[HN Gopher] Battery-electric fishing vessel marks a sea change f...
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Battery-electric fishing vessel marks a sea change for small
commercial fishers
Author : geox
Score : 33 points
Date : 2023-09-10 18:48 UTC (4 hours ago)
(HTM) web link (www.nrel.gov)
(TXT) w3m dump (www.nrel.gov)
| londons_explore wrote:
| 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.
| coryrc wrote:
| IIRC planing versus displacement is about 10x increase in
| energy for the same speed. That's why all ocean-going
| freighters are displacement hulls.
| coryrc wrote:
| 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.
| mojomark wrote:
| 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.
|
| 1. https://images.app.goo.gl/Yn3znGUBgiM9jkB4A
| coryrc wrote:
| > Displacement hulls are more efficient at lower speeds for
| the same displacement
|
| Yes. I thought it was obvious I was comparing at
| displacement speeds only; I'm sorry for not being more
| clear.
| Xylakant wrote:
| > 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,
| hedora wrote:
| This is nice progress, but international regulation (and
| enforcement) of emission controls, banning plastic nets, and
| ending slave vessels would have much more impact.
| [deleted]
| bastawhiz wrote:
| 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.
| everybodyknows wrote:
| Apparently the diesel can in one mode be coupled to the propeller
| hydraulically:
|
| https://www.transfluid.us/wp-content/uploads/2022/09/ehmt_10...
| [deleted]
| Animats wrote:
| Electric trolling motors for small boats have been around for
| decades. Just enough motion to drag a line, not enough noise to
| scare the fish away.
| _whiteCaps_ wrote:
| https://oceanvolt.com/ makes some interesting marine electric
| motors.
|
| 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.
| phh wrote:
| 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)
| wffurr wrote:
| Said underwater turbine is already present: the prop. As a
| bonus, it can reduce rigging loads at hull speed by
| dissipating some energy.
| JoeAltmaier wrote:
| Somehow electricity and saltwater seem an ill-conceived
| combination.
| Gys wrote:
| Yet most boats today are full of electronics anyway
| toast0 wrote:
| 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.
| TaylorAlexander wrote:
| 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.
| topspin wrote:
| Commercial fishing vessels are already festooned with electric
| motors, batteries and electronics. Somehow all that functions
| in saltwater.
| SoftTalker wrote:
| > 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.
| [deleted]
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