Hire a small canoe or a yacht and crew?

You can hire smaller boats, from canoes and kayaks up to boats with 40 hp outboard motors, from Ro-No in Mariehamn. You can hire water-skis, life jackets and other items from them as well.
If you're after a more substantial experience, you could hire the cargo boat Rewinda in Mariehamn. It is 33-foot wooden cargo boat that can be used for guided sailing trips in the waters around Mariehamn.
Large boat hire companies like Aland Boatcharter or Midnight Sun Sailin rent sail boats, auxiliary-powered vessels, houseboats and motor boats.