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Serious problem with steering please help

R

rayb

Member
"In Sydney Australia it is now

"In Sydney Australia it is now the middle of summer and I hope that some of you guys in the US are still reading these posts, during your winter.

I have an Australian 26'Mariner 30 years old, weight 3.5 tons with a Chrysler LM 318. The boat appears to be like your Trojans and in fact looks quite similar to FastJeffs boat, by the picture.

The max speed was 12 mph, I fitted trim tabs, and got a slight improvement but still would not get on the plane.
I took some advice and changed the prop from a 3 blade 15 inch by 17 pitch, to a 4 blade 15 inch by 15 pitch. The difference was astounding. The boat now has a wot top speed of 28mph at 4200 rpm,with no flat spots or any cavitation. It gets on the plane at 13 mph at 2300 rpm and cruises really well at 14.5 mph at 2500 rpm.

The problem is that once on the plane the boat will not steer except for straight ahead, it requires enormous force on the wheel to change direction to the extent I think something is going to break. To change direction I need to slow down to alter course.

Even worse, in a following sea the boat surfs, and immediately tries to commit suicide by veering quite sharply to starboard and trying to broach.

This is happening with the trim tabs fully withdrawn.


The only way I have found to overcome this is to speed up and try and stay on the back of the wave in front, but inevitably the following wave eventually gets me, and it seems sometimes dangerous to be speeding to stay in front of even quite small waves.

The Rudder is located only 1.5 inches from the prop and the rudder is very small. It appears that as I never had the problem before that it is either the speed that the rudder can't handle, or the increased volume of water going past the rudder that makes it hard to steer.

I now don't know whether to go for hydraulic steering, or do I need a new rudder set up of some kind, or is something else going on altogether that I am missing entirely.

Has anyone else had this problem ? Is there any advice that you may be able to give me. Any assistance at all will be sincerely appreciated."
 
"Raymond,

I have a Trojan F

"Raymond,

I have a Trojan F-26 with a single LM318.

When I bought the boat, both the steering cable and rudder stock had mechanical issues that made steering very stiff at all speeds. I replaced the steering cable and had the shaft straightened which dramatically reduced the steering stiffness. One way to check this out is to disconnect the steering cable from the tiller. You should be able to turn the wheel freely and move the rudder easily by hand. If either are stiff, you may have a mechanical issue.

Are you having difficulty turning the wheel at high speed only or also at low speed? Corrosion affects the steering cable and it doesn't take much to bend unsupported rudder shafts. Snagging the rudder on a mooring line could be enough to make it stiff.

My original rudder was very small for this boat. 26 ft LOA, 10 ft beam about 3 ton displacement. The original rudder blade was about 12 in. tall by 5 in fore-n-aft. The boat had some difficulties tracking straight, but nothing as extreme as you described. I upgraded to a larger rudder, 17 in . tall x 12 in. fore-n-aft (purchased from a salvage yard). I also added a 6" extension on the keel to further improve tracking stability. The keel extension increased drag and probably contributed to reducing top end performance below the advertised 25 knots for this boat, but it significantly improved tracking. You can see a photo of the keel project at this link. http://www.trojanboats.net/wforum/viewtopic.php?t=152

Here is some torque speed data for several Aqualoy-22 high performance rudders that should be in your size range. This came from http://www.aqualoy.com/downloads/pdfs/WBM_AQ_22_RUDDERS.pdf

In this table, rudder length (A) is the height, width (C)is the length of the blade fore-n-aft.
14284.jpg


One other suggestion is to post your question at the link below. I know some Naval Architects respond to posts on that forum and you might be able to get some more knowledgable advice.
http://boatdesign.net/forums/

Good Luck!
Chuck"
 
"Chuck,
Thanks.Your post and

"Chuck,
Thanks.Your post and links are very informative.
The steering problem is not mechanical, as steering is fine, even fingertip at any speed up to about 12 mph, it is when the boat is on the plane, and it gets harder to steer as speed increases.
Your picture of your boat's prop and rudder set up seems identical to mine, except that I have the 4 blade prop. Was that picture taken before or after your keel extension ?
One other thing, on the heel of the rudder there is a small metal deflection plate running about 3 inches from the heel downward and about1 inch in width with a deflection of about 20 degrees.
What is the purpose of this plate, and should I experiment with removing it? I thought it may have something to do with having a left hand rotating prop but who knows.
I welcome any and all comments. Once again thanks Chuck."
 
"Raymond,

The photo in my p

"Raymond,

The photo in my profile was taken after the keel extenstion & rudder replacement, just before she went back in the water.

Did you try the boatdesign.net forum? I picked up the following quote from a post by Eric Sponberg there.

"but in Professional Boatbuilder magazine #78, Aug/Sep 2002, there is a very fine article by Don Blount (one of the foremost powerboat designers in the world) called "Rudder Design for High-Performance Boats", page 72. Therein lies a wealth of information, everything you need to know about rudders, their design, and their placement in relation to the propeller. You might be able to get a copy from Professional Boatbuilder at http://www.proboat.com/ ."

Below are photos comparing my new vs. old rudders as I got ready to install the larger one.
I don't follow the description of the deflection plate on the rudder you described. You can see from the photo , my original rudder had a plate about and inch wide along the top of the blade. I'm not too sure what its function is.
However, it doesn't sound to me like a larger rudder is the obvious choice to address your issue. Have you been able to locate another vessel the same as yours to discuss performance with other owners?
14303.jpg


I also suggest you look for this book. Try a library or you can order online

Principles of Yacht Design
By: Larsson, Lars Eliasson, Rolf
ISBN: 0071353933
DOI: 10.1036/0071353933
Format: BB 352 pages
Pub Date: 2000-06-02
Copyright: 2000
Edition:2

It has a chapters on rudder design & high speed hydrodynamics. http://books.mcgraw-hill.com/getbook.php?isbn=0071353933&template=

Good Luck!
Chuck"
 
"Chuck,
I will take you advic

"Chuck,
I will take you advice and talk to some other owners who may have had this problem when trying to improve their performance.

I think I will stay away from getting too deeply into the principles of design, and keep working towards finding a prctical solution.

I will now try to attach a photo of the rudder set up which shows the deflection plate bolted to the heel and look forward to your comments about that picture.

If no picture appears it means I don't know what I am doing with the upload.

Looking forward to your comments."
 
"Chuck,

The system will not

"Chuck,

The system will not let me upload the photo as it is larger than 50kb (230kb) If you care to reply to this post with your email address, I will email it to you for your comment.

Thanks"
 
"Raymond,

Looking at the ph

"Raymond,

Looking at the photos, it occurs to me that your rudder has a very small area forward of the stock. This balancing area decreases the force needed to pivot the rudder, and according to a reference I found is typically up to 20% of the rudder area.
14353.jpg


See: http://www.glen-l.com/weblettr/webletters-4/wl38-rudders.html

Also, the shape of the blade almost suggests that someone might have removed a portion of the blade by sawing off part of the trailing edge. Perhaps they experienced the steering diffuculty you are having and sought to "fix" the problem by reducing the area to making the rudder easier to turn.

The deflector on the trailing edge also looks like an after-thought to me. I would guess you are correct that someone might have tried to compenstate for the LH screw, but am not sure what affect this has. (My guess is it increases drag and imparts a natural turning inclination.)

The relatively shallow keel on the boat is a likely contributor to the erratic steering behavior. The original Trojan F26 keel tapers down from the stem to the point where it extends about 5-1/2 inches below the bottom of the hull, whereas yours remains horizontal, and looks like it only extends a couple of inches below the hull. I extended my Trojan keel using laminated mahogany strips, which were encapsulated with 1/4 inch of fiberglass cloth and mat to extend another 6" below the original for improved tracking stability.

Good Luck,
Chuck"
 
"Chuck,
Thanks for all your t

"Chuck,
Thanks for all your time and comments. I will go and talk to other owners and have a look around a few slipways and see what I can learn.

I will let you know the outcome, it may take some time. Thanks again."
 
"Fascinating thread! One look

"Fascinating thread! One look at the rudder tells me why it doesn't want to steer with the throttle open: The rudder area AHEAD of the pivot axis is WAY too small.

Think of it this way: If the area on both sides of the rudder pivot axis was the same, then the rudder would be easy to turn at speed. If the area ahead were far greater, however, it would slam to one side and stay there until you slowed down. With the area behind the axis much larger (as in this case), the rudder is held by hydraulic forces in a straight line--unless you have the strength of Hercules!

Also, there's no where near enough rudder area, period! I have a 32 footer with twin rudders, and each of them is twice as large!

Jeff

PS: Rudders ALWAYS have a bit more area in the rear to prevent "flutter", a violent side-to-side action that would soon destroy them. But not THIS much! "
 
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