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A ship can not go faster because it has a powerful engine or a near limitless energy source. A ship's speed is limited by design, especially with hull length. Y

by laydn 7y ago

A ship can not go faster because it has a powerful engine or a near limitless energy source. A ship's speed is limited by design, especially with hull length. You cannot make a cruise ship go with 50kts.

ErikCorry 7y ago
50mph not 50 knots. I took one of these on a 75 minute trip last weekend. They cruise at 47mph and top speed is 55mph. https://en.wikipedia.org/wiki/HSC_Fjord_Cat https://en.wikipedia.org/wiki/HSC_Fjord_Cat They use huge amounts of diesel fuel, but that would not be the case for a nuclear version. Edit: This version does 67mph and is powered by two 25 megawatt engines. https://en.wikipedia.org/wiki/HSC_Francisco https://en.wikipedia.org/wiki/HSC_Francisco
- laydn 7y ago
  Sorry, when you said cruise ship, I was thinking "royal carribean" type ships. Cats can go much faster obviously. My point is that the power alone can not make a ship faster. Hull length and shape determines max speed.
  - ksec 7y ago
    Still not quite understanding the point. You mentioned even with unlimited amount of energy and power the speed is still capped and limited by Hull Length and Shape. This reads to me if I could get a Nuclear Fusion reactor in my ship that has 10 times the power my Max Speed would still be the same. This doesn't sound right to me.
    - willis936 7y ago
      Drag increases dramatically above the hull speed. Obviously more power means more speed, but if you want more speed for a fixed power then your hull dimensions really matter. https://en.wikipedia.org/wiki/Hull_speed https://en.wikipedia.org/wiki/Hull_speed
      - hanniabu 7y ago
        > if you want more speed for a fixed power then your hull dimensions really matter. So in other words there's no max speed since we're not talking about fixed power.
        willis936 7y ago
        I’m not sure I understand. Power isn’t what’s important. It’s power per volume/weight. If you have an infinitely dense power source then you can send matter at the speed of light through any medium. Is this really an important point to make? Edit: Oh I see what’s going on above in this thread. It’s nuanced but I believe the original point was that in the Real World with Real Power Sources you have a Real Top Speed. You can’t just always dump more power into your ship to increase it and the right way to increase the max speed is to control hull dimensions.
    - dboreham 7y ago
      It's a well known property of boats. Due to fluid dynamics. This is why boats are big. Longer the waterline the faster it can go. Also why fast boats use multi hull designs.
    - Xylakant 7y ago
      > This reads to me if I could get a Nuclear Fusion reactor in my ship that has 10 times the power my Max Speed would still be the same. Hull speed is a pretty simplistic approximation of the actual physics behind it, but generally the rule holds: A displacement hull cannot exceed its hull speed. What will rather happen is that the bow wave will pile up and eat your energy. It’s actually a problem if a very powerful boat pulls a smaller one, the bow wave on the smaller boat piles up, making the smaller boats bow rise up until the stern slips under the water and it sinks. (Or something else gives in under increasing strain before that happens) Now, other hull forms can be built: glider hulls for example that glide on the water surface (think fast sports boats etc.), but scaling those up will certainly be problematic if you’re trying to aim for high carrying capacity. Cats/Multi hull designs sort of cheat the physics: the determining factor is roughly the length of the water line and multi hull designs obviously have more waterline for a given total length.

by laydn 7y ago

ErikCorry 7y ago

50mph not 50 knots. I took one of these on a 75 minute trip last weekend. They cruise at 47mph and top speed is 55mph. https://en.wikipedia.org/wiki/HSC_Fjord_Cat https://en.wikipedia.org/wiki/HSC_Fjord_Cat They use huge amounts of diesel fuel, but that would not be the case for a nuclear version. Edit: This version does 67mph and is powered by two 25 megawatt engines. https://en.wikipedia.org/wiki/HSC_Francisco https://en.wikipedia.org/wiki/HSC_Francisco

laydn 7y ago
Sorry, when you said cruise ship, I was thinking "royal carribean" type ships. Cats can go much faster obviously. My point is that the power alone can not make a ship faster. Hull length and shape determines max speed.
- ksec 7y ago
  Still not quite understanding the point. You mentioned even with unlimited amount of energy and power the speed is still capped and limited by Hull Length and Shape. This reads to me if I could get a Nuclear Fusion reactor in my ship that has 10 times the power my Max Speed would still be the same. This doesn't sound right to me.
  - willis936 7y ago
    Drag increases dramatically above the hull speed. Obviously more power means more speed, but if you want more speed for a fixed power then your hull dimensions really matter. https://en.wikipedia.org/wiki/Hull_speed https://en.wikipedia.org/wiki/Hull_speed
    - hanniabu 7y ago
      > if you want more speed for a fixed power then your hull dimensions really matter. So in other words there's no max speed since we're not talking about fixed power.
      - willis936 7y ago
        I’m not sure I understand. Power isn’t what’s important. It’s power per volume/weight. If you have an infinitely dense power source then you can send matter at the speed of light through any medium. Is this really an important point to make? Edit: Oh I see what’s going on above in this thread. It’s nuanced but I believe the original point was that in the Real World with Real Power Sources you have a Real Top Speed. You can’t just always dump more power into your ship to increase it and the right way to increase the max speed is to control hull dimensions.
  - dboreham 7y ago
    It's a well known property of boats. Due to fluid dynamics. This is why boats are big. Longer the waterline the faster it can go. Also why fast boats use multi hull designs.
  - Xylakant 7y ago
    > This reads to me if I could get a Nuclear Fusion reactor in my ship that has 10 times the power my Max Speed would still be the same. Hull speed is a pretty simplistic approximation of the actual physics behind it, but generally the rule holds: A displacement hull cannot exceed its hull speed. What will rather happen is that the bow wave will pile up and eat your energy. It’s actually a problem if a very powerful boat pulls a smaller one, the bow wave on the smaller boat piles up, making the smaller boats bow rise up until the stern slips under the water and it sinks. (Or something else gives in under increasing strain before that happens) Now, other hull forms can be built: glider hulls for example that glide on the water surface (think fast sports boats etc.), but scaling those up will certainly be problematic if you’re trying to aim for high carrying capacity. Cats/Multi hull designs sort of cheat the physics: the determining factor is roughly the length of the water line and multi hull designs obviously have more waterline for a given total length.