Almost self-sufficient?

Maybe, if solar panels are added?

New electric boat motor uses wind and water to recharge its batteries at sea https://electrek.co/2023/04/05/new-electric-boat-motor-saildrive-servoprop-25/

 

On another thread recently, mention was made of articles in journals about products that were simply press releases (very positive naturally) written by the manufacturers - portacruise's article in the link above seems to be in this same boat (ooops, sorry for the pun).

They mention this :
"When back in propulsion mode, the motor can output 25 kW continuously, though it has a peak power rating of 30 kW for 15 minutes. As is usual with electric boat motors, their lower power figure is equivalent to a much more powerful combustion engine. In this case, Oceanvolt says that the 25 kW nominal power is similar in performance to a 75 kW (100 hp) combustion engine drive.
The instant torque and 5,000 newton (approximately 1,100 lb.) thrust force are major advantages of the electric setup."

They also mention this all-encompassing statement "The 419 lb. (190 kg) saildrive is suitable as a propulsion motor for boats up to 70 ft. in length and weighing up to 27.5 US tons (25 metric tons)."

I am intrigued - is the 25 kw electric motor similar in performance to the ICE Motor when it is also producing 25 kw, or is it similar to the ICE motor when it is producing 75 kw?

They include a diagram (copied below) comparing an ICE saildrive unit with an electric saildrive - which (rather confusingly) now mentions 75 hp rather than kw.



The power is proportional to the revs multiplied by the torque, so if the 25 kw electric motor is similar to the ICE motor when it is producing 75 kw, and the ICE and the electric motor have similar size propellers, what makes the electric motor propeller so much 'better'?

 

This is the typical sales pitch of how power output from an electric motor is equivalent to a lot more power from a different source. It is completely untrue. Power is the same regardless of source. It is calculated by RPM x Torque x a correction factor depending on the units used. There is nothing in the Power calculation about the source. As far as torque and thrust, they are two different values. Thrust is the forward force generated by the propeller and a function of power, not torque alone. Ignoring transmission losses, two motors with the same power output at different RPM can be made to have the same torque at the propeller through gearing ratio.

 

As our marine engineering lecturer at college many moons ago used to like to remind us that "You don't get owt from nowt"
Or in other words, you cannot get something from nothing (he was a very dour but friendly and helpful Yorkshireman, and this was / is a popular expression in those parts).

And as Gonzo says 'Power is power' - doesn't matter if it is from an electric motor or an ICE, it is still power. And electrical kilowatts are not worth more in power than petrol or diesel kilowatts.

 

Yes, that link looks to be be Vapor ware, just threw it out there for any useful commentary, that might result. I was curious if a single piece unit could conceptually reach the efficiency of a dedicated prop tow behind generator, while at the same time using the same propeller for efficient propulsion? Propeller shapes and sizes don't necessarily match when being used in propulsion versus generation mode?

Power is power, may be true, but from the Practical standpoint it would appear to depend on the application, when it comes to real world machines.

Here's a very large and powerful Diesel, that seems to be impractical power compared to a smaller power electric motor,

Why Diesel Locomotive uses Electric Motor to Drive Wheels? - Electrical Concepts https://electricalbaba.com/why-diesel-locomotive-uses-electric-motor-to-drive-wheels/

Such examples may help to explain why there is confusion about the power of IC versus Electric, or not..

 

It's not mysterious. At zero speed enormous torque at no rpm is required at the output. A gearbox can't be built that can do that. The operator must slip the clutch, but even when accepting the efficiency losses it's an impractical gearbox with such a range of output ratios between super low and top speed . The torque converter improved the situation immensely, but in applications where energy efficiency is more important than mass or volume electric transmissions do a better job of allowing the ICE to stay at it's best operating point for specific fuel consumption.

The confusion arises because the information on performance of electric motors comes to the market from salesmen, which is a nice way of saying professional liars. They tell the lies that sell their products.

 

Well, it wont be long before we get a detailed review of the system in operation

"The Xc 47 is the first boat in the world to be outfitted with Oceanvolt’s brand new and overall DAME Design Award-winning HighPower ServoProp 25, thanks to X-Yachts’ development partnership with Oceanvolt. While electric propulsion is logged as an option, the Oceanvolt arrangement combined with the 11-kw Fischer Panda generator was such a beautifully engineered solution, allowing for kilowatts of energy generation while underway, that it would be tough not to tick the box.

Stay tuned for a full review of this new boat in the April issue of SAIL."

https://www.sailmagazine.com/boats/xc-47-preview

 

This causes very boggy ground for inexperienced folk basing purchase decisions on internet reviews. I am aware of the practice and find it difficult sometimes to ascertain if the writer actually used the device they waffle on about in a real world situation or if it is a verbatim copy of factory blurb.

Also on the subject of electric motors. Since I started physics in high school (a few years back) I have been told that electric motors increase torque to match loading until such point that the supply cannot meet power demands, or the motor overheats and fails. This is surely a big selling point for this emerging technology as it creates a motor vehicle where the wheels are directly driven by motors, and the advantages in the rolling hills of the ocean are obvious? Yet I rarely see it mentioned, or is it because I live under a mushroom?

I had been thinking about testing the electric motor ability of being a generator as well, just with a little Minn Kota that people give away and about a 12' sailing dinghy, just to see if the electricity obtained is worth the drag in a cruising boat scenario, considering there are much less performance impacting engineless battery charging solutions. I did think of using a sealed electric motor with a propeller and some directional stabilisation, streamed aft for drag that is traditionally obtained in various other ways, even with bare rope. The device could then be used for emergency charging when the drag was undesirable. An automotive alternator might be a good starting point for this with a reinforced epoxy housing and suitable propeller.

Fuel supply is the bane of electric boating and once this issue is solved I suspect we will see very few internal combustion engines on boats. They offer pretty much vastly better everything right now except range. Back in the 1980s I worked on a large cutter dredge called the Castor which used electric motors all over the vessel, including two driving the cutting head via a two in one gearbox and one driving the big centrifugal pump on the ladder which was fully submersed at times. They were running Bolnes diesels the size of small houses to provide the power, and when she was moored in Port Hedland, someone commented that she had more generating capacity that the diesel engined powerstation that powered the town, which had major industries to feed. The only engines on the Castor driving mechanical devices were two huge 8 cylinder inline Deutz that drove pumps and some smaller ones driving emergency water pumps and compressors. It was state of the art in the early 80s, including computer control, and I believe she is still working.

 

There are many types of electric motors. The windings (Delta or Wye) and whether they are AC , DC or stepper make a huge difference in torque, power and operating speed. Anybody talking about electric motors as if they are all the same, either doesn't understand them, or are giving a sales pitch.

 

More details with less confusion if you look directly at the Oceanvolt website for details. The propeller blades are fully symmetrical with no twist, that gives minimal drag when feathered, but compromised when generating either thrust or electricity but not nearly as compromised as trying to use a standard propeller as a turbine because the blade camber is then wrong, or if the propeller is turned to face the flow (for correct camber) the leading edge then becomes the trailing edge and vice-versa.

 

A propeller and a turbine have different operating parameters. Either one can work on both applications, but will be most efficient on only one. Ocenvolt is making a compromise where the propeller/turbine is mediocre at both modes of operation.