From personal experience, my issues with saildrives is from the maintenance
point of view. I have had Yanmar
saildrives for about 3 years. Despite having a tube that goes all the way to the bottom of the drive changing the oil
is still a PITA that lasts several hours. The first half pumps out pretty quickly with a vacuum based oil
changer but it takes several hours to get the rest out because it takes a while for the 90 weight to get down though the passages to the bottom. I have had one shaft seal
destroyed by monofilament which required pulling the boat from the water
. Fortunately or unfortunately I had to have the boat hauled anyway because the front main seal on the other transmission
blew out. The issue is to service
you must take the lower unit out of the hull
. On most shafts I have seen you can disconnect the shaft from the transmission and the transmission from the engine
it without hauling the boat. Some saildrives have worse reputations than others. The Yanmar
SD-40 was in production only a few years before they were discontinued. Of course that is what I have. I don't worry too much about submerged objects because I have keels in front of my drives. The props I have have rubber hubs which are supposed to spin if the blades come to a sudden stop. It is my fervent hope that I won't be testing that feature. I expect that some day that rubber will deteriorate and become a maintenance
issue as it has on several outboard
props I have owned, but it sure beats ripping your engine
off of its mounts (I hope).
I once hit a crab pot at night with a shaft drive. It broke the coupling and the prop slipped back and jammed the rudder
. This meant going over the side at night to get the rudder
freed up, rigging
a line on the shaft to keep it from backing out into the rudder again, pumping the bilge
from the now leaking shaft seal
. I don't see how my saildrives could jam my rudder so that is in their favor. I also don't think it is likely that a fouled prop would cause a leak, though I suppose it could happen if you broke the engine mounts.
From my point of view Saildrives are not better or worse than shaft drives, just different.