Thunder boat Rudder location

[Joenagy]

I've got a used fiberglass thunder boat with the rudder on the right side. seeing I'm doing a re-fit would it be wise to move it to the left? How far back of the transom should it be? What turn fin would you recomend?

 

[Hydro Junkie]

Rudder location is more personal preference than anything though, with that said, there are formulas that some use to determine locations that are supposed to be optimized for the boats. Whether those formulas work or not, I don't really know and am not going to say if they are right or wrong.
As to how far back from the transom, I generally keep the rudder bracket as short as I can. The reason for this is that the further aft the rudder is, the longer the boat acts. If you put the rudder right at the transom, the boat will act like it's length, let's say 30", from turn fin to transom as a arbitrary figure. If you install a 6" long bracket instead, the boat will act like it's 36" in total length because of the longer bracket, even though the boat is only 30" . Depending on the boat, it could cause handling issues but that wouldn't be known until you start testing. One other issue with using a longer bracket is it requires a longer rudder pushrod. A longer pushrod usually means it needs to be heavier so that it won't bend when trying to turn the boat. I run 4-40 pushrods for my scale boat rudders but would probably move up to 6-32 if I was running a 6" bracket.
Let the flaming begin

 

[Joenagy]

Thank You

 

[RobertDoak]

Hydro junkie....thanks for the info...and makes sense...I ever really gave any of that stuff much thought..I just did what the manufacturer suggested...kinda funny though...on full scale hydros...you don't see the rudder 4 feet off the transom...thanks for the info...

 

[Hydro Junkie]

Actually, Robert, I hadn't thought about the full-sized boats when I posted my reply above. You got me thinking about it and here are two pictures of common rudder assemblies used on the boats. The first one is from the 1973 Pay'N Pak. It's one version of what was used from the early 1950s through, IIRC, the mid 1990s. One thing to note is that the rudder is pulled during a left turn, the direction the full-sized boats race:

In the case of this set up, the rudder barely clears the lip of the bottom which extends an inch past the transom.
The second picture shows the modern set up, in this case from the 0706 Oberto hull:

What is interesting is that the rudder bracket extends back between 8 and 12 inches from the transom, is mounted on the right side, against the air trap and is pushed to turn the boat to the left, everything being the opposite from the 33-year older boat.

 

[Hydro Junkie]

I'm almost in shock. I figured that, by now, someone would have said I was wrong and had something else they felt was "the correct answer".

 

[rhomodel]

Well if that is what you want to read: Mark you're wrong, nothing about personal opion only left mounted is correct!

 

[Hydro Junkie]

It's not what I wanted to read, more like the normal response to many of my posts. I do appreciate the thought, got a bit of a laugh out of your post. THANKS!!!

 

[John Finch]

ok Mark,

I will bite. I have found right side mounted rudder always worked better on all my scale, thunderboat, and riggers. also rudder further back reduces prop walk. May not look like a real boat but works best for me and I don't need left rudder to go in a straight line. I can also make left hand corrections without the left sponson coming off the water, which can cause a blow over. I have tried the left side rudder many many times and always converted back to the right side.

 

[FloridaScaleBoater]

I would refer to the rule book, as there is a max distance off transom the hardware can extend.

 

[Hydro Junkie]

ok Mark,

I will bite. I have found right side mounted rudder always worked better on all my scale, thunderboat, and riggers. also rudder further back reduces prop walk. May not look like a real boat but works best for me and I don't need left rudder to go in a straight line. I can also make left hand corrections without the left sponson coming off the water, which can cause a blow over. I have tried the left side rudder many many times and always converted back to the right side.

And that was the kind of response I was hoping to get. I was hoping to get a differing opinion that would give reasons that were valid rather than just a "YOU'RE WRONG!!!!" Thanks John