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We did it, purchased 2 Motenery 1115 10kw motors, 2 Sercon Gen4 controllers from Thunderstruck motors. Sold the 2 Crusader 270 gas burning engines on eBay in December. Hardest part was fabricating motor plate to hold the Baldor/Dodge 4:1 reduction gear sets, electric motors and bearing box out of 1/2" stainless steel (this is a salt-water boat!). Power comes from 2 banks of 12V lead-acid 150AH batteries wired in series to give us 48V.
We figure 8-10 mile range, need to do sea trials on speed/range. Huge props like to run at 500 RPM so 4:1 gearing puts the motor at 2,000 RPM for efficiency.
Motors and programmed controller came from Thunderstruck Motors.
More work to do, but we probably have the only electric Silverton Motor Yacht right now!
Check out the videos:
Maiden Voyage
Motors during a U-Turn
 

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I dunno that I'd trust a marine craft with a belt drive. Though I suppose you aren't going far from shore with a pair of 10kW motors and that battery pack.

Looks cute!
 

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The Crusader "270" engines are marine adaptations of Chevy 350 CID (5.7 L) small-block V8's, in the 270 horsepower version.

We did it, purchased 2 Motenery 1115 10kw motors, 2 Sercon Gen4 controllers from Thunderstruck motors. Sold the 2 Crusader 270 gas burning engines...
Did you really replace two engines capable of producing 270 horsepower (201 kW) each with two electric motors capable of producing just 10 kW each?

It obviously works for a slow cruise and is nice and quiet, but the planing ability of the modified vee hull is presumably now irrelevant, as it likely can't get up on plane. I assume that the intent is to operate it as a pure displacement hull (no faster than about 5 knots / 7 mph / 10 km/h), and 20 kW should be more than enough for that. :)

I'll likely never own a boat, but I'm curious about their energy consumption. At the speed that rich people like to cruise at in the big yachts the energy consumption is enormous; even a very practical boat at low speeds seems to use as much fuel as a large motorhome of the same length at highway speed.
 

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I dunno that I'd trust a marine craft with a belt drive.
While perhaps not ideal, I don't know that I would be concerned about it, although I would want to ensure that they stay clean and dry, and I would want to see a spring-loaded tensioner that these don't have (so the belts are whipping). Automotive toothed belts run for many years reliably.

A spare is easy to carry. Hopefully the belts are easy to change, although it doesn't really look like it (with no tensioner to release and no swinging bracket for the motor). Maybe that's an area for refinement in the next phase of the project. :)
 

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Power comes from 2 banks of 12V lead-acid 150AH batteries wired in series to give us 48V.
We figure 8-10 mile range, need to do sea trials on speed/range.
Is that two banks of four 150 Ah 12 V batteries each, or 150 Ah @ 48 V total? I'm guessing that it is two independent banks (for redundancy) of 150 Ah each,

Assuming 150 Ah per bank, that's nominally 3.6 kWh total (150 Ah * 12 V * 2). With 8 to 10 miles of range, that's 360 to 450 Wh/mile or 224 to 280 Wh/km, which would not be much for a vehicle of this size on land... but a land vehicle would be going much faster on a highway. Interesting data - thanks!

The 150 Ah rating is likely on a 20-hour basis (C/20), and usable capacity if discharged over perhaps two hours capacity might be around 90 to 100 Ah, or 75 to 80 Ah to 80% DoD. If you can really get 8 to 10 miles on 75 Ah per bank that's only 180 to 225 Wh/mile (112 to 140 Wh/km).

That's probably about 400 kg of battery, for only 3.6 kWh, but I suppose the weight is not a problem and is needed as ballast to balance the boat with the engines out. :) The modules of an entire salvaged EV battery, reconfigured for the low voltage and in two banks, could provide several times as much energy for the same weight, and still fit in the available engine spaces... but of course there would be cost and battery management issues.
 

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Discussion Starter · #7 ·
Baldor/Dodge gearset belts are very strong, we will carry a spare but we over-engineered the HP rating of the gear/belt set. Very precise tolerances: .43mm on gear centers, we're almost spot on so likely don't need idler wheel. Belt slips on over large gear or the gears are easy to pop off.
Each battery bank uses 12v AGM battery w. 150 AH, x 4 = 48v and 150AH. Motor can pull 200 amps, we're hoping to cruise (putter?) around the bay at 5 knots and 60-90 amp-hour draw. Each motor fed by independent bank of batteries. Weight of lead-acid batteries is not a concern in a 18,000lb boat. Batteries weigh 110lb each or 440 lb for each 150AH 48volt bank. I know we can only draw down to 30%-40% unless we want to hurt the batteries...
We need to finish up the instrumentation (current draw shunt and meter, GPS) and do some sea trials to see what kind of speed/range we get. Stay tuned for results. We are not expecting much: cruise at 5 knots, range <8 miles will be fine for our purposes with some extra power available for getting out of trouble or into a windy slip.
Next year we want to add a diesel with 2 alternators (60-80 amps at 48v) to make it a true hybrid.
In the year 2026 with the lead-acid batteries at end-of-life we'll do version 3.0: 300+ HP electric motors, glass batteries or some other 2026 vintage power technology, get the 18,000lb boat up on plane again at 20 knots. Technology isn't here yet for this, but it will be....
 

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Weight of lead-acid batteries is not a concern in a 18,000lb boat. Batteries weigh 110lb each or 440 lb for each 150AH 48volt bank.
I agree - the current setup is likely lighter than the original engines.

Next year we want to add a diesel with 2 alternators (60-80 amps at 48v) to make it a true hybrid.
At only 6.7 kW, this would presumably be a little one-cylinder or two-cylinder engine.
The plug-in hybrid approach makes sense to me, with engine power to match average demand and much higher battery and motor power to handle the peaks. Of course you won't be able to use the high power much, and as with any hybrid overall fuel consumption at moderate power won't be much different than just running appropriately sized diesels directly; the advantage comes if typical use is way off the optimal operating point of the engines.

In the year 2026 with the lead-acid batteries at end-of-life we'll do version 3.0: 300+ HP electric motors, glass batteries or some other 2026 vintage power technology, get the 18,000lb boat up on plane again at 20 knots. Technology isn't here yet for this, but it will be....
We can hope, but since 2021 battery technology is essentially the same as 2016 battery technology, 2026 battery technology seems unlikely to be radically different.
 

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Baldor/Dodge gearset belts are very strong, we will carry a spare but we over-engineered the HP rating of the gear/belt set. Very precise tolerances: .43mm on gear centers, we're almost spot on so likely don't need idler wheel. Belt slips on over large gear or the gears are easy to pop off.
I'm more accustomed to automotive applications of belts, in which exact spacing isn't important because the tensioner handles it, and operation with a tensioner (for a high-power toothed belt) wouldn't be considered acceptable because belts stretch. This fixed approach does have the advantage of working equally well in forward or reverse. :)
 

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.I'll likely never own a boat, but I'm curious about their energy consumption.
Hey Brian, think about this:
When you’re tooling down a level road on a calm day at a steady 2000 RPM with your 350 Chevy car or truck, you might be using 40 to 60 hp (tops) to push it through the wind and overcome rolling resistance. Nowhere near the HP that the engine is capable of producing at that RPM.

If you encounter a hill, you need to give it more gas, to produce more horsepower. Your speed and RPM are the same, but your HP and fuel consumption will increase.

if the hill gets steeper and steeper, at some point you will reach the HP limit for that engine at that RPM. A look at the RPM vs horsepower curve for a given engine will tell you what that the maximum horsepower is for that RPM. You will need to downshift, to increase your mechanical advantage, (through the transmission) along with increasing your RPM (and thus HP… higher on the curve.)

Think of a boat as going uphill ALL the time. At any given RPM/speed, the engine will be producing the maximum horsepower it can, and using the maximum amount of fuel, according to the engine HP curve. If it is cannot produce enough horsepower to maintain a given speed, the boat will slow down. If you want to increase speed, you will have to increase RPM, and thus increase HP. Up to its limit… the maximum HP it will produce, corresponding to the maximum boat speed.

So, grossly oversimplified, a given throttle setting will correspond in direct proportion to your RPM and HP and fuel consumption.

I say oversimplified, because your speed and HP demand will vary, according to the wind and sea state and current. And remember, water resistance increases exponentially with speed.

But you get the idea… In a boat, you are never tooling down the road at high speed, using just a fraction of the HP that the engine is capable of producing. It is always producing maximum HP for a given RPM. Always “going uphill.”

So Brian, if you are “curious about (boat) energy consumption,” Find out what engine(s) it has, and what RPM the owners cruise at. Then look at the fuel consumption curve for that engine at that RPM.

Or look for a boat review online for that or a similar boat… They often have RPM/speed/fuel consumption charts as part of the review.

Remember, that curve represents the maximum HP or fuel consumption that engine can produce at that RPM… In a different application, other than boats, it can always operate BELOW that curve.

So given the massive reduction in HP for the electric motor versus the gas engine, yes, the Silverton‘s boat speed will be significantly limited.

That’s why most electric boats are used for relatively short range, or slow speeds, or environmentally sensitive places; i.e. short bay cruises, trolling motors, or for research or eco-tourism in marshes and such, where the low noise level is significant to the boat’s working purpose.

Ever hear of a Duffy? Perfect example. Low speed bay cruises. Forever they have been driven by essentially a low-HP DC golf cart motor and lead acid batteries, though I’m sure newer models have better technology.

I don’t know what else is out there, but there were some boats called “Epic wake boats.” They could operate about nine hours at low speed, or one hour at high speed, pulling wakeborders and water skiers. Long gone now, a victim of economic realities. I think Ski Nautique made some electric ski boats too, but I don’t know anything about them.

 

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Think of a boat as going uphill ALL the time.
I would say it's only like it's going uphill all the time if it is planing, and the best analogy for that is probably fixed-wing aircraft flight. As a displacement vessel (such as a Duffy), it's just like driving level but possibly (depending on hull design) with very high drag, as if the tires are nearly flat or the vehicle is pushing a barn door through the air. Rough water is very much like a rough road - it's harder slogging.

When I said I was curious, I meant that I wondered what was possible - the available specifications are for available vessels, and under only some specific conditions. The principles are all very familiar and the typical performance (in fuel consumption terms) of conventional designs have been easy to find, but of course fuel consumption combines the energy consumption of the hull with the (unknown) efficiency of the engine.
 

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Ever hear of a Duffy? Perfect example. Low speed bay cruises. Forever they have been driven by essentially a low-HP DC golf cart motor and lead acid batteries, though I’m sure newer models have better technology.
I like the idea of Duffy's Power Rudder™ drive system (although there's no indication of the motor type), which is their rendition of an azimuth thruster (with the motor above the waterline).

I wouldn't count on any improvement in technology at Duffy. It looks like they still use lead-acid... probably on the basis that weight doesn't matter and discharge power demand is low enough (6.5 hours to full discharge even at top speed in the model that I checked). I couldn't find anything in their website about the motor (other than the nominal operating voltage of 48 V), but the Power Rudder drawing makes it look like a brushed DC motor. They have a Facebook page with an "About" section that says they use Advanced DC motors, which are of course old series-wound brushed DC; it may be outdated, but I wouldn't be surprised if nothing has changed.
 

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I would say it's only like it's going uphill all the time if it is planing,
Planing is a great example of the engine constantly producing max HP.

In displacement mode, you continuously increase throttle and HP, pushing against continuously increasing resistance.

Then suddenly, the hull starts to develop lift, and plane. Resistance drops dramatically, speed increases, and the RPM begins to increase rapidly. Why?

Because in transitioning to plane, water resistance has suddenly dropped, and quite suddenly the engine is making more HP than the boat needs to maintain speed. So the speed increases and so does RPM.

When does the boat speed (and RPM) start to level off? When the resistance (and HP requirement) starts to approach the engine's HP rating. The "curve."

The opposite happens "falling off" plane. The engine is no longer making enough power to maintain speed, even at the lower water resistance being on plane. When the boat falls off plane, water resistance suddenly increases, increasing the need for power, and decelerating the boat. The engine is no longer making enough power to maintain speed against the higher resistance, so the boat decelerates (and RPM decreases) to the point where the engine IS making enough power to maintain speed. Right at "the curve."

The long and short of it: In transitioning to or from plane, the engine can temporarily operate below the curve, but when the transition is done, it settles right back down...the engine produces the maximum power it can at that RPM.
 

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Congratulations! Simply take a whole bunch of speed vs. current (and actual voltage) readings. You'll be amazed at how low the current draw is at 2-3 knots (resulting in a significant range increase)! Converse is true the faster you go. Then do the math and be sure to include the non-linear battery 'capacity' vs current specs; also, don't go below 65%SoC if you want the batteries to last a bit. Pity you can't feather at least one prop so you can 'cruise' on one motor. Careful if the wind picks up as you have a lot of windage...
 
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