Looking into upgrading 2000 Malibu Response LX to electric drive

[Footer613]

Hi,

Every few years I work through the math to see if upgrading a water ski  boat to electric drive is feasible.  I just purchased a 2000 Malibu Response LX that I am very happy with BTW.  There is yet newer electrical systems out now so it is time to work through the feasibility again, but now with the Malibu.  It looks  like it has a Monsoon V8, 310 Hp which may produce about 400 ft-lb of peak torque. 

1. Does anyone know what the actual peak torque is? 

2. However, the most important question is, what is there a gear reduction in the transmission (if any)?  Torque is not as critical, since an electric drive will put the V8 to shame with torque. 

The goal is to size the motor to exceed the torque, match the prop speed and then size the battery.  The challenge is typically related to the batteries. ... light enough and enough capacity (say 3 hours of heavy use) before re-charging and of coarse at a respectable cost.  Safeties exist to protect people from a high voltage battery if the boat sinks.  The plan would be to replace the  engine and transmission with a direct drive electric motor.

Regards,

Rob

[barefootpaul]

This sounds really interesting. I'm one of the few people who would love to have an electric dd. Even at one hour of runtime. Post up what you are finding.

Pretty sure dd transmissions of that era are 1:1. Or do you even need one? Do these systems go backwards natively?

[asnowman]

these guys have put in a ton of work, I understand they have worked extensively on the electric Nautique.

http://www.ltsmarine.com/english/

 

[uk_exile]

Looks like LTS have done a Malibu too http://www.ltsmarine.com/english/bateau-hybride-ski-vague-lts/ 

Seems to be plenty of businesses getting into electric crate motor swaps that direct mount into existing V8 mounts.

https://electricgt.com/gte-motors/

https://electricgt.com/413-egt-motor/

https://www.motortrend.com/news/tesla-crate-motor-ev-conversion-small-block-v-8/

The battery will be the more challenging part to obtain

 

Edited June 28, 2022 by uk_exile

[COOP]

Those less than an hour run times can be tempting.

[Tsumi]

At the same weight? No, you are not going to get 3 hours of runtime. You will need at least triple the current energy density-weight ratio.

[justgary]

Let's scratch on the back of an envelope for a minute....

Assume that you have a 300 HP motor in your boat.  Yes, I know the label says 325.  300 HP * 746 W/HP = 223,800 Watts.  Let's use the common 3/5 rule on electric motors, so we get 134,200 Watts of electric motor for the boat.  We also know from your link above that LTS is getting about 30 MPH on 100kW and 40.5 MPH on 160kW, presumably without towing anyone.  That means our conversion is close since you have a smaller boat, but I want to barefoot, so I'll assume a 200kW motor.  Now we need a battery.

I personally think the battery of choice here is Lithium Titanate (LTO), but they are fairly expensive and not that energy dense.  I don't like Lithium Ion due to the instability issues, so let's look at the much safer Lithium Iron Phosphate (LFP).  A 304 Ah 3.6 V cell runs about $150 delivered to the US right now.  We'll figure 930 Watt hours per cell since you don't want to fill them full or run them empty, which would greatly reduce the life.  In order to run the boat at 32 MPH pulling a skier, you would need (I estimate) about 120kW or so.  One hour of pulling a skier (the great thing about electric is that it uses zero energy idling) needs 120kWh of energy stored on board.  That would take 129 of our 304 Ah cells.  Add a few hundred for battery management systems and chargers and you are probably right at $20,000 for LFP batteries.  Per hour of run time.  You will want to charge the batteries at around 0.5C, or 150 Amps.  A full charge will take two or three hours.  If you want to spring for LTO, they can charge at much higher rates (like 6C) and don't really care about temperature.  They would cost at least double what LFP costs and take much more space.

129 of those cells weighs 1,558 pounds, but you would need to add about 50 pounds for the other electronics and battery cases, so assume 1,600 pounds for the batteries.  They would need almost 12 cubic feet (0.336 cubic meters) of room in the boat.

[Footer613]

On 6/28/2022 at 10:39 PM, justgary said:

Let's scratch on the back of an envelope for a minute....

Assume that you have a 300 HP motor in your boat.  Yes, I know the label says 325.  300 HP * 746 W/HP = 223,800 Watts.  Let's use the common 3/5 rule on electric motors, so we get 134,200 Watts of electric motor for the boat.  We also know from your link above that LTS is getting about 30 MPH on 100kW and 40.5 MPH on 160kW, presumably without towing anyone.  That means our conversion is close since you have a smaller boat, but I want to barefoot, so I'll assume a 200kW motor.  Now we need a battery.

I personally think the battery of choice here is Lithium Titanate (LTO), but they are fairly expensive and not that energy dense.  I don't like Lithium Ion due to the instability issues, so let's look at the much safer Lithium Iron Phosphate (LFP).  A 304 Ah 3.6 V cell runs about $150 delivered to the US right now.  We'll figure 930 Watt hours per cell since you don't want to fill them full or run them empty, which would greatly reduce the life.  In order to run the boat at 32 MPH pulling a skier, you would need (I estimate) about 120kW or so.  One hour of pulling a skier (the great thing about electric is that it uses zero energy idling) needs 120kWh of energy stored on board.  That would take 129 of our 304 Ah cells.  Add a few hundred for battery management systems and chargers and you are probably right at $20,000 for LFP batteries.  Per hour of run time.  You will want to charge the batteries at around 0.5C, or 150 Amps.  A full charge will take two or three hours.  If you want to spring for LTO, they can charge at much higher rates (like 6C) and don't really care about temperature.  They would cost at least double what LFP costs and take much more space.

129 of those cells weighs 1,558 pounds, but you would need to add about 50 pounds for the other electronics and battery cases, so assume 1,600 pounds for the batteries.  They would need almost 12 cubic feet (0.336 cubic meters) of room in the boat.

Good points, approximations and respectable math.  I agree that the battery/ energy storage related issues are the primary challenge.  …energy to weight and cost are still the limiting issues.  I think I’d still go with Li-Ion batteries though.  As much as they can be unstable, that risk can be effectively managed via design and has been proven enough with the existing vehicles using them.  …aircraft continue to crash, but I still travel by air, since the odds and quality are there.  It would be nice to get a better handle of the actual power/torque needed.  Horsepower in gas engines can be very misleading.  Depending on how an engine is propped (often for increased hole shot) and that peak Hp is only reached in a very small rpm range, typically somewhere in the 5,000 to 6500 RPM range, a boat may not actually be using all the rated Hp and definitely not all the time.

I think 1 hour of actual run time could represent a morning of skiing.  I slalom and barefoot, but an actual BF run would be <5 min. at 40 mph and the rest of the runs at 36 for slalom.  So averaging 200KW may be a bit high.  However, even at 150KW the needed battery weight is still higher than I would want to put in my boat and the Li-Ion cost is lower, but still too expensive.  
 

Better environmental solutions to boat related water sports don’t seem to be here yet, but they are continually getting better.  Powering an engine with hydrogen may also be an option, particularly if a better hydrogen storage system is developed.  Hydrogen isn’t a perfect zero emissions solution, but a lot better than gasoline.  There is some research being done related to being able to dissolve hydrogen into a liquid to improve its storage.  I assume something like how acetylene  gas is dissolved in acetone for storage, although that is done primarily for stability/safety.  
 

For now I’ll need to stick with my gasoline engine which leads to my next post - how to make it quieter 

thx for all the comments

regards 

Rob 

[Bluefishcay]

Really hard to get enough battery to make it work for any amount of time.  Another way to figure it out is look at how much gas you burn on a normal day of boat use.  Say 5 gallons per hour, that is 5* 33.7 ( kwh per gallon of gas) = 168kwh of energy used. Now electric motors are 3-4x as efficient as a gas v8.  So you can divide by 3 or 4.   Which is 56 to 42 kwh of electricity.  Now you want to stay in the 15-85% of the discharge range to have decent battery life, so divide by .75.  That gives a pack since between 56 and 75 kwh.  Roughly the same pack in current ev’s, 950 - 1050 lbs.  thats assuming one hour of use at 5 gallons per hour.    If you are going for 3 hours that’s more battery than the weight of the boat.