Re: Adding a auxiliary outboard.
Are you taking a tender? A hip tow arrangement with a powered tender would get you out of most trouble spots if the yanmar takes an inopportune holiday.
I've also seen workable examples of an emergency outboard mount that goes on a deployed stern ladder.
1984 Fast/Nicholson 345 "FastForward"
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)