Important drive line details

[DISAR]

There a couple details which I believe greatly affect the motor-ESC-batteries performance.
1) Thrust bearing. Reduces load from motor bearings and endbell. This bearing must be placed against the motor casing or the motor mount? In case the motor mount hole diameter is bigger than the thrust bearing then the only solution is that it is fitted next to the motor casing, is that ok?

2) Distance of drive dog from end of stringer for flexshaft. In the past I heard that it should be same as the shaft diameter, but now I see that it gets smaller (1-1.5mm). I also use a teflon washer. How much should that distance be?

I think that if these two items are correct then motor can run cooler hence less heat-amps, better performance. If anyone has experience on these, it would be great to share!

[Fluid]

The thrust bearing does not know where it delivers the thrust, but you want it to be against the motor mount or the motor PTO end. It really does not matter if it pushes against the mount or the motor housing. But most quality motors have bearings large enough to take thrust just fine. An incorrectly installed thrust bearing can do far more damage than not using one at all.

The gap between the drive dog and the strut should be the diameter of the flex cable. This can change depending on the size of the cable, the inside diameter of the stuffing tube, whether the cable is fully within a brass tubing or if some of it is exposed, whether you use a teflon liner, the power of the motor/packs, the weight of the boat, and the prop size. Just follow the recommendation and leave the gap equal to the cable diameter. A thrust washer at the strut is pretty useless, you don't want the drive dog to touch the strut with or without a "teflon washer".


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[ED66677]

Fluid,
I understand that a flex shorten under load so the prop get closer to the strut, if the gap is too small the friction increases causing power loss.
If I understand correctly (pardon me if I'm french ) you consider that the thrust have to be "tranfered" to the motor bearing via the flex and not to the strut?
BTW I wanted to PM you for some cat advice but...

[DISAR]

Thank you very much Fluid for your input. I also knew the gap to be the flex-shaft diameter but I see lately smaller gaps. I believe that the longer the flex is, this gap is necessary and if the flex is short like in monos with the motor aft this gap may be slightly smaller. In any case the drive dog must not touch the strut when in operation. Appreciate.

[Fluid]

Ed, it is virtually impossible to correctly take the thrust on the strut with a flex cable. The cable shortens to different lengths depending on load and rpm, so how can you use a fixed gap to compensate? You cannot. Thrust should be taken at the motor - meaning the the thrust is transferred to the hull at that point.

A lot is made by a few of the supposedly different reactions of a hull to taking the thrust at the strut versus at the motor. The fact is that for most FE installations the sum of the vectors involved is virtually the same for both methods. Differences in handling caused by changing where the thrust is taken are more perceived than real.


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[ED66677]

Clear for me Fluid!
The only way would be to have a square end on the flex, that allow the flex to shorten without pulling on the motor or the prop shaft! Reliable at 30000+ rpm? Isn't it the way gassers do it?

[DISAR]

Just for your consideration, in my mono hull I leave a gap of about 3/16 same as flex-shaft diameter I have also a thrust teflon washer. After 3 years in operation the teflon washer is like new not a sign of use, which means that never the drive dog pushed against the thrust. If I add a thrust bearing on the motor I believe that everything will be better.

Ed I saw the hardwarer of the chinese Agitator and it is like that. The flex has square end but is not glued to the prop. shaft. The prop.shaft has a square female and the flex slides into it.
The prop.shaft slides into the strut only from forward secured in place with the drive dog, and then the flex slides into the prop.shaft again only from forward. Working fine until now but it takes much more time to take out the flex because you have to remove everything (strut,motor even rudder)

[ED66677]

Yeah I did not want to mention the chinese one but I had it in mind! :-)