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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 troug
by pp19dd 5y ago
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 5y agoMikael 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!
- pp19dd 5y agoMikael, 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 5y agoHi, 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 5y agoHow 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.