As long as the Motorcraft has the right rating, it's a Ford product and probably ok. You might want to shy away from the generic Walmart brand although they are probably all ok in reality. I'd be a bit leery about an off brand's QC and would worry that what it says on the can might not be what is actually inside. Could be a REAL expensive error to save a couple of bucks. I use Pennzoil in my cars and trucks. My last Subaru was still running fine at 365,000 miles when I traded it. Changing oil religiously in cars or boats, diesels or gassers is the key to long engine life. With Yanmar, it's 100 hours which comes around pretty fast. I never go cruising without at least 3 oil changes and filters on board.
The old CD rating is listed for Yanmar diesels. It's not really available anymore but the HEAVY DUTY DIESEL C
ratings are what you need to look for.http://www.api.org/certifications/en...010_120210.pdf
Light automotive diesel oil won't cut it.
That's a perfect engine for your boat.