Line Threading Mechanism for Trident



Many people who’ve spent time attaching boats to moorings have probably heard of line threading mechanisms like the Swiftie and EasyMoor. I’ve noticed several posts on the forums here where people have said they’d like to use Trident to retrieve heavy items from the sea floor, so I thought I’d try adapting this concept to work as a Trident payload. Using our laser cutter, I made a polypropylene part with holes to attach to the 50mm-spaced inserts on the bottom of the Trident, and I bent some piano wire in a shape that would both work as the threading gate as well as create spring pressure so the gate would close itself after being threaded.

In the future, I’d like to make a design with a wider gate and a protrusion beyond the gate so things don’t slip off while you’re pushing against them. In the meantime, I thought I’d attach some images and videos of my first attempt to get people’s minds turning on the concept.

I’ll aim to post CAD files for the parts once I get everything refined.

Let me know what you think!


Is this payload going to work?
Support for marine mammal bioacoustic work

Probably easy to use for shallow water.
For heavier object and deeper water, try to have a carbine hook in front instead. then you don’t have to retrieve the Trident to start lifting.


That is awesome, I did a double take on that video when the line threaded through. What witchcraft is this!! I want and need one of these!!!


I agree with lmm. As designed you would need a light line to pull down a heavier line and it would have to be double length to return to the boat and then pull from the center. This would be good for heavy recovery, provided you could thread the line down and back again. Don’t abandon this design as it had it’s merits.

An alternative design would be to mount a caribiner with a snap closure in a way that it could be pushed onto the item to be retrieved, then released as the Trident backs away. This would allow direct attachment without having to bring the line all the way down and back to the boat.


Amazing. Getting a line attached opens up so many options.


Excellent, work @Eric_Stackpole. I can see this being very useful in the near future. :grinning:


This Sea-dog looks like an ideal basis for a lightweight device as per your alternative suggestion.


That is exactly what I had in mind


No laser cutter or 3d printer. just a saw, drillbit and glue. Look like shit but works! Can remove the bolt and just shove other arms/grippers in as it suits.


I love this!! Do you have any video of it working? It’s been really busy here, but I’m planning to iterate on my design and post as well. Can’t wait to see other renditions of this concept!


Nope. Somehow I get an error on the film when I try to download or share it from the app.
have two screenshots.
Going to test it some more during the weekend. Will test it on ropes up to 10mm as well.
Might have to slim the tool arm I made a bit. It is creating a lot drag when going in full speed, so the ROV is suddenly sideways… But having it in clear plastic was good, doesn’t reflect much of the led lights, and it is see through


fantastic! This is great to see. There are tones of derilict pots here in the Chesapeake. Good student project. Thanks!


Good work lmn. This looks like another option, using wire to hold the carbiner. They use these in rock climbing to snap the rope to the first bolt from the ground. This design looked simple, google Stick Clip for other ideas. Just ordered my Trident, can’t wait to get it.


Was just seaching for a snap mechanism and this looks like an ideal carabinerl for this application:

Skip to 4:56 in the video for the carabiner


Found one more climbing clip that looks promising for this application. Open in front like the line threading mechanism, but snaps securely shut.

Kong Frog Clip


It would be cool to refine the arm that holds the clip so that when the clip is set for “trapping” it is positively locked onto the arm. As soon as the clip is tripped, a pin or something is retracted and the clip is un-locked/detached from the arm. Another nice feature would be a way to mount the clip in a different orientation in the case where that would be an advantage for connecting to whatever item you’ve found.


First of all, thanks all for this discussion thread. This is super useful. I needed a similar design to retrieve acoustic recorders from the sea bed and all your ideas were very inspiring. I ended up using a light plastic pipe from the hardware store and a big carabiner. When the carabiner detaches from the Trident, it pulls a nail which acts as a quick release and closes the carabiner. Not exactly fancy but it works and is easy to repair in the field. I had to add some flotation to compensate for the weight of the carabiner. The maneuverability of the Trident was still very good !

Here is a video:


Nice work, I like the pipe idea for a release. I am working on a mount for something similar with the Mad Rock Trigger Wire Carabiner, posted above. In garage testing it works well to pick up bottles, clip to things, etc. Kong Frog is bulkier but works well for clipping a line or something like a crab pot, but can’t fit in a bottle neck.

Will post back when water tested.