I've never been to one, but I believe they do a secret ballot.
From the IA GOP website:
At 7:00pm, each precinct will be called to order by the temporary chair, an individual appointed by the county party. After a permanent chair and secretary are elected by the body, business can begin. Since 2016 is a presidential election year, the first item of business will be to conduct a presidential preference poll. After the results are tabulated and announced, other state and county party business will proceed. This official business includes:
Electing county Republican central committee members
Electing delegates, alternate delegates, and junior delegates to the county convention
Electing members of standing committees to the county convention (depending on the county)
Discussing, submitting, and voting on platform planks to the county convention
Following the precinct caucus, an additional three tiers of conventions will be held, moving grassroots delegates and platform proposals from the precinct level to the county, congressional district, and state conventions. If you are interested in participating in the work of the Republican Party of Iowa, consider running for delegate to the county convention!
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