Wikipedia:Reference desk/Archives/Miscellaneous/2023 October 16
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October 16
editFastest multi-deck boat in 1940?
editLegend of Korra has a situation where they are trying to get away from a Crazy Waterbender, and the boat (which appears to have two decks) speeds up very quickly. Given that LoK technology sort of runs in the 1920s-1940s punk situation (ending with something that is definitely at the A-Bomb wonderweapon level), I thought I'd ask about the fastest a boat of that time period could go... Naraht (talk) 19:04, 16 October 2023 (UTC)
- The USCGC Fir (WLM-212) could run at 12 knots, but I don't know how well the ship could accelerate. It was not designed for high acceleration. I suppose with 1940 technology, when aiming at high acceleration, a much lighter multi-deck boat could have been built, resulting in much lower water displacement and thus better acceleration, while still using 1,350 shp engines or even more powerful ones. --Lambiam 19:48, 16 October 2023 (UTC)
- USS Maury of 1938 could manage 42.8 knots (49.2 MPH), although that was a full-sized ship. The British MTB 102, a 1937 motor torpedo boat which had a crew of twelve, could make 44 knots (50.5 MPH). Civilian boats were rather slower, except for racing motorboats which generally only had a cockpit - Miss England III of 1932 managed just under 120 MPH and her competitor, Miss America X, did just under 125 MPH. Multi-deck motor yachts were more sedate; most of the inter-war yachts I looked at didn't exceed 15 knots (17 MPH). Alansplodge (talk) 21:18, 16 October 2023 (UTC)
- Using the drag equation, I find that the magnitude of the initial acceleration under full power of a boat initially at rest is given by
- in which stands for the power, for the mass of the boat and for its top speed. To apply this, you need to convert the given values from horsepower, tonnes and knots to SI units. --Lambiam 07:08, 17 October 2023 (UTC)
- That formula may be a useful rule of thumb, but it's not hard physics: first, it assumes that maximum effective power is available at top speed; second, it assumes that thrust is independent of speed.
- BTW, the drag formula isn't very useful for boats. For a surface vessel, the drag coefficient depends not only on Reynolds number, but also on Froude number and therefore speed in some complicated way. Practically speaking, big ships have a drag proportional to speed, but for fast boats, when getting close to the hull speed and when dealing with planing hulls, things get complicated. PiusImpavidus (talk) 09:55, 17 October 2023 (UTC)