Planing electric boat with 40kw battery bank

Hello,

First off, I am a boat builder, but I’d easily get a failing grade on any advanced electrical systems test. This post will be long, so for that I apologize.

I am 2/3 the way through a new house project, on the water with an 18KW array of LG solar panels into 2 planned 7,500KW all in one solar inverter/charge controllers. I should easily have a surplus of solar charging capacity as the panels should more than cover my household electric need, even with heat pump all electric heat/AC at 1800sqft.

I may have the opportunity to acquire a significant amount of Valence U1-12RT lithium batteries(12V 40ah) with roughly 1/2 of their life cycle remaining directly from a major hospital system regular maintenance swap out. These batteries were used exclusively in hospital equipment and likely had an easy life to date.

https://mesa-tec.com/wp-content/uploads/2014/05/Mesa_Valence_U_Charge_U1-12RT.pdf



In my area, NJ coast, we have full retail value net metering, and power outages are pretty rare. So a dedicated large capacity battery backup system for our home is a tough sell normally.

But if I can get my hands on a large quantity of these matching Valence batteries(at a VERY low cost) that may change things.

There are rack style batteries made for back up battery systems like those from SOK, EG4, etc to compare to.

So as I’d prefer a large battery bank as backup if I had one, I’d look at it in one of 3 ways.

1- Buy something like a Ford Lightning electric truck with its huge battery and its “Ford intelligent backup power”system. So it’s a useful truck, and a backup battery.

2- set up about 80 or so of the Valence batteries into the house in a permanent installation.

3- make use of all that battery power into something fun rather than just sit idle 24/7 waiting for the rare need to put them to use.
That brings me to an electric boat. Seems a natural conclusion.

I could make use of both a more conventional 25 something foot narrow displacement hull boat running 5knots for many hours with ease, or something more aggressive designed around modest planing speeds. 20-25mph seems plausible with a very lightweight carbon/foam composite hull designed to achieve easy planing on modest power and significant overall weight(80 Valence batteries alone comes to 1200 lbs.)

I was involved (volunteer/partial sponsor) with the Stevens Institute of Technology collegiate solar splash contest program. Fun contest with the need to excel in 3 performance perimeters. A slolom course, a drag race, and a 2 hour endurance race with a few hundred watts of solar panels and a 100lb cap of off the shelf lead acid batteries. 36 volt max.

The 16’ shallow V carbon composite planing mono hull weighed 54 lbs, a liquid cooled DHX40 motor mounted to a modified 1950s Mercury KG7 Quicksilver racing lower unit with modified 2 blade race props pushed it to 28mph and it was a blast(and did VERY well against the competition). Only good for 1 fast drag race(as designed) of 200yds and 2 more a bit off pace.

I’ve seen a handful of newer companies offering all electric 20-25ft lightweight planing boats. Some using Torqueedo deep blue outboard systems with marinized BMW 40KW battery banks.

I could anticipate a 24ft carbon/foam composite shallow V hull, basically an enlarged version of the custom designed and extensively tow tank tested Steven Institute hull, with a bare hull weight around 4-500lbs. Battery bank at 1200lbs, controls and electrical around 75lbs, and drive system in the 150-200lb range.

These are totally off the cuff (somewhat WAG) estimates. But in total, just shy of 2000lbs minus people and gear.

assuming 4 people max and 50lbs gear, roughly 750 more pounds.

That’s 2750 lbs all up with a 24ft (22.5LWL) boat with a low sheer height race boat type design specifically designed to squeeze great planing performance out of minimum power output. Reducing capacity to 2 people for planing speeds wouldn’t kill me either.

It seems fundamentally plausible to be able to run 20mph for perhaps 10+ miles, or run 6 mph in displacement mode for many hours even with a less than ideal shaped hull for displacement mode use. Where I live, most regular destinations are on my body of water are from 1/2 mile to 2 miles away. I’m not talking about going offshore fishing here….

A typical day may be 2 miles on plane at 20mph, then 2-6 mph trolling speed while watching the sailboat races for 3 hours, then 2 miles planing home. That might be pushing it. A planned stop to a 50amp marine outlet for charging mid day is possible as well.

I’m curious if I am being realistic here. And I welcome any thoughts on bench racing a drive setup. I’m in the broad strokes stage here.

I’ve read a fair amount of posts here and clearly there are some really intelligent and talented members here in the electric boat world. I am humbled….

Thanks,

George

 

a few random, beer infused thoughts

I almost gave up reading your post, by the way. Start off with boats next time.

Impractical hull weight.

The current problem of batteries being awfully heavy does not vanish by pretending you can build a 24' boat that comes in under 500 pounds.

When you want to build a semi-displacement hull that performs well at low speed and has the available displacement for a ?1500 pound engine and fuel; you start to push practicals. A 50 gallon fuel tank and gas weighs 350# and a single engine 90hp same, so you are competing against 700-800 pounds roughly.

Pretending you can erase that in the boat is simply too expensive and results in a customized boat that really has poor engineering attributes with a skin/core misalignment..

So, something has to give.

The Bluejacket 24 is a beautiful boat that would be a good compare. Dry hull weight is 1850, with available displacement of 1000 pounds to waterline. So, your battery bank is already too big iirc @>850#.

So, let's say you build in foam and get the weight to 1000 pounds hull. Offers you 1850 for 'engines' and people and you limit pax to 6 and run below dwl on a full manifest.

More practical..

 

Yes, again sorry for the long post.

The Stevens boat hull above is 16’ long and 54 lbs. It’s a bare bones shell with a carbon composite construction. That’s 3.37 lbs per foot. And it has, FWIW, easily handled a significant chop at full speed with zero ill effects and stayed remarkably rigid. Frankly it’s a bit overbuilt as a pure race boat but a high safety factor was considered mandatory.

A 24ft boat weighing 500lbs is 20.8 lbs per foot. Or 6 TIMES the weight per foot as the Stevens boat.

Of course I am not talking about a production fiberglass boat meant for open seas and large power, or a fwd cabin high freeboard plans built plywood boat.

I am talking about a performance minded one off composite construction hull with little compromise for any whistles and bells, with a modestly higher proportional freeboard compared to the Stevens boat.

I could replicate the open racing Stevens hull scaled up with the same proportions to 24ft and come in at a mere 150 lbs.

I budgeted a further 250-350 lbs as the boat would be geared toward a bit higher weight carrying capacity per foot and a few more modest finish details.

An argument could certainly be made that such a light construction is not practical for the purpose at hand. But I assure you it can be done. And without question, for planing performance using electric power puts a huge premium on minimizing hull weight. This is why I am only considering such a specialized minimalist hull form and ultra lightweight construction.

George.

 

The Stevens raceboat would be designed for maximum displacement of engine, rider, and fuel at 16'. It is a vessel designed for speed; not the load of 1500 pound engine and a 200 pound single passenger. Most 24' boats would have available displacement for 8 pac as well or 1000 pounds.

You are mixing apples and oranges and calling it applesauce. Let a few others respond.

If you launch off a wave going 25mph with a one ton load in a 150 pound boat; make sure and be vested. Actually, make sure you are vested adding the load.

 

If you don't pass the advanced electrical systems test you should begin to study. As you buy them the batteries will be useless, their BMS is not designed for what you want. You will need to cut them open and reconfigure the cells in something you can use, then add an appropriate BMS. Not exactly a beginner grade job with 18650 cells.
From your use description you don't need a 40kWh battery. If the boat needs 40kW to achieve desired speed but you only stay at this speed 12 minutes you will need ~10kWh. To this we add the 3h of hull speed, wich is maybe another 3kWh. So your total need for a typical use case is 13kWh. Given that the cells are rated 3C, you need a minimum of 13.3kW to pull 40kW from them, add some safety factor and account for used cells and you end up with a battery around 20kWh. Just like that I have lost you 600lbs.

 

I fully agree that a 150lb hull would not cope well with a 1500 drivetrain load minus occupants in a rough sea state at speed. That is why I am quoting 400-500 lbs. 6 times the weight per foot as the Stevens boat. It would be a significantly more rigid hull more capable of handling the much higher weight carrying capacity per foot.

I can see the weight numbers appear impossibly light.

I own a 12’ 1953 Sid Craft A/B utility raceboat meant for a KG-7 acing outboard. It was among the leading A/B class raceboat designs of its day. Lightweight plywood construction, kneeling only rider position. Truly bare bones. Yet it weighs 135lbs as a bare hull, dead on the 1954 Sid Craft brochure specs. Imagining an arguably overbuilt race boat 4ft longer weighing a mere 54 lbs just seems impossible by comparison. Yet here we are.

 

Very helpful thank you. You unfortunately confirmed my greatest concern. That the batteries in question were not fundamentally suitable for the higher performance task at hand. Is it safe to say these batteries(as is) are more suitable for a more traditional 5-7 mph only use in a slippery displacement hull? I have no desire to cut open and reconfigure these batteries.

And yes, I have a LOT to learn about electric drive systems and batteries. I’m more comfortable with the boat end of things as that is where my experience lies.

George

 

George-what is a 24' boat design that would be suitable? And why 24', specifically?

 

I’m fortunate in that I have no specific need to fulfill. I own a 22ft outboard powered boat center console with a 48mph top speed, pleasantly high cruise speed, and good sea keeping ability. It’s a very useful craft for my area and use.

Any electric boat would frankly fall into the fun toy category. In our area we have two truly elegant 100 year old wooden launches fully and recently restored, running with the newest Elco inboard drivelines. There are quite a few fiberglass day launches in electric as well. All full displacement designs that suit their owners well.

I am not aware of any planing hull electric boats in my area. The concept intrigues me. The inevitable range restrictions is offset by the availability of the current standard outboard boat.

However, my main driver at the moment is the potential availability of a large volume of these specific high quality Valence 12V 40ah batteries that may potentially be gifted to me. The new retail cost of these batteries is quite high. At roughly halfway through their discharge cycle life or less, it’s a worthwhile incentive to make use of them. The title of the thread probably should have been, “If you had 80 mid life Valence 12v 40ah batteries gifted to you, what type of boat would you build around it?”

So what I really should have asked is the suitability of this specific type of battery for EV use. The larger Valence U27-12XP model is designed specifically for EV and house battery use(but not available to me). The smaller 12v 40ah battery was specifically designed for portable hospital devices and medical device (rolling cart based) outage backup. Since there are presumably no large surge type loads placed on the batteries, I’m not surprised if these batteries as produced wouldn’t be suitable for the specific battery demands of a planing hull.

And as I mentioned, I’m not inclined to cut open and reconfigure the 18,000 or whatever cells into another battery layout, upgrade BMS type, etc. It’s not impossible, but it would certainly be a massive jump in complexity and man hours(and I would certainly be bringing in someone far more talented in that work to help make sure that was done properly, or do it for me)

So assuming the consensus is these batteries(unaltered) are unsuitable for a planing hull, the next question is whether they are suitable for a displacement only launch which seems far more likely.

If that is the case, I’d likely be looking into the possibility of a large 48volt layout that is capable of being plugged into the house in case of a powered outage in the same function as a Ford Lightning highlighted in my original long winded post. Park the boat on its trailer next to the garage(the solar charge controllers are located on the inside of that wall), plug in the boat, and the battery bank becomes the power source for the home in reduced consumption mode in a rare power outage.

With a large and up to +/- 1200lb battery bank, I’d be looking at the 23-26 ft LOA range for a displacement launch type boat(also happens to be the ideal length boat for my boat slip) . I could possibly locate a suitable vintage wooden or fiberglass inboard launch to restore and convert from ICE to electric. I may be able to get my hands on a nice used AGNI 95 or 95R model for a reasonable cost.

Regardless of boat type, I’m certain that the end use would be occasional. Perhaps once or twice a week for the 5 months season at most. So perhaps 20-40 charge/use cycles per year. So batteries with several thousand cycles left on them would last far longer than I would.

George

 

Look, I might have been exaggerating when I said they are useless to you. The problem is that with the present BMS they can only put out 30A, and series connection is limited to 48V (and you need a U-BDI module). This means one series string can only put out 30A×48V= 1440W. For increased capacity you need to parallel more of this strings. Four 48V strings would allow 5760W wich is a good match for a 4kW electric motor, and that is fine for a displacement type boat like a launch.
For anything needing more power you need to go deeper down the rabbit hole and at least change the BMS. I understand that on the green cased ones it's possible to reuse the existing wiring. The next step is to completely rebuild the battery.

If someone gifted me 80kWh of this battery type I would certainly start studying how to modify them for my intended use, then decide if I can do it or hire someone to do it for me, or even sell the batteries and use the money to buy something else.

 

Rumars,

Thanks for the feedback. Very helpful.

So with a 48 volt limit, in groups of 4 batteries wired in series, is there a fundamental or realistic limit in how many 4 battery groups that can be then connected in series? You mentioned 4 groups of 4 in your example. That’s 16 batteries.

Is this essentially scalable such that for example 8 groups of 4 rather than 4 groups of 4 (both at 48 volts) would simply offer greater range for the same continuous power output? It would seems so….

George

 

The BMS is accessible in a separate compartment on the top of the Valence 40ah battery. In regards to the potential for battery modification, if the main battery case and cell wiring/packaging can remain intact, is there potential for swapping out the BMS for a more suitable version that could effectively convert these batteries into a suitable battery bank for a planing hull application?

George

 

Only Valence can answer that and advise on the correct configuration. In theory each string acts as an independent bank and should regulate itself and there is no limit. Practice might differ. Adding strings will increase available power, you would need 28 strings to pull 40kW.

Regarding the BMS you need one with a master-slave arhitecture as used by the XP series, for example Batrium.

 

I can share my experience in the subject

 

I found my five-meter cat to perform acceptably well with 6kW of power (via ePropulsion Navy 6.0 Evo outboard). 12mph top speed with two passengers, and 50-mile range at 5mph (48V, 10kWh battery).



Twenty of those Valence 40Ah batteries should be able to power the Navy 6.0, and get you close to the 10kWh I have. All eighty batteries won't quite fit due to the roughly 1,000-pound maximum carrying capacity. And even twenty will weigh around 300 pounds 'packaged', so your top speed would likely drop to more like 10mph. So maybe not the best way to use those batteries. Part of the problem is their low energy density: the pack I have weighs 160 pounds: