If you get the industrial vinegar (it's about 30% compared to 4% for regular vinegar), you can saturate a rag with it and lay it on the window. Ideally, out of the sun. It'll be hit or miss as to whether or not it work depending on how long the window has been like this. Same with compounding - it'll be hit or miss. It should, at least, get a little better.
On the other hand, older boats like yours have flat glass and a local glass company can make new, tempered glass for you. Windshields are pretty easy to disassemble/reassemble.