Here's a quick way to make oars out of two by fours and other scrap lumber. It's a lot quicker to do it than to read about it.
More paddle and oar making projects:
Here's the quickest way I know to make a paddle.
How to make an Eskimo style kayak paddle from a 2x4 in 1.5 hours
Make a steering oar for a Marshall Islands Racing canoe.
Step 1: Sharpen a Pencil in a Funny Way
Get one of those wide flat pencils from the lumberyard. Sharpen with a knife as shown so it's flat on one side and sharpened on the other side. Finish by rubbing it on a piece of sandpaper.
Step 2: Trace around an oar you like
Find an oar you like and a piece of thin scrap plywood or sheet metal to trace it on.
Lay the oar on it.
Pound some nails around the oar to keep it from moving. Clamping it down would work also.
Trace the oar onto the pattern. You can hold the pencil vertical by holding it against either a spirit bubble level or a square.
Step 3: Cut out the Pattern
Don't cut yourself. A bandsaw is dangerous and cuts meat really well. Then sand down to the line with your favorite power sander.
You could skip the patternmaking step and trace right onto the lumber you're making oars from.
Or you could make one oar freehand and trace that for your second oar.
I'm making a pattern because I'm planning to make more oars later. I'm planning to let other people use the original oars I'm copying, so they'll probably get lost in some adventure. Then I'll still have the pattern.