I have lived half of my life time duol sa dagat. Pierme ko kabati and did use too the word 'bayanan' when speaking of shells sa kinhason or mga umang. There is indeed a word used in spoken cebuano nga "bay." Oher than shortcut sa abay (friend) the word can refer to a house (where people live). It can also refer to the shells sa mga kinhason. Etymologically, "bay" and "balay" are the same as the "bahay" of the Tagalogs - depending usually on the origin of the speaker. Most cebuanos living in and near the capital city, use the contracted form "bay" while as you move away from the city going either north or south, you get to hear people saying the complete form. 
The word "bayanan" is therefore a derivative of the contracted form "bay." In a southern town of cebu, for example, one can still hear "balayanan" to mean "bayanan". The conrtracted forms are seldom - if not ever - used in formal cebuano write ups.