Setting up the frame for Patterning

Before starting on the patterning of the top you must first tie up the frame in the position that it will eventually be in when the final installation is done. Materials used are the straps that will eventually be used for supporting the bimini , and or hard kickers , strapping tape, webbing or whatever works best for you. The things to consider are that you don’t want any movement during the patterning so use something sufficiently non stretch that stability is guaranteed.
Tie all four corners of the frame so the head height is at the required elevation. This will require also making up a drawstring to support and adjust the bows at the center. Make it look like this for later adjusting the camber of the bows.

It’s a good time to measure and mark the exact center of the outside bows also. Make a drawstring similar to the one above to support the center bow to the one its hinged off of. You now should have straps on the four outside corners of the frame, one supporting the center of the front and back frame fore and aft, and one supporting the center bow.
Make sure the corner straps are secure then its time to set the camber on the fore and aft bows. This is done by pulling on the drawstring and bending the frame center inwards. The more you camber the bow the tighter the center of the bimini will be , but keep in mind that this camber will have to be bent into the frame every time the bimini is set up. It it takes a monumental effort to pull the frame into shape and clip the straps it makes setting up the top a chore. I usually use about 2 inches of camber , but this changes from aluminum to stainless and narrow tops will need less camber than wide tops. After the camber is set as desired adjust the center bow so it is centered between the fore and aft bows ideally, but some frames are not concentric and the main idea is to put it where it looks like it belongs. Sometimes this is a matter of matching the angle of the frames so they lie parallel and sometimes setting the bow for height above the fore and aft bows to facilitate water drainage.

Patterning the Blank
First thing to do is to make layout marks on the frame. I use a sharpie black marker. Make a mark at the center of the fore and aft bows (1). I run my tape from the ends up and around the curves then eyeball the center making a mark and noting the measurement. Then I do the same thing from the other side marking the same measurement . Then it’s a simple matter of making the center mark between the two marks that have been made from the identical measurements. Then mark where the top will end on the sides(2). You can either make the center bow mark level with the front and back, or raise it a bit, some find this adds some aesthetic appeal. If sides for an enclosure are to be added later, I recommend making the sides straight.

Make marks on the center of the blank on the fore and aft edges , on blanks that require a center seam this won’t be necessary. Lay the blank over the frame lining up the center marks on the tubing with the center of the blank. Start clamping the blank to the frame working from the center outwards pulling out the wrinkles , make the canvas lay as smooth as you can with as little sags and wrinkles as possible. You will find that near the center bow at the bends it won’t be possible to remove all the slack. This is where you will have to make darts to take up the excess material, we’ll get to the darts a little later. After you are satisfied with the way the canvas is stretched its time to start marking the blank.
Depending on what color you have used some different choices for marking the fabric are available. I usually use fabric pencils for dark colors with contrasting colors , for white and light colors a regular #2 pencil will do fine. To make the lines at the front and back of the fabric you must visualize where the seam will be. Looking from the front and back the seam will follow the center of the tubing across and around the curves. Iv’e found if I use the flat side of the pencil and hold it as shown it follows the center nicely.

After the ends are marked mark the stopping point where the canvas terminates coming down the sides on the fore and aft long bows. Mark where the center bow contacts the blank to orient the center pocket location. I also give myself an x to later determine which side of the bow the pocket will be placed.

Time to start on the darts! This part often makes the difference between a good looking bimini or a great looking one. Without moving the bow snug the fabric up in one direction till all slop is taken up and wrinkles are gone. Mark the elevation or stopping point of the sides on the inside of the bimini from the mark on the bow made earlier. Then while still keeping the fabric tight mark the outside of the fabric blank at the center of the bow where it is raised the most. Continue marking up and over until well past the curved section of the bow. Now pull the canvas so the other side is wrinkle free and mark the side elevation and center again. Your marks should look like a crescent shaped v on the outside and have two marks that are at different places up and down on the inside. Repeat with the other side and on all center bows. Time to head for the cutting table. Remove the blank from the frame and bring it to the table with more fabric.