A custom bimini top for an aft cabin (or any other area of your boat).

Our boat has a nice aft deck, however, it can get hot sitting out there. So, we figured a nice bimini top over the aft area would be a nice addition. However, the width of the aft cabin is around 11ft, and none of the standard pre-manufactured bimini tops are available in that width. Unfortunately, this requires a custom bimini top, and custom means... expensive.

Since I already own a Sailrite commercial grade machine, I figured I could make my own. So the next step - where do I get a set of 11ft wide bimini frames? That question went unanswered for a year or to, so this project went on the back shelf.

One day, the wife was thinking that we should think about re-upholstering our furniture in the boat, as well as making new curtains. We did a search of the available products, and found that Glen Raven (the makers of Sunbrella), makes a marine-grade furniture fabric. We live about 100 miles from Sailrite's main location, and I called and asked if we could come to their location and look at their fabrics. Its much easier to pick out a fabric in person vs. a web page.

We went to Sailrite and were eyeballing furniture fabric, when I noticed a bimini frame bending jig on the wall of the facility. This piqued my interest and after a short conversation with one of the owners, they agreed that they could custom make bimini frames under one condition - that I stop by and pick them up. They normally cut the frames for shipping, and include a spline fitting to re-assemble them, however, I wanted uncut bimini frames.

Well, the furniture project got put on the back burner, and I ordered a set of bimini frames. Sailrite suggested "bowing" the frames so that they were a few inches slightly wider than the needed width, which will ensure a bit of "spring" in the bows - which will look nicer. So we went with their recommendation, and I ordered all of the frame uprights a bit long, so I could cut them down as needed.



Surprisingly, Sailrite got the frames bent pretty quickly, and my wife and I were on our way to pick them up in just a couple of days. How do you transport 11ft frames? With a pickup, a few bungee cords, and packing material. We lashed the frames across the hood of my pickup and along the passenger side door. We took the back-roads for the 100 mi trip so that we would not have to drive any faster than 55mph. The frames arrived at home safe and sound.

To determine how long to cut each frame, I made this Bimini frame layout calculator. Even then, I kept each frame a couple inches long as I didn't want to ruin $400 worth of frames to my feeble attempt at math. As it turned out, my calculations were pretty accurate, but I'd still recommend cutting long, then test fitting as needed. Even though the frames were stainles steel, they cut pretty easily with a standard pipe cutter, although I had to change the cutting blade about half-way through the project.

With a couple of 2 x 4s, I layed out a mock up in my basement, and assembled the frame. With a 11ft wide frame, 6ft long, it was a challenge to fit the frame in my basement, and I had to work around a few pieces of furniture. A wood plank with a nail in the side made for a nice support to set the rear bow at the right hight.

A roll of strapping tape works great here, and I used it to assist in the proper spacing. This is the time to make sure the frame looks symmetrical. Also ensure that when you collapse the frame, all of the bows align.

get some heavy duty clear plastic and make a pattern for the canvas. You should have two pieces, one for each frame section, with the seam over the middle bow. Use tape, clamps, or whatever you need, but eventually you should get the plastic to fit on the frame just right.

Lay the plastic out with a Sharpie or other marking tool, and make sure to allow for hems. I like to lay a strip of strapping tape around the perimeter of each piece which helps the plastic roll up and retain its shape. Sailrite as a video tutorial on designing and laying out a bimini; as well, there are several how-to books covering the topic. Sailrite's tutorials are not expensive, and will perhaps keep you from making an expensive mistake.

After making the patterns, I cut the Sunbrella out on a garage floor. No matter how much you try to sweep the floor, you cannot get it clean. But with 11ft widths, you don't have a lot of choice where this can be done. I decided to sew the bimini at the boat so I could fit it as I went along. So using my bimini frame transport mechanism (my pickup and bungee cords), up to the boat we went.

Layout: The bimini should look something like the drawing below. Note how the seam works at the center, and how the seams work at the front and rear of the bimini. This allows for an overhang flap at the front and rear. Finally, all exposed edges should be sewn with binding material for a nice look, and to protect the seams.

The zippers are used to close the zipper flap, which contains the front and rear bimini frames. The flap can go the full width of the bimini or stop just short. It is far easier to use two zippers (left and right) rather than one long one. Zippers work better here than velcro as they tend to hold the frame better. For the center bimini frame, it is installed to fit after the rest of the bimini top is done. It should be narrower, and cut off just where the bimini frame bends on each side. Velcro or zippers can be used here (I used Velcro).

YKK #10 marine zippers were used throughout (available from Sailrite).

I decided to mount the bimini frame to the aft deck's stern rail. This was done by using split-rail adapters as shown here. These things are not cheap, but its better than cutting the railing. A supplier I used for much of the hardware for this project was Bo'sun Supplies, as they have a good selection of hardware and attractive pricing.

My trusty Sailrite sewing machine found its way to the table top in my v-berth. I was able to do some layout on the dock, but all of the sewing was done here. Working in a restricted area, 100 miles from home does require some planning, but it can be done.

Test fit, test fit, test fit... I had to do this several times during the construction of the Sunbrella top. This is the primary purpose for doing the sewing at the boat. If you look closely, you can see the raw edge of the Sunbrella along the portside. Also the center bimini does not yet have it's sleeve attached yet. Taking the project step-by-step, and test fitting after each step yielded satisfactory results. My hat goes off for those professional canvas workers that can do this in their shop without needing to make test fits.

No bimini top is complete without a boot, and it turned out that I had just enough material to make it. One thing I have not yet learned is how to accurately estimate how much material is needed - as I typically make a mistake or two. So, I usually add a yard or two to account for my inexperience.

I have to say that I am pretty proud of my first attempt at making a bimini from scratch. If I can do it, you can. The most important thing is to plan, plan, plan. Think of what you want to do, and adopt my personal mantra; "Think twice... cut once". I have determined that even without experience, you can just about do anything you put your mind up to (with the possible exception of brain surgery). Sure you will make mistakes - but that is simply the part of the learning process.

With the height of the bimini, I was concerned about side-to-side sway. My first attempt at solving thie problem was to add straps to the aft bow. This didn't work out very well, as the webbing has a tendancy to "sing", or flutter in the wind. I also used webbing to secure the front of the bimini, and those remained as there was no easy alternate solution.

So, $100 in fittings later and I installed rigid stainless steel supports. This worked out a lot better. The expense was mostly due to the split-rail adapters, again which were used so that I didn't have to cut any existing railing.


The next season, I constructed a "connector" to go from the aft bimini to the flybridge enclosure. The connector zips into place, and velcros over the zippers. Even so, it will leak around the zippers during a hard rain. But that's OK, since the main purpose of the connector is to provide a bit more shade from the sun. Of course, had it not leaked, I would have stated otherwise.

One noticeable part of the connector is the angular seam running across the top. This had to be done to keep the top taut. Essentially, I pinched off the top until it was taut, then sewed a seam in that location. This would be impossible without having a machine handy at the boat.

The center section of the connector rolls back so that you can access the flybridge without having to remove the entire connector. You can see a bit more of the Velcro'ed flap over zipper detail I used in this photo.

With the aft bimini erected and the connector deployed, the aft cabin turns into a nice shady area. The bimini rides pretty well when the boat is in motion, with generally no buffetting, which I believe is due to the large flybridge enclosure blocking the wind.

Another little addition I made were these Velcro straps that I can use to hold almost anything, including patio lights, or thinks I cannot describe that my wife tends to hang on the boat. Also you can see the detail of the binding I used around the complete perimeter of the bimini top.

In conclusion, making your own bimini top not only allows you to customize it to your needs, but to keep it in repair, and further modify it as you see fit.


Bo'sun Supplies

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