you know those bath chairs usually from the Medical dept - would they be ok in an ordinary bath or would it go through bath once the patient should sit on it?
When I had a broken leg the physios gave me a seat that fits across the top of the bath from side to side. Having said that I don't think a chair leg (with rubber feet) would go through the bath unless the bather was a real porker.
Oh, I thought from the title you were after one of those carriages old people had when I was a kid!
To answer your question, it would depend on the quality of the bath and if it was fitted correctly. Most baths have a big piece of chipboard glued to the bottom of the bath to strengthen and allow for supports.