I've had a few issues with the 2 Yanmar
SD20 saildrives in our boat. One had a shaft seal
leak not too long before I planned on hauling anyway.
After replacing shaft seals
both sides and relaunching, I soon found water
in one saildrive
. (Fast forward, I eventually concluded it was because the Yanmar
replacement drain plug oring is slightly different from original and easy to install improperly seated) I certainly didn't want to haul again, so I pumped out from the top what I could (about 1/3 of capacity) and replaced with new, repeatedly for a total of about 8 or 9 times, resulting in oil that looked good.
I had been troubled by the realization that the saildrive
is not vented and frequently has what i considered a significant pressure differential, both ways. My solution was an expansion tank I made and located at least a foot above the waterline. I ran this idea by Yanmar before I executed, but failing to get an answer, when ahead with it.
This, to me, is the solution. There is always a slight pressure inside the saildrive that should keep water out, barring a major failure. Checking/adding oil is much easier. I also use Amsoil synthetic oil for extended oil changes, which also claims to be able to perform with 10% water contamination.
I do worry about the aluminum
housing. Initially, I hung zinc guppies attached to each saildrive. But after installing a galvanic isolator
, this appeared to be unnecessary, so I stopped. My zincs last 2 years between hauling, and still have a lot of life. As an alternative, I have read of installing a disconnect switch in the engine
ground cable to be switched off when plugged in, but not sure that's a good idea. I've heard that saildrives are more prevalent in Europe
where perhaps shore power
is not used so abundantly.
Lastly, at 9 years , I still have the original saildrive bottom seals. Not sure when I should replace them, but I think about it. If I had a saildrive piercing the bottom of a keelboat (as opposed to mounted in the stern compartments of our cat), I'd think about it a lot more.