Over the years, I've built hundreds of bimini top, dodger, and spray hood frames for every kind of boat. Often I've worked on frames built by other marine canvas fabricators, some pretty decent and some outright deplorable. The building of your frame is important to the function and look of your canvas, as well as impacting your satisfaction and safety on the water.
The two most common materials for building bimini and dodger frames are anodized aluminum, usually 7/8" OD (outside diameter), and stainless steel, available in 7/8" OD, 1" OD, and 1 1/4" OD. The choice of material depends on three factors, in this order:
- What you are building
- The size of your project
- The cost and return on investment
Aluminum tubing offers two advantages: low cost and light weight.
Although anodized aluminum tubing comes in 3/4" OD, this size is unacceptable for use in the marine environment. For smaller bimini tops, 7/8" OD aluminum tubing is preferred where price is a factor, but should be used only on tops less than 72" wide and 72" long. Extending the aluminum bimini frame beyond these lengths decreases the rigidity of the frame, not only making your canvas look bad, but also leading to bending and breaking of the frame.
The maximum center line length between the bows on an aluminum frame should be around 40". In general, most aluminum bimini frames should only have three individual bows. If you need a four bow frame, you should upgrade to stainless steel tubing.
For the hardware on your aluminum bimini frame, use nylon eye ends, jaw slides, and deck hinges. Stainless hardware can corrode your aluminum tubing leading to catastrophic failure later.
For sailboat dodgers, aluminum frames are not recommended due to the tremendous stress placed on the dodger in foul weather conditions. Use 1" OD stainless steel tubing instead.
Stainless Steel Tubing
Stainless steel tubing comes highly polished to resist corrosion and pitting, and wall thickness is very important. The minimum wall thickness should be .065, about 1/16", and this holds true for 7/8", 1", and 1 1/4" OD tubing.
Sailboat dodgers up to 96" should be built with 1" stainless steel tubing. Dodgers over 96" wide should be made with 1 1/4" stainless tubing. Hand rails attached to the dodger should be either welded on or bolted on instead of using slip fittings. If slip fittings are used, through bolt the hand rail and fittings together or use 3/16" stainless steel rivets to secure them to the frame.
Use universal deck hinges when mounting your dodger frame to allow for folding down of the dodger if the design allows.
The maximum width for a 1" OD bimini frame is usually in the 100" range. At this point, the frame starts to lose it's rigidity. I generally prefer to start using 1 1/4" OD stainless steel tubing for biminis over 96" wide and up to 156" wide.
The center line length between the individual bows of your stainless bimini frame should be no more than 48". This makes the maximum length of a three bow stainless bimini frame at around eight feet and four bow frames about twelve feet.
The eye ends (I prefer the double set screw eye ends) on any support bars or prop posts should be pop-riveted or through bolted to the tubing to prevent them from slipping out under tension. If the boat is high performance and the bimini frame will be under a lot of stress for long periods of time, it is recommended that all the fittings be riveted to the tubing to prevent the hardware from slipping and possibly damaging the boat.
Mount the bimini frame to the deck using the appropriate deck hinge with #10 stainless steel screws. Through bolting the deck hinge hardware is not usually necessary if there is enough fiberglass or wood beneath the paint to get a good grip on the screw. Use 3M's 5200 Adhesive Sealer to prevent any leaks to the interior of the boat.
Many of the products mentioned here can be found at our new online store: MarineCanvasStore.com
For any questions about your canvas needs, please call me at 386-983-2470, or email me at