Sea Water Strainer
If you have a seacock that is easy to access then there is a good reason to lower the filter to remidy the effect of air lock. However if you don''t! It could get a bit hairy when the water starts to flood in and you can''t stop it.
On second thought! Your raw water pump impeller might be throughly worn out. I have Jabsco pumps that are at least a foot above the water line and never have a problem unless the impellers are shot. They''re not hard to repair.