Hydrofoiling
tbray.org
tbray.org
- Evoy hurricane inboard, 600 kW: NOK 1.497.000
- Battery pack: medium range, 252 kWh: NOK 1.476.000
In US dollars, that's $360,000 and I'd have to ship it from Norway. Closest second option was about half that price using BMW i3 batteries, at half power. Meanwhile, a new marine engine was $10,000 by comparison, or to repair exhaust and rebuild to last another 17 years, $5,000.
Boating is a luxury and I can't excuse it in environmental terms, same as I can't excuse electing not to walk 2 hours to my local starbucks for a consistent grande pike I enjoy in favor of brewing my own. But marine electric is currently nowhere near being a practical solution, and you cannot hydrofoil in all boating conditions, especially in choppy waters, or where there are seasonal floating obstructions.
Boats do have notoriously small efficiencies (1-4 mpg) in both displacement and planing modes, but consider that for an automobile to have its 25 mpg average we pour approximately 124,000 gallons of crude oil per mile every 5-10 years for a two lane asphalt road, a coarse byproduct of refined petroleum.
My whole point here is not to equivocate in any terms, but that it's easy to overlook externalized costs. Moving an object anywhere is a difficult problem.
People used to say that electric cars were "nowhere near being a practical solution" until suddenly they were.
The C-7 is a toy. I have no doubt that they can make a non-toy at some point in the future, but the future isn't here yet.
Here is what a 1.2 meter one looks like, just exiting an inlet: https://www.youtube.com/watch?v=rV41E9PQwiU
FWIW they were the most common automobile type at the turn of the 20th century. The naysayers were just internal-combustion apologists.
Worst case, couldn't you go slower and just act like a regular boat?
You now have two choices, steer to the left or right of it. Those split-second decisions have consequences, depending on which way the prevailing waves are headed. Say if you turn toward port, you might be parallel to the waves which you never want to do: they can capsize you. So you don't turn to port.
Heading toward starboard might be a better choice, but it's still not perfect - you might head toward a crest that will definitely slam into your bow violently. Or there is another boat wake you now have to deal with that wasn't a problem seconds ago. In either case, you need to alter your speed to either avoid it or cut through it more gently. You start dropping off plane, cut through a favorable section, and then angle yourself and go wide open throttles to miss a trough. Maybe you rise back on plane before you avoid it, or just slightly afterwards but on most V hull powerboats doing all this is not a problem. In normal traffic, this might happen a few times a minute.
But hydrofoils have two things going against them right there. They have massive drag at lower speeds and thus maneuver poorly in an emergency, taking more time to accelerate on plane or change direction. Then the weight ratio is a challenge: they need a lot of power for cruising speed, so they weigh more than you'd expect and then weight management is one of the primary design concerns. That all means the propeller is optimized for power over acceleration, and that means that these three congruent design choices have painted you into a corner, limiting collision maneuverability. Hydrofoils handle rough seas far worse than any conventional hull shape and more importantly, colliding with anything underway is far less forgiving than striking an object on the bow or outdrive.
Emergencies notwithstanding, being normally outside a propeller's designed operating range and you have cavitation and ventilation problems, which then erode the propellers. And that weight constraint means fewer seats, fewer people to carry, so less efficient per capita.
My general skepticism regarding hydrofoils comes from, quite frankly, not seeing that much damage with them because they don't exist 'in the wild' so much here to establish a conventional sense for most U.S. east coast watermen. Plenty of other issues that everyone I know is familiar with, most commonly groundings and striking objects, and occasionally catching cage lines on props. The petrol-era weight bias sticks around and this is where I hope you show us very wrong. I'd love to see some rough water videos of your C-7.
My original response from where everything else stemmed from is that right now this isn't a practical conversion for a common man with something like a 27' cabin cruiser, certainly not in the pocketbook. I do not know how much the C-7 costs, but was my sticker shock that far off?
The price stems from a high production cost, the whole boat is built like an aircraft, in carbon fiber (the designer used to work at Eurocopter) to be as light as possible. The weight of the hull and deck is about 240 kg. So our main goal for the future is to reduce the costs - by a lot. But think about C-7 as the Tesla Roadster. But our foiling ferry for the city of Stockholm will be launched next year, and then people using the Stockholm public transport system can go foiling for 2€.
Besides, it might not sink, but the collision will throw people around, and it's not like boats have seat belts or people accustomized to using them.
Hitting a rock might bend your prop and you might need to replace, many carry a spare prop on board as it can be replaced relatively easy even out on the water with an outboard.
That same situation with a foil boat would be disastrous, again just one very expensive and dangerous mistake.
Electric power density in either volume or weight is OK in a car, where once you've accelerated you're rolling on low resistance tires on a smooth surface and the weight is less important. But in a boat you're fighting the equivalent of the rocket equation where the force on your planing hull has to have more batteries to lift more batteries to go farther.
It's fine, though, for a lot of watersports uses, where you want to put out hundreds of kW for a few seconds to pop a skier up, do a set, talk to your skier without asphyxiating them in exhaust fumes and without shouting over engine noise, and then plug it back at the dock. Less fine for cruising, where you want a tank of fuel to last you whole day. You only need enough energy storage to outlast human quads and forearms, not more to outlast human bowels!
[1] http://www.ltsmarine.com/english/lts-water-ski-boat/
[2] https://nautique.com/models/super-air-nautique-gs22e/overvie...
I suspect their power declaration is marketing language claiming burst power, and that its nominal cruising range is well under it but regardless of any of that, the batteries costing $180,000 is still an issue.
Edit: forgot one important thing for that power matching, the weight. Replacing an engine and full gas tank -- the electric motor + mid-range battery pack overall adds about 2,500 lbs to the boat, so it'd be a 7,200 lb boat at that point and I'm not sure I could trailer it anymore.
I find this peculiar because hydrofoils were seemingly much more common in the 80-90's in industrial applications such as ferries, but now suddenly have become hugely popular in recreational space, and rapid innovation in the design and construction of foils across all of the domains. Very interesting if you are interested in boats and water sports.
Also, for industrial applications (and for recreational without self-imposed restrictions), high frequency automated active servo control is now very much in the realm of practicality. Back then it was all self-stabilizing, which led to some very bumpy rides.
http://trifoiler.info/media/index.php?title=Main_Page
https://www.youtube.com/watch?v=zXSgZCDVWOM
I don't know if modern consumer-level designs are sophisticated enough to be using much CFD, but it definitely seems like the easy availability of CAD should be playing a role.
I'm in the proces of learning to use a kitesurf hydrofoil, it's funny to see the gps tracks from a smartwatch on strava, very messy, like a child scribbling.
I get friends who aren't into surfing sharing links to these things just because they look so fun.
They're not quite Gravity Industries[1] cool but they have an “Iron Man on water” feel to them, and they're an interesting entry point into watersports for people who can afford to buy or hire the things.
[1]: https://gravity.co/
It looked like a landspeeder, and felt like watching a fake youtube video.
The closest thing I found was the “HydroFlyer”:
https://www.thehydroflyer.com/
The riding position is somewhat different to an efoil Speeder Bike, though, where your legs would presumably start in the water like with this design:
I remember seeing foils in the late 90s and early 2000s but they weren't available to purchase. I wonder why. Maybe it's because the construction process hadn't been commercialized yet.
I've been hydrofoil windsurfing (and have tried wingsurfing/wingfoiling as well).
Hydrofoiling has extended the lower range of wind speeds that I can go fast in. For instance, around 10kts wind I can pump the board and sail to get on the foil and go about 20mph. Pros push this even lower, to about 7kts wind speed.
I can also go upwind much higher and downwind deeper, at speed, than I could with just regular windsurfing on a fin. Control is a bit difficult downwind for me, still, but it's fun.
Paris Olympics in 2024 will have hydrofoil windsurfing. There was also a race this weekend around Lanzarote, which was almost 10hrs of racing and 130 something miles traveled on windsurf foils.
At Candela, we use hydrofoils to reduce the energy usage, to be able to make an electric boat that has long range at high speeds, above 20 knots. Conventional hulls are hard to electrify since they need so much power. However, we use a new type of hydrofoil: fully submerged hydrofoils, that are more efficient but needs active stabilization from computers and software. The on-board Flight controller adjusts the hydrofoils at 100 hZ, or 100 times per second, which makes for a craft that won't pitch or heave. This tech was available in the 1970's - it's basically a very similar Flight controller as in an inherently unstable jet fighter like F-16 - but thanks to drones and smartphones, the price reduction of sensors makes it possible for us to offer this tech in a leisure boat.
And - we're scaling our electric hydrofoil tech to commercial ships. Right now, we're starting the construction of the world's first foiling electric shuttle ship for the city of Stockholm. At its launch next year, Candela P-30 will be the fastest electric ship ever at 30 knots, as well as most energy-efficient ship ever built. Energy usage is 1/10th of conventional diesel ships. Check it out here:
Also can't help smiling at their use of "BLT" as an abbreviation for the company name, I guess we know what their Official Company Lunch is going to be [1]. :)
I wonder if there has been any progress, the site is kind of ... light on the details. The prototype single-container ship was cute, though.
- Why hasn't this been built before? Yes, minor hydrofoil ships have been built but why not cargo ones? (Constructor conservatism? Some issues that others have run into? Lack of technology before that)
- How does this fare in a marine thunderstorm?
- How many customers are time sensitive (but not much) so as to fit their window?
- What kind of problems can going 4x the speed on an open ocean can create?
- Is the actual cost 4x less once you factor everything in?
My bet is that this makes sense for shorter routes (like multiple ferry routes in Europe), maaaybe for "shorter" cargo routes, not so sure for the longer routes (though China-LA is not "too long")
I'm assuming that the additional of the weight of the cargo means that you would need to go much faster in order to lift the ship up on the hydrofoils, and this makes it infeasable.
Fuel means range so that all might get back to the mission: ferry or transoceanic.
Also, while fuel oil is buoyant, it still has mass and weight, and the fuel in a ship contributes its own weight's worth of displacement. Displacement, in turn, causes wave resistance.
The larger a ship gets, the less significant, proportionally, both wave and friction drag become, reducing the incentive for foiling. It seems significant that the YC company mentioned elsewhere in these comments (Boundary Layer Technologies) positions itself as competing with air freight rather than shipping (and, as flying in the thin air of the tropopause is pretty efficient compared with generating lift in water, I would guess part of their calculation involves building much larger-capacity vessels than current and projected air freighters.)
Hydrofoils obviously can't operate safely in heavy sea states. When a storm comes up they'll have to delay sailing, or route around. That will add some unpredictability to delivery schedules.
I enjoyed the article, so I'm not trying to pick on the author too much, but I always find it funny when technical people say this about engineered things. Each of those things is literally an entire discipline and you could still spend a career (or at least many years) only working on one of them. I think we have a tendency to think that because we can understand something and have taken some of the magic out of it that it isn't complex.
What I do wonder is whether automotive range extenders can be retrofitted instead of marine gensets. Seems way cheaper.
Maybe not a family transport option, but we're talking a surfboard filled with 18650 cells (or similar) riding on a underwater wing driven by a jet or small propeller.
They are relatively old with companies building competition models at least five years ago.
The technology at heart is an outgrowth of the portable electric vehicle industry and hydrofoil development in the windsurfing commnity.
If you think this article is neat, I would check out the technology. You can build a performance board yourself for sub 3 grand US (possibly less if you are willing to vacuum mold the board yourself).
Good resources are available from the portable electric vehicle or electric skateboard communities. Board building has been covered in depth by generations of surfers.
https://www.mynewsdesk.com/candela-speedboat-ab/pressrelease...
Basically, yes, for fully submerged hydrofoils you need to make sure you don't get too high or low. For surface-piercing you don't, they self-stabilize.
Question I have - do hydrofoils use ground effect to generate extra lift?
Edit: I realise now that you mean hydrofoil as in the boat rather than the submerged wing (it's confusing that they both have the same name). I don't think the ground effect from the boat's hull contributes much to the lift but it is something that the designers of the AC75 boats take into consideration https://www.sailmagazine.com/racing/36th-americas-cup-differ...
Ekranoplans have wings and aerodynamic control surfaces.
I also wonder (this may be the primary reason) if the speeds a hydroplane achieves are sufficient to generate much lift in air from something the size of a boat hull.
Most boat owners can't afford a hydroplaning boat.
Three kinds.
Regular planing boat. Cheap and fast but very inefficient and thus can't be electric.
Hydroplaning boat. Fast, efficient so can be made electric. But very expensive.
Non planing boat. Cheap, efficient. Can be made electric. But is slow.
Not that boats don't do a lot of environmental damage in other ways. Bilge tanks, anti-fouling paint flaking off, etc.
It seems like it would make sense to have a gas engine and propeller to get the foil on-plane from stopped, then when "gliding" switch to a battery powered jet pump to keep it at speed.
Hydrofoils significantly increase draft and nobody wants to dredge their ports and canals 20 feet deeper.
Also drag is proportional to velocity squared, so you can save a ton of fuel just by slowing down a bit. Much easier than designing a hydrofoil cargo ship.
Most normal pleasure boats regularly go in shallow waters and pull up on the beach etc. If you look at the skegs of any of these boats you will see where they have dragged or struck something and a normal outboard doesn't stick down anywhere near as far.
It's cool the the Candela can retract the foils, but again forget to do it one time and those foils looks very expensive and what do they do to the hull as they are being ripped off.