A big thing in boat design is the energy usage per mile at different speeds.
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.
> 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.
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,
Interesting! I wonder if this has to do do with the width of the boat vs length. For the same displacement, a narrower front, and therefore longer boat will clearly win. It's like a missile vs a peterbuilt
The width of the boat doesn't matter too much, surprisingly. It's mostly the length. From the waterline length you can guess how fast a ship is, regardless of the displacement. It's part of why the rumors that the Nimitz class can go 45 knots aren't believed by most people who know a bit about naval engineering: it doesn't matter much how much power the ship has, it's not going to go much faster.
> The width of the boat doesn't matter too much, surprisingly. It's mostly the length.
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.
Yes, it has to do with the beam, and some other things. A widely used method for estimating the propulsion power requirement for ships is the Holtrop-Mennen method. It has a dozen or so parameters, which you can play around with at an online calculator https://www.mermaid-consultants.com/resistance-prediction-ho...
May be it's because usually the longer the waterline the bigger the engine(?)
And the size of the engine is proportional to L^3. While the cross section is only L^2. I doubt with the same engine the bigger waterline has any positive effect...
My previous post is cut short, something something computers :(
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.
> 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.
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
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.
I'm familiar with fluids dynamics, thanks. Yes, bigger ending or smaller cross section is "better". You can downvote again if you have nothing to say. I don't care really.
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/
That's not really accurate. Displavement hulls are more efficient at lower speeds for the same displacement (i.e. payload mass), but at higher speeds, the speed-power relationship of planing hulls flattens allowing for MUCH higher speed transits, whereas the power requirements for displacement hulls just continues to skyrocket with increased speeds (1).
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.
And, actually, the speed doesn't matter, because the fuel usage of planing hull makes it uneconomic at any speed, even if such speed is greater than displacement hull speed, even though it's infinitely more effective than a displacement hull at those speeds (since a displacement hull cannot reach those speeds basically by definition).
And, a planing hull is not a great shape for displacement. I think they have significantly more drag, just 2x or 3x though, when operating at displacement speeds.
If anyone's confused about 10x in the GP post and 2-3x in this one, a given size boat with a displacement hull might have a hull speed of 6 kts and with a planing hull a hull speed of 5 kts.
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.
For container ships, engines that burn hydrogen derived ammonia, are more viable than electric to power these ships because of the long distances and the cubic area that ammonia storage would take to travel those distances is dramatically less than batteries. Man Energy Solutions is the farthest along with the engineering on these container ship engines and even has large scale commercial orders[1]. Ammonia has problems in that it is toxic and can produce NO2 if burned inefficiently. However, the relatively high energy density, ability to quickly refuel, and lack of need for pressurization is a huge benefit over electric.
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
Both are true, but both are true for internal combustion engines too.
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.
Assuming you're not just following the water flow, you should also be able to have an under-water turbine to generate even more water than you could with a wind turbine. (technically that power would still come from the wind, but from the sail you already have)
Hybrid sailboats are already a thing. An electric motor/generator sits in line with the traditional diesel engine and can a) drive the prop shaft, b) harvest power when the engine is turning the prop shaft, c) generate power by running the engine with the prop shaft clutch disengaged, or d) (the one you’re getting at) passively generate power when under sail by disengaging the clutch from the engine side and letting the prop spin the generator.
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).
Drag via the prop is nowhere going to reduce load at all. The resistence is the same and the force is square of the speed and surface area. So some drag ain’t doing anything. Even in a dangerous sea a drogue and lines would help, but way more than the surface area of a slowly or free spinning prop would offer.
I do wonder how electrification of ships this will affect navigation for larger vessels. A retired friend used to captain container ships, and during some unrelated story, he mentioned being able to navigate one particular channel because the ship’s draft was higher in the water from having less fuel (the old “fuel makes you heavy”).
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.
Reminded of the other sort of "battery", and USS Texas counter-flooding to induce a list so that she could elevate her guns beyond the design limit and achieve greater ranges while covering the Normandy landings.
I'm wondering what the "total ecological cost" is when also taking into account the sunken units.
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).
You mean compared to the oil & fuel leaking alternatives (when they sink, and also all the time) that when they are not leaking are basically burning it? Compared to a battery with some metals and chemicals in relatively small quantities that in the rare cases that they sink that may or may not leak out in trace amounts?
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).
It's a reasonable question, especially when you ask it about nuclear propulsion, but as you say the overall fuel saving hugely dominates.
(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)
I recently looked at a study about largemouth bass and discovered that in at least one lake, they don’t appear to be bothered by motor noise. Even if the boat is maybe 5 meters away.
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.
Huge benefit too is that you have a lot of surface space on the top of a boat that serves little purpose but to stop rain. Slap enough panels on the top of a boat, yeah it doesn't need to be a fully covered one, but if you do you could technically recharge while you're stationary and floating.
> Using a unique parallel hybrid battery-diesel system, the boat can travel at full speed using its diesel engine, then switch to a battery-electric motor when fishing
Submarines used this technology nearly 100 years ago.
This is nice progress, but international regulation (and enforcement) of emission controls, banning plastic nets, and ending slave vessels would have much more impact.
Inventing viable electric fishing vessels in no way takes away from anyone's ability to do those things. And the people doing this work aren't fungible: boat motor designers aren't ever going to be the same people banning plastic nets. It's not either-or.
Eh, everything that goes in the ocean requires a lot of engineering to survive. Batteries can be sealed if needed, electric motors can be sealed too. For example thrusters for ROVs are typically electric motors. They just enclose the motor in a housing and run the shaft out to the prop through a rubber seal. A lot of older stuff looks like it wasn't highly engineered because the important engineering was done a long time ago, and now the stuff is old and crusty. But there was a lot of work done to make gasoline engines work well in the water I suspect. We can do the same for electric.
> Batteries can be sealed if needed, electric motors can be sealed too.
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.
You overestimate the danger of batteries on boats. LFP batteries are commonplace on boats. Also, diesel electric propulsion is commonplace in large ships.
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.
My cat has a lot of real estate so I put a lot of solar. I rarely motor and mostly sail, but when I have extra power because the battery is full and the sun is shining, I can get a small speed boost for free. I have plenty of excess energy and have plugged into shore power maybe twice in the last year.
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.
I think pure electric is most common for sailboats. Where can get most of your propulsion from the wind and power from solar. My understanding is that range on electric is small. Fine for harbors but not enough if wind is wrong. It is usually possible to drift but that wastes time and can be problem in some situations. Most electric drive sailboats have a diesel generator as backup.
Power is common on a lot of docks. Just plug it in and charge it up.
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.
A gas tank, a propane tank, heck even a diesel tank, are all more dangerous than my LFP pack. Also my LFP pack weights 81kg, not a ton, definitely not multiple tons.
Larger boats are all diesel/electric series hybrids anyway (not sure if this is common at the scale of this particular vessel). Saltwater is nasty (and freshwater isn't great either), but avoiding electricity isn't easy.
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.
Teslas in NA use NMC chemistry (or a variant) which is much more dangerous than the LFP chemistry commonly used on boats. LFP cells are much harder to set on fire, and they don't burn anywhere as violently as more volatile chemistries.
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.