3 ms·

MHD is nothing new though, so if it has not yet replaced propellers I'm guessing it is because of practical issues like corrosion, electrolysis and so on allude

by ajnin 3y ago

MHD is nothing new though, so if it has not yet replaced propellers I'm guessing it is because of practical issues like corrosion, electrolysis and so on alluded to in the article that DARPA seems to have found solutions for but which are not going to be available for the general public for obvious reasons. Also it's all electric so it poses the usual problems like the added complexity of an on-board electric generator or the added weight and cost of a battery system.

hef19898 3y ago
So, the USN actually did park that Soviet sub captained by James Bond in a creek somewhere. I knew it!
gpm 3y ago
Per the article the previous generation was only roughly 30% efficient, which makes it just not competitive with propellers. Swapping out your diesel motor with rotating shafts going through your hull and an alternator to generate electricity for a diesel generator that just generates electricity is reducing complexity, not adding it.
- ImPostingOnHN 3y ago
  the alternator is already there, too, since modern diesel submarines are actually diesel-electric submarines, able to charge batteries with the diesel engine and then shut it off and run from the batteries to go quiet so, the difference is between props vs. no props, which is big.
  - gpm 3y ago
    In context I'm arguing for use on commercial surface boats and ships. But they too have alternators (and/or dedicated generators)... because it turns out electricity is really useful.
denton-scratch 3y ago
> because of practical issues Like fitting supercooled tesla-power magnets to a moving vehicle, perhaps. > the added complexity of an on-board electric generator But you don't need that if the vessel is electric-powered, like a nuclear-powered sub; and I believe some modern warships use a traditional motor to drive a generator, which drives an electric motor for propulsion (i.e. an electric ship powered by a fossil-fuel generator).
- Turing_Machine 3y ago
  > But you don't need that if the vessel is electric-powered, like a nuclear-powered sub Yep. > I believe some modern warships use a traditional motor to drive a generator, which drives an electric motor for propulsion Sure, like a diesel-electric locomotive. It turns out in some situations it's better to eat the conversion loss from electric generation rather than using a direct mechanical linkage, because then you can use flexible cables and electrical control systems rather than a bunch of mechanical folderol

by ajnin 3y ago

hef19898 3y ago

So, the USN actually did park that Soviet sub captained by James Bond in a creek somewhere. I knew it!

gpm 3y ago

Per the article the previous generation was only roughly 30% efficient, which makes it just not competitive with propellers. Swapping out your diesel motor with rotating shafts going through your hull and an alternator to generate electricity for a diesel generator that just generates electricity is reducing complexity, not adding it.

ImPostingOnHN 3y ago
the alternator is already there, too, since modern diesel submarines are actually diesel-electric submarines, able to charge batteries with the diesel engine and then shut it off and run from the batteries to go quiet so, the difference is between props vs. no props, which is big.
- gpm 3y ago
  In context I'm arguing for use on commercial surface boats and ships. But they too have alternators (and/or dedicated generators)... because it turns out electricity is really useful.

denton-scratch 3y ago

> because of practical issues Like fitting supercooled tesla-power magnets to a moving vehicle, perhaps. > the added complexity of an on-board electric generator But you don't need that if the vessel is electric-powered, like a nuclear-powered sub; and I believe some modern warships use a traditional motor to drive a generator, which drives an electric motor for propulsion (i.e. an electric ship powered by a fossil-fuel generator).

Turing_Machine 3y ago
> But you don't need that if the vessel is electric-powered, like a nuclear-powered sub Yep. > I believe some modern warships use a traditional motor to drive a generator, which drives an electric motor for propulsion Sure, like a diesel-electric locomotive. It turns out in some situations it's better to eat the conversion loss from electric generation rather than using a direct mechanical linkage, because then you can use flexible cables and electrical control systems rather than a bunch of mechanical folderol