I understand what you are talking about and there are reasons that you might do this but 99% of the time, leave the insulation alone. I have built and tested litterlly 10,000+ cables over my almost 30 years with my current company and have looked a lot of failure modes invovling leak pathways. We pressure test all of our cables in water to usually to 1000 psi … so I can give you plenty of sea stories on how they can die. I will discuss the particular cable that is currently used for the Thrusters etc.
This cable has a thermal plastic urethane (TPU) jacket and has individual conductors with Teflon insulation. There is no “water block” material between the conductors. Frankly for a system that is only going as deep as everyones units will go without never coming back … it is not a bad choice of cable at all.
The TPU jacket is friendly to a lot of compounds with the exception of certain epoxies. That is one reason I roughed up the cable jacket. This weakness could be countered by using a primer made for TPU material that will greatly enhance bond strength.
The Teflon on the conductors is a great choice from an insulation standpoint and Teflon is a outstanding dielectric. I haven’t calculated what the impedence is on this cable and I really don’t expect people to be using it for stuff that required a particular impedence value. If so, time to come up with your own cable. Teflon will normally not bond to about anything; however, you can get Teflon wire that has been “acid etched” and it will bond with various potting compounds.
So here is the bottom line with the Thruster cable. If it is cut through the jacket, water will travel down the wire and will have a high chance of a flood out. The cost for Blue Robotics to go out and have custom “water block” cable would be a little more expensive than what your typical at home ROV type will want to pay. I pay from on average $2.50 to $1000.00 per foot for cable at work.
So what is your trade off? Cost, added weight and the list goes on. One thing you can do is what is called a “dam blok”. There is a company that actually sells it. Checkout PMI’s info on the kits
This is one of the things we use in the Submarine world to handle issues with cable that is not water blocked and to enhance splices etc. Again, most at hom ROV types don’t want to incorporate stuff like this.
The bottom line is if you have money, you can engineer your ROV to go to Hades and back … but it is going to cost a TON of money. You can go the cheap route and put protective sleeving over vital cable runs. This adds cost and weight. Everything is going to cost you in some manner.