On the coast south of Dubrovnik we found there were many small water taxi services between D and smaller towns. The same may be true of Trogir to Split.

Based on previous years, there will be several boats daily between Trogir and Split.

The summer boats between Split and Trogir are run by Bura Line. There are four trips daily.
www.buraline.com
There are also frequent buses between Split and Trogir.

I wasn't able to get a schedule I could read for Split to Trogir at the link above and am wondering whether anyone could give an idea of the options for taking a boat/water taxi. I realize there are also buses but we enjoyed taking boats along short stretches of the southern Dalmatian coast when we visited Dubrovnik two years ago.

the bus aint bad, not aware of ferry but a little surfing and http://www.croatian-adriatic.eu/dalmatia/ferry-boats-central-dalmatia-guide.html

Thanks. I think we may have to explore the harbor area once we are in Split and plan to use the bus as a back-up if necessary.

When are you going? I was in Trogir in late May and the Bura Lines had ferries going every day. So it is not just a high season/summer thing... I don't think.