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A complete unit will require the following parts:

  • (1) hinge (either stainless or injection molded plastic)
  • (2) pieces of tubing - 7/8" or 1" O.D., aluminum (.058 wall) or stainless (.065 wall)
  • (1) piece of sleeve tubing - 1" or 1 1/8", stainless (.049 wall thickness)
  • (2) 1/4" - 28 stainless set screws (or those provided with stainless hinges)
  • (2) stainless spring balls


  1. Cut tubing to desired lengths (the hinge will add 1 1/2" to the struts overall length). Clean burrs from inside of tubing ends using a round file or rotary rasp.
  2. Drill for set screws 1/2" from the tube end. Use drill size 13/64". Use cobalt bits and cutting fluid.
  3. The strut design has the two spring balls positioned in relation to the sleeve as shown. They should protrude to their full height and capture the sleeve between themselves. This way the sleeve cannot accidentally be moved. If using a 5" sleeve, drill a 9/32" hole for each spring ball approximately 2" from the tube end. If using a 10" sleeve, the spring ball hole will be approximately 4 1/2" from the tube end. Place them in line with set screws.
  4. Install spring balls, then insert hinge into tubing. Align hole in hinge body with 13/64" hole in tubing. Install set screws.


Gemini folding strutsInstallation of Gemini System Folding Struts on Biminis and Dodgers

Gemlock folding struts can be added to any bimini or convertible top with no modification of the existing frame. The following instructions will guide you through a retrofit installation of struts on a bimini that is currently tensioned with straps. We use a simple patterning method that completely eliminates numbers and their frequent misbehavior. With a pattern, you know exactly what you have.

First, a strapless structure requires an aft set of rigid struts or legs that hold the frame up. These are frequently intended as storage legs when the top is folded. If your top now has four straps, you'll need to first replace the back pair. These use standard frame hardware and can be purchased at any canvas shop or marine supply store. The upper end of this strut is attached to the frame with jaw slides. The lower end will mount either on the aft rail or on the deck aft.

Gemini folding strutsTo begin, look at the photo (illus 1) to view the finished product. The struts are attached to the frame with four sliding side mounts; a standoff type fitting that allows the struts to bypass the middle frame(s). This allows you to mount the struts as high as desired. Most people prefer the struts up next to the cloth edge. The higher a spreader bar strut is placed, the more powerful it is as a lever arm.

Second, the strut will be less noticeable up next to the fabric and, if placed inboard of the frame, they can possibly be positioned behind the hem of the bimini cloth and nearly hidden. It makes no structural difference whether the struts face inboard or outboard. The choice depends entirely on the boat layout and what you are trying to achieve. Decide where the struts are to be placed. Slide the side mounts into position, first removing the lower jaw slides (mark their locations with a marker) that hold the frames together. With the side mounts in rough position, reassemble the frame to its original configuration. Tension the top in normal fashion.

Gemini folding strutsNow it's time to position the side mounts into their exact positions. A piece of masking tape stretched between the mounts will give you a clear line. My next step is to put the eye ends onto the mounts. If you use a nylon washer on each side of the eye end, you will be able to tighten the eyes securely. Align the eye ends into their working positions, facing each other (illus 2). At our shop we put the eye ends on now because it avoids making a deduction from the overall pin-to-pin measurement for the length of the eye ends. In other words, when you're done patterning, you'll know exactly how long to cut the tubing, without any adjustments.

Gemini folding strutsStep one for patterning: Get a piece of small line. Light wire, string, yarn or masking tape could all work, but a white piece of line will show your marks well. Tape or clamp the line to the outside of each opposing eye end (see illus 3 & 4).
Gemini folding struts

With a Sharpie or marker, mark on the string where you think the tubing will bottom out on the inside of the eye end. You'll only be off 1/16 inch at worst, so don't doubt your eye too seriously. These marks will be the cut ends of the strut tubing. Leave the string in place for the next step! Step two. You have just determined the overall length of the finished strut. Now you need to locate the center of the hinge along the length of the strut. Expect that your struts will have the hinge off-center along the length of the tubing. This is the norm. It has to do with the uneven geometry of the frames. Next, ease your old tensioning straps and fold the top back to its storage position (illus 5). The string is now hanging limp. Gently pull the string taut, parallel to the bimini's main frames. We want the finished struts to lie neatly alongside the frame (illus 6). Where the string is pinched at the fold point, mark the string. This mark is where the exact center of the hinge must be (illus 7).

After double-checking your work, you may remove the string. Keep port and starboard separate, as they may be different. Always believe the pattern. You now have a string with three marks. Lay the string on your already assembled Gemlock strut. The strut is in its full-extended position. Leave the sleeve off. Secure the string (tape) so that the middle mark is exactly on the center of the hinge (illus 8).
Gemini folding struts

The two end marks indicate where the tubing will be cut. Transfer the end marks from the string to the tubing. Remember that the port and starboard struts are mirroring images. Gemini folding strutsLay the struts out accordingly.

Before cutting the tubing to length (an ordinary hardware store tubing cutter does nicely. A hacksaw is fine also, but leaves a more ragged cut.), hold it up against the eye ends, both in the folded position and in the extended position to double check your work before cutting. It can't hurt. If you're satisfied with your achievement, cut the tubing to length, slide the sleeve back on and install the strut. When the struts are in position with their sleeves locked over the joints, you can remove the old tensioning straps. It is advisable to use blue Loctite on the bolts/screws that secure the eye ends to the sliding side mounts.

Gemini folding struts

Your finished job should look something like this. As a top ages, it may stretch. This can be accommodated by sliding the eye ends lower on the main frames. This will tighten the top.

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