http://www.go2marine.com/product/204262F/marelon-raw-water-strainer-1-5-in.html?utm_campaign=googleshopping&utm_medium=productfeed&utm_source=googlebase&WT.mc_id=gb1
Groco makes some heavier duty models -- but it really is an issue ow where you're going to install them and how. Also what type of thru-hull you have.
The top (when opened) should be just below the water line - in my opinion.