My pleasure. Jeez, glad people like this stuff. Gorn didn’t like the Froude post too much; have to say I didn’t either. Doing some RL things on period sailing ships that have a lot of meta stability stuff going on and am using modern techniques to judge performance. I’m kinda immersed in the concepts, anyway, so going from a Sané fregate to a modern ain’t too far a stretch.ORIGINAL: obvert
This stuff is amazing. Thanks for taking the time JWE
Yeah, ships make waves. Like any wave, they have peaks and valleys. Poking along, a ship is under the bow wave peak, is floating on her lines, and everything is wonderful as shown in the green lines of the diagram. As speed increases, things shift aft and eventually, she’ll get to the point where the bow-wave peak goes aft enough that her bow is in the trough of the generated wave train and is pushing/plunging against the face of the medium as shown by the red lines in the diagram. It’s like ploughing your face through mud. Drag increases non-proportionally. Ok, that’s Froude-1; the economic limit.
As speed increases further, the bow wave trough constructively interferes with the stern wave trough and you get a really deep trough under the stern. The diagram is of the bow wave; the stern wave is a bit different. The stern then drops and parks. So now you are dragging ass. Don’t think I need to detail the effect on drag with this configuration. So her butt is in a hole and it’s gonna take a poopload of extra power to get her out of it. That’s Froude-2; the hull speed limit.
Note: red and green waveforms differ by phase and are centered on the midships of the vessel. That’s why we thought it important to mention Froude numbers as a function of the vessel characteristic length. Wave formation is seriously dependent on the vessel’s length.
I hope this is better. Ciao. JWE
