Being slightly over-propped enough to burn up 2 transmissions in 400 hours?

[Jim Cate]

G'Day SgtP,

We've got a ZF10 too, coupled to a Nanni 43. The original box died just after we bought her, with an unknown but fairly low number of hours on it. At that time I should have replaced with a ZF12 which is a drop-in replacement, but didn't know about it. Larger ZF's are NOT a drop in replacement.

I was a bit worried about longevity and did a it of research. Found a site where there was much discussion of these problems, but no I longer have the URL. There was reasonable consensus that these trannies needed to have their oil changed quite frequently - at each oil change at 200 hour intervals -- and to be sure to use Dextron III rated ATF. You may have noted that the thing only holds 350mL of fluid, and I suspect this contributes to the problem. If yours is running hot (and I suspect that it is) you might consider their bolt-on external oil cooler. Might make the difference and would be much cheaper than shifting to a different tranny.

So far we have about 2500 hours (eight years usage) and so far it is ok. We don't generally motor hard, though, and the prop is correctly sized. I've got my fingers crossed -- for both of us!

Good luck!

Jim

[sgtPluck]

Thanks Jim,
I will try to change the oil more frequently than the manual suggests. Probably with my engine oil change. The oil is cheap. I'll also try to get a better oil pump to really suck every drop out of there when I do change it.
I think that rather than replace the ZF10 with a different type of gear, I will reduce the pitch a bit on my prop. I figure that at least shouldn't hurt anything, and possibly may help prevent overloading/heating. If my current gear still fails after a low number of hours then I'll bite the bullet and go for a bigger unit.
Of course I'll also sail a lot more, and if I do head back up the east coast of the US I'll do longer offshore hops, rather than chug along in the ditch. I was planning on going the thorny path route to the Caribbean, i.e. against the wind the whole way. I'll have to think about that.
I did look at the optional cooler, although the guys at ZF felt it really shouldn't be necessary on my 25hp engine.

I'll get my last gear fixed so that I at least have a spare on board if it does fail again in somewhere lacking facilities.