Rudder selection and why?

[Zackthrills]

hey everybody I have a question as you all know I'm looking to build a catamaran boat and I have a few things that I was trying to take in and wanting to learn a little bit more about. My question is how do you go about selecting what size rudder and what determines whether or not you should place it off set or place it in the center? What is the reason you would want to offset the rudder?any new website with the instructions or information on this would be great if I could get the link.

[Heaving Earth]

Center mount rudders are for twin hulls, offset are for single drive.
On a single drive, having a center mount rudder behind the prop causes bad handling characteristics.

[Zackthrills]

so then maybe I should go with an off set rudder to make it stable. What's do you guys suggest?

[Rumdog]

What hull dude?

[Heaving Earth]

I dunno zack. First you wanted to build it yourself, then you're going to have Keith build you one.... Nobody knows if you're building a twin or single drive. You aren't gonna hit 100 on single drive. Figure out what you're doing man.... It's one thing after another. Whatever happened to your 90mph spartan?

[properchopper]

Offset rudders are the primary setup for race monos, which only need to turn right. Hydros as well.If a mono hull leans left the rudder lifts out of the water to some degree. Even so, many Offshore race (right and left turns) monos use offset rudders, maybe a bit longer. In-line rudders on cats, which don't lean in turns can do fine with in-line rudders. They don't cause handling problems. If the driver is aware that the prop thrust cone contacts the rudder and the radial deflection adds to the boats rotational force the boat handles just fine if driven with this in mind. Case in point : My 2006 SAW National record holder Drifter Cat had an offset rudder and turned like a dump truck - barrel roll city. My 2012-2013 SAW record holding Drifter Cat has an inline rudder and loves to turn both right and left.

Furthermore, most of the scale-looking long/narrow offshore cats won't do well in high speed turns. Cat hulls by Aeromarine are wider (as is the FCR Cheetah) and turn nicely at speed.

[Heaving Earth]

Then why did proboat start offsetting their rudders one their cats?

[runzwithsizorz]

Offset rudders are the primary setup for race monos, which only need to turn right. Hydros as well.If a mono hull leans left the rudder lifts out of the water to some degree. Even so, many Offshore race (right and left turns) monos use offset rudders, maybe a bit longer. In-line rudders on cats, which don't lean in turns can do fine with in-line rudders. They don't cause handling problems. If the driver is aware that the prop thrust cone contacts the rudder and the radial deflection adds to the boats rotational force the boat handles just fine if driven with this in mind. Case in point : My 2006 SAW National record holder Drifter Cat had an offset rudder and turned like a dump truck - barrel roll city. My 2012-2013 SAW record holding Drifter Cat has an inline rudder and loves to turn both right and left.

Furthermore, most of the scale-looking long/narrow offshore cats won't do well in high speed turns. Cat hulls by Aeromarine are wider (as is the FCR Cheetah) and turn nicely at speed.

Tony, doesn't having an off-set rudder mounted on the right of a mono also help to counter the pull, or torque of the prop spinning counter clock wise?? Thus running straight, the keel would be even??

[properchopper]

Tony, doesn't having an off-set rudder mounted on the right of a mono also help to counter the pull, or torque of the prop spinning counter clock wise?? Thus running straight, the keel would be even??

Sounds good in theory, have no empiricals to verify but very likely.

[Darin Jordan]

Then why did proboat start offsetting their rudders one their cats?

To keep it in clean water, and to make it easier to get the prop shaft out... I suppose.

But what do I know?? :)

[properchopper]

To keep it in clean water, and to make it easier to get the prop shaft out... I suppose.

But what do I know?? :)

Enough I suppose to encourage me to finally get the offset bracket for the Drifter to bump up the record. C'Ya in Nov ?

[Heaving Earth]

To keep it in clean water, and to make it easier to get the prop shaft out... I suppose.

But what do I know?? :)

Fair enough. Just asking. From my gatherings they handled better this way... But hey, I read ALOT of different stuff.

[Doug Smock]

You aren't gonna hit 100 on single drive.

Wrong. It's very possible.

[Heaving Earth]

So it's possible, but doesn't it make more sense to build a twin to do it?

[Rumdog]

Really? For a complete beginner who has never built a boat? Those kind of speeds are much easier to reach with twins.