We were in India in November/December 2007, and wanted to get 2 people and one bike to Thailand.

I met someone, a Czech, who swore, that there is a ferry (or anyway some kind of a ship that should be capable of transporting a 4x4, which they were travelling with) going between Chennai and Singapore. He even gave me some Indian cellphone number, and I tried it many times, it never answered.

Later on I noticed, that somewhere on the net, there was a big cargo ship with a few (like 10-15) cabins for passengers, that was doing this route, that could be what he was referring to. But at least on those pages, the prices were higher than if we, as well as the bike, would be flown across the Bay of Bengal, so not an option for us.

There is a service from mainland India to the Andaman&Nicobar islands, but from there to Thailand, it seems to once again get very complicated. Could be worth a try, if you feel adventurous, and have lots of time, but may end up very expensive.

We actually freighted our bike by air from Chennai to Bangkok, the bike was about 600 euros total, and our flight tickets were about 200 per head, so roughly 1000 altogether.

I believe you won´t be disappointed if you expect there to be very, very few long-distance international passenger ferries operating anywhere in SE Asia.