Reply
 
Thread Tools Search this Thread Display Modes
 
Old 05-26-2017, 09:51 AM   #1
Guru
 
City: Italy
Vessel Name: Didi Mau
Vessel Model: Currently looking for next boat
Join Date: Jul 2015
Posts: 1,063
rudder angles

I noticed yesterday for the first time that my rudders are not exactly parallel. When the rudder connected to the rudder sensor is parallel to the prop shaft, the other rudder is out by a few degrees. I would have thought both would be parallel, but this is my first two engine-boat.

A friend told me that if both are parallel, I will get vibration from the rudder, because of disturbed water going by the rudders. Does not seem intuitive to me.

Thanks in advance.

Gordon
Gordon J is offline   Reply With Quote
Old 05-26-2017, 10:14 AM   #2
Guru
 
Xsbank's Avatar
 
City: Pender Harbour, BC
Vessel Name: Gwaii Haanas
Vessel Model: Custom Aluminum 52
Join Date: Sep 2013
Posts: 3,791
Rudders are frequently toed in a bit to compensate for torque.

I find it interesting that if you look carefully at a twin engine prop airplane, the vertical tail is mounted with the vertical tail offset, it's not oriented "square." Same principle.
__________________
Don't believe everything that you think.
Xsbank is offline   Reply With Quote
Old 05-26-2017, 10:18 AM   #3
Valued Technical Contributor
 
DavidM's Avatar
 
City: Litchfield, Ct
Join Date: Aug 2012
Posts: 6,434
Quote:
Originally Posted by Xsbank View Post
Rudders are frequently toed in a bit to compensate for torque.
And to put a little water pressure on them to avoid the prop wash vibration.

David
DavidM is offline   Reply With Quote
Old 05-26-2017, 10:20 AM   #4
Guru
 
Nomad Willy's Avatar
 
City: Concrete Washington State
Vessel Name: Willy
Vessel Model: Willard Nomad 30'
Join Date: Oct 2007
Posts: 18,582
Xsbank,
That would not be best. In a way.
But in reality it will come to pass that one rudder will compensate for the propwalk (not torque) and together they will keep the boat going straight.

Interesting part pf this is that the single screw vessel will not require nearly as much rudder deflection to compensate for the propwash .. the rudder being so much larger. A detail that would make the single more efficient. But there are other factors. Fly stuff of course.
__________________
Eric

North Western Washington State USA
Nomad Willy is offline   Reply With Quote
Old 05-26-2017, 11:07 AM   #5
Moderator Emeritus
 
Comodave's Avatar
 
City: Au Gres, MI
Vessel Name: Black Dog
Vessel Model: Formula 41PC
Join Date: Jul 2015
Posts: 17,490
If they are truly parallel you may get some flutter in the rudders. With some toe in, there is some pressure to hold the rudders steady.
Comodave is online now   Reply With Quote
Old 05-26-2017, 02:57 PM   #6
Guru
 
Nomad Willy's Avatar
 
City: Concrete Washington State
Vessel Name: Willy
Vessel Model: Willard Nomad 30'
Join Date: Oct 2007
Posts: 18,582
Comodave,
Why dosn't my single screw ever flutter?
__________________
Eric

North Western Washington State USA
Nomad Willy is offline   Reply With Quote
Old 05-26-2017, 03:19 PM   #7
TF Site Team
 
Larry M's Avatar
 
City: Jacksonville
Join Date: Nov 2008
Posts: 10,842
Quote:
Originally Posted by Nomad Willy View Post
Comodave,
Why dosn't my single screw ever flutter?
Maybe the alignment of your rudder or your bearings are extremely tight? I have no idea. I get a flutter occasionally at certain RPMs/sea conditions but its so infrequent I don't worry about it. I have to be by the rudder post to hear/feel it.
Larry M is offline   Reply With Quote
Old 05-26-2017, 05:01 PM   #8
Guru
 
Nomad Willy's Avatar
 
City: Concrete Washington State
Vessel Name: Willy
Vessel Model: Willard Nomad 30'
Join Date: Oct 2007
Posts: 18,582
Larry,
Rudder not that tight at the shoe.
With my small prop (18") and small power (40hp) the turbulence is probably low. Also the rudder is large so LE to TE distance probably drops some turbulence too.
__________________
Eric

North Western Washington State USA
Nomad Willy is offline   Reply With Quote
Old 05-26-2017, 05:51 PM   #9
Moderator Emeritus
 
Comodave's Avatar
 
City: Au Gres, MI
Vessel Name: Black Dog
Vessel Model: Formula 41PC
Join Date: Jul 2015
Posts: 17,490
I am not sure why a single doesn't flutter, maybe less connections and no tie rod?
Comodave is online now   Reply With Quote
Old 05-26-2017, 06:20 PM   #10
Guru
 
psneeld's Avatar
 
City: Ft Pierce
Vessel Name: Sold
Vessel Model: Was an Albin/PSN 40
Join Date: Oct 2011
Posts: 26,101
My single flutters under certain conditions...maybe a worn bearing in the keel shoe, but cant duplicate by hand every hauout.
psneeld is offline   Reply With Quote
Old 05-26-2017, 07:09 PM   #11
Master and Commander
 
markpierce's Avatar
 
City: Vallejo CA
Vessel Name: Carquinez Coot
Vessel Model: penultimate Seahorse Marine Coot hull #6
Join Date: Sep 2010
Posts: 12,502
No flutter here. A three-degree port rudder, however, is needed to counteract prop walk while underway.

__________________
Kar-KEEN-ez Koot
markpierce is offline   Reply With Quote
Old 05-26-2017, 07:36 PM   #12
Guru
 
Xsbank's Avatar
 
City: Pender Harbour, BC
Vessel Name: Gwaii Haanas
Vessel Model: Custom Aluminum 52
Join Date: Sep 2013
Posts: 3,791
If your rudder flutters, it's more likely to be the linkage. Mine started vibrating and I needed a new gudgeon pin. The new Wagner pins have grease nipples.

I bet dollars to donuts the rudders on a twin are no more likely to flutter unless something is worn. It makes no sense.
__________________
Don't believe everything that you think.
Xsbank is offline   Reply With Quote
Old 05-26-2017, 07:45 PM   #13
Guru
 
ulysses's Avatar
 
City: Gulf Shores, Ala.
Vessel Name: Ulysses
Vessel Model: Romsdal 1963
Join Date: May 2013
Posts: 878
Quote:
Originally Posted by markpierce View Post
No flutter here. A three-degree port rudder, however, is needed to counteract prop walk while underway.



Please educate me on that port rudder/ prop walk. Is that not a Rt. hand screw? Would that not create a prop walk in the same direction rather than an opposed direction ?
ulysses is offline   Reply With Quote
Old 05-26-2017, 07:58 PM   #14
Guru
 
Sailor of Fortune's Avatar
 
City: St Augustine,Fl
Join Date: Sep 2009
Posts: 3,690
That looks like a left hand wheel to me. Counter clockwise rotation, will back to starboard.
Sailor of Fortune is offline   Reply With Quote
Old 05-26-2017, 08:11 PM   #15
Master and Commander
 
markpierce's Avatar
 
City: Vallejo CA
Vessel Name: Carquinez Coot
Vessel Model: penultimate Seahorse Marine Coot hull #6
Join Date: Sep 2010
Posts: 12,502
Correct, it backs to starboard and turns to starboard going forward under power without a three-degree port rudder.
__________________
Kar-KEEN-ez Koot
markpierce is offline   Reply With Quote
Old 05-26-2017, 09:28 PM   #16
Guru
 
Nomad Willy's Avatar
 
City: Concrete Washington State
Vessel Name: Willy
Vessel Model: Willard Nomad 30'
Join Date: Oct 2007
Posts: 18,582
Same w my boat Mark.
Left hand wheel, back to stbd and pull to stud going fwd.

LarryM just the mass of my big rudder probably keeps it from fluttering.
Attached Thumbnails
DSCF1679 copy 2.jpg  
__________________
Eric

North Western Washington State USA
Nomad Willy is offline   Reply With Quote
Old 05-26-2017, 09:39 PM   #17
Guru
 
Benthic2's Avatar
 
City: Boston Area
Join Date: Feb 2017
Posts: 2,358
could the difference be that single screw rudders are often attached top and bottom, while twin screw rudders are often only attached at the top ?
Benthic2 is offline   Reply With Quote
Old 05-26-2017, 09:40 PM   #18
Guru
 
Sailor of Fortune's Avatar
 
City: St Augustine,Fl
Join Date: Sep 2009
Posts: 3,690
Quote:
Originally Posted by markpierce View Post
Correct, it backs to starboard and turns to starboard going forward under power without a three-degree port rudder.
Eric, maybe no play in the rudder tube, or tight bushing in the drag link would be why you have no play or "chatter".
Sailor of Fortune is offline   Reply With Quote
Old 05-26-2017, 10:42 PM   #19
Guru
 
Nomad Willy's Avatar
 
City: Concrete Washington State
Vessel Name: Willy
Vessel Model: Willard Nomad 30'
Join Date: Oct 2007
Posts: 18,582
Well it dosn't chatter and I'm not upset about it.
__________________
Eric

North Western Washington State USA
Nomad Willy is offline   Reply With Quote
Old 05-26-2017, 11:59 PM   #20
Dauntless Award
 
Wxx3's Avatar
 
City: Wrangell, Alaska
Vessel Name: Dauntless
Vessel Model: Kadey Krogen 42 - 148
Join Date: Jan 2013
Posts: 2,812
Quote:
Originally Posted by markpierce View Post
No flutter here. A three-degree port rudder, however, is needed to counteract prop walk while underway.

Me too, but it's 3 degrees to stbd
__________________
Richard on Dauntless,
New York

a Kadey Krogen 42 currently: https://share.garmin.com/dauntless
Blog:
https://dauntlessatsea.com
Wxx3 is offline   Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


» Trawler Port Captains
Port Captains are TF volunteers who can serve as local guides or assist with local arrangements and information. Search below to locate Port Captains near your destination. To learn more about this program read here: TF Port Captain Program





All times are GMT -5. The time now is 09:59 PM.


Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2022, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2006 - 2012