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Thirty years ago, I worked for the Navy and had some exposure to propeller design for submarines. Military propellers at that time were already employing comple
by pge 4y ago
Thirty years ago, I worked for the Navy and had some exposure to propeller design for submarines. Military propellers at that time were already employing complex shapes for efficiency (and noise reduction). While it certainly takes time for military technologies (especially classified ones, which propeller shapes were) to propagate into the civilian world, in this case, I think the issue is primarily cost. Civilian props have remained quite simple because the cost of manufacturing complex shapes is high (often requiring multi-axis milling machines). In addition, repairability and other concerns may be more important than efficiency.
While I don't work in fluid dynamics anymore, it's cool to see people explore some of these ideas in the civilian world. Unfortunately, they may be solving the wrong problem for the vast majority of their users, for whom the cost doesn't justify any performance benefit.
- michaelcampbell 4y ago> for whom the cost doesn't justify any performance benefit. These are boat owners, remember.
- kibwen 4y agoGiven what we're learning about the effect of propeller noise on marine life, I can foresee certain countries outlawing the sale of noisy propellers if reduced-noise versions become broadly available, even if they are more expensive.
- rexreed 4y agoWhen I saw the word "cavitation", submarines was the first thing I thought about. Blame the Hunt for Red October for that word association. You'd think that this approach to propeller design would be adopted due to quieter running, but sounds like not.
- pge 4y agoCavitation isn't just a noise problem; it also causes damage to the blades. The forces on the blade are surprisingly strong. When a propeller has been experiencing cavitation, you can see the pitting on it, almost like you hit it with a pointy hammer. If it continues, cavitation can seriously weaken the blades.
- ri0t 4y agoI'd wager to say that on most civilian vessels, the engine noise is far louder than what the prop could generate. I'm happily using a 600W outboard electrical - while it would be different than with a combustion engine, i don't think it can get much quieter even with better prop-design. It's a blessing! Almost like sailing the boat, i.e. not much louder than a gust of wind. Energy efficience on the other hand.. It is driven by a fairly average car battery, so every little Watt saved helps keep the drinks cooled.
- FPGAhacker 4y ago600W? Is that a typo? That’s less than 1HP.
- fwipsy 4y agoI don't know anything about boats, but some boats can be rowed by a single person, which I guess would typically be much less than 600w. It fits with the car battery part too.
- simne 4y agoMost people are capable to do about 500-800W for long time (30 minutes or more), and up to few kilowatts for short time, 1-3 minutes.
- andreareina 4y agoSource? In cycling those numbers are elite level if not beyond. Numbers for rowing are hard to come by but lower[1], probably drag lowering efficiency (bicycle drivetrains are 90+% efficient). To put it into perspective, 250Wh translates to 800~900 calories burned in a half hour[2]. That's not something most people around me can do. [1] https://rowinglevel.com/rowing-times/10000m-times https://rowinglevel.com/rowing-times/10000m-times 250Wh = 900kJ = 215 kcal at 100% efficiency; humans are ~25% efficient at turning food into mechanical work so ~860 with error bars