Your call, but I'm not sure why you would skip an island just because of the ferries -- even in off season, you have many options, and you're going in high season -- August -- right?

I must admit that I think it would be a shame to be in the area and skip an island. JMO.

I thought the ferries book up and weeks in advance and its hard to get on. Yes the beginning of August, Lets say we want Hvar or Korcula.

Ahhhh - now I just found the site where you can prebok the ferry ....
https://www.jadrolinija.hr/en/schedu...31746/02082018

And unless I'm very much mistaken, you can just walk on the car ferries -- unless, of course, you were planning to take a car? I'm not sure having one would be particularly to your advantage....

only keeping the car in split to do day trips (krka - will go very early from here - and trogir, may add another) will return before leaving for islands.
Booked a hotel in hvar - 2 nights. hubby said just do nonrefundable so you cant change your mind!

Trogir is only about 1/2 hour from Split by public transportation. It would probably take that long to reach your parking space, drive to Trogir, find another parking space, and then walk into the pedestrian-only town.