[_jbcv]

Imagine cruising at 30-40 mph, angled so you cut through waves perpendicularly. Mostly you head straight, but you do need to lazily avoid some crests and troughs, aiming for that sweet middle. You then see a mostly submerged log 30 feet ahead, just barely under the surface.

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.

[Candelaboat]

Mikael at Candela, the maker of C-7, here. This post is inaccurate and frankly makes no sense. First, the waves will never capsize the boat. Due to low cog, it's virtually impossible to do - we've tried. You can manoeuvre just fine at all speeds, but at high speeds it's correct that you might not be able to avoid running over a log or other submerged objects. Same goes for regular planing boats at high speeds. If you hit something, the foil will withstand smaller objects - branches, debris - but is designed to come off should you hit a bigger object, such as a log. While the foil breaks off, the hull will stay intact and avoid damage. Now, on the other hand, if you hit a log with a conventional boat, there's a risk the hull is pierced and the boat sinks. Regarding the "weight ratio": hydrofoil boats are super energy efficient and need very little power at cruise speed compared to a traditional hull, which is why we use them for C-7. At 22 knots, the C-7 uses about 25 hp, which is pretty remarkable for a 25-foot boat. We have a passenger capacity of six persons, but have actually taken off with 10 persons on board - using a motor rated at 65 kW!

[_jbcv]

Mikael, my hats off to you and your fine product and sweat you poured into it. My apologies if in any way I seemed to criticize performance of your craft, far from it. I know nothing of it, and electric is going to be the only way in the near future. The context got shifted toward it somehow.

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?

[Candelaboat]

Hi, no problem, just wanted to clarify. The price is 250 00 euros, which indeed is expensive for a 25 foot boat, but still about 100 000 euros less expensive than conventional electric boats that can go fast - but not that far.

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€.

[SigmundA]

How much does it cost to replace the foils should you tear them off? Because honestly on a pleasure boat say in Florida where I am your not going to hit a log but you will drag bottom at some point due to shallow waters and tides. Most outboards have some sort of skeg damage due to dragging bottom or strikes. Replacing props and lower units or repairing the skeg is very common.

[lstodd]

Total loss. Even on an alumunium hull, not to mention composite.

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.

[timbray]

It is really not obvious that it would be worse experience than sitting it with your fiberglass hull. (Clearly worse than an aluminum hull though.) This happens all the time in the Pacific Northwest where I boat, floating logs. Worst are the deadheads, waterlogged so they float vertically just below the surface. Never known anyone to actually sink, but there've been a few destroyed propellers and thousands of bucks worth of hull repair.

[SigmundA]

Again here in FL dragging sandy bottom is pretty common and most of the time no big deal, maybe scuffing your skeg. Many times what happens is you're out of the channel on a plane no problem, then you slow down come off a plane and oops the water is too shallow and your lower unit /prop hits being the lowest part of the boat.

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.

[karmicthreat]

My guess would be treat it like when you pull the chute on a Cirrus GA aircraft. Total loss, but you didn't die!

[Candelaboat]

Mikael at Candela here. The cost of replacing the foils vary, but considerably less than the lower unit of an outboard on 25 foot boats. I actually ran over a submerged chain and broke the foil once - the only time that has happened in Sweden. Took us an hour to replace it, so no big deal You hoist the foil/struts down completely and insert a new one.