Electrically Powered Yachts


No I don’t mean the submarines, I mean putting electric power into a boat. This has been a difficult challenge because of the power that it takes when you get close to planing. Boats draw very little power when they are at hull speed. For example, the Silent Yachts 55 (55 foot long boat), draws 10kW at 6 knots, but 30kW at 8 knots because that’s the so called hull speed.

As an aside, this means that pushing through water is way more expensive than through air which makes sense, 10kWh for 6.9 miles is 1.5kWh/mile whereas a Tesla Model 3 is running at 250Wh/mile. The difference is that the Tesla weights 3,552 pounds (no passengers) whereas the Silent Yacht 55 weights 17 tonnes (assuming these are short tons), this is 34K pounds. So if you calculating kWH/mile/pound, then you see the Tesla requires 250WH to move 3,552 pounds one mile, or 70mW/pound/mile.

While this Silent Yacht 55 the calculation is 1.5kWh to move 34K pounds a mile or 44mW/pound/mile which is why ocean transport is so efficient for big cargos. So it is more expensive to push through water, but you can carry much more weight when you are doing it.

And this is really a massive boat that is 55 feet long with 4 guest cabins and 2 crew cabins. Plus all the fixings of luxury living.

The Silent Yacht 55 for instance has 140kWh of battery and has solar panels that allow up to 10kW of charging and on a typical day, you can recover 60kWh in a sunny Mediterranean day. What that means is that on a typically day, if you recharge to 140kWH in port (this is possible because most ports have 240V x 50 amp circuits so you can get 12kW. It doesn’t say what it is using, but if you get two circuits, then you get 24kW and for boats this should be fine for overnight recharging.

Then during a sunny day, with say 10 hours of cruising plus the additional 5-10kWh draw, you are using 10kWh x 10 hours = 100kWh and there is more than enough in the battery to last a whole day if you are going 6 knots. The article was right, this is more like a sailboat than a power boat.

The keys appear to be: a) making the boat as light as possible so this craft is several tons lighter than a traditional yacht, b) being in a bright part of the world for recharging.

The other option is to use a kite because at low speeds, it acts much like a sailboat. You can buy a $50K kite rig and in low winds, it can run the boat at 6 knots. Kind of perfect for those sunny California days.

There are quite a few other options, you can get a diesel plus electric motors so a true hybrid. You can also get different sized motors. From dual 130kWH ones that can go up to 20 knots but then only for 20 minutes. Or a 30kWH motor for slower cruising.

And for backup, there is a diesel generator onboard that can produce as much as 100kW, so in this sense, this is a diesel-electric hybrid.

Of course this thing is expensive starting at $1.6M, but you also charter it. That makes sense, given the speed with which technology is developing.

The second example they are just about to ship is the Silent 44 which is smaller and less expensive. This one is 44 feet long with a displacement of 11 tons (22K pounds)

It has either 2x30kW motors or 2x80kW motors, the 30kW has a maximum speed of 12 knots, but the 80kW up to 15 knots. Cruise is the same at 6 knots probably at the same 10kW. It has a 120kWh battery. You can get it with either a 22kW or 100kW diesel generator as a backup. It has 9kWp solar panels.

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