Hiring a small motorboat for the day is one of the best things you can do on Čiovo. No licence is required for boats under a certain engine size (typically up to 5hp, though this can change — check locally), and the coast of the island is dotted with coves that are either hard to reach on foot or completely inaccessible by road.
Boat hire operators are concentrated in Okrug Gornji, with a few in Mastrinka and Slatine. Prices vary by season; in peak July and August expect to pay around €60–90 for a day, less in shoulder season. Fuel is usually included or charged separately. Pick up a laminated map of the local coves from the hire operator — they often mark their favourite spots for swimming and snorkelling.
With a boat you can also cross to the south coast of Trogir island or head further out toward the uninhabited islets in the channel. The passage between Čiovo and the mainland is shallow in places, so follow the hire operator's advice about which channels are safe at different tides. Early morning departures beat the afternoon wind that builds in summer.