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attempt #2 propwash

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MJH
  • Member since
    April 2005
  • From: Melbourne, Australia
Posted by MJH on Friday, December 14, 2007 7:19 AM

I have to add my voice to those who suggest this effect just isn't 'doable'.  The linear effect you've produced above isn't realistic - when the prop is pulling full power water would be dragged in from a wide area, not simply from straight ahead, creating a massive vortex and, as suggested above, unless the vessel was travelling at a hugely unrealistic speed would never be left behind in a solid 'tube' as depicted.  Add to this the movement of the hull itself through the water and the result is a chaotic maelstrom - the boiling wake that any ship leaves is evidence enough of that....

The idea is fascinating but I admit I have no idea what the answer might be, if any.  I've been trying for years to find a realistic depiction of a spinning aeroplane propellor and still haven't found an answer that looks right to me - motorizing the prop doesn't cut it.

The idea of using clear plastic 'shavings' has merit but how to suspend them?

The best I can come up with is to mount the hull in clear resin and stir in something to represent the foaming wake before it sets, but even I can see the practical difficulties inherent in that.... 

Michael 

!

  • Member since
    April 2003
  • From: PDX, OR
Posted by Umi_Ryuzuki on Saturday, December 8, 2007 10:23 AM

It would be interesting to find actual images of propeller cavitation under water.

http://www.nrc-cnrc.gc.ca/multimedia/picture/engineering/nrc-iot_cavitation_2_e.html

however I guess being under a boat as it passes over head would be dangerous...

Nyow / =^o^= Other Models and Miniatures http://mysite.verizon.net/res1tf1s/
  • Member since
    March 2005
  • From: West Virginia, USA
Posted by mfsob on Saturday, December 8, 2007 9:58 AM
You've got a fine looking model there ... and I know very well how easy it is to get fixated on some cool-looking "thing" that you want to be able to rise to the challenge of reproducing to add that unique Wow factor to your model ... but ... This ain't it.
  • Member since
    March 2004
  • From: Spartanburg, SC
Posted by subfixer on Saturday, December 8, 2007 9:30 AM

For one thing, if a ship had a propwash this linear, tubular and non-expanding, it would have to be travelling at an incredible speed. And I am talking SPEED! In order to get a spiral like that, the screws would have to be spinning so fast that they would fly off the shafts. Screws are actually turning relatively slowly. Think about it, the prop is pulling the ship through the water, not pushing it. Once the screw passes the water through it, it doesn't matter what happens to it. The water just sloshes along behind it, twisting, writhing, turbulent beyond recognition. It isn't recognizable as a solid entity of its own. One of the fears of a sailor is if he falls overboard, "Am I going to be sucked down into the screws, chopped up, and thrown up and out of the propwash?" It is very turbulent down there even if the props are only turning an RPM of 150 (which is, on an aircraft carrier, pretty quick) and making 22 knots for flight ops. I hate to tell you this but, lose the prop wash, it's not working. Replace it with some kind of roiling, frothing mess.

I'm from the government and I'm here to help.

  • Member since
    February 2005
  • From: springfield
Posted by prowannab on Friday, December 7, 2007 6:22 PM

 Okay,first thanks yall for the advice,so i need to ad more wire for the prop cavitation,i can do that fairly easily,i'm going to add some more pipe on the outer rudder to make it look like it is going thru the wash,but it won't be much givin that the rudder is to the extreme outer edge of the wash line.Question should i fade the cavitation out as it extends further from the ship? Oh by the way i'm doing the waves and all to ,actually i'm taking alittle break from that right now,but here is a first attempt pic of the water line without the waves.

but instead of the glass i'm doing it in wood since i'm laid off from work and have absolutely no money at all and i have to work from what i have laying around.

Patriae Fidus (FAITHFUL TO MY COUNTRY)
  • Member since
    August 2005
  • From: Mansfield, TX
Posted by EdGrune on Friday, December 7, 2007 5:45 PM

What Bob said,  it still looks lame.    It looks like a spiral notebook spring in a clear tube (That was my first impression and I couldn't shake it). 

Also, the rudder goes through the propwash, not around it.

If you're going to do this you need to have 4 or 5 wires wrapped helically around one another.  Each wire on your forward edge of your 'wake tube' is attached to the outside edge of a prop blade and spirals back. 

I still think it is doable with some spiral cutting waste from a drill bored into a block of plastic.

Less is sometimes more. 

 

  • Member since
    October 2005
Posted by CG Bob on Friday, December 7, 2007 4:57 PM
It does look a little better than your first attempt, but it still looks lame.  To make it look right, you're going to need to set the hull in a piece of acrylic and do the bow wave and everything else.  I'd only run the acrylic about 6" aft of the hull. 
  • Member since
    February 2005
  • From: springfield
attempt #2 propwash
Posted by prowannab on Friday, December 7, 2007 11:45 AM

 Well i took alot longer to get this attempt in than origanally thought.I completely agree with all of you about attempt 1 it was really bad.But i went back to the drawing board and came up with this,please lend your advice,as it is welcome and needed since i stare at this thing all day long and fresh eyes help out.Thanks

Patriae Fidus (FAITHFUL TO MY COUNTRY)
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