A Third Rudder

[Steve1.0]

This is on a 46' Classic in S. Florida. New owner said according to PO it helps a lot. Don't know if the Prop Speed will work on the rudder and trim tabs though.

 

[Cigatoo]

This is on a 46' Classic in S. Florida. New owner said according to PO it helps a lot. Don't know if the Prop Speed will work on the rudder and trim tabs though.

Helps what? Martini’s and boobs come to mind here. One is not enough three is too many.

 

[Mako]

Seems to me it would have been easier to either enlarge both rudders, or at least add a fishtail to both.


Guy has a SD boat powered probably with big Cats, and he's wondering why it handles like garbage at 7 knot trawler speeds and in heavy following/quartering seas.

 

[SIBERNUT]

So it's only 46 ft and a stern thruster (& prob bow thruster too) w the twin screw and he needs a 3rd rudder?
No. He needs a paid Captain.

 

[kthoennes]

I think he needs more stuff on the transom. Sheesh.

 

[rslifkin]

Seems to me it would have been easier to either enlarge both rudders, or at least add a fishtail to both.


Guy has a SD boat powered probably with big Cats, and he's wondering why it handles like garbage at 7 knot trawler speeds and in heavy following/quartering seas.

Agreed, larger / better rudders in the 2 existing positions would have been a much better way to do this. Like many SD boats, that GB looks to be under-ruddered from the factory to either idiot-proof handling at high speeds or to get a little more top end speed. In my opinion, unless the boat is a go-fast, the rudders should be sized for cruising just below hull speed and accept the slightly loss of top end (and that applying full rudder at high speeds may be a bad idea).

 

[Steve1.0]

It does have a bow thruster, stabilizers as well. IMO the thrusters, meh, but I can appreciate the desire for better steerage.

I too feel the GB's are under ruddered and would like better low speed and heavy seas control. I cross a bar coming in the Jupiter inlet (narrow and swift) and in a following sea its thrilling.

Would adding a fishtail unbalance the rudders too much? How much area would be needed to appreciably improve the handling? Anyone done this?

 

[Mako]

Yes you can run the calculations for rudder sizing. Get Skene’s Elements of Yacht Design or similar.

 

[High Wire]

Maybe there’s a jet drive nozzle in the keel hidden behind the port rudder.

 

[Blissboat]

Helps what?

My question too. Three rudders . . . that's a new one on me, other than on a boat with three engines, such as an older Pluckebaum or the like, built back when diesel was less than a dollar a gallon.

 

[Keysdisease]

Not so uncommon on Tugboats, called "Flanking Rudders." For the obvious reasons of slow speed control, these "extra" rudders are mounted as twin behind the props, outboard, or even in front of the props.
Given what this probably cost, articulated rudders may have cost close to the same but provided better performance. I have no experience with them myself, but everyone that has raves about the performance and I've never heard of someone second guessing the choice.

 

[Lepke]

One is not enough three is too many.

Three is just right.


Extra rudders help at slow speeds but not as much at higher speeds and add to drag.

 

[rslifkin]

Three is just right.


Extra rudders help at slow speeds but not as much at higher speeds and add to drag.

But unlike enlarging the 2 existing rudders, that third one isn't very useful in close quarters as there's no prop wash over it.

 

[rgano]

The fore and aft position of the rudder stock on that extra rudder is quite different too.

 

[Circumnavigator]

Dave Gerr goes into rudder sizing in detail in his book, "The Nature of Boats".


I agree that it adds drag and won't help much at low speeds. -- I'd take it off and, if necessary, add area to the two existing rudders. That assumes that their shafts are robust enough to stand the increased loading that would generate.


Jim