Doubt if you will find a smaller machine than the Eumenia, now called Eudora Soba I note, and I believe the only one designed for a marine environment - click image.
My Contest yacht was almost built around one as all the others, Candy, Zanussi etc. were a few mm too big in one dimension or other. The Eumenia just dropped through the aft bedroom hatch and fitted perfectly in the dedicated cupboard. Not cheap but it proved very reliable over the 12 years I had the boat which included running it without issue from onboard genny thanks to electro-mechanical controller.