cat setups?

[Strykerjoe]

Just bought a thundercat,Undergoing mods at the moment! Its 36" L -11" W. .32 right now, single rudder going to a double,prop is a 1.60 x 2.60. Anyone have some cat setups? Trim tabs? Had a 42" mono (Jet stream 3000)that I modded out with skags,trim tabs,tuned pipe and a O.S .32(ABS hull)! Loved it,Sold it went to a cat(fiberglass).

[engineman351]

You should not need trim tabs on a cat. Remember if you do try them whichever rear side you lower will lower the bow on the opposite side. Again, you should not need them. You should not need a 'spin' fin either. I like to check CG with maybe a half tank of fuel and get the hull to balance on a dowel at 29-30% of its hull length (9.5-10 inches from the transom). Set the centerline of the prop shaft either even or slightly above the bottom of the rear ride pads. Start with the strut at "0" deg to the transom...neither angled in nor out. If the boat airs out at WOT, leave it alone. If the boat is "wet" (plowing too much water), kick the strut angle back a degree or two. If the boat wants to come off the water..do the opposite. Also start with the rudder at "0" degrees. If the boat "digs" the front in the corners (you are turning right most of the time, aren't you?)...kick the rudder in a degree or two (will raise the bow in the corners). If the boat is bouncing a lot in the corners...do the opposite. A cat (really any boat) will handle better if the prop is very, very sharp. You will get less prop walk. The prop it comes with looks ok to me for the Dynamite .32. It's always good to try size larger or smaller just to see what happens. Remember, it's tough to judge if you are going a mph or two faster or slower. If you have to know the TRUTH...measure runs between bleach bottle buoys 100 ft apart with a stopwatch...or if you have a small GPS that will be as accurate. Good luck. RC

[engineman351]

FYI...I can't remember if the rudder is behind the prop or offset. If you want to turn almost as good to the left I'd move the rudder to the center if it is offset to the right. Two rudders usually are used on large high horsepower hulls or hulls that the rudders are too small or not long enough...on a Thundercat they will just slow you down. Use the money to buy more fuel!! RC

[Strykerjoe]

Thanks! Leeding edge of rudder is in front or prop and 90deg to the transom. Not adjustable, I'll try to fix that. Center of shaft is slightly above pads. I'm useing a JR sevo for steering,a ST125MG 125oz torque at 4.8v .21sec/60deg. I'll try to put some picks up but it keeps telling me the file to big?

[Ron Olson]

Do yourself a favor and spend a dollar to upgrade the rudder linkage to 4-40 rod instead of the 2-56 that it came with.
If you want to do a mild engine mod that will give you some more speed, the header is in bad need of port matching. The exhaust flow is really getting choked there. Pull off the headerand see where the exhaust stain is, that area needs to be removed and smoothed to go from the flange to the pipe. That area needs to be watched when modded so that you don't go through where they meet. Taper it. A Dremel with a short stack of cut-off wheels does a fast job in there.

[Strykerjoe]

Thanks for the info! I've allready right off the bat change the rod to a 4-40, I'll check the header next. Does anybody know or have anything to say about moving the rudder inline with the prop? I would like to turn good both ways.

[Strykerjoe]

Checked the header, It was matched allready ,but the weld was ugly(inside the man. to the header).Cleaned it up! Looking into stainless angle stock to change over to inline rudder setup?

[engineman351]

Strykerjoe, Before you change the rudder...give it a try with the offset. Cats are normally better at turning both ways because there is a lot of inside chine to bite the water when turning. Then, if you don't like it...then change it. RC

[Strykerjoe]

Allright I'll try it first before I mod the rudder location,should the bottom of the rudder be sharp? The leading edge is somewhat sharp allready.Checked cg and allright there. Polished header and pipe,Looks cool now! I'm trying to track down stainless props in the local area,So that will be the next task. THANKS!!!

[engineman351]

The rudder should be sharpened too to reduce drag. Sometimes rounding the leading edge at the bottom improves control. RC

[Ron Olson]

The bottom of the rudder should be round. A flat bottom works as another planing surface.