I have been told that a S shaped shaft tube is a good thing because
1 cancel harmonics
2 increase speed
plus others that pass me by at the moment

question...what angles are best for the "S" given 16 to 18000 RPM
thanks for any info
Gordon

The most efficient/best angle for any flexible cable transferring torque, is as small as possible. The more angle/curve you have, the more friction/whipping the cable will produce. A VERY gradual "S" curve will help to cancel out the whipping and reduce the localized friction of a single curved configuration. Offset drives lend themselves really well to an "S" set up. A straight section of cable leaving the collet, and another at the strut/stinger, will add reliability and stability to the torque transfer. The majority of the distance in between, can be formed into a long "S" curve. In the case of the stuffing tube being open to water spray at speed, you want that section of tube parallel to the running surface so as not to induce any side thrusts.

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I use as little bend and as small a angle as I can. I also try and make the radius as big as practical. Seems to work the best. The heat Jim saw in his test was friction and friction needs power to overcome. The setup with the least heat will be the most efficient.
Jimmy

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We do have to take into account the "in-boat" configuration of the drives, when discussing/testing the systems. So many variables present different requirements. IE; obviously a short cat drive will be the worst case, with a rigger the easier, in terms of angularity. The friction/heat generation from a collet locked cable ( transferring torque in two directions through the drive ) will be different from a square drive with a floating cable. The amount of loading from various props and similarly from a heat racer when loads are higher through the turns, also clouds results.

For the average model boater, it comes down to finding a drive that is user friendly and reliable, while getting the power to the water.

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Your observation Jim ( about the outboard ) IS interesting! I wonder if any heat that may be building up is "refrigerated" out through the water washed housing?

All our cables are square drives on Teflon, and none of the hulls ( cats and monos ) have ever shown any drive heating. Of course the cats are wash cooled. My lube is Permatex #22063 full syn. ( -40 to + 400* F ) and works very well for us. I think stainless/ceramic brgs. in the struts help to reduce drag/heat as well.

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That's a interesting point you made Jim. Smaller cables will flex considerably more and have less contact in the same sized stuffing tubes we all use. A 1/4" cable will have a higher outter dia rotational speed over 3/16", the 2 cables put side by side in the same ID tubes will show the smaller one having much less drag and also will not have even close to the same whipping effect at high rpm due to it's weight savings, and increased flexability. This is why the 3/16" cable runs smoother and cooler in your test.