function flipLayer (layername)
{
// turn all the layers off one by one
document.getElementById('sailcruising').style.display = 'none';
document.getElementById('specials').style.display = 'none';
document.getElementById('powerboating').style.display = 'none';
document.getElementById('motorcruising').style.display = 'none';
document.getElementById('shorebased').style.display = 'none';

//turn the layer you want to show on
document.getElementById(layername).style.display = 'block';
}