TAMIYA Thrust Ball Bearing

[RaceMechaniX]

I’m talking about hydros... Go under water? Serious drugs are being used here. Do any of you ever think that any racing hydro with an inboard engine are pushed from the back? We go to great lengths to design thrust packages in racing hydros to get the push as close to the CG as possible. Huge effects in turning stability! Whether RC or full scale, the force vector diagram is the same.

Many of the worlds fastest hydro's are pushed from the strut or a split between the strut and motor. Hulls have to be set-up differently depending on where they are pushing from. Not only FE, but many of the fastest nitro and gas boats also use square cables so they are not pushing on the engine even though they all have ball bearings in the engines and only plain thrust washers in the strut.

The fastest 5 hydro's in the world all push off the strut using either a wire drive or square cable.

[sammyha]

To my way of thinking the bearing behind the motor only takes the thrust and transfers it thru the motor mounts to the hull. The strut directs the prop thrust cone. The strut is attached to the hull. So the thrust vector is transferred entirely thru the hull.

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[CraigP]

Serious question. I want to learn. If it pushes close to the cg, behind the motor, then why does strut angle matter? It would be pushing thru the flex cable and at an angle up to the motor. If what you're saying is true, then it would push the bow down, right?

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It depends where the transfer weight point is... Applies to all hulls. Think of a teeter-totter, the closer you push to the hinge point, the more the small length of the moment arm with its upward angle is swamped out. The overwhelming force vector becomes the lateral push... If your running SAW then as a Tyler states, it can be designed successfully from a rear pusher to a mid pusher. But on any boat, the positive/negative angle of the prop becomes much more reactive the further it is from the CG. It’s just Physics... I have to make boats turn at 180mph, full throttle down the straight, then turn the rudder. The push needs to be as neutral as possible to maintain a good ride characteristic. The Physics are identical to our full sized, 1600hp hydro and my 34” hydros. And even with a zero angle on the prop, there is STILL an angle being formed from the lower strut position up to the cord of the CG, which is the 3-dimensional balance point.

[CraigP]

To my way of thinking the bearing behind the motor only takes the thrust and transfers it thru the motor mounts to the hull. The strut directs the prop thrust cone. The strut is attached to the hull. So the thrust vector is transferred entirely thru the hull.

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This is correct, but it all changes if the hub of the prop makes contact with the strut. I noticed it on my RC hydro because the stern started to jack up, there was a change in the ride characteristic. And an 1/8” flex winds up more that a 3/16” flex. I liked the idea of using a stub shaft and square drive in the flex and use a thrust roller bearing in between the prop/strut, but the force vector diagram I made up showed that I would lose turning stability.

[sammyha]

Hmmn. Maybe the bearings held it more accurately and the result was something really was a bit off.

We got a lot of hay down boys...

Sooo... with the strut angled up slightly in the front, if you extend that line it will be somewhere between the 3 dimensional CG and the bottom of the sponsons. That's not necessarily downward thrust. The sweet spot will be somewhere between the 3 dimensional CG and the drag on the sponsons.

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[CraigP]

Ideally yes... but all of that can be brought into balance by how much air under the boat, the AOA of the sponsons and where the CG actually is. When the boat, like your UL-19, carves a corner, much better stability can be achieved by pushing close to the CG. If you ran you boat on a tether, where would you attach the cord for best performance? At the CG, and you would want your lateral driving force to be at the same point. You get it Sammya... If your just going straight then I think it matters much less. I carve corners... That’s where the fun is for me!

[sammyha]

Thanks, great stuff there CraigP...

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[T.S.Davis]

The fastest 5 hydro's in the world all push off the strut using either a wire drive or square cable.

The only square drive I've seen up close leaked like a rain forest. Has to make for less friction loss in a stuffing tube.

I used to build my wire drives with ball bearings. The last in the strut being a flanged stainless bearing with an extended inner race. Really really works well but failure is imminent. Especially if you turn a lot of laps. It's not an if. It's a when it fails. That flanged bearing really isn't made to do what I was asking of it. I got tired of them failing at the most inopportune moment. Like.....on race day.......during a heat. haha Plus I was spending $50+ on bearings every time.

Doug Jr had a limited mono set up with a stainless thrust bearing and a stinger. That was maybe 4 years ago. Probably the 2014 nats. I could never understand what he was doing about the wind up from the flex. Hind sight, maybe he was running a square drive back then too.

[CraigP]

Terry, I thought about using a stack of wavy spring washers to take up the slack. The distance of the spring washers from min to max would be a distance greater than the flex windup. So the thrust bearing would move forward with the windup and the spring washers counteracted it... But the vector diagram I made indicated the better pushing point is at the motor, which is almost exactly on the CG cord. But it would have been a trick setup! I even located some C’bore tools to modify the end of the strut. That tooling went instead to getting the lip seal in the back of the strut to stop grease loss and prevent water from getting in the stuffing tube. I get about 20 runs before having to freshen up the grease, keeps me bloody fingers clean!

[madmikepags]

I use these on pretty much all of my boats between the strut and the drive dog, doesn't need to be perfect around but needs to "ABSORB THRUST" I didn't read a 1/4 of this post but you can use them on the shaft between strut and drive dog, I've been using them for years, I don't know why other than they look cool but I've never lost a cable because of one?

[RaceMechaniX]

The only square drive I've seen up close leaked like a rain forest. Has to make for less friction loss in a stuffing tube.

I used to build my wire drives with ball bearings. The last in the strut being a flanged stainless bearing with an extended inner race. Really really works well but failure is imminent. Especially if you turn a lot of laps. It's not an if. It's a when it fails. That flanged bearing really isn't made to do what I was asking of it. I got tired of them failing at the most inopportune moment. Like.....on race day.......during a heat. haha Plus I was spending $50+ on bearings every time.

Doug Jr had a limited mono set up with a stainless thrust bearing and a stinger. That was maybe 4 years ago. Probably the 2014 nats. I could never understand what he was doing about the wind up from the flex. Hind sight, maybe he was running a square drive back then too.

Square drives are tricky to seal, but not impossible. There are ways of completely sealing the drive-line to same level as a welded cable set-up. Just takes a little creativity. The pic of the P-hydro uses a double square cable. Hyperformance 5mm to .150 square coupler on the motor side and a 3.5cc outboard stub shaft setup on the strut. The cable is fully enclosed in the stuffing tube.

I only use ball bearings in SAW boats were longevity is not a concern. The bearings also tend to be larger than what is typical in the common set-ups and bearings are often doubled up.

I have run my Q mono with a 3mm wire drive for years now and it leaks a little, but it has been rock solid. I can get away with bushings in the strut because there is very little bend in the drive-line.

[Shooter]

Love the idea. In fact, I think I started the same thread a few years ago! Putting the thrust at the strut eliminates side load of the flex cable on the stuffing tube. I was never able to find a long enough 0.150 cable with a square end for sliding. 3/16" cables seem to be easy to find.

Tyler - Where did you find that squared end 0.150 cable? Or is that just a short outboard cable?

[RaceMechaniX]

Dave Ripey at Hyperformance will make double square cables in any length.

[longballlumber]

Love the idea. In fact, I think I started the same thread a few years ago! Putting the thrust at the strut eliminates side load of the flex cable on the stuffing tube. I was never able to find a long enough 0.150 cable with a square end for sliding. 3/16" cables seem to be easy to find.

Tyler - Where did you find that squared end 0.150 cable? Or is that just a short outboard cable?

Pete,

I have been running a .150 square/square set up in my PT Stealth for 3-4 years now.

[Shooter]

Woah! I had no idea!!! That looks great!