What type and year yanmar. Is this a new problem, a new to you boat? how long has it not been used, other history. do the injectors get fuel? How charged are the batteries? What is the outside tepature where you are. At a normal temp your glow plugs may not be needed. When was the last time it was running.
That derelict boat was another dream for somebody else, don't let it be your nightmare and a waste of your life.