question

Hi Caver. There's a few articles in the Victron blog that should interest you: https://www.victronenergy.com/blog/?s=electric+propulsion

That's an interesting (not to mention extremely $$$) endeavor ;)

But I wish you the best and look forward to your followup posts on progress.

I'll take a crack at the 3 battery banks scenario.

You'll really need 3 different chargers, or ways to control the charge individually per bank.

You should not have mismatched capacities running together as if they're a single system -in parallel. Your two nacelle banks might likely be the same, but your house loads are likely considerably smaller. Not to mention the different voltages :)

So you'll either need 3 chargers or a way to relay control the charge to each bank separately -again voltages have to obviously match.

You'll definitely need a different battery monitor (BMS for the cells and BMV for the "battery" composed of those cells) for each bank.

Based on your descriptions above, a single inverter is all you'd need for house loads. Its size will greatly depend on expected load. But a 5Kw Quattro would be a good candidate to start your consideration.

The remainder of your system is relatively simple after that. Your batteries are DC, your motors are DC, and your charging system will be DC.

I'm curious about the 48V motors and their ability to deliver the torque you'd need. Tesla motors, for example, are in the hundreds of volts. And hombrew EVs are running above 100 volts. Plus to deliver the kind of amps required to propel that beast, you'd have to have wires the thickness of your arm :)

So I think it might be time for a review of the plans?

Anyway, hope that helps and good luck.

Hi - there's a few different forums which specialises in exactly what you're looking at, including electricseas.org, and I see from the tagging you're already on CF. Nordkyndesign.com is also a good reference site.

Re: 15kwh motor, I assume you mean 15kw. I suggest that if you're serious about continuous 15kw draw that you look at a higher voltage bank. You're looking at ~300A which is getting to the upper end of what batteries can supply with decent life times and more importantly heat management will become an issue, at the batteries, for the cabling and at the controller/motor. You really don't want to mess with water cooling for the batteries on top of all the complexities you will encounter. With high voltages you'll encounter other issues though. Once you're above the 5-10kW motor range there's a step up in cost in terms of material and engineering imo.

On IP ratings, you probably have to take that on as part of the design with enclosure for the batteries (including physically securing them for heavy conditions)

I have a system with Victron HE batteries. The batteries are great, but the device that makes the system is the required Lynx Ion BMS. Victron uses a Master/Slave BMS configuration where the Master is the Lynx Ion BMS and the Slaves are the internal battery BMSs'. The master BMS interfaces with the control device, CCGX, Venus GX, etc. and provides integrated control, through DVCC, for all the charging sources (Inverter/Chargers and MPPT Solar Charge Controllers).

Do some research, it's a great system.

Pat

Lots of good comments already!

I'd also advice to make 1 big battery bank, and try to aim at a maximum (continuous) current of 0,5C (so if you have a 50kWh battery, 25kW of power)
You really want to protect your battery bank from (salt) air / water so a sealed battery compartment / housing is the way to go. It helps if the battery doesn't need extra cooling (if the battery has enough capacity and is located in a (relatively) cool location you might be able to do without active cooling)

a 52' cat might really need to full 2x 15kW output at times, so I'd say 50-60 kWh of battery capacity.

30kW is also in my opinion still ok for a 48V system.

In terms of propulsion motors, you can also put a 3 phase AC industrial motor in the 'possible' list, I've equipped a couple of 60'-85' boats (steel barges, converted for recreational use) with those.
3x8/10/15k Quattro to create 3 phase 400 VAC, Variable Frequency Drive to control the motor(s)

The inverters can also be used for the house loads, although you might want to be able to switch them off for saving power (using a smaller inverter for low load situations).

Hi John

Thanks for links. Schematics helpful to understand system components but no systems listed that cover off all the issues we are considering. There are presumably ways to achieve a decentralised system which we prefer for weight and redundancy but it seems to be rather complicated (see my comment to Kai). Does Victron provide engineering advice ?

Cheers Rob

Hi!

We build electric houseboats with Victron components. I wouldn't recommend the Lithium-Ion HE Battery for propulsion. It was not designed for high current discharge, hence the 60A recommended discharge current. You would really need to parallel quite a few to be able to support around 300A. We opted for the smart LFP batteries, we didn't care about the weight, it was better from a cost perspective.

Also, I played around with many motors both AC and BLDC. My suggestion is that go with the one that has the most install base in your location. There are many so specialize is marine motors, Most of the time the software of the controller needs to be slightly adjusted to best fit your boat and if something breaks it is essential that you get proper support and spare parts. I can recommend suppliers in Europe.

You don't need to select the same batteries for both house and propulsion, the HE ones would be easily sizable to support the house loads. And actually this would answer the question about one or more battery banks to use. I understand why it makes sense for you to split them. Generally we also tend to go for one bigger, but having complete redundancy is quite an advantage for a boat.

Also keep in mind that some places don't have reliable 16A 220v shore power so it is also an argument for using two smaller chargers.

What's the displacement of the boat?