Hi Bruce ...not being an engineer, I can only rely on what I have learned over half a century of actual mechanical experience. I am not disputing the robustness of the conventional clutch. My statement was that the cone clutch is more reliable in a straight drive configuration than when used in a sail drive with it's double right angle, geared, progression to the prop. You will also notice I used the word "inertial." Both types of clutch incur their major wear when initially engaged. The amount of "slip" involved in each case, it seems to me, would be in direct relation to the amount of inertia or initial resistance that must be overcome . I can not see how a cone clutch will not see more initial slip, hence wear, as it looks into two right angle gear progressions before reaching the prop (keep in mind, I am saying "on initial engagement"). On my own conventional straight drive system with cone clutch (in neutral) I can turn the prop with with my little finger and feel almost no resistance. When turning a prop on a saildrive I have experienced a good deal more initial resistance and have always attributed that added resistance to it's configuration - and the fact that the two additional gears sets are immersed in a heavy lubricant adding a certain hydraulic component as well. Now once inertial resistance is overcome and the clutch (plates or cones) have "locked up" so to speak, then wear is no longer a significant issue.

My real objection to a sail drive is the bucket size hole in the hull ...and as you mention, the aluminum components in sea water - coupled with the centrifugal prop force at the end of a shaft hanging down from the belly of the boat (which of course is what necessitates the large hole and rubber gasket). I do understand that there are certain boat designs that are best served by this configuration and certainly there are many folks who are quite happy with them. The ones I have had to work on did not make me happy