Drive train protection / Blown Gears / electromagnetic retarder

[ChrisN67]

I have finished installing new ZF two speed splitters on my ZF 110 ATS marine gear. From what I understand, when these splitter fail, the failure point is the Sprague clutch. This Sprague is susceptible to damage mostly by 1) downshifting when at high speeds (my gear ratios are 1.7 /1.2) this is the automotive equivalent of downshifting to 1st gear on the highway. The second is the drive train shock resulting for spin up and re-contact with the water when the prop exits the water (this is of particular concern to me as these are surface drives). Both the aforementioned events apparently account for most damage to these gear systems.

ZF produced a RPM block to prevent downshift at higher RPM; I added an additional safety of a GPS based block that requires the boat to be under a predetermined set speed before shifting.

With regards to the second issue of shock to the drive train when the propeller exits and reenters the water; I was wondering if anyone ever used an electromagnetic retarder (eddy current brake) that would be controlled by a processor that follows RPM and in the even of a quick increase in RPM (most likely the delta of the acceleration would trigger this system) the eddy current brake would kick in and load the system so that it would remain at or near the same rpm prior to departing the water.

The units I have seen are heavy; here are some specs:




Dimension (mm) Weight of Stator (Kg) Weight of rotor(Kg) Max torque

DHB06
440×420×220 56 33 600

DHB09
440×420×220 65 33 900

DHB12A
580×550×230 93 63 1200

DHB13
460×460×220 70 49 1300

DHB15
580×550×230 101 63 1500



Just wondering if anyone uses any system like this to control rev-out and preserve consistent load on drive system when running ?