attack angle

[Tom w]

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[DON MAHER]

The worlds fastest 21 hydro is powered by a CMB-21 with a sq. drive system, owned & driven by Mark Grim. 110+ mph two way average!!!

I too run sq. drive on all my boats with teflon thrust washers & have NEVER wore one out in over 35 yrs of boating!!!

Don

 

[Marty Davis]

The worlds fastest 21 hydro is powered by a CMB-21 with a sq. drive system, owned & driven by Mark Grim. 110+ mph two way average!!!I too run sq. drive on all my boats with teflon thrust washers & have NEVER wore one out in over 35 yrs of boating!!!

Don

Don:

Curious whether you run a teflon liner in your tube? Many of the West Coast guys used to do that and I have not kept up in a long time with that.

By the way, Norm Doerr had the best explanation that I have seen. Two boats side by side and which one has less friction.

While at Charleston last Fall, I showed John Finch my 67 hydro square drive setup and he was amazed at how free it was. From him, that is significant, as he experiments more than anyone that I know.

 

[Marty Davis]

Maybe I take more pains with my setup than most, but I will explain how I set up a square drive in a hydro.

I use leaded teflon bushings in the strut. They are pressed in.

After I get them in the strut, I take a piece of drive shaft and use a dremel cut off wheel and cut a shallow groove along the length of the piece of shaft.

I put this piece of shaft in a drill and insert into the strut through the bushings. I use it as a reamer just a little.

Now that the bushings are completely in line and fitted to size, I polish the stub shaft like a mirror.

I put one hole in the strut through the side for water to lube the stub shaft.

As I described before on how I solder the flex cable to the ferrule, is SUPER IMPORTANT.

I allow a little bit of end play at the engine so that the cable floats.

The strut tube is shorter that with a conventional setup and I cut the strut tube about 1/2" shorter than the soldered joint for the ferrule and the flex cable.

That's it....

 

[Charles Perdue]

The worlds fastest 21 hydro is powered by a CMB-21 with a sq. drive system, owned & driven by Mark Grim. 110+ mph two way average!!!

I too run sq. drive on all my boats with teflon thrust washers & have NEVER wore one out in over 35 yrs of boating!!!

Don

Hello Don, maybe that is because the thrust washers are "Water Cooled". Just curious if you or Mark are running a single curve in the driveline or the "S" bend.

Charles

 

[DON MAHER]

Marty,

I quit using teflon liners 20 odd yrs ago, when they started "balling up". My thinking was to much heat caused this. I also run lead teflon bushings in the strut. I use a stub shaft in the drill press & WD-40 to "align and break in" the bushings.

Charles,

Both Mark, Chris & I run a single curve driveline. We find this to be the freest setup when used w/sq. drive, very little friction or drag when properly aligned. The "Water cooling" the thrust washers is also my thinking

Don

 

[Marty Davis]

Marty,I quit using teflon liners 20 odd yrs ago, when they started "balling up". My thinking was to much heat caused this. I also run lead teflon bushings in the strut. I use a stub shaft in the drill press & WD-40 to "align and break in" the bushings.

Charles,

Both Mark, Chris & I run a single curve driveline. We find this to be the freest setup when used w/sq. drive, very little friction or drag when properly aligned. The "Water cooling" the thrust washers is also my thinking

Don

Don:

Exactly what I am running. I could never understand why people put an S Bend in their driveline. The bottom line is the freeness of the system. I also do not run teflon liner for the same reason. Have you used the method for aligning the ferrule and the flex cable in the lathe. It makes it silky smooth.

 

[Kim J]

Rod G tested this and found out the S-Bend had the lowest drag.

Newer seen the actual test - but he measured the amps drawn from a electric motor.

Maybe he would chime in and explain the test and also if he tested both the square drive contra the non square drive system.

Kim J

 

[DON MAHER]

Marty,

Yes I use the same method as you to align the cable & ferrule, the lathe. Comes out perfect every time!!!

Kim J,

I don't know the particulars of Rods test, but I do know that if you run a pinch collet on the motor you have to have a lot of clearence between the strut and the drive dog. Most will say that this is due to "cable windup". I disagree, if you hold one end of a cable in a vice & turn the other end. it will not "windup" more than a few thousands (.010-.020) unless the inner winds of the cable are broken.The "S" bend is the problem, a cable in an "S" shape will will try to go back to a straight position. When the cable is in the stuffing tube it rests on the bottom of the tube, now put forward thrust on it and it will go to the top of the tube & put pressure and friction at this point. That is the "windup"!!! Clear as mud, right :lol:

Don

 

[NAMBA860]

A lot folks will argue;BUT on a especially a 21 the square drive is key.. less friction, less useless load on the engine. You want to load the engine with the prop not shaft drag.

I would like to hear more on how a square drive would have "less friction" that a properly set up conventional collet. You still have a stuffing tube that the flex cable runs through & shaft bushings in the strut and even add the drive dog making direct contact against thrust washers at the back of the strut which does not happen on a conventional collet set up. As far as the cable at the motor once it's under load the squared end is bound in the collet. But hey, I'm always open to new thoughts or ideas so I'm all ears on this one...............

Heck I am far for an expert or even experienced with RC boats,but hear is my 2 cents.

Teflon is its own lube so I am using lead Teflon bushings and a pure Teflon thrust washer.

I am using a flex shaft soldered on to the stub shaft and a Colet up at the eng with a small gap for cable shrink.

As far as the square Collete as the shaft shrinks it will slide in the Collete and unload the eng.

Spray a little Prolong in the tube and of you go.

I can feel the difference with my hand on the drag. Not much HP with the 21.

I'm no expert either but:

Being smoother when it's just sitting on the table turning it by hand is one thing. What happens when you spin the drive dog at 25000 rpm while being pushed up against the Teflon for a period of time? I don't think it will last long before the Teflon is machined away by the drive dog??? I'm asking as I don't know.

-Buck-

I have polished the strut and drive dog. Don't need it to last long washers are 12 for $.05 have lots of spares.

Hope to try today will let you know.

worked pretty good with a dremel hooked to it, pulled as hard as I could didn't miss a beat.

don maher is a wealth of info you will be smart to listen to him i have watched since i was 13 years old and now im 38

 

[Tim_Duggan]

I'm no expert either but:Being smoother when it's just sitting on the table turning it by hand is one thing. What happens when you spin the drive dog at 25000 rpm while being pushed up against the Teflon for a period of time? I don't think it will last long before the Teflon is machined away by the drive dog??? I'm asking as I don't know.

-Buck-

The wear on them is not as bad as you might think..... even on big engines, but you may have inadvertently riased a valid argument for the square drive system / disadvantage of a fixed collet. Where the flex cable is rigidly attached to the motor via a collet - the thrust force you are talking about is pushing directly at the crankshaft, with only the flex in the engine mount to try and reduce the load.

With the square drive at the engine end (and provided the end of the cable is not flush with the crankshaft), this force at the crankshaft is somewhat eliminated as it is taken at the strut and thrust washer, as you said. Also, it is possible to use a roller bearing thrust rather than teflon washer if chasing even less friction, although it has a higher likelyhood of failure.

Whether or not these forces are enough to justify a sqaure drive system - I don't really know. On a 21 engine however - every little bit helps!

 

[Marty Davis]

I'm no expert either but:Being smoother when it's just sitting on the table turning it by hand is one thing. What happens when you spin the drive dog at 25000 rpm while being pushed up against the Teflon for a period of time? I don't think it will last long before the Teflon is machined away by the drive dog??? I'm asking as I don't know.

-Buck-

The wear on them is not as bad as you might think..... even on big engines, but you may have inadvertently riased a valid argument for the square drive system / disadvantage of a fixed collet. Where the flex cable is rigidly attached to the motor via a collet - the thrust force you are talking about is pushing directly at the crankshaft, with only the flex in the engine mount to try and reduce the load.

With the square drive at the engine end (and provided the end of the cable is not flush with the crankshaft), this force at the crankshaft is somewhat eliminated as it is taken at the strut and thrust washer, as you said. Also, it is possible to use a roller bearing thrust rather than teflon washer if chasing even less friction, although it has a higher likelyhood of failure.

Whether or not these forces are enough to justify a sqaure drive system - I don't really know. On a 21 engine however - every little bit helps!

Tim:

As for the fast wear out of the teflon washer, I have had the same washers on my 20 boat for 2 years and they are still fine. No significant wear.

Now, if you the ball bearing thrust washer assy, you will find that they saw through the shaft. Once there is a little bit of wear on the shaft, it accelerates the wear and it will cut right through the shaft.

 

[dwilfong]

I'm no expert either but:Being smoother when it's just sitting on the table turning it by hand is one thing. What happens when you spin the drive dog at 25000 rpm while being pushed up against the Teflon for a period of time? I don't think it will last long before the Teflon is machined away by the drive dog??? I'm asking as I don't know.

-Buck-

The wear on them is not as bad as you might think..... even on big engines, but you may have inadvertently riased a valid argument for the square drive system / disadvantage of a fixed collet. Where the flex cable is rigidly attached to the motor via a collet - the thrust force you are talking about is pushing directly at the crankshaft, with only the flex in the engine mount to try and reduce the load.

With the square drive at the engine end (and provided the end of the cable is not flush with the crankshaft), this force at the crankshaft is somewhat eliminated as it is taken at the strut and thrust washer, as you said. Also, it is possible to use a roller bearing thrust rather than teflon washer if chasing even less friction, although it has a higher likelyhood of failure.

Whether or not these forces are enough to justify a sqaure drive system - I don't really know. On a 21 engine however - every little bit helps!

I tried the ball bearing thrust and it did grove the hardened shaft.

I was not sure how long the Teflon washer would last, but your reassurance makes me believe I made the right chose.

Tim:

As for the fast wear out of the teflon washer, I have had the same washers on my 20 boat for 2 years and they are still fine. No significant wear.

Now, if you the ball bearing thrust washer assy, you will find that they saw through the shaft. Once there is a little bit of wear on the shaft, it accelerates the wear and it will cut right through the shaft.

I tried the ball bearing thrust and it did grove the hardened shaft.I was not sure how long the Teflon washer would last, but your reassurance makes me believe I made the right chose

 

[Ian Inverarity]

I'm no expert either but:Being smoother when it's just sitting on the table turning it by hand is one thing. What happens when you spin the drive dog at 25000 rpm while being pushed up against the Teflon for a period of time? I don't think it will last long before the Teflon is machined away by the drive dog??? I'm asking as I don't know.

-Buck-

The wear on them is not as bad as you might think..... even on big engines, but you may have inadvertently riased a valid argument for the square drive system / disadvantage of a fixed collet. Where the flex cable is rigidly attached to the motor via a collet - the thrust force you are talking about is pushing directly at the crankshaft, with only the flex in the engine mount to try and reduce the load.

With the square drive at the engine end (and provided the end of the cable is not flush with the crankshaft), this force at the crankshaft is somewhat eliminated as it is taken at the strut and thrust washer, as you said. Also, it is possible to use a roller bearing thrust rather than teflon washer if chasing even less friction, although it has a higher likelyhood of failure.

Whether or not these forces are enough to justify a sqaure drive system - I don't really know. On a 21 engine however - every little bit helps!

Tim:

As for the fast wear out of the teflon washer, I have had the same washers on my 20 boat for 2 years and they are still fine. No significant wear.

Now, if you the ball bearing thrust washer assy, you will find that they saw through the shaft. Once there is a little bit of wear on the shaft, it accelerates the wear and it will cut right through the shaft.

Marty,

With nitrided tool steel shafts the ball thrust washers dont wear through. I use ejector pins from plastic injection molds.