Hi,
I think you need to make clear what motor and what arrangement this applies to, otherwise you will scare folk off direct drive, which I may add works very well on my sailing yacht. Is this only the Motoenergy motor that you refer to. I don't know John Fiorenza who I believe designed them, but understand he is a good engineer. Does he, in that case, supply them with the warning you state?
I run a Lynch D135 with double row angular contact bearings that accept axial and radial thrust. I do not use a separate thrust bearing. I limit my prop diameter to 12". My pitch is 14, 52% BAR and 3 blade which all has to be taken into account on a sailing boat whilst surfing down waves above hull speed and the consequent forces involved. I run a cutlass bearing, with PSS shaft seal, R & D half couplings with flexible coupling and R & D isolation mounts.
After doing some bollard pull tests I did the load calcs with SKF tech support using their online bearing load calculator. I was looking for a saftey factor of 2 or better. After 600 miles last year, including surfing conditions and applying braking re-gen, my system works well and it seems safely. This year my prop is the 3 blade referred to above. Last year was tests with the old 2 blade 12 x 10. My voltage and current predictions for the 3 blade and subsequent loads after a few days back on the water this season, concur with my winter calcs so I have a good idea of any change in shaft loadings. I also understand that my magnets effectively float the rotor, reducing any axial load on the bearings.
Have you built a direct drive system on a sail boat Cal?
John currently aboard Yacht Elektra
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