Drunkskunk wrote:In order for a propultion device to be efficent, it needs to transfer energy to the water without moving the water. You want the boat to move in the water, you don't want the water to move
Honk wrote:Hi again.
Iv'e been thinking some about power input vs force created.
In Javaprop I designed a 74% efficient prop at 0.3m dia 2-blade for 1100 RPM and 270Watts shaft power.
It was calculated to generate a force of 99N (approx 22 lbf).
The thing is....I have tested the force of a 2-blade plastic Motor Guide prop at 270W and it
generated 40 static lbf, almost twice the force of the calculated prop at 22 lbf and this is very strange to
me as a good and efficient prop should convert energy to a lot of thrust to push the hull efficiently forward.
Efficiency for me is maximum thrust being generated, but 22lbf is a lot less than actually measured 40lbf
from a real prop. Perhaps the thrust calculation in Javaprop is way of from real world results....I don't know?
Do you have any input on this Jeremy?
Jeremy Harris wrote:Watch this space with regard to a semi-hydrofoil, as I have a part built foil that I intend testing on the aft end of my boat in the next couple of weeks, the intention being to lift it up and reduce viscous drag!
The fingers wrote:One idea to reduce drag, air bubbles!
Drunkskunk wrote:The textured surface idea works. the boat I mentioned in my first post was painted with a non glossy paint. I'm not sure what sort of micro surface it might have had, it was 80's tech, but that reportadly gave it a few seconds faster time. My friend promptly painted it glossy blue.
Making the paddlewheel efficent I can understand, as I've seen one in action. The propeller I can't. I can know that it is because people who know said so, but I don't understand it, something hasn't clicked in my head yet.
How can a prop reach that efficancy while it has to travel so far through the water? Since the tips of the blades have to move several feet through the water (and displace that water) for every inch forward the boat moves, how can they be efficent? I don't dispute it, I just don't understand it yet.
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