My ZF5 (Hurth HBW 50) gearbox is slow going into gear, and seems to slip a bit before getting the boat moving. What is wrong?
Usually when ZF gearboxes do that it means they have worn or damaged forward clutch plates and need to be rebuilt. If it does start slipping badly when you’re motoring you can usually get into the slip after sailing home by using reverse, which usually still works OK. The usual cause of forward clutch plate damage is sailing with the transmission gear lever in forward, instead of reverse (to lock the shaft when using a feathering or folding prop) or neutral (to allow the shaft to spin to reduce propeller drag when using a fixed blade prop). The other usual cause is overload caused by motoring close to hull speed, since that puts such a load on the gear that the thrust washers on the end of the forward gear start to slip. Always motor for long distances at least 1 – 2 kn slower than maximum boat speed. While testing for short periods of less than a few minutes (ie. The intermittent rating of the engine) at maximum speed/full throttle in normal sea conditions the engine tachometer should
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