Well - here's an opportunity for us to LEARN somthing, rather than GUESS at something.
Perhaps the OP could install an oil sample port (likley easy to do by the way he's described the plumbing). Then he can get UOA's, perhaps every 25 hours.
My suspicion is that the wear results are much more similar to a work-truck engine that most would realize. But, if you want to convince me I'm wrong, then post up results. Let's see the UOA's.
However, to convince me, I'll need to see several successive UOA's, at even intervals, with the understanding that this is a new engine and therefore being "broken in", and using good control theroms such as consistent use of oil brand/viscosity, and noting any atypical usage patterns. Post up the UOA's for all to see, and I'll run them for analysis in my staticial analysis programs.
While I agree that there is a much greater fuel consumption rate in a pleasure boat versus a car or truck, the relationship of BSFC, oil comsumption, wear metals and such is NOT directly proportional. In other words, if a car gets 20 mpg and a boat gets the equivilant of 10mpg, does it also use up 2x as much oil, or generate 2x as many wear metals, or are the insolubles doubled? - DOUBTFULL! The only issue that would be reasonble to suspect highly effected is that the TBN might drop quicker because a marine environment is, by definition, going to provide more moisture for the production of more acids, thereby effecting the TBN.
Still - rather than us guessing, how about the OP posting results in a controlled experiment. That will tell the tale. Rhetoric doesn't provide much opportunity to learn; data does.