Strut and rudder location (cats)

[T.S.Davis]

I neve gave this much thought before. Interested in hearing some ideas.

What happens to a cat as you extend the rudder and/or strut away from the trans?

What happens when you shorten it up?

[T.S.Davis]

Holy crap. Nobody is sure.

I'm going to repost over at IW. See if I get any more hits.

[Boaterguy]

extending it backwards should put more weight on the strut/prop, and vice versa (this is a guess)

[steveo]

longer strut will make the boat feel longer and less likely to blow over

[T.S.Davis]

Some of my own thoughts.

If the strut is far from the trans, when you change the height of the strut it will change the angle that the boat rides.

If the strut is close to the the trans, a change in strut height could change the actual ride height of the boat.

Same effect with higher pitch or lifting type props. 6 series prop jams the nose in the water. More so the further back the prop sits. Can be okay if I compensate for it.

Longer strut, less likely to blow over. That seems reasonable. But more sensitive to adjustments. Plus, if the strut is too far back the boat runs too flat and can't pack air. Never flies like a cat is supposed to.

Been thinking on rudder position too. Far back equals lots of torque to turn the boat. If the angle of the rudder is funky it could effect the nose height as you turn. ...........ahooka! Or the boat doesn't turn until you slow down. Then it hooks.

I have a franken boat to play with this summer. Have to experiment.

[longballlumber]

Terry,

I think the biggest factor you need to consider is the distance from the trailing edge of the ride pad to the prop.

I would guess the further away the prop is the more "work" the prop will need to do to lift the boat...

Don't forget the prop is lifting the boat too, not just air from the tunnel...

In my defense, I AM NOT a Catamaran expert, I am just thinking out loud.


Later
Mike

[crrcboatz]

Gassers me as one, will tell you to NEVER extend the prop via onger strut back on a cat. Most will also tell you to never extend the rudder more than 3-4 inches. I do not know the reason but have never seen a cat built that way and not a single manufacturer recommends it either. I have seen a bunch of cats in my time and never seen one built that way.

Curt

[T.S.Davis]

I've built a bunch of cats and I'm still no expert.

I have seen cats with a rudder extended way back but I didn't get a chance to watch it run though. I swear I remember Randy having a Scat 32 like that at the 05 nats.

These big twin cats have struts that are really long. The center mounted rudders are even further behind the trans. I supose handling is a non-issue with those beasts though. Go fast in a straight line. I'm not talking about one of those.

So nobody recommends an extend setup. Okay, what if the prop was barely behind the trans? Think one drive dog like a scale boat.

Mental exercises guys. Thanks for the input.

[crrcboatz]

Companies like insane, rcboatworks, aeromarine, seducer, stryker, none of those do and they represent probably 90% of the gas cat business. The scale stuff you referred to r boats that don't oval race well rather go fast in a straight line. Never once seen a scale cat race with success in gas oval racing.

[AlanN]

Geez Terry, give us some time to answer. Not all of us live on the net.

The farther back the rudder is the more leverage it has. Thus pushing the nose down harder in the turns. This would have a tendency to make the boat spin out more easily.

Elongating the position of the strut makes it harder for the cat to turn. Sort of the same physics as the rudder placement but rotating the fulcrum point 90 degrees.

Remember that big ole cat you had painted with the flag colors? Think about how you had to make it turn, especially to the left. You had to unload the prop to make the boat turn then get back on the throttle to set it right again.

Hope that clears it up a bit for you.

[T.S.Davis]

HAHA Come on Alan. I gave you guys 9 hours before I started talking to myself. I type fast.

That Aero Team USA I had was evil. So speed sensitive in the turns. Get it wrong (and I usually did) and it went straight through the turn or turned completely around in 5'.

Totally a love/hate relationship with me and that boat. Pretty sure Vacarro has that boat these days. It's been all over the place. Even showed up in RCBM once.

[Rumdog]

I've had good luck using very short rudder brackets on cats. I've seen no ill effects on steering with that type rudder. I usually don't run an extended type strut either. Some cats, you have no choice because they have a built in standoff.
I'd think that longer strut, and rudder will definately be more snsitive to setup.

[AlanN]

Terry,
I liked that little cat you vacu-formed. Similar to the Key West. Ever thought about enlarging it? Might make a fun lso or cat class.

[T.S.Davis]

Fred ran one of those in P and it was stupid. Plenty fast enough but forget it in traffic of any kind.

I haven't messed with the vac machine in a while. I really think we're going to fast for what I was doing. The boats don't hold up. At least the vacuvee has some re-enforcement to hold it together.

I wonder how a Graupner Systems cat would run with an Aquacraft setup in there. We saw them on 700's. Snore. Then Howard ran that one on 24 cells or some such nonsense. 4s LiPo and the UL motor might be just right. I know I still have one of those somewhere.

[AlanN]

I was thinking of you pulling a bigger F/G version of that cat. C'mon you know you have the time to do it. :0

Sounds like your basement is as bad as mine. Finally disposed of a key west hull that I had forever and now starting to chop up a big mono for the dump. Still have plenty of untouched hulls looking for some love.

Howard will and I may drive up this Sunday if you're still planning on racing.