Rudder toe in/out

[mstailey]

Question:

What effect does toe in/out have on tracking say at idle, hull and cruise speeds?

Thanks.

 

[primecut]

Question:

What effect does toe in/out have on tracking say at idle, hull and cruise speeds?

Thanks.

Talking generally here as I have been experimenting with what your talking about with another style boat...
...The way the hull is shaped determines how water flows below it and of course out the back.
...Most boats have a v shaped hull will require that the rudders face in some at bow and out some at the stern this enables the water to flow smoothly on out when on plane instead of fighting the v or keel....etc. That said I have noticed/experimented on a different hull shallow v hull 4 degree deadrise that as I increase toe in, I lose some low speed steering but appear to gain directional stability at speed. In other words perhaps less toe makes the boat steer to fast and at speed in rough water your always steering the boat.

Some other thoughts some race boats...as part of tuning would sometimes disconnect a rudder ....the slave to the other and let it find the path of least resistance then hook it back up
also rudders can act in a way like trim tabs if they are in or out too much.
hoped this helped?
SO WHY THE INTEREST?

 

[Boss Lady]

The purpose of toe in or out is to prevent flutter of one of the rudders by keeping them preloaded. Rudder size has more to do with slow speed handling than this. You have to reach a happy medium between rudder size and drag. I personally feel that our rudders are too small on the full keel hulls. Their size in relation to the keel is a fraction of the surface area. I will be experimenting with add on tabs to increase the size of my rudders when Boss Lady gets splashed later this year.

 

[SKYCHENEY]

The purpose of toe in or out is to prevent flutter of one of the rudders by keeping them preloaded. Rudder size has more to do with slow speed handling than this. You have to reach a happy medium between rudder size and drag. I personally feel that our rudders are too small on the full keel hulls. Their size in relation to the keel is a fraction of the surface area. I will be experimenting with add on tabs to increase the size of my rudders when Boss Lady gets splashed later this year.

I couldn't agree more. Hatteras used rudders which are too small. I have seen similar semi-displacement hulls with much larger rudders and I doubt there is any detrimental effect from as much as a 20% increase in rudder size.

 

[primecut]

Not trying to bust chops ....but, Rudder Flutter? Preload needed to keep them from fluttering? Sorry i'm not buying into this... If your rudders are fluttering then you likley have bearing problems/play in the linkage.
They are going to be loaded or preloaded to some degree no matter how they are set, Although I would imagine at slow speed in various prop/shaft speed with rudders set for least resistance with little to no toe in, this could occur somewhat, although I think you'd need a hypocollucus valve to measure it correctly.

 

[Walter P]

Chris & Sky, I definately agree that our rudders are too small. Several times I have contemplated replacement with larger size but have not done so. Chris you mention adding "tabs" - how would you do that (I assume you mean some sort of extensions to the rudders?)

My present 1982 48 MY is my 4th Hatteras and to be sure, I do like Hatts, but they are terrible in following seas (as are many boats). Some years ago I was a fairly young retiree and to combat boredom I served as a delivery Capt up and down the East coast of the U.S. Much to my surprise some fairly inexpensive boats handled better than my Hatt in following seas and I suspected one of the reasons was larger rudders.

If anyone on this forum has personal experience with larger rudders on Hatts, please post your result,otherwise I guess some testing will need to get done.

Walt....

 

[Boss Lady]

Not trying to bust chops ....but, Rudder Flutter? Preload needed to keep them from fluttering? Sorry i'm not buying into this... If your rudders are fluttering then you likley have bearing problems/play in the linkage.
They are going to be loaded or preloaded to some degree no matter how they are set, Although I would imagine at slow speed in various prop/shaft speed with rudders set for least resistance with little to no toe in, this could occur somewhat, although I think you'd need a hypocollucus valve to measure it correctly.

Here you can argue with these guys since I am an idiot.
http://scitation.aip.org/getabs/ser...00126000001000084000001&idtype=cvips&gifs=yes

Michael E. McCormick
Department of Naval Architecture and Ocean Engineering, US Naval Academy, Annapolis, Maryland 21402

Luca Caracoglia
Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801

(Received February 2002; revised February 2003)

As the operational speeds of surface ships and submarines increase, so does the probability that unwanted vibrations caused by the hydroelastic instability (flutter) of the special class of hydrofoils called control surfaces. These include rudders and diving planes. By nature, these are thick symmetric hydrofoils having low aspect ratios. The 3-D tip effects become more pronounced as the aspect ratio decreases. In the present study, the added-mass and circulation terms of the 2-D flutter equations are modified to include three-dimensional effects. The modifications are performed by introducing quasi-steady coefficients to each term. The results predicted by the modified equations are found to compare well with experimental results on a towed rectangular foil having an aspect ratio of one.

©2004 ASME

P.S. don't forget about the pulses induced by the individual propeller blades! When doing you calculations.

 

[primecut]

I'm pretty sure I said the same thing they did just in much simpler terms.

I wasn't to sure you wanted to hear about Quasy-steady coefficients... My apologies
to the boss lady whom I must say is quite knowledgable, and from what Iv'e seen does great work. Also to all naval architects that had to study that drivvle.

Notice they don't mention rudder toe in angle because now it's getting ridiculously complicated and in the end someone is just steering a boat

Also Mr Caracoglia is talking about surface ships and submarines ie...he's living/and talking about ships. does some of this translate? Absolutely. Only I don't think all that much has changed in hull design and rudder oops call it a hydroil, design in the last 50 years to justify half of the thinking they're doing

Anyway yes I believe as I said these impulses, flutter if we must are caused by prop/shaft speeds, the bigger props less blades slower shaft speeds make stronger impulses. this is why 4,5,6, blades all else equal don't vibrate/impulse/flutter as much as their 2,3 blade counterparts.
I'm sure I'm not telling you much you don't know.
Anyway, you can lessen the effect of sloppy rudder bearings hiem joints by changing the toe in perhaps adding more or less to some degree. this is what most people feel as flutter.

On bigger rudders I too have wondered about this as from reading architects. they have general formulas for calculating effective rudder areas for given hulls. I have noticed that most boats don't have enough. I have also considered adding some area /extensions to the rudders.

There appears to be many reasons for poor downsea/following sea performance. Will larger rudders cure this I'm not so sure. One of the reasons is usually a steep forefoot/flatter stern so that the stern lifts and drops the bow. From there the boat wants to bow steer, it loses some of the effective rudder, so that said I think bigger rudders perhaps deeper/wider might help some. I would also recommend trying to keep as much weight as possible towards the stern and not load up the v in the bow.
In new england, lobster boats downeast hulls are typically deep forefoot and flat stern and are notorious for poor downsea characteristics when compared to v-hulls. Hopefully they are heavily loaded in the stern coming in because it's almost always in a following sea.
On a side note, on the boat I've been playing with, I think it runs better in a following sea with more toe in. Perhaps it allows the stern to drop? changes the running angle a degree or two? In any case its just trial and error for most
Again apologies to anyone who sees things differently, no two boats are exactly alike and also perceptions vary widely.

 

[mstailey]

From Primecut:
"I would also recommend trying to keep as much weight as possible towards the stern and not load up the v in the bow"

After all the 50 cent terms from you guys who are MUCH smarter than I this last statement hit the nail on the head.

So, I've noticed running at speed (17 knts) I can't hold course for any length of time without some wheel input - note this is even in calm Great Lakes waters, no bow-stern-beam winds and since it is the Great Lakes no current to speak of. In my case following seas are not the issue.

It seemed to me the boat would bow steer after a bit. Now playing with the trim tabs I learned the closer to zero tab position the better the tracking got. However, I loose speed running the tabs at zero position and can hear the engines working harder. Also, from past experience driving road race cars if they had to much toe-in the race car would dart around on high speed straight aways. Hence my question on toe in/out.

Keep in mind I have Naiad stabs but when doing my trim tab position test they were in the center position. Not sure if this is inducing a problem or not as I'm just not that smart on hull design.

This is my first Hatt and first set of diesels and I was hoping it was just a case of a faulty interface between the helm seat and the wheel but I'm thinking this is not the case. I've owned quite a few boats but none with this pronounced of a tracking problem.

I'll call the factory and ask for the rudder toe specs and check it out unless you folks think that is a waste of time. Also not quite sure if I really need to increase my rudder area at this point - at least until I confirm toe specs. Also forgot to mention I checked the rudders and steering linkage for play - none to speak of and the steering system holds 25 psi and fluid level is per spec.

 

[SKYCHENEY]

Mike,
Check your stabilizers for true center. I don't think it has anything to do with the boat darting from side to side, but it would affect holding a course if not truly centered. On the top of the shaft is a mark and it aligns with a mark on the bearing cap. Those need to lined up to be at the center position. If they are not, then you need to pull the cap on either end of the Vickers valve and adjust the set screw to bring them to center. This assumes that the center marks actually mark center mind you. If the mounting plates for the Naiads were not installed exactly square to make the marks center, then who know where the exact center really is.

 

[Boss Lady]

Walter,

I plan on extending them by drilling, and bolting some extension tabs made out of silicon bronze. I will taper them to try an retain the same aspect ratio. My calculations show that about a square foot of surface area per rudder should increase the responsiveness at the speeds I will be running (20-25 Knots). To do this properly you need to add to the front and the trailing edge, otherwise you will wind up with too much leverage from just adding extensions to the trailing edge. The key is to maintain the same balanced load around the pivot point of the shaft.

If you are going to be running 10-15 knots you can use a lot more rudder than I can and may be able to get away with just adding tab extensions to the trailing edge. Call me if you have any questions.

Chris