta axial flux pancake motor. This Propel D1 launch edition can be used...




shop.propel.me


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