Need help determining repower requirements

I just picked up a 26ft JC Tritoon with a 4cyl Mercruiser
outdrive just rebuilt, engine needs "minor" work (head gasket, so the head is probably warped...)
I want to remove as much weight as possible, as I am going to construct a "shanty" on the vessel to use as a floating bait store.

My first choice "from the hip" is to use a small sailboat type diesel inboard, or a small 4 stroke outboard, as I only need to be able to move the barge at crawling speed, and of course selling bait involves fishing which involves being quiet...

from previous experience, I know an I/O can get real expensive, real quick, so I don't want to dump anything into the existing powertrain, would rather part out, and replace with something small, efficient, reliable and quiet.

First, how do you go about calculating the minimum req'd HP to move a given vessel at or below displacement speeds, second, where can I find physical dimensions of common diesel inboards (Yanmar, Perkins, etc...)

also, it it possible or rather, FEASIBLE to mate a small (10-25hp) diesel inboard to a Mercruiser outdrive?

thanks for any help

 

Running the 181 GM 4L at modest speeds, will not hurt it and you don't have to replace anything. The head doesn't have to be warped, just because it spit out a head gasket. The cheapest way to go is fix what you got, keep it in good repair and have fun.

Opting for a hybrid system of some concoction will just cause you untold issues. An outboard is an option, though you already have a propulsion system, which would need to be hacked out, areas reinforced and patched, just to mount the thing. A diesel would be nice, but again you'll need to fabricate quite a bit to marry it to the outdrive.