I have investigated Freighter Travel in the past (2005) and found that it tends to be more expensive than just shipping yourself and the moto by air.
It does appear to be an interesting way to get around, but it is not the "cheap way to travel" that it might have been 30 years ago. Instead, the industry seems to be switching to more of an upscale, bespoke travel experience for folks who have a lot of time on their hands. I am sure it would be possible to arrange movement of a motorcycle along with yourself on a passenger carrying freighter, but it would have to be something that is individually arranged, thus, it won't be simple nor will it be cheap.
FWIW, my motorcycle has been back and forth across the Atlantic about a half a dozen times, and the most expensive shipment I ever made was by ship - that cost me more than twice what the next most expensive air freight shipment cost me.