3 ms·

Not a huge amount of information to comment on (They don't even show the fully-loaded weight of the boat which is probably the most important factor), but the f

Not a huge amount of information to comment on (They don't even show the fully-loaded weight of the boat which is probably the most important factor), but the focus on a lightweight hull seems like the right path and is similar to other startups in this field. Electrification of boats is uniquely challenging because it's a delicately balanced optimization problem -- You need to keep the boat up on plane to get a reasonable range and compete in the same class as other recreational motorboats. Getting on plane requires a high peak power output, but that in turn requires a heavier battery pack, making it harder to get up to speed... Battery energy density is not quite at the point where you can just stick a battery and electric motor in an existing boat hull and expect it to perform, so the theme of all these companies is using a custom lightweight hull or hydrofoil to reduce drag/weight enough to avoid the energy density problem. Another interesting startup is Candela (https://candela.com/ https://candela.com/) who is taking on the problem from a similar angle; they use hydrofoils and a complex controls system to keep the hull foiling which is very low drag. That said, I'm not sure Arc has done their research on the market fit for aluminum hulls. Based on their concepts it will take a lot of work to convince the recreational boating scene to buy a $300k aluminum boat with an inboard motor; typically aluminum hulls are used for fishing and shallow waters, and in those use cases an inboard doesn't make sense -- it might be better equipped in that case with a jet drive but would hit power issues there.

nitrogen 5y ago
Getting on plane requires a high peak power output Could a capacitor bank be used to deliver a burst of power to plane out? Or does the weight and volume of capacitors still exceed what's practical? Also seems like it wouldn't work for wakeboarding, where the goal is to generate a big, inefficient wake all the time.
- chrisdalke 5y ago
  The power required to plane in a boat looks a bit like a normal curve -- Power consumption scales upwards exponentially with speed until you either 1) Get going fast enough to hydroplane and reach a high efficiency regime 2) Hit the peak power of the drivetrain and fail to accelerate further A capacitor bank wouldn't really help here, since that power has to come from somewhere. The issue isn't that the batteries aren't capable of outputting that peak power -- Even small battery systems are more than capable of outputting the 50kw+ it might take to get on plane. The real issue is that doing that repeatedly requires you to scale up your battery capacity and weight, which is a positive feedback loop. Boats are not just getting on/off plane once on a tank of gas, they're doing it 10-20 times depending on driving conditions, surroundings, no wake zones. This might happen 100s of times for watersports like wakeboarding. So a big part of the equation is finding a way to save weight elsewhere that can then be used to insert more batteries.
JimTheMan 5y ago
One advantage is you could put your battery bank at the very bottom of the hull, making your otherwise pretty lightweight ship more stable. However the sum of my boat knowledge comes from this amazing post... https://ciechanow.ski/naval-architecture/ https://ciechanow.ski/naval-architecture/
djhn 5y ago
Since it seems like a bit of a cool toy more than anything, I don't quite understand why they wouldn't go for carbon fibre at that price point?
xoa 5y ago
>Another interesting startup is Candela (https://candela.com/ https://candela.com/) who is taking on the problem from a similar angle; they use hydrofoils and a complex controls system to keep the hull foiling which is very low drag. Candela is what I immediately thought of when I saw this, and looks like a much more interesting approach that I like both for boats and aircraft. There is no getting around present disadvantage in energy density for batteries vs fuel, even if efficiency helps make it a bit less bad than it'd look like on the tin. But electric drive trains have their own fundamental advantages too in terms of motor power for a given volume, lack of plumbing required, torque, etc. So the more interesting designs seem to be leaning into that to do things that just plain wouldn't be feasible with ICE/turbines. Like with aircraft NASA's X-57 concept [0], electric allows simply having a ton of little motors all over so rather then needing a large wing to try to prevent stalling (inefficient at high speed) they can simply actively force air over a thin wing then shut them all down. Or with Candela they can do interesting things with motors on small foils with the boat fully out of the water. I'm not expert, but attacking the entire problem space from a different angle rather then just swapping engine for electric and fuel tanks for batteries seems like an interesting way to go long term. Though of course probably makes for more challenging engineering. ---- 0: https://www.nasa.gov/specials/X57/ https://www.nasa.gov/specials/X57/
- chrisdalke 5y ago
  Absolutely agree, couldn't have said it better myself. It's a systems engineering problem and requires rethinking of nearly every component, from the propeller design to the architecture of motors and controls. Torqeedo is an interesting example, they've been very successful with low-power electric outboards because in contrast with other companies they've invested heavily in rethinking propeller designs to be suitable for electric motors. The result looks nothing like a gas motor: They have huge, slow-rotating propellers that peak at <1200rpm and a high-speed brushless motor that gets geared down so it operates at the top of its RPM and efficiency range.
chrisdalke 5y ago
Okay, so I've looked more into the stats based on their marketing material, and I just don't see how the math works out... They're claiming a 200kWh battery which seems a bit high for the size of the boat. An equivalent battery system for marine environments that exists today is the Deep Blue BMW i3 (https://www.torqeedo.com/us/en-us/technology-and-environment/battery-technology.html https://www.torqeedo.com/us/en-us/technology-and-environment...) which is a Torqeedo-BMW collaboration. That battery is 40kWh and 278kg. Now, obviously there is a BMS and other parts that don't need to be replicated 5x, but scaling that up to a 200kWh pack gives 1390kg. That is absolutely ridiculous. Candela's entire C-7 boat weighs 1300kg, and it's only able to maintain a good range by utilizing hydroplaning extensively. I'm not sure how a conventional planing hull that might weigh well over 2000kg with interior components, passengers, etc will get any reasonable range, and I suspect they don't show average range or loaded weight in the stats because it just doesn't look great compared to their competitors.

nitrogen 5y ago

Getting on plane requires a high peak power output Could a capacitor bank be used to deliver a burst of power to plane out? Or does the weight and volume of capacitors still exceed what's practical? Also seems like it wouldn't work for wakeboarding, where the goal is to generate a big, inefficient wake all the time.

chrisdalke 5y ago
The power required to plane in a boat looks a bit like a normal curve -- Power consumption scales upwards exponentially with speed until you either 1) Get going fast enough to hydroplane and reach a high efficiency regime 2) Hit the peak power of the drivetrain and fail to accelerate further A capacitor bank wouldn't really help here, since that power has to come from somewhere. The issue isn't that the batteries aren't capable of outputting that peak power -- Even small battery systems are more than capable of outputting the 50kw+ it might take to get on plane. The real issue is that doing that repeatedly requires you to scale up your battery capacity and weight, which is a positive feedback loop. Boats are not just getting on/off plane once on a tank of gas, they're doing it 10-20 times depending on driving conditions, surroundings, no wake zones. This might happen 100s of times for watersports like wakeboarding. So a big part of the equation is finding a way to save weight elsewhere that can then be used to insert more batteries.

JimTheMan 5y ago

One advantage is you could put your battery bank at the very bottom of the hull, making your otherwise pretty lightweight ship more stable. However the sum of my boat knowledge comes from this amazing post... https://ciechanow.ski/naval-architecture/ https://ciechanow.ski/naval-architecture/

djhn 5y ago

Since it seems like a bit of a cool toy more than anything, I don't quite understand why they wouldn't go for carbon fibre at that price point?

xoa 5y ago

>Another interesting startup is Candela (https://candela.com/ https://candela.com/) who is taking on the problem from a similar angle; they use hydrofoils and a complex controls system to keep the hull foiling which is very low drag. Candela is what I immediately thought of when I saw this, and looks like a much more interesting approach that I like both for boats and aircraft. There is no getting around present disadvantage in energy density for batteries vs fuel, even if efficiency helps make it a bit less bad than it'd look like on the tin. But electric drive trains have their own fundamental advantages too in terms of motor power for a given volume, lack of plumbing required, torque, etc. So the more interesting designs seem to be leaning into that to do things that just plain wouldn't be feasible with ICE/turbines. Like with aircraft NASA's X-57 concept [0], electric allows simply having a ton of little motors all over so rather then needing a large wing to try to prevent stalling (inefficient at high speed) they can simply actively force air over a thin wing then shut them all down. Or with Candela they can do interesting things with motors on small foils with the boat fully out of the water. I'm not expert, but attacking the entire problem space from a different angle rather then just swapping engine for electric and fuel tanks for batteries seems like an interesting way to go long term. Though of course probably makes for more challenging engineering. ---- 0: https://www.nasa.gov/specials/X57/ https://www.nasa.gov/specials/X57/

chrisdalke 5y ago
Absolutely agree, couldn't have said it better myself. It's a systems engineering problem and requires rethinking of nearly every component, from the propeller design to the architecture of motors and controls. Torqeedo is an interesting example, they've been very successful with low-power electric outboards because in contrast with other companies they've invested heavily in rethinking propeller designs to be suitable for electric motors. The result looks nothing like a gas motor: They have huge, slow-rotating propellers that peak at <1200rpm and a high-speed brushless motor that gets geared down so it operates at the top of its RPM and efficiency range.

chrisdalke 5y ago

Okay, so I've looked more into the stats based on their marketing material, and I just don't see how the math works out... They're claiming a 200kWh battery which seems a bit high for the size of the boat. An equivalent battery system for marine environments that exists today is the Deep Blue BMW i3 (https://www.torqeedo.com/us/en-us/technology-and-environment/battery-technology.html https://www.torqeedo.com/us/en-us/technology-and-environment...) which is a Torqeedo-BMW collaboration. That battery is 40kWh and 278kg. Now, obviously there is a BMS and other parts that don't need to be replicated 5x, but scaling that up to a 200kWh pack gives 1390kg. That is absolutely ridiculous. Candela's entire C-7 boat weighs 1300kg, and it's only able to maintain a good range by utilizing hydroplaning extensively. I'm not sure how a conventional planing hull that might weigh well over 2000kg with interior components, passengers, etc will get any reasonable range, and I suspect they don't show average range or loaded weight in the stats because it just doesn't look great compared to their competitors.