I know it has been a while since this was posted but to help anyone who needs it...
First, Amazing video. Thank you for taking the time to record and post it.
Second, cable splices can be sealed effectively using 3M "130C Linerless Rubber Sealing Tape" and put 3M "Super 88" tape over the top, wound in the opposite direction to cap it off. Make sure when you are applying the sealing tape that you keep firm, slightly stretching, pressure on the tape as you apply it and that you half lap your tape. Heat the splice up with a hair dryer after you are done to set the adhesive in the tape.
I use this method at work on low voltage (30mV max) cables submerged in 2' of water for years with no leakage.
Also, if you think you may have water in a cable, the only sure way of determining for sure is to use a megohmmeter to test it with. You test all of the inside wires twisted together to the shield wire. cables will dry out if you leave them in a warm well ventilated area for... (some period of time)
I taped up a pencil to show what I am talking about. The loose tape is there for reference only.
Hope this helps...
Well here is the DIY towfish....video
Problem is we added 240' of low impedance cable, and either we screwed up a splice or it is just not working...like not working at all.
No depth and the sidescan is scrolling super slow...