SAILDRIVE LUBRICATION: Our yacht has a Hurth/ZF SD10 saildrive. I understand these are fitted to several brands of engines, not just Nanni.
They are rated at up to 60HP.
When it came to changing the oil in it there was considerable confusion as to the best grade. Different websites and agents had different advice.
Although the drive unit had done less than 800hrs, the previous owner reported expensive problems with the internal clutches. The lubricant had always been ATF. The top of the saildrive has a sticker with this advice.
Eventually I contacted the service manager at Nanni agents General Marine Services. He told me that since 2012 the strong advice had been to fill the saildrive with 15/40 oil.
Now the unit seems to run more quietly. ( Colin Moore, Raven 31, Mimic)