When we bought our 1994 Sailfish 6 years ago it already had a retractable aft Bimini that laid across the top of the aft end of the hardtop. It was GREAT! Tons of shade for cruising/running and out of the way for fishing!
When we bought the 2001 Marlin two years ago it had a fixed aft Bimini as the boat was a party barge only. We had to modify it to retract and the initial modification was unsatisfactory. So, I contracted with a canvas company here in Lauderdale to re-do the whole thing since it needed new canvas as well.
The original mod placed the frame slides right in between the two rod holders on the gunnels. When retracted, this blocked the aft rod holders, so step one on the new mod was to slightly bend/crown the overall frame to place them in the new slide tracks that were to be installed inboard of the rod holders. Here's the guys adjusting and measuring out the frame.
Here's the newly laid slide tracks.
To attach the canvas to the aft end of the hardtop, they installed a slide track there as well. This is a plastic one that I had them replace with an aluminum one. Two sections of canvas slide in there with long zippers on the aft ends. The main canvas then zippers onto this short flap to easily allow me to take the entire Bimini, frame, canvas an all, zip it into a canvas boot and stow it away in the garage if I so chose (think--hurricane!).
Once it was all fitted, some final adjustments were made on the two canvas straps that clip onto hooks on the gunnels right where they start to bend down beyond the transom. Here's the slide track and frame location when it's fully up.
I have to mention one thing. This frame was never designed to retract. I was forced to decide to try and modify this frame or start from sctrach. I chose to live with the fact that when retracted, it does block the aft rod holders somewhat. Designed from scratch, the frame would have to slide farther forward to have been clear of these rodholders. This was a $1,500 job as it was and since we don't do a whole lot of trolling, I have learned to live with it. You can see here that my buddy David was not bothered by this!
Here, on a really hot day in the Abacos, you can see that there is no breeze, so we have learned to leave the Bimini up, but to unhook the aft straps and tie them off and then just fish around the frame in order to enjoy the shade. A true compromise, but no complaints from anyone on a hot breeze-less day! This rod broke about 2 minutes later with no fish to show for it by the way! That's another buddy named Dave......
Here is it fully deployed, at the dock at Treasure Cay, Abacos last summer. Another excellent benefit to having it up at the dock is that the bolsters and other cushions, etc, take a far less beating from the sun. It's about 8 feet off the cockpit deck, so it makes the cockpit like a nice patio!
And here's two more shots of why everyone loves this thing! Here's my good buddy Kevin taking his normal snooze on the way over to Abaco last summer, an 8 hour run!
And finally, if you have to endure an 8 hour, non-stop run home from the Bahamas in August, it's sure nice to be in the shade with a nice breeze! Notice the two canvas straps that keep it all taut........
And finally, here she is all ready to shove off for a day of trolling off Lauderdale. Bimini retracted and tied down and gunnel mounted Lee 18 footers ready to slip under several bridges to get outside.
My suggestions would be if you end up doing this are:
Hire a company that has done these before.
Make sure that they understand that the frame must slide a few inches forward of the forward rod holders.
You'll want it only as far aft as about the transom. Much farther aft and you'll capture a lot of engine noise. Mine is about 6-8" too far aft.
We LOVE this addition and will never have another boat without one!
When we bought the 2001 Marlin two years ago it had a fixed aft Bimini as the boat was a party barge only. We had to modify it to retract and the initial modification was unsatisfactory. So, I contracted with a canvas company here in Lauderdale to re-do the whole thing since it needed new canvas as well.
The original mod placed the frame slides right in between the two rod holders on the gunnels. When retracted, this blocked the aft rod holders, so step one on the new mod was to slightly bend/crown the overall frame to place them in the new slide tracks that were to be installed inboard of the rod holders. Here's the guys adjusting and measuring out the frame.

Here's the newly laid slide tracks.

To attach the canvas to the aft end of the hardtop, they installed a slide track there as well. This is a plastic one that I had them replace with an aluminum one. Two sections of canvas slide in there with long zippers on the aft ends. The main canvas then zippers onto this short flap to easily allow me to take the entire Bimini, frame, canvas an all, zip it into a canvas boot and stow it away in the garage if I so chose (think--hurricane!).

Once it was all fitted, some final adjustments were made on the two canvas straps that clip onto hooks on the gunnels right where they start to bend down beyond the transom. Here's the slide track and frame location when it's fully up.

I have to mention one thing. This frame was never designed to retract. I was forced to decide to try and modify this frame or start from sctrach. I chose to live with the fact that when retracted, it does block the aft rod holders somewhat. Designed from scratch, the frame would have to slide farther forward to have been clear of these rodholders. This was a $1,500 job as it was and since we don't do a whole lot of trolling, I have learned to live with it. You can see here that my buddy David was not bothered by this!

Here, on a really hot day in the Abacos, you can see that there is no breeze, so we have learned to leave the Bimini up, but to unhook the aft straps and tie them off and then just fish around the frame in order to enjoy the shade. A true compromise, but no complaints from anyone on a hot breeze-less day! This rod broke about 2 minutes later with no fish to show for it by the way! That's another buddy named Dave......

Here is it fully deployed, at the dock at Treasure Cay, Abacos last summer. Another excellent benefit to having it up at the dock is that the bolsters and other cushions, etc, take a far less beating from the sun. It's about 8 feet off the cockpit deck, so it makes the cockpit like a nice patio!

And here's two more shots of why everyone loves this thing! Here's my good buddy Kevin taking his normal snooze on the way over to Abaco last summer, an 8 hour run!

And finally, if you have to endure an 8 hour, non-stop run home from the Bahamas in August, it's sure nice to be in the shade with a nice breeze! Notice the two canvas straps that keep it all taut........

And finally, here she is all ready to shove off for a day of trolling off Lauderdale. Bimini retracted and tied down and gunnel mounted Lee 18 footers ready to slip under several bridges to get outside.

My suggestions would be if you end up doing this are:
Hire a company that has done these before.
Make sure that they understand that the frame must slide a few inches forward of the forward rod holders.
You'll want it only as far aft as about the transom. Much farther aft and you'll capture a lot of engine noise. Mine is about 6-8" too far aft.
We LOVE this addition and will never have another boat without one!