Yes.
The excellent discussion so far is very good, and has lots of merit, imo.
I am of the long expressed opinion that very large area, and very low
rise, are the correct solutions.
Because;
1.
Physics supports this.
So do textbooks.
2.
Tugboats and other low-speed high thrust uses use this type of setup
3.
Slower rise => lower slip
Lower slip => more efficiency
Also, lots of observational data prove that HP of approx 1/10 that
commonly used is more than enough, including in commercial use.
Early commercial freight haulers, sea-going, used to have about that
much, or 1/2 hp / metric ton, for 200-400 ton displacements.
Mentioned in the pretty good "Onedin line" TV series in passing.
Was also an early rule of thumb for naval architects.
Some of the very good points made, correct imo, are:
- change of efficiency/physics as the boat moves
- prop speed at root vs at tip has an effect
- vortices etc. have an effect
Current production props are "all wrong" wrt. efficiency.
A common "good" prop for ICE engines is near square, ie rise == diameter.
Thus, some obvservations based data gives rise to surprising real-world
results using the current-production props.
An example is the large-square prop (with high rise) getting good
efficiency.
On 29/12/2015 03:05, moriartybob@yahoo.com [electricboats] wrote:
> We're in an a posteriori world with respect to ideal prop
> configurations. Observational data is what's needed in our highly
> variable world of props, displacements, LWLs, bottom conditions, speed
> through the water, amps used, motors and battery systems.
> --Bob M
--
-hanermo (cnc designs)
Posted by: Hannu Venermo <gcode.fi@gmail.com>
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