I had a Shetland on a mooring in West Bay harbour which dried out on the west side every low tide. The bottom was sandy and there were ladders down so access to the boat, on foot, was easy.
The harbour is being dredged between 8th and 14th March so access should be good but it is shallow at the entrance.
A hefty chunk of Lyme Bay is Chesil Beach which is pebbles and shelves, Lyme Regis is shallow in places, there is a cardinal buoy to the east of the entrance where it gets v. shallow. Harbour itself dries out.
My first ever mooring was in Lyme Regis, still one of my all time favourite places. The bottom is hardship sand, not entirely flat. If your props are protected you will be able to dry against the wall either in front of the aquarium, or the North wall, but check with the HM first. But unless you actually want to dry our for a particular reason I'd suggest either anchoring, picking up a mooring or tieing up to the seasonal pontoon, all well protected from offshore winds and westerlies, but a pig in anything with E in it. Be sure to say hi to Harry, everyone knows him, mention scallops and he'll know who I am