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Author Topic:   Keyhole
jimh posted 09-17-2013 11:01 AM ET (US)   Profile for jimh   Send Email to jimh  
During the installation of my Lowrance HDS-8 multi-function display, I encountered a problem in passing the three cables needed to attach to the device through an existing hole in the helm console. I then found a useful solution, which I will describe in the hope that it might benefit others.

The HDS requires three connections to its rear panel: power, transducer, and network. The power and transducer connectors are rather large. They require a hole with a diameter of at least 7/8-inch to pass through. At the helm, there was an existing hole of 7/8-inch diameter, and I used this for the cables.

The cables had to be passed through the hole in a sequence. First the transducer connector and cable were passed through. The cable attached to the connector then reduced the effective diameter of the hole, making the hole too small for the power connector. However, the power connector has two attached cables that terminate in a pigtail of wires on the other end, so it could be passed through the hole by working in the opposite direction, that is, by passing the two cables and loose wires through the hole and then connecting them as needed; the connector for power never actually was passed through the hole. At this point the hole has three cables passing through it, so its effective diameter is significantly reduced.The network connector is much smaller, only about 1/2-inch in diameter, so it could pass through the hole, even with the hole filled with three cables. This approached worked for the installation. The three connectors and their four cables passed through the 7/8-inch hole.

Later I wanted to change transducers. As it happened, I had used an extension cable, to I could switch the transducers at the joint between the extension cable and the transducer cable, which occurred below the helm. I did not have to change any of the cables passing through the 7/8-inch hole.

Finally, I installed a new transducer whose cable was much longer than the previous transducer cables. I decided I did not want to use the extension cable to connect it to the HDS unit. Now I had a problem. The cables presently passing through the 7/8-inch hole were effectively captivated in place. I could not remove the transducer cable without disconnecting all of the conductors in the two cables of the power connector and removing them from the hole. The network connector would also need to be removed from the hole, too, but that was not a big problem. Disconnecting all the power and data cables from the power connector was a problem. This is when I found the solution.

Instead of enlarging the 7/8-inch hole, I turned it into a keyhole shape from its round shape. I drilled a 1/4-inch hole just adjacent to the 7/8-inch hole so that they would just overlap. Using a file, I removed the helm material from the 1/4-inch hole until it became a notch or keyhole in the larger hole.

Now, to remove the transducer cable, I first removed the network cable from the hole. Then I pushed the cables from the power connector into this notch or keyhole in the larger hole, getting them out of the way. This allowed me to pass the transducer cable connector through the hole. The addition of this notch or keyhole permits both the large power or transducer connectors to be passed through the hole without having to remove the cables from the other connector. I thought this was a much better solution than enlarging the 7/8-inch diameter hole. I was also able to make the notch or keyhole while the cables were captivated in the original 7/8-inch hole, which was an advantage.

I thought this solution was a good one for reducing the size of the holes needed to pass multiple cables with large connectors. It may be a useful solution in other applications of installing devices at the the helm.

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