45' solar catamaran

Choosing the right prop is challenge .Mostly done by trying. For me hydro/aerodynamic is overkill sometimes . I'm not engineer and some sophisticated computer countings need hammer hit sometimes. I've heard about correcting flow around bow bulb literally by the hammer , despite all software.

 

I hope you not consider often flips and submerged .
Batteries you choose are most advanced batteries available . It's possible to buy brand new cells .

 

Software does not do the thinking for you, it makes calculations faster. Trial and error sometimes is made to work. However, sophisticated calculations will save a lot of time and money. For example, do you have the time and money to test 4 or 5 different engines and gears combinations with a variety of propellers? Assuming a bad design can be fixed with a hammer leads to owners adjusting to a badly performing boat, or any other equipment.

 

NMC

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It is very dangerous on a boat, even cars after several fires are abandoning that chemistry in favor of LiFePO4

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British woman and husband found dead after failed Atlantic crossing https://www.google.com/amp/s/amp.theguardian.com/world/article/2024/jul/21/british-woman-and-husband-found-dead-after-failed-atlantic-crossing

I think that is very probable that this tragedy was a fire, a NMC battery fire

 

I think there is important correction to do here:

OEM start to use LFP because those batteries are cheaper. They still continue to use NMC chemistry because of the higher energy density, so more range for a given weight/volume.
If NMC was cheaper, no one will use LFP.
Any lithium battery chemistry will be dangerous when in contact with salt water.

Yes, I also think so.
It's not given at everyone to build a marine lithium battery.
Even if you take a Torqeedo or an Oceanvolt battery and there is a damage who allow salt water intrusion, there will have big problem.

 

You are absolutely right that good software can save lot of money . But watching Haulover inlet at yt , "no replacement for displacement" seems to be just way .
4x600hp is a standard setup. 5x600hp is better and 6x600hp is the best

 

More engines is not a solution. A boat that would handle well with 4 engines may be too low at the stern with 6 and sink. Good design is the result of a global approach.

 

There is a huge difference in torque at low rpm, that is the basis of the comparison. This is why an electric car can accelerate so fast without a transmission. As far as top speed there will be no real difference between ice and electric motors of the same ultimate power output. The electric motor will just accelerate a lot faster due to it's torque curve. It is a somewhat dishonest claim, but not entirely without merit.

 

The difference isn't that big. Diesel engines are very heavy, equivalent hp electric motors are light; partially, but not entirely, making up for battery weight.

 

I'd be a little worried about using anything but LFP batteries in a boat. I'd at least go for tesla modules, well tested ones, if you are using automotive modules. And a housing that will divert a potential fire. Quality bms/overcharge/over-discharge protection. Waterproof critical components.

 

The entire system is the compare. Until batteries become lighter; the engine weights are not an issue.

 

An all electric boat that had a normal cruising range of 3000 miles would have no volume left for passengers, etc.

 

Yes, an electric boat that relies on energy storage alone to go long distances is not feasible. It would take many tens of thousands of lbs of batteries to go 3000 miles. Solar is the key, but even then you are basically limited to pretty slow speeds because of the limited real estate.
My very loose estimate would be about 2000 lbs of lfp batteries and at least another 2000lbs of rigid solar panels to keep you going around the clock at maybe 100 miles a day in the tropics. The structure to support all this, wiring, electronics, motors, etc would be at least another 1000 lbs. You could cut that weight by a lot by using flexible solar panels, but they don't last. Using batteries with a lighter chemistry could also save a lot of weight, at the cost of safety. You would have to cover the entire footprint of a large catamaran in solar to achieve this. You'd probably want another 500lbs worth of fuel and generator to go faster for a few days if necessary.

The planet solar boat maintained an average of over 5 knots around the world. 85 tons, 5800ft2 of solar(about 90kw), 1000kwh of batteries.

 

All technology have limitations. I believe there are many advantages to electric boats. However, the problem is the current idea that Li Ion batteries are the only energy storage medium to use. AGM batteries have lower cost, wider temperature range, are completely and easily recyclable, and don't need sophisticated electronic controls. In a slow boat the extra weight is not a problem. For example, a 27 foot sailboat with the keel included will move happily at 5 knots with 6HP. It may need more with strong wind on the nose. Replacing the weight of the keel with batteries, and some modification to the hull, would be a good start on a design. The main problem in the debate of ICE vs electric is the speed expectations.