Building a Bimini from scratch

[Bigjim]

I have wanted to add a Bimini to my boat for a couple of years. We have sailed in all conditions and having some shade on a sunny day or shelter in rain would be really handy. My original plan was to get some stainless steel tubing and have it fabricated from my own designs and then have it attached to my existing stern pulpit.

In our area, this was harder than I thought it would be, but a friend suggested using tubing connectors to assemble the Bimini frame. So, last winter I set about designing the frame and tracking down the connectors that would put everything together.

I ordered the connectors and several 1" tubes from Sailrite, but the longest tube they sell is 7 feet. I needed 8 footers to span my cockpit. A friend who owns a machine shop ordered 2 - 20 foot tubes and even cut them to my specifications. By spring I had everything in place and we were planning a 10-day cruise on Lake Michigan for the end of June. I had only a couple of weeks to put everything together and then cut and sew the canvas.

Everyone who saw my initial design kept suggesting that I bend the cross members to put a slight arch in the Bimini. I borrowed a tube bender and put a 3-4 inch arch in the tubes. I cut the verticals and the two side tubes and started assembling everything.

Working alone, I installed the vertical supports and had the sides and cross members nearly finished and suddenly the port side tube fell off into the water next to the pier. I was devastated. My pier neighbor happens to be a diver so I asked her to help and she came out a couple days later and rescued the tube and parts from Davey Jone's locker.

This time I tied parachute cord on every tube and put some tension on the ropes. I had no more tragedies and in less than 3 hours the entire frame was complete. I then measured the finished dimensions, which were surprisingly similar to my original design.

Another friend owns a marine canvas shop and sold me some Sunbrella and allowed me to use one of his sewing machines. (I had constructed my boat cover there a couple of years earlier.) Making the Bimini cover took only about 4 hours, including the window in the center to allow me to see the mainsail and windex. Another hour later I had grommets installed on all four edges. The Bimini cover was ready to install.

The next day, I brought the cover to the boat and started installing it. I started at the front edge, thinking that if I was off on my measurements, I could hide the error at the back end which hangs over the water. It only took about an hour to lace the cover to the frame. And it looked marvelous.

Eventually, I may make another version with flaps to allow me to attach sides and a back to create a little cuddy for cold weather sailing. I may just leave it as is, since it looks and works so well, so far.

The final goal is to get the frame welded to the stern pulpit to provide a bit more strength and security and side braces. The connectors are nice but one good push could tip the frame over to one side. I have web straps to replace the last few parachute cords but after nearly a month, everything seems to be working exactly as I envisioned it.

[kayakerChuck]

40+ year canvas pro here.

That looks great!

The side to side loads can be astronomical in a big blow- so plan your bracing accordingly. Straps, tubing, whatever- it just needs to be strong.

[fxykty]

Looks really good. In addition to the bracing comment (just think how much load there’s going to be when you’re heeled!), I would also suggest redoing your edges. Those grommets are going to pull out as the tension loads are very high - you can see the scalloping already. In addition, you need way more grommets - they should be no more than 150mm/6” apart.

Our previous canvas bimini wrapped around the poles so that the grommets edge is underneath and just inside the edge. A flap with matching grommets is sewn onto the underside of the canvas so that there is a gap of about 50mm/2” between the two sets of grommets. Because the material wraps around the pole you effectively halve the load on each grommet. This means you can apply more tension and the eventual failure will likely not be the grommets. The canvas wrapping around the poles was doubled for chafe resistance.

You can use the current grommets edge as the inner flap, and sew on extra material on each edge (back from each grommet edge so that they are effectively a flap and accessible from both sides for tensioning line) to wrap over and around each pole. Use double material for chafe resistance and strength not just for the edges but along the interior poles as well - it’s along the poles where a canvas bimini wears with every flap of the material.

[Bigjim]

Originally Posted by fxykty

Looks really good. In addition to the bracing comment (just think how much load there’s going to be when you’re heeled!), I would also suggest redoing your edges. Those grommets are going to pull out as the tension loads are very high - you can see the scalloping already. In addition, you need way more grommets - they should be no more than 150mm/6” apart.

The scalloping is more a factor of my parachute cord than the wind. It's tied pretty tight, right now. As for loading, so far so good. We sailed for 10 days a couple of weeks ago in 10-15 knot winds twice with no issues. The first time we were heeled 15 degrees or so. We were also anchored in 20-30 knot winds (and heavy rain) with no issues at all. I'll be keeping an eye on those stresses and respond accordingly. Thanks.

[cr180]

Turned out well! What tube bender did you use?

[Bigjim]

Originally Posted by cr180

Turned out well! What tube bender did you use?

The one from Harbor Freight

https://www.harborfreight.com/tubing-roller-99736.html

[Tedd]

Looks fantastic, great job! And inspiring for me as I'm contemplating some canvas work on my boat, though not as elaborate.

For cheapskates who are interested in copying your work, I came up with a simple method for making large radius curves in tubing. I make a form from a 2x10 (or whatever width is required for the bend radius and length) and cut a round groove along the curved edge with a quarter-round router bit. (Once each direction, to make a half-round groove.) Then I clamp one end of the tube and pull the other end down over the form with whatever means is handy (usually another clamp).

The radius on the form needs to be quite a bit tighter than the desired bend radius because of spring back. I found a formula on the web to estimate the spring back but, in the end, I determined the radius on the form by trial and error.

[cr180]

Originally Posted by Bigjim

The one from Harbor Freight

https://www.harborfreight.com/tubing-roller-99736.html

Thanks

[Bigjim]

Originally Posted by Tedd

Looks fantastic, great job! And inspiring for me as I'm contemplating some canvas work on my boat, though not as elaborate.

For cheapskates who are interested in copying your work, I came up with a simple method for making large radius curves in tubing. I make a form from a 2x10 (or whatever width is required for the bend radius and length) and cut a round groove along the curved edge with a quarter-round router bit. (Once each direction, to make a half-round groove.) Then I clamp one end of the tube and pull the other end down over the form with whatever means is handy (usually another clamp).

The radius on the form needs to be quite a bit tighter than the desired bend radius because of spring back. I found a formula on the web to estimate the spring back but, in the end, I determined the radius on the form by trial and error.

I've also heard that people will use a torch to heat the tubing up before bending, this allows you to bend them more easily and when they cool they hold the bend better. But, to make it clear, I bought the bender and then returned it for a full refund. So, the cost was zero $.

[Sun and Moon]

Nice job!
Can you give us an idea what your costs were?

[Bigjim]

Originally Posted by Sun and Moon

Nice job!
Can you give us an idea what your costs were?

The tubing probably cost $400 and the fitting another $400. Some of the tubing was donated by a friend.

The Sunbrella and window was about $100.

So, all-in, I would guess around $1,000.

[suiramor]

What kind of sewing machine does one need to work with the materials needed for a bimini?

[Bigjim]

Originally Posted by suiramor

What kind of sewing machine does one need to work with the materials needed for a bimini?

That depends on what material you use for the cloth. I used Sunbrella which is a median weight material. I folded it over once along the edges. For that application most good sewing machines should be sufficient. I was using a professional machine that can basically sew through almost anything.

[psk125]

Nice work- looks very good, and solid! Using connectors reduces costs a lot.
For SS tubing, checking with junkyards may be worthwhile. We paid $2.50 per pound for 1" 316 SS tubing. It may be up to $3.50 now. Hospitals use it for oxygen supply lines and they often rip it out to revamp their facilities.

[glenn.225]

I have a 1970's Kenmore that was gifted to me by a friends Mom. It's a metal bodied model that does straight, w-stitch and reverse. Very simple and it works well on Sunbrella and sails.

Here's one like mine, maybe a bit overpriced. https://www.ebay.com/itm/166223428040

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