Re: Screw size and speed

[Greg Teiber <wolfe19@megsinet.net>]

Hi, I'm new to the list, but I have some signifignat experiance in powerboating......  Basicly I've been around and on boats since the age of -9 months :) From the bottom....

For ducted fans, both undrewater and above water, if the cowling is relitivley close fitting, efficancy can be markedly improved.  the propeller don't have the spill off at the tips creating those wingtip vortecies.  those really cool looking streams of bubbles comming off the tips of propellers are actually huge wastes of energy.  If you can, keep to a ducted design, and maybe put a grate over the intake to help get rid of junk that might try to ruin your thrusters day :)

When it comes to fishlike/whale like propulsion, it's been done........  bearly.  It's like the bird thing, we understand it, but we are having troubble dublicating it.  We can get a tail setup working, but the main body of the vessel is completely unstable, and directional control is very very weak.  Researchers are getting somethign of what they expected in efficancy, but control still is a major problem.

Basicly, stick to propellers, ducted preferably :)

*********** REPLY SEPARATOR ***********

On 7/19/99, at 10:19 AM, Dick Morrisson wrote: 

>John,
>This not an answer to your question, but a related one.
>
>Fish have a pretty good propulsion system for underwater use that works at both
>high and low speed and it almost never gets tangled in the garbage (they may
>choke on it but their propulsion system nearly always remains clear!).  Does
>anyone in the group have experience with "non-propellor" (fish style)
>propulsion?  Is this a possibility for a small sub?  And for those who need
>lots of horsepower, think "blue whale"!
>
>Dick Morrisson
>
>
>John Brownlee wrote:
>
>>         In RE: Superiority of big geared-down screws, any thoughts or
>> experience on fouling? Problem with being a "bottom dweller" is that there
>> are -things- you can wind up amuck in, like cables and so on. I worked
>> around ducted small screws to keep a clean smooth profile, but realize the
>> performance penalty. Hearing more about the Perry subs has really piqued my
>> interest, though.
>>         Did any of the Perry boats ever have trouble with those big screws
>> and entanglement when they weren't under power?
>>
>>                                                         John
>>
>> John Brownlee
>> Lunar and Planetary Lab
>> University of Arizona
>> jonnie @ lpl . arizona . edu