You have to be able to sketch. Notice I said sketching and not drawing. They are two different things. It is one thing to look at an object and recreate it on a piece of paper — in that instance you are drawing what you see and know to be true. When you sketch you are capturing what you don't know but what you can envision. Designing is less about being true and more about proving that it can be true. (It is also important to note that sketching doesn't have to be done with a pencil. I know plenty of designers that are much better at working in 3D and create mini sculptures to get their ideas across.) The reality is that you are trying to communicate an idea of what you visualize for your design. Whatever you need to do to make that vision a reality you should do. Design teams welcome all things creative, so be creative with how you create!