Twin Rudder Alignment

[Tom Kenny]

I repaired a leaking rudder port that meant I needed to drop the rudders. The tie rod was in bad shape so I manufactured a new tie rod. I am putting thing back together and I found myself asking the question, ‘how should the rudders be aligned? I intend to clamp a straight edge to the keel and have it stick out past the newly installed rudders.

My question is, should the rudders be set with ‘toe in’, or ‘toe out’, or aligned straight to the keel?

Searching the web has not produced much. Some of what I did fine says ‘toe in’ while some others say ‘toe out’, no consensus of opinions.

If it is ‘toe in’ or ‘toe out’ then the next question is by how much, 1/8”, ¼”, 1”,?

Pictures can be found on the web site - Select “Repairs”, then click on “Lazarette”

Hope to hear for many of you.

[John Meachen]

Could you build an adjustable linkage similar to the drag link that used to be fitted to older style cars?If so,it ought to be a matter of adjusting the length of the linkage while underway to discover the setting that gives the greatest speed.It just needs an accurate enough log to determine the change of speed that might occur.When the boat is subsequently hauled a number of us would probably be interested to learn what the rudder geometry had evolved into.

[Tom Kenny]

The tie rod is adjustable with a clevis screwed on to each end of the new stainless steel rod.

[Gary E]

Toe ??? the rudders on a twin screw boat??
Make them Parallel, there is no reason to make them anything other.
Automobiles are set with toe so slight that it's hardly measurable without an alignment rack.
I looked up the spec for toe on my car
Front wheels +0.16 degree +/- 0.20
can you measure to that accuracy?

[Lew Barrett]

My experience tends to make me agree with Gary. The toe in/out equation on a cruising boat is mainly about straight line stability and tracking. In practice I have found that it's easiest to set the rudders to be straight ahead and that the boat tracks true with that arrangement. Your boat could be different than mine of course, but I did go through the same mental gymnastics when I dropped and then reinstalled my rudders a few years ago, and by trial and error I ended up with no offset whatsoever, and that gave me the best results.

[Tom Kenny]

I just spoke to the fellow that surveys my boat. He has been doing boat surveys since Jesus was a fisherman. My surveyor told me that all twin rudder boats should have their rudders slightly ‘toe in’ by just a couple of degree. We settled on me setting the rudders in by approximately ¼”.

[carioca1232001]

Do an archives search on 'Professional Boatbuilder' magazine and you should come across a series of articles on 'Rudders' authored by Dave Gerr (I think it was). Addressed are Rudder design, placement/alignment, sea trials and a wealth of ancillary info.

Also suggests on which way the twin-screws should turn - inwards or outwards - depending on how the rudders are offset in relation to the former.

[JimConlin]

If you want to get really confused, google for multihull ackermann steering .

[Tom Kenny]

Good news and great reading.

First off Thanks to everyone and in particular - carioca1232001 and Jim Conlin.

Dave Gerr last article in Professional Boatbuilder was exactly what I was looking for and needed. From it I learned that for the size of the beam on my boat (14’ 6”) the rudders should initially be set to ‘toe in’ 10 degrees.

Later in his article he goes on to detail the steps one can take to fine tune the ‘toe in’ rudder setting.

Now if I can only find my dial indicator. . .

[Gary E]

Dave Gerr last article in Professional Boatbuilder was exactly what I was looking for and needed. From it I learned that for the size of the beam on my boat (14’ 6”) the rudders should initially be set to ‘toe in’ 10 degrees.


What is the reasoning that leads to that conclusion?

[Hwyl]

If you want to get really confused, google for multihull ackermann steering .

Yup Ackerman is your man, not to be confused with the unfortunate builder of the Leavitt, but the one who designed the steering for King George's funeral carriage.

Simply, they should be parallel going straight, but in a turn the outer one should turn less.

[Stiletto]

Hwyl &Jim, I had considered posting about that , but mutihull rudders (catamaran) are a long way apart. I think that any advantages from going the Ackermann route would be negligible on a monohull. In my opinion it is the straight ahead setting that is more important in this case.

It shouldnt be too hard to set them parallel and then a little trial and error to get the best feel in use.