Sorry for dredging an old post, I guess you already tried by now? How did it go?

I never tried it. I suspect the motion of a boat will most of the time not be a problem. There are sometimes jolts and that may damage the vinyl.

You may get good results putting the turntable on a table which is suspended on string from one point because then the only force on the system will be an apparent increase in gravity – as long as it can’t bump into anything when it swings.

Here is a product…  oh, no links to products. There is a tray on a large online retailer which does it, called spillnot. I hope that’s OK, I just needed the nearest thing to illustrate the idea.

(They claim it’s a marvy new invention but I saw one attached to a Segway with three strings from the tray up to a point on a long stick at the front – it’s the same thing, and it held the coffee mug without spilling.)