Need help w/dual outboard cat setup!!!

[blackcat26]

Looks as though the cavitation plates on the lower units are acting as hyperactive trim tabs,i.e., the prop wash deflecting off of them is forcing the nose down. Wild A$$ guess !!!

I agree with Float. Your prop height looks fine. I think those plates are being pushed up from propwash and pushing the transom up and bow down.

[tiqueman]

Just asking, but if that is the issue, wouldnt every boat these are on do that?

[blackcat26]

That is some good logic Tique. Maybe it's because there are 2 of em on there? If it was me I'd take em off (if they come off) and try it. Cheap way to see if it's the problem.

[steveo]

i would cut the plate down little by little, if you have any adjustment try rasing the motors up, it strange the height looks good on the motors, but this is uncharted waters it may take an unorthodox setup who knows

[Team FFRB]

Scott,

IMO raising the motors will help, but I would say that there is alot of lift being generated by your lower units.

Kris

Kris,

I agree with you advise.

I would be running props the same height as you would with strut/stinger drive.

The higher the motor is mounted on transom will give the hull bow lift and the opposite the lower you go.

Also I would be using X series props to give you more leverage.
Maybe even use a X442/3 counter rotating.

[carlcisneros]

he is using x-442s now.
but I do agree, by the looks of the pictures of the lower units, the cav. plates are pretty big.

Carl

[Team FFRB]

he is using x-442s now.
but I do agree, by the looks of the pictures of the lower units, the cav. plates are pretty big.

Carl

Carl, You a right they are X442 2 blade props.

I said X442 3 blade props.

[carlcisneros]

oh, yeah, thats right. can you say DUH!!!!!!!????????
LOL

he also might want to try the ABC 1614/3 chopper props as well.

Carl

[forescott]

I was able to raise the motors about 3/8-1/2 inch easily without any re-drilling to the hull or major steering linkage mods. I'm gonna give it a try. If its the same or worse I'll move em down instead. I'm curious as to where the propshaft centerline is at on the stiletto as compared to the hull bottom. My original theory was to move the outboards up causing their weight to push down on the transom, allowing the bow to come up. Worse case its gonna cavitate like crazy and not even plane! I'd rather move the outboards around first before buying a bunch of different props. I do have the original set of same rotation grim 40/57/3's I can put back on once the setup is better. I actually can't really see or feel a difference in the way it drives between counter-rotating and same-rotation drives.

[GP73]

I keep the prop shaft of my Stiletto slightly less than 1/8" below the sponsons.

I'm curious as to where the propshaft centerline is at on the stiletto as compared to the hull bottom

[forescott]

I just got about 45 minutes to play this morning so I had time to get the cat out on the water for a couple of minutes. Half drained batteries but what the heck. It did seem to run a little better with the motors raised, and I was suprised there was no cavitation. So I'm gonna give it a little positive angle on the drives and re-charge my lipos and try to get it back out on the water later today.

[tiqueman]

Sound slike progress. I like it! Keep us posted

[forescott]

I remember an old post somewhere here on the forum of another tc-31 dual outboard cat w/sv-27 motors on k&b outboard legs that ran really good, so I know its possible to get this thing running correctly. Soo many different possibilities of motor height/angle and battery placement. I think my head is gonna explode!

[Darin Jordan]

I remember an old post somewhere here on the forum of another tc-31 dual outboard cat w/sv-27 motors on k&b outboard legs that ran really good, so I know its possible to get this thing running correctly. Soo many different possibilities of motor height/angle and battery placement. I think my head is gonna explode!

That was one of the guys that is in our club. I seriously doubt the issue is with the outboards themselves.

Just out of curiousity, which outboard is spinning which direction??

His wasn't running counter-rotating. The boat ran great around the course.

If you are having lift issues, then you might consider using low lift props, or kill the lift in your existing props.

[Darin Jordan]

Also, generally speaking, when you raise and outboard up, you raise the nose of the boat. When you lower them, you lower the nose of the boat. The back of the boat is going to try to ride on a specific area of the prop (generally thought to be the centerline of the hub, but it's actually a little further out on the blade). So, where the prop is affects where the transom will ride, which, in turn will affect the angle of attack and ultimately, the height of the nose.

It makes sense that it would be better with the motors raised up on THIS hull.

The Stiletto, on the other hand, likes to fly with the tips up a bit in the first place, so it may work better with the lower unit down a tad, so help keep the tips from getting too high.

Sounds frustrating, but you'll get it. Will be really cool once you do.