Like most things in Yellowfin, you can customize the loading spinner with a few lines of CSS:

In your custom css file add:
#canvasLoader{
display: none !important;
}
.clWrapper{
height: 100px;
width: 100px;
z-index: 4000;
background: url(/customimages/rippleloader.svg) no-repeat center center;
}Add your loading animation to the ROOT directory of Yellowfin, and adjust the background url accordingly. In this example, my animation is at:
yellowfin/appserver/webapps/ROOT/customimages/rippleloader.svg