Power boat, sailboat and yacht builders and dealers

 Bulletin: RollerTrol™ Automation Systems is Launched!  
  • We have been busy making and selling 12v marine roller blinds for some time, and we have decided to start selling the components at RollerTrol.com so others can do the same.
  • Take a look at our online store for tubular motors and other associated products - make your own custom blinds that fit your boat perfectly!
  • While you're at it, check out our tubular motors with built-in radio controllers. When used with our multi-channel remotes, you can control all your blinds with a single remote!
  End Bulletin: RollerTrol™ Automation Systems  
Bimini construction with stainless steel - build a rainproof bimini with retractable panels on a sailboat
Installing a stainless steel bimini on your sailboat
with retractable panels that deflect rain, sun and wind
by Adrian Biffen

I like rain and the cleansing effect it has on the environment, but I certainly don't like getting wet while I'm sailing. These days, as I leave my youthful years behind, when I get wet and cold nothing short of a hot Jacuzzi tub will get me warm again. I don't have an on-board hot tub yet, so one of the first projects I tackled when we bought Serenade, our 30' sloop, was the installation of a bimini structure that covered the cockpit.

I initially made a simple cover out of aluminum tubing covered with a tarp, just to see how it might work. It was fine for a while, but there were a number of problems. First, it allowed water droplets to bounce off the outer deck into the cockpit seats, so you couldn't sit down. Then I found that the tarp roof was not strong enough to prevent pooling while at rest, and one morning I awoke at 4 am to the sound of a loud crack as the overnight rain, collecting in a large pool, brought it down. I had also tried shaping the roof with PVC tubing into a slight concave form to shed the rain, but a 20 knot wind bimini construction with stainless steelwhile beating to windward soon removed them, and I made yet another contribution to Davey Jones. Finally, I noticed that the natural inclination of crew members was to grab hold of the aluminum posts, which really weren't all that strong. It was at this point that I decided to start over and build something much more robust.

I chose 1" stainless steel tubing for the structure as it was readily available, has an attractive appearance, is very strong, and resists corrosion extremely well. I didn't want to have anything welded at this point because I needed to be able to change the structure as it evolved, and it could be assembled using standard stainless steel elbows, T joints, and other miscellaneous rail fittings. It wasn't cheap, but nothing good ever is, and I'm finding the $1,000 that I spent was well worth it. I used 7/8" tubing for the wing panels to save weight, but I didn't see the point of making the main structure any weaker than it could be. The result is shown in the picture above.

Based on my experiences with the original aluminum structure, I had a pretty good idea of the feature set I would require:

 -strong enough to handle gale force conditions
 -sturdy enough to allow crew to grab it for stability in panic situations
 -retractable 'wing' panels to deflect rain, sun and wind
 -support for the solar panel, interior cockpit lighting, and sail viewing skylight
 -full standing headroom, with the boom over the top
 -corrosion resistant and aesthetically acceptable
I  started by building the four corner posts supporting the top frame, and although this was promising, it wasn't sturdy enough for my needs. bimini construction showing stainless braces on corner postSo I added front and rear center posts, and braces to the corner posts (you can see the braced structure on the forward corner posts in this picture). That did the trick, and I determined that I could throw my 215 lbs at it while simulating a fall overboard, and it barely moved, transmitting the momentum to the hull itself as it heeled somewhat. I could easily move up to the foredeck, holding onto the front corner post with all my weight, even hanging off the toe rail if I wanted. There is very little movement in the structure, and it gives one a feeling of confidence when moving forward onto the deck in rough conditions. It is also great to be able to grab it hard when coming back off the foredeck, as you swing around and return into the cockpit.

There is easily 6' of standing head room underneath the bimini, and the boom passes cleanly above it, completely out of harm's way.

This close-up picture reveals a number of structural details that are key to the strength and design of this bimini. The rear vertical corner stainless steel rail fitting detailsposts are coupled (A) to the existing 1" stern rail with a T connector that slides on and is locked tight with allen screws. 

Moving up that corner post, we come to the rear lateral strengthening brace, which uses angled fittings (B) at each end to clasp the horizontal and vertical struts as they pass through the fittings. It also doubles as a convenient hand hold. 

Moving on to area (C), everything connects to horizontal side runner (D) with 90 degree T connectors. This includes the vertical corner strut, the horizontal rear runner, and the rear wing joint. The wing fitting can swing freely on the side runner, depending on the tension setting of the knob which has replaced the allen screw in the T fitting. The remaining corners are handled in much the same way. 

At the end of the side runner (D), you can see the lifting block and tackle for the tender outboard; the 1" side runner has more than enough strength to lift the 50 lb Yamaha 4 stroke. You can also see one end the strengthening rail that bisects the wing panel.

Here are some pictures of the most commonly used rail fittings as described above:

Stainless steel rail fitting - right angle TStainless steel rail fitting - 60 degree angleStainless steel rail fitting - right angle elbow

The rear vertical posts also made convenient places to mount other handy devices.Force 10 barbeque rotates on bimini post mount The Force 10 stainless steel barbeque pivots around the starboard post on an arm, and it also rotates 360 on its base mount, so you can position it in almost any way that suits your needs. It will swing out over the water while in use, or pivot back into the cockpit under cover if it is raining. This also allows you to set the most comfortable cooking position, depending on where you want to sit or stand - you can even cook from the dock, if you prefer. It swings back out of the way over the stern railing when not in use, under cover of the rear tarp panel. The tension adjustment is the same mechanism used on the extendable wings and it can be locked securely into any position.

I also added a small rotating crane for the tender outboard so that I can position it easily over the transom on the inflatable dinghy, and then lift it up with the block and tackle and swing it up and over onto the stern railing on Serenade when I want to carry it onboard. rotating davit crane for outboard motor This can be a real back saver at times, and would facilitate the use of a much larger engine than my 50 lb Yamaha 4 stroke.

I built the centerpiece of the roof that runs the length of the structure out of double sided oak plywood (protected with numerous coats of Cetol), to save weight and provide an little aesthetic wood appeal. It supports the solar panel, cockpit lights, and skylight, and provides an edge for attaching the roof material. I added two 1" horizontal stainless struts along both edges of the center panel, which made the structure even more rigid. The picture below was taken from inside the salon, looking up the stairway. You can see the solar panel at the rear (it tilts up 4 ways and can also be removed), high efficiency LED cockpit light, and skylight. It also provides an area at the front of the bimini (not visible) where electronics can be mounted at eye level that provides for easy access, yet keeping them out of the way. 

There are some aluminum parts used in the construction of the roof centerpiece (and the whole solar panel frame is aluminum), but because of the oak frame, there is no contact between dissimilar metals anywhere in the bimini structure, and thus no corrosion due to electrolysis.

Our Navitrol command console is mounted there and works very well in that location. If you need to  switch to manual override in a hurry, or engage it and adjustcenter bimini roof panel holds solar array course heading, the switches are right at your fingertips, in front of your eyes when standing up, holding the tiller. All the power and data wiring is concealed, and connects to the rest of the boat by traveling down the inside of the rear center strut.

At the moment I'm just using white industrial tarp as the roof covering material as it is cheap and looks reasonably good. I don't want to spend the money on the final covering until I have the design fully developed, as it has already changed a number of times. We found that white was the best color, permitting the most amount of light into the cockpit and blending very well with the white hull color, causing the bimini structure to stand out less than with darker colors. Because the roof is almost flat, it further reduces the profile of the bimini from an aesthetic point of view, and it almost disappears when the wings are folded in, when viewed from the front or side.

The tarp material is stretched tight across the roof, lashed with bungee cord through grommets at the outer edges, and even with only a very slight slope to the structure it sheds water under any condition. You can see the bungee cord in this picture at the left side of the center panel - that is actually the outer edge of the retractable 'wing' panel that has been folded inward into its retracted position. You don't see it on the right side because the other wing is fully deployed in its extended position.

There is a separate panel that can be extended across the back end that causes any run-off to exit off the stern of the boat (and very nicely blocks the cold airflow on your neck when running downwind). There is also a front panel that can be raised to provide a wind and rain shield on the front of the structure. The vertical struts also provide a structure that could support external panels to completely enclose the cockpit for foul weather transit, if desired. 

Speaking of 'wings', here is the crowning touch of this system. They can be fully retracted, or extended at any angle, either to shed rain or block the sun and wind. The trap stays taut, no matter which position they're in because of the elastic bungee cord tension along the outer edges. They also create an extra measure of privacy while staying dockside. The following pictures show the various stages of deployment positions:
Here, the port side wing is extended to provide some shade, while the starboard wing is fully retracted. If it had been raining, the port side of the cockpit would be dry as the rain water is shed directly into the chuck. retractable wings on bimini structure shed water and block sun
This is a closer view, taken from a different angle, of the port side wing extended. There are adjustable friction knobs front and rear that allow either wing to be set at any angle.  bimini structure showing extended wing
Here the starboard wing is partially deployed. starboard bimini wing being deployed
The starboard wing at the same stage of deployment as above, viewed from inside the cockpit. starboard bimini wing being deployed, view from cockpit

We have initiated a number of improvement projects for Serenade since she was purchased, and we have created a series of articles detailing the work that has been done. Here are the relevant pages in this series:

Wireless remote control autopilot
 (2) Diesel removal & 4 stroke outboard engine mount
 (3) Cockpit Bimini (this page)
 (4) Tender davits on stern
 (5) Waste management holding tank system
 (6) Solar panel, PWM charge controller and deep cycle battery system
 (7) Propane Fireplace