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Old 25-09-2007, 11:54   #1

Join Date: Sep 2007
Location: Tampa to New York
Boat: Morgan 33 OutIsland, Magic and 33' offshore scott design "Cutting Edge"
Posts: 1,594
A bimini construction method

Take a good look at your cockpit and determine: height, forward and back limits you would like. Then look at the attachment point that will lie halfway between these points. See if you are blocking winch handle travel, sheet lines, or other potential snafus. Take an imaginary look at your egress and ingress to the foredeck and make sure you arent creating too much obstruction or having to climb where there arent sufficent handholds. After you take these into consideration you should have 3 measurements. height width and length. Divide the length by two, =A The height =B
use Asquared + Bsquared =Csquared with C being the length of the long legs of the bimini Then add the width of the bimini to C2 and you have the length of the two longer tubes then C+width will be the length of the center tube.
Mark the center of all three tubes.
Cut a 8-9" radius out of a piece of 3/4" plywood.Make sure it is nice and smooth or the pipe will kink during bending process.
Nail the plywood to a deck or shop table of appropriate size. Nail another piece of plywood near this and use it as fulcrum and put a small amount of bend in the center of the tube on the center mark. Line all three tubes up together and make sure the same amount of bend is in each one.
Make a mark on your fulcrum block and move it so its half the distance of the width of the bimini away from the outside of the radius, less the tubing diameter. Here you have to calculate about where the leg will be bent far enough. I find out how much the tubing is bent in the width from straight. mark that below the fulcrum center mark, make a straight line from there to top of the radius then square down the outside of the radius to get the desired amount of bend. Then you line up the fulcrum block mark with the center mark on the tubing and bend one leg at a time to the line you squared down.
After all three are bent adjust the legs length for the fittings and so they line up evenly when folded. Check your measurements when unfolded to your specs.
Then screw down the deck hinges and tie the long bows to the desired length and a separate line holding the middle bow up in the center of the other two. Make separate lines and attachment points to tension where straps will be, if using hard kicks place them below where you will want to stop the fabric. Tension the four lines evenly till there is some camber in the center of the bows. this camber assures the top will tension from the center out and not leave puddles or looseness in the center of the top.
Make a fabric blank larger than the top of the frame, I like topgun because of the 62" width often theres no seam necessary, if top is too big for fabric join two pieces with seam down center. from front to back. Here you need some spring clamps, I use about twenty that I get for a buck apiece at home depot. Stretch the fabric from the center out getting it as tight as possible with minimal wrinkles clamping as you go. The seam for long bows pockets is then marked on the fabric in the center of the tubing looking from back and front . mark a v for the dart at the center bow by taking up the slack in both directions and marking at the tubing center to get the seam line. Mark the position of the center bow from the bottom to get center pocket placement. Remove the canvas and lay out on a table. I cut a piece of fabric about 5/8" wide and mark all my seam allowances on long bow seams. Then cut the 5/8" line and the other is the stitch line. Use the canvas as pattern and scribe the same pattern at fore and aft ends to make the pocket patterns put alignment marks on the pocket piece and the canvas top blank on the outside edges to aid in assembly the more the better. Make another scrap 6" long and use it to follow the pocket pattern to make it uniformly wide and cut it leaving 1-1/4" at ends for hemming the pocket ends. Cut strips 4-1/4" wide and longer than the outside radius of pockets for the tails. Cut two more at 6"for outside edges reinforcement hem. Cut a piece for the center pocket and its ready for assembly. If your using straps cut the u shaped recesses on the outside radius of the fore and aft pockets. I then stitch the pieces as follows. fold the tail pieces in half and baste sew together. Hem the inside radius of outside pockets and hem ends at same time. run binding around u shaped strap recesses. pin dart from inside and remove pins as you sew. fold side reinforcements in half and fold hems in to envelope sides with. sew sides reinforcements in. staple pockets in fore and aft edges lining up marks as you go. the first time across this seam I sew about 3/8" and dont worry about exact seam placement then remove staples and do the second pass being careful to hold 5/8".fold the pockets over on seam , lay flat and sew the other seam to complete fore and aft pockets. all thats left is to sew center pocket on mark fold over and sew other edge and your done.
Some notes:hard kicks make a much smoother top as the strap pockets cause wrinkles.
A center strap and no center pocket makes a much smoother top with less water leaks as the pocket creates wrinkles and leaks in field of top through stitches. My top and bimini are virtually smooth with no wrinkles with no straps and with hard kicks throughout. Hope this is clear enough, ive done hundreds of tops and this has proven to be the fastest cleanest method for me. Stitchin Steve
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Old 25-09-2007, 17:55   #2
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Thank you thank you thank you!

I haven't completely digested this, and I'm sure I'll end up coming back here to ask for clarifications and further help, but this is a great start!

On the internet, nobody knows you're a dog anchored in a coral atoll.
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Old 25-09-2007, 19:52   #3

Join Date: Sep 2007
Location: Tampa to New York
Boat: Morgan 33 OutIsland, Magic and 33' offshore scott design "Cutting Edge"
Posts: 1,594
your welcome, I dont see an edit tab anywhere so I guess Ill have to make addendums as I catch them. I noticed I missed putting the tail pieces between the pocket and the fore and aft ends of canvas when stapling them together, run the tails wild past each end. After you sew the pockets cut the tails straight at the corners and fold the unfinished edges back inside the tail then sew a short seam to hold it, It makes a nice finished appearance and gives a double layer to attach zipper for enclosures.
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