It looks like you have updated the connection on the page to be MySQLi, but you haven't updated the Recordsets on the page to MySQLi. Both need to be updated.
Looking at the page, it appears you may not need the old Recordset code that is still on it.
Try deleting lines 2-59
Then update the two references of:
<?php echo $row_rsBoats['Manufacturer']; ?>
<?php echo($WADAboats_details->getColumnVal("Manufacturer")); ?>