Reply
 
Thread Tools Display Modes
 
Old 07-01-2015, 02:03 PM   #1
Guru
 
City: Satsuma FL
Country: United States
Vessel Name: No Mo Trawla
Vessel Model: Hurricane SS188
Join Date: Jul 2014
Posts: 1,675
Da rudder please

Several TF posters from time to time have complained that their rudders are too small and too non responsive. Some have increased the size of the rudder but it sounds like a trial and error process or maybe just personal preference.

I have found our rudder is not as responsive as I would like it to be. I assume it is due to the rudder being too small.

How is optimal rudder size determined? Why do manufacturers install undersize rudders if this condition does in fact exist?

Standard disclaimer - there is no intent to turn this into a "Your rudder is too small, it is too unresponsive and it leaks" discussion.
__________________
Advertisement

Donsan is online now   Reply With Quote
Old 07-01-2015, 02:08 PM   #2
TF Site Team
 
Larry M's Avatar
 
City: JAX, FL
Country: USA
Vessel Name: Hobo
Vessel Model: Krogen 42-120
Join Date: Nov 2008
Posts: 5,733
Here's a link from a former TF member and what he did to get better control at the helm. The boats a DeFever/PassageMaker 40.

Rudder
__________________

Larry M is online now   Reply With Quote
Old 07-01-2015, 03:12 PM   #3
Guru
 
City: Satsuma FL
Country: United States
Vessel Name: No Mo Trawla
Vessel Model: Hurricane SS188
Join Date: Jul 2014
Posts: 1,675
Quote:
Originally Posted by Larry M View Post
Here's a link from a former TF member and what he did to get better control at the helm. The boats a DeFever/PassageMaker 40.

Rudder
Nice article. Unfortunately, I couldn't find the results after his installation and sea trial.

I assume the issue I am having is my rudder was designed for a twin engine boat and it's rudder area is closer to 2.5% of the underwater profile instead of 5% which a single engine boat would require.

He brings up a good point on the rudder shaft. Obviously. if you increase the rudder surface area, there will be more loads on the shaft.

So it turns out to be more complicated and precise than I thought it might be and there might be other considerations since my rudder has a bottom skeg.
Donsan is online now   Reply With Quote
Old 07-01-2015, 06:16 PM   #4
Guru
 
City: Venice Louisiana
Country: United States
Join Date: Dec 2013
Posts: 1,097
Dave Gerr's book, Boat Mechanical Systems Handbook, covers this subject very well. And its just in general a good book to have around.
kulas44 is offline   Reply With Quote
Old 07-01-2015, 06:40 PM   #5
Guru
 
City: Hotel, CA
Country: Fried
Join Date: Sep 2011
Posts: 8,328
Quote:
Originally Posted by Donsan View Post
Nice article. Unfortunately, I couldn't find the results after his installation and sea trial.

Larry stole my thunder but search the forum and you'll find that Mike had a comprehensive thread about the subject. I'm pretty sure it included the follow up results his blog post missed.

I sure do miss Mike.
__________________
Craig

It's easier to fool people than to convince them that they've been fooled - Mark Twain
CPseudonym is offline   Reply With Quote
Old 07-01-2015, 06:56 PM   #6
Master and Commander
 
markpierce's Avatar
 
City: Vallejo CA
Country: USA
Vessel Name: Carquinez Coot
Vessel Model: 2011 Seahorse Marine Coot hull #6
Join Date: Sep 2010
Posts: 10,262
Show us your rudder. My rudder is quite sufficient, but I don't expect much if any from it moving slowly while not in forward gear.


__________________
Kar-KEEN-ez Koot
markpierce is offline   Reply With Quote
Old 07-01-2015, 07:31 PM   #7
Guru
 
City: Satsuma FL
Country: United States
Vessel Name: No Mo Trawla
Vessel Model: Hurricane SS188
Join Date: Jul 2014
Posts: 1,675
Quote:
Originally Posted by CPseudonym View Post
Larry stole my thunder but search the forum and you'll find that Mike had a comprehensive thread about the subject. I'm pretty sure it included the follow up results his blog post missed.

I sure do miss Mike.
What happened to Mike? Did he have an adverse event or just drift away? Do you know his handle? A search on rudders yields all kinds of unrelated posts. I need some better words to search on or his handle. He seems to have been from my hometown area. I certainly envy his machine shop.
Donsan is online now   Reply With Quote
Old 07-01-2015, 07:53 PM   #8
TF Site Team
 
Larry M's Avatar
 
City: JAX, FL
Country: USA
Vessel Name: Hobo
Vessel Model: Krogen 42-120
Join Date: Nov 2008
Posts: 5,733
Quote:
Originally Posted by Donsan View Post
What happened to Mike? Did he have an adverse event or just drift away? Do you know his handle? A search on rudders yields all kinds of unrelated posts. I need some better words to search on or his handle. He seems to have been from my hometown area. I certainly envy his machine shop.
Sorry to say Mike passed on. His wife Mellissa, has been gracious to keep his blog active. There's some good stuff there. He was a great contributor to TF.


http://www.mvfullstep.com/index.html
Larry M is online now   Reply With Quote
Old 07-01-2015, 09:05 PM   #9
Guru
 
City: Hotel, CA
Country: Fried
Join Date: Sep 2011
Posts: 8,328
I cannot recall his exact monicker now, perhaps someone else does. To narrow your search in the advanced mode set the date for +/- 6 months of the date of his blog post Larry linked to. That should get you the right rudder thread.

Once found search threads started by him for more good stuff. Trust me, Mike new very well how to use his machine shop and offered excellent advice.
__________________
Craig

It's easier to fool people than to convince them that they've been fooled - Mark Twain
CPseudonym is offline   Reply With Quote
Old 07-01-2015, 10:30 PM   #10
Guru
 
City: Satsuma FL
Country: United States
Vessel Name: No Mo Trawla
Vessel Model: Hurricane SS188
Join Date: Jul 2014
Posts: 1,675
Quote:
Originally Posted by CPseudonym View Post
I cannot recall his exact monicker now, perhaps someone else does. To narrow your search in the advanced mode set the date for +/- 6 months of the date of his blog post Larry linked to. That should get you the right rudder thread.

Once found search threads started by him for more good stuff. Trust me, Mike new very well how to use his machine shop and offered excellent advice.
Tried that and found his handle was "pull" and he only made about 39 posts. Nothing was posted on how his rudder design turned out. I have little doubt it worked well if he got it installed and trialed prior to passing but it would have been interesting to read it firsthand.
Donsan is online now   Reply With Quote
Old 07-01-2015, 10:38 PM   #11
Guru
 
City: Hotel, CA
Country: Fried
Join Date: Sep 2011
Posts: 8,328
Hmmm, I'll poke around a bit when I get near a real computer instead of this phone but that doesn't sound right at all. This forum used to be formatted with Sparklight software, when we switched to the current V-bulletin software some data corruption happened. It sounds like Mike's profile may have been affected by that, dammit.
__________________
Craig

It's easier to fool people than to convince them that they've been fooled - Mark Twain
CPseudonym is offline   Reply With Quote
Old 07-01-2015, 10:43 PM   #12
Guru
 
O C Diver's Avatar
 
City: Fort Myers, FL... Summers in Crisfield, MD
Country: USA
Vessel Name: Slow Hand
Vessel Model: Cherubini Independence 45
Join Date: Dec 2010
Posts: 4,813
While I have not changed the rudder on a trawler, I did build with a friend, a new rudder for my dive boat (Downeaster). The original rudder was too small and did not have enough leading edge which made it difficult to steer at higher speeds as the boat has mechanical not hydraulic steering. From talking to people in a couple of boat yards where rudders are occasionally fabricated, we came up with the following parameters.

1. Rudder should be as tall or taller than the diameter of the prop.
2. Top of the rudder should come close to the hull so that water following the hull curve doesn't miss the rudder.
3. The leading edge (part in front of the shaft or pivot point) should be 25 to 28% of the trailing portion (part behind the shaft or pivot point).
4. Clearance between the leading edge and the propeller shaft is important. General rule of thumb is to have enough clearance to be able to remove the propeller with the rudder hard over. The more clearance between the propeller and the rudder, the less effective the rudder will be.

What we ended up doing was to make measurements and lay out a drawing that allowed for the biggest rudder within the above parameters with out moving the rudder and stuffing box or shortening the propeller shaft.

Don't have the height dimmension, but the rudder is 12" long behind the shaft and 3.25" (28%) long in front of the shaft. My new rudder is perfect! Boat turns on a dime, I can back it in a straight line, and at 15 knots you can steer the boat with 2 fingers. Increasing the leading edge made a huge difference in the steering effort and more water hits the rudder when turning which dramatically increases the rate of turn at slow speed.

Don't have any pics of the old rudder, but here is the boat and the new rudder:


Click image for larger version

Name:	DSCN0918.jpg
Views:	71
Size:	115.2 KB
ID:	41626

Click image for larger version

Name:	DSCN0925.jpg
Views:	81
Size:	142.9 KB
ID:	41627


Ted
__________________
Blog: mvslowhand.com
I'm tired of fast moves, I've got a slow groove, on my mind.....
I want to spend some time, Not come and go in a heated rush.....
"Slow Hand" by The Pointer Sisters
O C Diver is offline   Reply With Quote
Old 07-01-2015, 11:18 PM   #13
Guru
 
Nomad Willy's Avatar
 
City: Concrete Washington State
Country: USA
Vessel Name: Willy
Vessel Model: Willard Nomad 30'
Join Date: Oct 2007
Posts: 13,709
My rudder is large but it also moves through 90 degrees of deflection (45 each way). Since my speed is less than 7 knots this big rudder responds very well to that much deflection. And w/o the prop turning she responds well from a slow walking speed up. The side view gives an idea of how big the rudder is compared to the profile of the hull.
Attached Thumbnails
Click image for larger version

Name:	STH71262 copy 3.jpg
Views:	65
Size:	175.1 KB
ID:	41628   Click image for larger version

Name:	STH71261 copy 2.jpg
Views:	62
Size:	116.1 KB
ID:	41629  
__________________
Eric

North Western Washington State USA
Nomad Willy is offline   Reply With Quote
Old 07-01-2015, 11:34 PM   #14
THD
Guru
 
City: Seattle
Country: US
Join Date: Apr 2012
Posts: 1,142
I know there was a discussion here some time back about "fishtail" or "Schilling" rudders. The general concept is to create a rudder that is more of a foil than the flat plate so many rudders are. A search on either term might turn up the thread. As I recall, retro fitting can be done for a not so exorbitant cost. Rudder efficiency is substantially increased.
THD is offline   Reply With Quote
Old 07-01-2015, 11:44 PM   #15
TF Site Team
 
dimer2's Avatar
 
City: Houston
Country: USA
Vessel Name: Baobab
Vessel Model: Bayliner 4788
Join Date: Aug 2013
Posts: 2,193
They even have an app for this now on Google play

Boat Rudder Calculations
Nod Technologies - March 8, 2015
-
Everyone

Tools

I have not used it but for $2.75 it might be worth checking it out.
__________________
No one who achieves success does so without acknowledging the help of others.
dimer2 is offline   Reply With Quote
Old 07-02-2015, 06:14 AM   #16
FF
Guru
 
FF's Avatar
 
Join Date: Oct 2007
Posts: 16,524
One big hassle is the boats attempt to be too many things from the same hull build.

A displacement boat will need a big rudder , mostly to be handier when docking or slow manuvering.

A semi plaining boat would be handy capped dragging a big rudder thru the water at speeds , and an autopilot with good authority might have a difficult time at speed..
FF is online now   Reply With Quote
Old 07-02-2015, 07:52 AM   #17
Guru
 
City: Satsuma FL
Country: United States
Vessel Name: No Mo Trawla
Vessel Model: Hurricane SS188
Join Date: Jul 2014
Posts: 1,675
Quote:
Originally Posted by O C Diver View Post
2. Top of the rudder should come close to the hull so that water following the hull curve doesn't miss the rudder.
Interesting that your rudder appears to come so much closer to the hull than markpierce or manyboats. Seems like the gap on the Coot is substantial.

Pull was apparently working on a Schilling type rudder. Your approach appears to ignore the loads on the shaft but those loads may be higher on a Schilling rudder which looks heavier and is not support by attaching at the bottom to a skeg.
Donsan is online now   Reply With Quote
Old 07-02-2015, 09:05 AM   #18
FF
Guru
 
FF's Avatar
 
Join Date: Oct 2007
Posts: 16,524
Most rudders can be improved by drilling a hole somewhere near the trailing edge.

This gives a place to add a shackel , to which lines can be attached for emergency steering.

"Be prepared".
FF is online now   Reply With Quote
Old 07-02-2015, 11:12 AM   #19
Guru
 
AusCan's Avatar
 
City: Adelaide
Country: Australia
Vessel Name: Kokanee
Vessel Model: Cuddles 30 Pilot House Motor Sailer
Join Date: Jul 2012
Posts: 2,095
Quote:
Originally Posted by O C Diver View Post
1. Rudder should be as tall or taller than the diameter of the prop.
2. Top of the rudder should come close to the hull so that water following the hull curve doesn't miss the rudder.
3. The leading edge (part in front of the shaft or pivot point) should be 25 to 28% of the trailing portion (part behind the shaft or pivot point).
4. Clearance between the leading edge and the propeller shaft is important. General rule of thumb is to have enough clearance to be able to remove the propeller with the rudder hard over. The more clearance between the propeller and the rudder, the less effective the rudder will be.

Ted
Interesting.
My rudder fails rule #3. I haven't measured it but from this old photo I have, but the rudder stock appears to be only about 10% back from the leading edge.

I'd assume this would require more force to turn the rudder, although my steering seems light, even though its cable driven and the rudder is quite large.
Attached Thumbnails
Click image for larger version

Name:	Hull inspection.jpg
Views:	54
Size:	119.3 KB
ID:	41641  
AusCan is offline   Reply With Quote
Old 07-02-2015, 01:49 PM   #20
Guru
 
Nomad Willy's Avatar
 
City: Concrete Washington State
Country: USA
Vessel Name: Willy
Vessel Model: Willard Nomad 30'
Join Date: Oct 2007
Posts: 13,709
AusCan,
Looks like you have a perfect rudder for your boat. So does Diver's Dive boat.
My hydraulic steering is not as light as the cable steering it replaced. Seal friction me thinks.
Don't back up very fast w that rudder (applies to me as well) because the water load on the rudder may snach the helm from your hands and slam the rudder against it's stops or tear out your mounting bracket loose or worse. I back 2 or 3 knots but hold on to the helm real tight and the rudder on hydraulic systems has far less feedback.
__________________

__________________
Eric

North Western Washington State USA
Nomad Willy is offline   Reply With Quote
Reply

Thread Tools
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





All times are GMT -5. The time now is 03:39 PM.


Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2006 - 2012