O.K., to start with, the aft window is 31 1/2" in length, the forward window is 32 1/2" in length. But this is almost irrelevant. The bolts of common material is in yards, so at 36" wide, this is about right for the length, as you will/should be hemming it, and the curtain should be "bunched up" a little, as most are, because a curtain stretched straight across looks, well, not right. Look at any curtain in a home.
On hems, double hem everything. If you don't, it looks like some rookie attempt, and although it may be just that, I try and make it not seem so. If you don't know, a double hem is just that, doubled. Fold it on the edge one half of an inch, iron it down, fold it again, and iron it again. It will be difficult to do if you don't iron it, just trust me on that one. You will note from the aforementioned measurements that that will take up an inch on each side, two total on your 36", leaving 34", which is about right for the Catalina window length.
I used a common 7/16' inch diameter rod, so I just single hem the top, fold it down 2 1/2", so again, you've "lost" 3" of material there. Once it is sewn at the bottom of this 2 1/2" inches, sew a straight line down the middle of this loop at top, so your rod, wire, whatever you use to suspend this with, (yes, wire works great), because that leaves some material on top of the rod, instead of just looping over it. It's just conventional curtain technique. And there's no use in it looking like you were sitting in the basement, while drunk, building this. And while we probably are, we're making every attempt to disguise this fact..
O.K., the fun part. As you know, the windows are tapered, and so should be the curtain. You should already have the loop sewn at top, so THE CUT LENGTH should be as followed. From the center of the rod, forward window, front of boat, 10 1/2"; rear of forward window, 13"; 13" front of aft window, (because they should match up), and the rear will be 15 1/2". Double hemmed at the bottom of course, and this should hang about right in the old style Cat.
I went to JoAnns fabrics here in Wilmington and found a nice nautical themed fabric for this, it had sailing ships, compasses, and crap like that on them, for about nine bucks a yard. Buy 3 yards. If you've done some rough math on this, you may be thinking, "I can do this with two". No, you can't. Save yourself two trips to the fabric store and get 3 yards. Those tapers on this will lose some cloth. And at the price of a decent pizza.
One more thing. don't fear the Singer. These are not technological marvels, it's a machine, with directions. Nobody is going to be on your boat counting stitch lengths. And if the village idiot can do it, (me), it can't be that difficult...
