Rudder Toe-In?

[SKYCHENEY]

As noted, the point of toe in/out is to keep pressure on the rudders and avoid fluttering. I can't see how it makes any difference at all whether the toe is IN or OUT as long as it is within the spec for the dimension.

It seems that toe in or toe out would have some effect on stern lift. If the water is channeled between the rudders more, it would provide lift. If it were channeled away to the outside, it would provide some suction or down pressure on the aft area of the hull. Maybe this little bit of differential is not enough to notice, but there must be some effect.

 

[mike]

Sky, (not to hijack this thread) I also have to re-install my rudders and want to get it right; and any lifting effect would be a further plus. However, I am a little slow and trying to understand, are you saying having the trailing/aft edge of the rudders closer may have a small lifting effect? thanks, mike

 

[SKYCHENEY]

Sky, (not to hijack this thread) I also have to re-install my rudders and want to get it right; and any lifting effect would be a further plus. However, I am a little slow and trying to understand, are you saying having the trailing/aft edge of the rudders closer may have a small lifting effect? thanks, mike

That is my thinking. If you try to push water through a smaller opening, it will tend to push up and down to try to get through there, thus creating some lift. Stabilizer fins can be used to "trim" the boat in the same manner.

 

[mike]

Got it, thanks, mike

 

[Trojan]

It's my understanding that you measure toe by stretching a tape measure across the boat between the trailing edges of the rudders, then taking that dimension and subtracting the dimension you get when you measure between the leading edges (for toe-in).

The only reason for toe is to keep slight pressure on the rudders so they can't jiggle around. Any more than necessary for that just creates drag.

For my 36C Hatteras told me 1/2 to 3/4 of an inch. But it may be different for different boats.

And yes, I most certainly have set my rudder toe-ins. Ironically, it was previously set up the way you describe. Not by Hatteras, but by a yard re-assembling the arms incorrectly after a repair. That one inch of toe as you describe it led to a total of five inches of toe between the fronts and the rears. Since I set it up my way my boat is seven knots faster than it was before. I'll keep doing it my way.

You are welcome to do it anyway you want. Your way is the way you do for cars when you have no equipment to do it correct. I just used the drawings and information from a previous boat that I reset the rudders on and then replaced the rudders. I have measured and reset about a dozen boats. If you gained 5 to 6 knots from resetting your rudder toe. That's good 10 MPH is a lot of speed to loose. They were obviously never properly set. You also said the yard didn't replace the arms correctly. Then what makes you think they set the toe correct. How would know? Toe is used for two things. One is to reduce rudder flutter. Two is to reduce the effort required to turn the rudders. The amount of offset determines the turning effort reduction and in the reduction of flutter. The rudders on a 36 are not long. And using a 1 to 4 ratio with a 1 inch of toe on a 15 inch rudder maybe. The max toe at rear trailing edges is only 4 inches oal.. On one side you will have 1/2 inch toe at the leading edge and 2 inches at the rear edge of one rudder. That is not a lot of toe. It surely would not produce a loss of speed as you stated. But I'm only guessing the ratio to produce a set of figures. Though I would think it's close. Most likely the rudder is smaller than the figures I used. I'm trying to remember what my 43 has.
Something else when dropping the rudders make sure that you mark on the rudder which side it belongs on. Some rudder shafts have the key ways cut in different places or they have a pin hole drilled through them once set. Also make sure you don't mix up the rudder arms or turn them upside down. They also only go on one way. If you know your rudders length and the shaft offset position from the leading edge.You can figure out the ratio and the offset you will have at the trailing edge.
There is no way that adding toe will give you more lift. Adding anything hanging down below will cause drag not lift. Adding any extension to the hulls bottom at the stern will add lift.

BILL

 

[SKYCHENEY]

Bill,

I think you need to look at your boat when it is out of the water. Toe is measured as the difference in distance from the leading edges vs the trailing edges. No recreational boat has a toe of 4 inches. That would cause too much drag. And, any foil that is projected below the hull will produce drag and disrupt water flow. Diversions in flow can create lift or suction or side thrust. Point your stab fins in (toe out) and you will direct water under the stern that will lift the stern, turn them so they dirrect water out (toe in) and the stern will squat. Same goes for rudders, but on a much smaller scale as they are too far back to make much of a difference.

 

[SKYCHENEY]

Here is a direct copy of what MikeP got back from Hatteras regarding toe adjustment:

I just received the toe-in info I requested yesterday eve for the 53MY from Hatt. Here is their email response: You need to have 3/4" to 1 1/2" of difference between the leading edge
and the trailing edge either in or out.

Best Regards,

Hatteras Yachts Customer Service Department

It's interesting that their post clearly indicates that it doesn't matter whether the rudders toe in (wider at back) or out (wider at front).

 

[Trojan]

Bill,

I think you need to look at your boat when it is out of the water. Toe is measured as the difference in distance from the leading edges vs the trailing edges. No recreational boat has a toe of 4 inches. That would cause too much drag. And, any foil that is projected below the hull will produce drag and disrupt water flow. Diversions in flow can create lift or suction or side thrust. Point your stab fins in (toe out) and you will direct water under the stern that will lift the stern, turn them so they dirrect water out (toe in) and the stern will squat. Same goes for rudders, but on a much smaller scale as they are too far back to make much of a difference.

Well your first 2 statement are true. I do look. I don't go with the next two statements. It's 1/2 inch of toe at the front and 2 inches at the trailing edge per side not 4 inches of toe. 2 inches in 15 inches is not a lot of drag. It's 10 degrees of taper not 4 inches of drag. If you reduce the distant at the trailing edge you will not have any measurable toe in the front. Depending on the rudder shaft offset and ratio. Thus defeating the reasons for toe and be on the edge of flutter. Rudder size was hypothetical so we could see some numbers. Unless you mark the 4 places on each side of your boat where you take your 2 readings. Each reading will be different. The boat sides are not parallel are your readings parallel. Chances are the rudders are not in the same location from the center of the boat out. The center of the boat most time is close. What is the +/- dimension for close. What is the dimension from the center out to the Lt. and rt. rudder post center line. You need that to figure the shaft off set from the boat center. Now you have 8 measurements to deal with. Now the adjustment. Your also now dealing with 2 loose rudders which one do you move first and how much? How close do you want to hold this toe in to? Have we got the toe set yet. How many people are required to set the toe your way. Hell after lunch we can throw all the measurement shit away and just eye ball it. Thanks but I'll stick with the boat builders drawings and the book.
Were talking rudders here not stabilizers. But even stabilizers cause drag. Anything that pushes water under way has drag. Why not mount a V hydro foil on the stern and get some real lift with little drag.

BILL

 

[mike]

I believe Hatteras already did that for us given the shape of the rear struts....

 

[Trojan]

Not quite the same. But your thinking. Bill

 

[bobk]

How do you determine tow-in for Niads? Mine just flop when out of the water. I always suspected them of causing too much drag on the boat, maybe towed too much?

 

[bobk]

That is my thinking. If you try to push water through a smaller opening, it will tend to push up and down to try to get through there, thus creating some lift. Stabilizer fins can be used to "trim" the boat in the same manner.

Sky, the faster water flow could be balanced by the Bernouli effect creating reduced pressure and in this case pulling the stern down. I wonder if anyone has studied the question.

Bob

 

[Avenger]

If you gained 5 to 6 knots from resetting your rudder toe. That's good 10 MPH is a lot of speed to loose. They were obviously never properly set. You also said the yard didn't replace the arms correctly. Then what makes you think they set the toe correct. How would know?

But see, that's the point. It wasn't correct. It ended up the way you describe it, with one inch difference between the leading edges and the shaft center distance.

This is how it happened: My rudder arms are keyed 7° offset. So if you put the arm on one way it makes the rudder kick to the right of center. If you flip it over it kicks left. After the repair the yard put them on upside down so the trailing edges were kicked out 5" from the leading edges. If I flipped them over the leading edges were 1/2" wider than the trailing edges. This is the way Hatteras built the boat. The yard didn't "set" anything. No adjustments had been or could be made. The tie-rod ends were female tapered pipe thread onto male taper threaded pipe. Made once and stayed that way.

Toe is used for two things. One is to reduce rudder flutter. Two is to reduce the effort required to turn the rudders. The amount of offset determines the turning effort reduction and in the reduction of flutter.

Offset reduces steering effort by partially balancing the water forces on the front and back of the rudders. If anything it would increase flutter which is why we use toe to load the linkages. For loading purposes water force acts across the entire surface of the rudder, not just the forward offset. So I don't understand why you think you need all that toe to stop flutter.

The rudders on a 36 are not long. And using a 1 to 4 ratio with a 1 inch of toe on a 15 inch rudder maybe. The max toe at rear trailing edges is only 4 inches oal.. On one side you will have 1/2 inch toe at the leading edge and 2 inches at the rear edge of one rudder. That is not a lot of toe. It surely would not produce a loss of speed as you stated.

It is a HUGE amount of toe. You're describing exactly the toe I had and it created a very effective speed-brake.

I also don't understand your answer to Sky's post where you refer to centerlines, offset from center and which rudder to adjust first. The tie-rod adjustment only sets the relationship between the two rudders, not their relation to center. Center is adjusted with the ram linkage, unless your steering linkages are very different from mine.

BTW, the person at Hatteras that I spoke to was in agreement with you about toe-out vs. toe-in. He stated that toe-out had a tendency to make boats wander and gave the autopilot a hard time. In automotive steering geometry this is certainly correct. I don't know if it works the same with fluids, but I ended up re-making my tie-rod to achieve toe-in.

 

[SKYCHENEY]

Sky, the faster water flow could be balanced by the Bernouli effect creating reduced pressure and in this case pulling the stern down. I wonder if anyone has studied the question.

Bob

That may be true but in either case, I doubt it would have much effect since the water quickly reaches the transom and is not forced under much of the flat hull surface.

How do you determine tow-in for Niads? Mine just flop when out of the water. I always suspected them of causing too much drag on the boat, maybe towed too much?

You will need to pin the Naiads in the center position, then measure the distance from the leading edge to the keel on each side and from the trailing edge to the keel. They should be slightly closer at the trailing edge (toe out). This conforms to the natural water flow and CAN provide some stern lift depending on how much they are adjusted.

To change the toe, you will have to pull the fins. They are on a tapered shaft and can be re-installed in the proper position and re-torqued. Be careful not to get them too far toe-out as this can create unsafe conditions in following seas as the bow will be pushed down as the stern gets more lift.

 

[MikeP]

Wow, sounds like a total PITA dealing with those dang Niads. You should just pull them off and toss them.

Tell you what, I'll help you out by paying the shipping on them to MD!

 

[SKYCHENEY]

Wow, sounds like a total PITA dealing with those dang Niads. You should just pull them off and toss them.

Tell you what, I'll help you out by paying the shipping on them to MD!

LOL, They're really quite simple and I know anyone with mechanical ability such as you, Mike, would really enjoy getting a set tweaked just right.

 

[Trojan]

But see, that's the point. It wasn't correct. It ended up the way you describe it, with one inch difference between the leading edges and the shaft center distance.

This is how it happened: My rudder arms are keyed 7° offset. So if you put the arm on one way it makes the rudder kick to the right of center. If you flip it over it kicks left. After the repair the yard put them on upside down so the trailing edges were kicked out 5" from the leading edges. If I flipped them over the leading edges were 1/2" wider than the trailing edges. This is the way Hatteras built the boat. The yard didn't "set" anything. No adjustments had been or could be made. The tie-rod ends were female tapered pipe thread onto male taper threaded pipe. Made once and stayed that way.
Offset reduces steering effort by partially balancing the water forces on the front and back of the rudders. If anything it would increase flutter which is why we use toe to load the linkages. For loading purposes water force acts across the entire surface of the rudder, not just the forward offset. So I don't understand why you think you need all that toe to stop flutter. It is a HUGE amount of toe. You're describing exactly the toe I had and it created a very effective speed-brake.

I also don't understand your answer to Sky's post where you refer to center lines, offset from center and which rudder to adjust first. The tie-rod adjustment only sets the relationship between the two rudders, not their relation to center. Center is adjusted with the ram linkage, unless your steering linkages are very different from mine.

BTW, the person at Hatteras that I spoke to was in agreement with you about toe-out vs. toe-in. He stated that toe-out had a tendency to make boats wander and gave the autopilot a hard time. In automotive steering geometry this is certainly correct. I don't know if it works the same with fluids, but I ended up re-making my tie-rod to achieve toe-in.

The answer for the statement on which rudder to turn first. Refers to the installation of NEW rudders.
You failed to read one line. I said that the ratio, size and numbers were hypothetical. I was trying to generate the 5 inches that was said the trailing edges measured. Without the actual ratio and numbers I could not duplicate or prove ether way. Two inches of trailing edge or 10 degrees is not a lot toe. Nor a lot of drag. Its a taper, not a brick wall. I would bet that using real numbers the toe would not be 2 inches.
You also stated that when the yard flipped the levers over the trailing edges were kicked out 5 inches. That's 10 inches overall. Depending on the ratio and rudder size you could easily loose 8 knots. Being a smaller faster boat, the rudders are always smaller.
Not having a load on the entire surface will let the rudders flutter. Having almost no load on the front portion of the rudder in front of the shaft. Will be the same as unloading balance of the rudder. I have yet to sea a boat where there is no play in the rudders. I don't disbelieve that the boat gained 8 knots, But I really find it hard to believe that the leading edge was set with one inch of toe. Without actual numbers. I rest my case.:d BILL

 

[bobk]

Mike P

Rots o ruck. You'll get my Niads over my dead body. And I'll have the kids charge 2X the shipping. Oh' you want the rest of the stuff too?? 4X

Bob

 

[Avenger]

Picture of a speed-brake

Bill, captddis was right, you are a stubborn man. First of all, please refer back to Sky's quote from Hatteras regarding how toe is measured. This is how I'm doing it, measurements between the two rudders. I know that you're using theoretical numbers, but they look to be fairly close to the actual dimensions if I'm understanding you correctly. Also, you seem to be measuring from center to one rudder. Why? The tie-rod only controls the relationship between the rudders, not how they line up with the keel.

If it helps clarify, I've attached a CAD drawing that shows how the rudders were positioned when I got the boat. You'll see that there is almost a one inch difference between the leading edge dimension (62.453) and the shaft center dimension (63.500), and almost five inches TOTAL difference between leading/trailing dimensions (67.338-62.453), not per side. This produces an angle from straight ahead of almost 13.5° per rudder, giving us a total of 27° between the two rudders. Since the trailing surface of the rudder is much larger than the leading surface it doesn't take 13.5° of angle into the stream to get it to produce more pressure than the leading edge and eliminate flutter.

Keep doing it any way you want, but my boat is much faster now, and steers and tracks just fine with no flutter.

 

[Traveler 45C]

Is the drawing showing toe in or toe out (the way your boat was set up)?