Ceramic coating all passages and combustion areas of heads run 2k per motor.

Innovation marine and Donovan had a joint venture where they made all aluminum engines for the us navy. The reilabily/durability testing they had to do to get the contract was pretty extensive 300+ hrs non stop at wot . I have a pair of them in my boat. I have not personally run them enough yet but i hope they last at least that long.
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I think this is enough information, It seems like the aluminum blocks will work for offshore use.If mercury can use it then it is good enough for me.
why would the passages be damaged if you always rinse the motor after taking the boat out of the water,I am talking about run it and then take it out in some hours and flush it with fresh water...?

Im pretty sure the Hawk engines back in the day were aluminum tall deck Donovan's

You running in salt water?

Every modern day outboard is all aluminum even the 7 marine that is corvette motor with a blower. I would see no issue

Bare aluminum ? If not, what coating or process ?

Closed cooling is the only way. My 2 cents 😀

Yes running in salt water
But I remembered now one time I found a beer can on the beach in the water all aluminum and it was damaged -but there was no corrosion or anything wrong with it from the saltwater,I dont know how long it was there but what is the real problem with saltwater and aluminum? I am also saying to use the boat for some hours and then rinse the engine well with fresh water

A beer can in water does not have any steel, stainless steel, and etc bolted to it nor pressed into it.

Search and study electrolysis. I see issues in fresh water with people who do not address it.

Also, I believe Corey331 ran into issues this past year with his aluminum LS motor. Engine is just 1 or 2 yrs old.