Battery-electric fishing vessel marks a sea change for small commercial fishers
nrel.gov
nrel.gov
A typical rowing boat (human powered) will have a displacement hull. It is a streamlined curved shape which can move very efficiently through the water at slow speeds. It has a maximum speed, and if you try to push it beyond that, efficiency drops a lot and you put in a lot more energy for small speed increases.
A 'planing' hull is normally used on speedboats and the like. It has two efficient modes - either displacement, or planing (where the boat rises most of the way out of the water and only has a small contact area). Typically there is a region in between - a speed the boat cannot travel at a fixed throttle - it can go faster or slower though.
There are lots of other possible hull designs - but in general you need to pick your ideal speed or range of speeds (and loads, and wave conditions), and optimize for minimum energy consumption at those speeds.
In the modern world, you normally combine this with a cost optimization - trading off the salary and depreciation and opportunity cost of travelling slower, with the saved fuel of travelling slower.
In an electric boat, where energy storage is really expensive, it is even more important to do a really good job of this optimization - and I forsee we'll see more people attempt esoteric yet theoretically very efficient hulls, like hydrofoils, to try to have a big edge in a market where energy efficiency is suddenly a big driving factor.
Freighters are generally displacement hulls because they carry thousands of tonnes of cargo. This sizable displacement would make it impractical for these vessels to "get up on plane" (assuming their hulls were shaped like planing hulls vice displacement hulls). You can simply carry more payload in a displacement hull than a planing hull. Planing hulls like to be lightweight. It's not impossible to make a planing freighter, just impractical - and all of that inertia and mechanical stress on the hull structure while traveling at high speeds would be very difficult to design against, not to mention very difficult/unsafe to amneuver in a sea lane or inclement weather. There are certainly high speed ferries, which are generally catamarans (for added stability) with similar speed-power characteristics to planing hulls, but those are still carrying relatively lighter cargo (humans, some cars) over shorter distances compared to fairly dense bulk liquid/material/container cargo transiting accross oceans.
Yes. I thought it was obvious I was comparing at displacement speeds only; I'm sorry for not being more clear.
At 2 kts, they'd both probably be in displacement, but the planing hull would be using 2-3x power.
At 6 kts, the planing hull would be using about 10x power, because it would be operating in planing mode while the displacement hull is still operating in the very efficient displacement mode.
Only the planing hull could exceed 6 kts.
The most interesting thing about the maximum speed of a displacement hull is that it depends on the length of the waterline. Larger (longer) hulls have a higher top speed. There are some hull shapes that allow higher speeds while in displacement mode,
The same engine in a longer waterline may have some effect. The underlying physics is that the length of the waterline influences the wake system that a boat creates between its bow and stern wave. Those waves interfere constructively and at a certain speed, they start adding up to significant waves - the bow wave starts to pile up more and more. The boat needs to ride up the wave. Drag rises sharply at that point - so a stronger engine helps little at this point.
This used to be called the “hull speed”, the maximum speed that a hull can achieve. (It’s grossly simplistic and outdated concept, but a workable estimate).
Going beyond requires either a longer waterline or switching from displacement to planing. Some hull shapes can exceed their nominal hull speeds somewhat, but not indefinitely. Some hulls (keelboat for example) can never transition to planing.
Hull speed is a concern if you tow a small vessel with a larger vessel that can run faster than the small vessels hull speed. You can sink a boat by creating a large enough bow wave.
oof I never thought about that
The speed of sound in water is 1480 m/s (at 20C), and is independent of the length of the vehicle.
Ships are sort of special because they operate at the surface of the water. Submarines operating submerged have no such "hull speed", and their wave-making resistance is insignificant.
This explains something that didn't make sense to me when I first encountered it 25 years ago.
There's a board game, Star Fleet Battles, which is superficially set in a fork of the (original) Star Trek animated series[0], but the mechanics are all much closer to ~WW2-to-cold-war naval combat[1].
The specific mechanic you've just explained is that if you grab a small vehicle like a shuttle craft in a tractor beam and drag it along the map too fast, the shuttle will be destroyed by going too fast.
[0] and therefore has Kzinti
[1] Q-ships named as that; "drones" that act like torpedoes, photon torpedoes that act like missiles
Well.. The length and the speed determine the Froude number the ship is operating at, and yes, the length to a large extent determines the achievable top speed. However the beam, prismatic coefficient ("fineness" of the hull shape) and a host of other factors do definitely affect the total resistance quite a lot. Ships designed for high speeds, like warships, tend to have large length/beam ratios and low prismatic coefficients.
> From the waterline length you can guess how fast a ship is, regardless of the displacement.
So are you saying the Seawise Giant was considerably faster than the Nimitz, considering it had a waterline length of ~450m (!!) vs. a "mere" 317m for the carrier? ;)
But yes, I'm quite sure Nimitz doing 45 knots is unrealistic. I'm also quite sure that given the hull shape and size, and engine power, are known, that potential adversaries who have a naval engineer or two on the payroll have a decent idea of what the actual top speed is.
Spot on. The Candela C-8 is an excellent example: https://candela.com/candela-c-8/
Ripple Boats has a concept of injecting air to a space underneath the boat with a fan. Seems like a concept that would be easier and cheaper to scale up (in both size and number of ships produced) https://www.rippleboats.com/
[1]https://www.maritime-executive.com/article/shipping-company-...
Another great option is hydrogen fuel cells.
Check this out. The "Sea Change" ferry, hydrogen fuel cell powered.
https://ww2.arb.ca.gov/lcti-zero-emission-hydrogen-ferry-dem...
They take renewable hydro power from Hetch Heychy Reservoir, pipe it to the SF waterfront where they have already invested in a big electric backbone along the water to be able to power the cruise (and other) ships that dock there. Normally these large ships run their onboard engines/generators while docked because of the insane amount of power they draw. Not in SF, they're powered by clean hydro while docked there. They then have a floating fuel barge that is right where the ferry docks. That fuel barge takes that clean hydro power and disassociates sea water into hydrogen and oxygen. That hydrogen is then pumped onto the ferry and bam. End to end renewable giant boat.
Based on the power and range needed, as you suggest, I think solutions like these are more suitable for this application
We have platinum in the catalytic converters, and engines last the projected life of the vehicle.
From what I've read, fuel cells are being designed for similar lifespans. As with many things, internal combustion engines included, we can choose how long they're designed to last, that's a design input. If they have limited lifetimes they're designed as such. If we want longer lifetimes, we just design them to achieve that.
Using one in a sailboat seems ideal for offshore cruising as you can recharge your batteries while underway. If it's not windy, then it's probably sunny, so combined with some solar panels, you could be very self sufficient.
Sailboat props are often variable pitch to allow for better efficiency (i.e. they can be turned completely parallel with the flow of water when not in use), which also allows them to be set at an optimal angle for power generation (with minor speed losses, obviously).
I first heard about this system design from the Tally Ho rebuild: https://youtu.be/xohxmwPfctg?si=RoJV2za9ZgPldrJJ&t=1497
Batteries don’t have this feature, so it gets interesting: it could be that a less energy efficient route overall needs to be taken for some trip. If it results in less emissions overall, it’s obviously a win, but there’s some interesting subtleties to consider in this problem space that aren’t immediately obvious.
Also, batteries are heavy.
For a traditional vessel, the main pollutant will be from the burning of fuel, and then leaking fuel when the vessel sinks.
How much does a tank full of diesel (in additional to the pollution released during opteration over the life time of the vessel) in comparison to a battery pack leaking into the ocean ?
These are questions, not challenges, I think it'd be very interesting to know, it might be that dumping some battery packs in the ocean is still overall better for the environment than burning fuel (and leaking some).
There's absolutely nothing clean about burning bunker fuel, which is the nasty toxic mess that is left after more pure fuels are refined from oil. If it burns, thick, toxic black exhaust comes out. And if it ends up in the water, it's nasty as well. And that of course happens a lot.
Batteries are mostly just a bit of electrolyte and some metals that mostly occur naturally in sea level already (like lithium). The electrolyte compares quite favourably to bunker fuel probably. There may be some chemicals in there that probably aren't that great. But diluted in an ocean of water, they won't do a lot of harm. Mostly, you'd recycle the batteries as they are full of valuable commodities. So, dumping them in the ocean or a land fill would not be a common thing.
However, small correction, I don't believe small fishing vessels use HFO, I imagine either diesel or gasoline is used there.
But yes, that's basically my question, how they stack up, like, "if we sink this battery boat" versus "if we sink this fossil-burning boat" then what are the ecological consequences, which is worse,and after long might the inflection point be where one becomes "better" than the other (if the best one does not consistently stay best).
(I could counter argue that for the ecological damage caused by fishing, in both species depletion and nets lost to sea, the better solution might not to be allow small boat fishing at all for a few decades)
They also appear to have interesting and unexpected seasonal migrations and spawning patterns. They will situate themselves for prolonged periods in very different parts of a lake, over and over. Almost like they have vacation homes, haha.
But perhaps most surprising to me was their lack of response to loud motors and water disturbance by boats.
I have no doubt motors do spook some species, like trout or salmon.
https://www.transfluid.us/wp-content/uploads/2022/09/ehmt_10...
Submarines used this technology nearly 100 years ago.
A gasoline/diesel engine will just seize up when exposed to water, and if it's on fire it will be extinguished. Same for electric motors.
Batteries however? No bueno. Both the Americans [1] and Russians [2] lost submarines to battery fires. Batteries are hard and marine environments are among the nastiest you can get with corrosive saltwater and mist everywhere and continuous extreme mechanical shock events from waves and storms.
This is also why I believe that it's a fools errand to waste any non-fossil fuel (no matter if "sustainable" production from grains, frying oil or similar, or synth-fuels) on heating homes like it has been proposed in Germany or driving cars with it. The stuff is far too valuable, we'll need it for a long time to power aviation and maritime navigation until we get batteries both high-capacity and safe enough for these cases.
[1] https://en.wikipedia.org/wiki/USS_Bonefish_(SS-582)
[2]https://www.theguardian.com/world/2019/jul/23/russia-submers...
Nowadays, even small yachts are becoming hybrid or pure electric. My friend's 37ft sailing monohull is pure electric, so is my 35ft sailing catamaran.
Range is not really a problem if you plan carefully and are patient. I try not to motor much anyway -- it being a sailboat and all. I do have a back up generator though.
If you do an image search for "marina" you can even spot them on most stock photos.
Many folks have a generator in case they need more range and there isn't enough wind. But I personally haven't needed it yet, but I also don't sail long distances. I would probably bring a generator if I did, in case there's no wind and I need to move.
My friend has a generator aboard but hasn't used it once yet, and he made it to Puerto Vallarta from SF.
One need not imagine such things. It took a week for the Freemantle Highway car carrier to stop burning, something 90% of HN denizens are blissfully unaware of due to narrative blindness, and only about 15% of its cargo was electric.
While a burning electric fishing vessel won't do well, understand that these operations are already fraught with risk and regularly experience minor disasters. The small operations are borderline piratic and the big operations are highly lucrative. It is unlikely that they will forgo whatever benefits they imagine due to some unquantified fire risk.