I think most sailboat installations/environments tend to be pretty darn clean. This being the case for us, I took my disintegrated filter and cleaned away the remainder of the foam material with a brass wire brush. You are left with just the coarse metal cone which should suffice to keep the big chunks out.
Never tried the hand-crank start, but previous experience with on our Laser 28 with a single cylinder Bukh, we could only start it with the flywheel pulley and decompression lever if the engine was warm. Cold start, no way. If you had a way to heat the up the cylinders and intake region.
Up here in the chilly north of Georgian Bay, I know a few folk with worn diesels who manage to get them going on a frosty Autumn morning by first "pre-heating" by blowing in warm air using a hair drier.
By the looks of your photo, air temperature is not a problem where you sail