Twin Screw Question
#2
My Feedback: (6)
Join Date: Jul 2005
Location: White hall, IL
Posts: 1,030
Likes: 0
Received 0 Likes
on
0 Posts
RE: Twin Screw Question
They should turn inward. If you looking the back they should go clockwise on the left hand side and counterclock wise on thr right. So the answer to your question is down the middle.
#7
RE: Twin Screw Question
Actually Most large ships run with figure 2. We also seem to be finding that many river tugs will run with figure 1.
Here are Titanic's propellers...
.
.
.
.
.
http://www.encyclopedia-titanica.org...volutions.html
Here are Titanic's propellers...
.
.
.
.
.
http://www.encyclopedia-titanica.org...volutions.html
#9
RE: Twin Screw Question
Also noted in the other forum... US and European prop makers are opposite in their LH/RH definitions!
Of course, makes no difference if you're buying a pair...
Of course, makes no difference if you're buying a pair...
#10
My Feedback: (10)
RE: Twin Screw Question
hi
i guess it all depends on who you ask last year i ran a left and right three blade on my 5'pt boat left conter and right clockwise it ran good not as fast as i would of like it but playing around with battery power i blew the esc now i work on it this winter with two esc and have the props turning in on each other i will find out which way is better in the spring i also send a e-mail to abc props where i got them from and ask him if he e-mails me back i let you guys know thanks rye
i guess it all depends on who you ask last year i ran a left and right three blade on my 5'pt boat left conter and right clockwise it ran good not as fast as i would of like it but playing around with battery power i blew the esc now i work on it this winter with two esc and have the props turning in on each other i will find out which way is better in the spring i also send a e-mail to abc props where i got them from and ask him if he e-mails me back i let you guys know thanks rye
#12
Join Date: Jul 2007
Location: Blackpool Lancs, UNITED KINGDOM
Posts: 1,432
Likes: 0
Received 32 Likes
on
32 Posts
RE: Twin Screw Question
The wisdom that was passed to me was that turning one way was better for steering, turning the other was better for performance. Cant say tat I've really noted a difference either way. If modeling a real ship, copy that.
The Titanic, like most liners, was intended for running fast and straight - the rudder was more of a trim tab. Serious steering would have been done with differential engine speeds, and changing the speed of a huge great reciprocating engine going flat out was not an instant operation. Even today, 50-odd thousand tons doing 20Kt takes a lot of persuading to go in a new direction.
The Titanic, like most liners, was intended for running fast and straight - the rudder was more of a trim tab. Serious steering would have been done with differential engine speeds, and changing the speed of a huge great reciprocating engine going flat out was not an instant operation. Even today, 50-odd thousand tons doing 20Kt takes a lot of persuading to go in a new direction.
#13
Member
Join Date: Dec 2007
Location: Rainhillmerseyside, UNITED KINGDOM
Posts: 33
Likes: 0
Received 0 Likes
on
0 Posts
RE: Twin Screw Question
A lot of fast boats built from the 30s onward UK , had both props turning the same way couple of pictures of ww2 boats running gear.
Peter
Peter
#14
RE: Twin Screw Question
Both turning the same way is just plain CHEAP ! There is NO way a twin screw boat can dock in a tide & wind equally well, IF AT ALL, with both screws in the same direction.
CHEAP & DANGEROUS.
Rich
CHEAP & DANGEROUS.
Rich
#15
RE: Twin Screw Question
ORIGINAL: cyclops2
Both turning the same way is just plain CHEAP ! There is NO way a twin screw boat can dock in a tide & wind equally well, IF AT ALL, with both screws in the same direction.
CHEAP & DANGEROUS.
Rich
Both turning the same way is just plain CHEAP ! There is NO way a twin screw boat can dock in a tide & wind equally well, IF AT ALL, with both screws in the same direction.
CHEAP & DANGEROUS.
Rich
It's a historical precedent. Probably still happens to this day.
#17
Member
Join Date: Dec 2007
Location: Rainhillmerseyside, UNITED KINGDOM
Posts: 33
Likes: 0
Received 0 Likes
on
0 Posts
RE: Twin Screw Question
I think you may find it made them go faster, they where still using this methoud up to the 60s, have you looked at what was used on pt boats ?
Peter
Peter
#19
Member
Join Date: Sep 2005
Location: Roanoke, VA
Posts: 34
Likes: 0
Received 0 Likes
on
0 Posts
RE: Twin Screw Question
So, while this thread is kicking, is the rotation "design specific"? Tugs go this way, ocean liners go that way or is it individual boat specific? I'm working on a Darby with my father and we were wondering about this topic (a-la the rcg thread and the drawing I did). Our original question was specifically about the Darby tug, and the responses were got were all "fig 2". Is there some hydrodynamic reason some go like in fig 1?
Thanks,
Whitt
#21
Senior Member
Thread Starter
Join Date: Feb 2007
Location: Gilroy, CA
Posts: 147
Likes: 0
Received 0 Likes
on
0 Posts
RE: Twin Screw Question
Wow, appreciate all of the input.....but still confused.....let's disect this a bit (then you can set me straight). Tugs may want the stern to be sucked down, that would mean thrusting up in the center? Kinda makes sense....the speed guys may want the rotation down in the center to left the stern.....but does that push the bow down too much?
#22
Junior Member
My Feedback: (1)
Join Date: Feb 2008
Location: Anaheim,
CA
Posts: 3
Likes: 0
Received 0 Likes
on
0 Posts
RE: Twin Screw Question
Well it does not make much difference its just the way in fig.1 kicks up the silt on the botom of ports. (that makes it so they have to dredge more often) so large ships use fig.2. you do get better manuvering with fig.1.
#23
My Feedback: (26)
RE: Twin Screw Question
Good question. I am just finishing a Shelly Foss, and I assumed figure 1 would be correct, as it would draw the water from outside and push it down in the center away from the hull instead of pushing it up against the hull. Easy enough to change once I run it to see if it changes performance. It would be interesting to see if it makes a difference on a tug vs. a faster hull as well.