rudder alignment

BobCT · Post by **BobCT** » Wed Jun 15, 2011 8:47 pm

Found this online, interesting way to align the rudders. I might try the free flow method:

A: Your friend is correct in that tweaking the alignment of your rudders can add speed to your boat. However, improperly done, this tweaking can also hinder your boat. Misaligned rudders produce drag and affect trim levels at speed, creating larger wakes and turning radius.
There are two procedures that can make existing rudders more efficient when running straight ahead or when turning.
As a boat moves forward through the water, many assume that the water underneath the hull is running parallel to the centerline of the boat; hence, in line with the rudder blades. If your boat has any degree of deadrise at the transom, this is not true. If you were to follow an air bubble under the boat at centerline, it would travel outward toward the chine, climbing up the deadrise - certainly not parallel to
centerline.
The only way to align your rudders with the flow of the water is to let them flow free at speed. This is done by running the boat straight ahead in smooth, open water and disconnecting one end of the tie bar. The disconnected rudder now has the freedom to find its own "free-flow" position. When this balance is found, adjust the tie bar end and reconnect. Do the same to the other rudder and you will have balanced rudders when you need them most ... at speed.
A second procedure to improve the turning performance of your rudders is an adjustment to your tiller arms. This, unfortunately, is not as simple as the previously mentioned fix. It has been found over the years that if the tiller arms (not the rudders) are "toed in" roughly 8 to 10 degrees from centerline, the rudders will be more effective in turns. The reason lies in the geometry of the arrangement. When your boat turns, you are following an arc circle. As you travel through this arc, one rudder will be closer to the center than the other. Therefore, the inboard rudder should follow a tighter radius than the outboard rudder. Simply put, with this toed-in arrangement of the tiller arms, the inboard rudder of a given direction (port or starboard) will turn sharper, following a path closer to the actual radius of the turn, producing
less drag.
This procedure, however, will more than likely involve either machining a new keyway or replacing the tiller arms altogether. Contact a qualified marine facility for more information.
- Robert Ullberg,
Ullberg Yacht Design

RWS · Post by **RWS** » Thu Jun 16, 2011 6:10 am

The question is this:

A) how can you determine (say out of the water) if your rudders are set at a less than ideal setting and

B) Why not get her up and running at cruise, note the speed, then disconnect one of the rudders and note any change in speed.

Does B make sense?

RWS

gettaway · Post by **gettaway** » Thu Jun 16, 2011 1:48 pm

My Trojan F-32 1977 owners manual describes the method to align the rudders and even has a diagram.
I can scan and post if anyone is interested.

BobCT · Post by **BobCT** » Thu Jun 16, 2011 3:25 pm

gettaway, thanks. That's on the forum here already, that's what I found and used a few months ago. I either did it wrong or it's different for the International hulls.

To RWS's questions:

1) I think it's just a simple measurement front/back to determine the distance which translates in a degree setting. The specs I've seen are # degrees in/out.

2) Yeah, that does make sense. I think the running/disconnect method has to yield the best speed because the rudder is going to find the position of least resistance.

Obviously that's dictated by the way the water flows down the hull which as the guy describes above, isn't necessarily going to be a straight line.

I'm going to try it this way over the weekend and see if it makes a difference on my boat.

In the meantime, if anyone has the specs for an Int'l that would be great. My manual has a side view diagram of the rudder but doesn't say anything about alignment. This comment is interesting though "Only when water flows past the rudders striking them at an angle does the boat respond".

Doesn't that contradict the disconnect method?

Update - The spec is in the manual but under "Steering system", not Rudder. Anyway, here's what it shows:

"With the rudders in the dead ahead position, the trailing edge of the rudder blade must toe out 1.5 degrees and the tie bar between the two rudders should be set so that the forward end of the arm is toed in at 10 degrees"

So, who's a math wiz here? How can I get these measurements in degrees?

Bob

RWS · Post by **RWS** » Thu Jun 16, 2011 3:46 pm

Better have the engines synchronized exactly or the rudder adjustment will be invalidated.

Makes sense?

RWS

BobCT · Post by **BobCT** » Thu Jun 16, 2011 3:52 pm

I have a fairly new engine synch I installed last year. It was pretty darn close but I should check it again with the handheld tach just to be sure.