Need help with the main strap holding the tube


#1

hi folks,
first big dive test today, -20 m and again, when i pull the rov of the water, the two sides of the main tube are almost totally removed :’((((( it s quite a miracle that no water went in.
Before i dive, i make sure that the black strip is set propelly and VERY tight. it seems that , due to pression, or water, this strip is getting looser.
what alternative can i use for avoid a disaster?
what do you guys use?
thx for your help, i need to find urgently for a solution as i might next week, go for a wreck hunt at -50m

best regards
herve


#2

The primary best practice is to soak the straps before tightening. They expand a bit when wet. Anyone else?


#3

I use these straps from Sea to Summit. You can tighten them much more than the stock straps, and they don’t seem to stretch as much when wet. In the USA, they’re available at REI.

-W


#4

thank you very much just ordered a set :slight_smile:


#5

The reason why this is happening is due to the following problem:

as the electronics inside the tube are running, they generate heat that makes the air inside the tube expand. The same will happen if you leave it running out of the water for a while. At depth, the pressure on the outside keeps the endcaps in place, however, when you breach the surface (or the last couple of meters), the pressure on the inside becomes greater than the pressure on the outside, making the endcaps “pop”. This should not be a problem if you bring the ROV straight out of the water.

Another solution to the problem, and the one I always recommend, is the extract some of the air inside using a vacuum pump. We have successfully used the Mightvac MV7000 for some time now, but there are different models out there that can do the same thing; look for an automotive break fluid bleeding kit. Using a vacuum pump you achive 2 things:

  1. You get to test for leakages pre-dive; you generate a underpressure of say, 0,5 bars, and leave it like that for 5 minutes. If there is no change in the pressure then you have a tight container.
  2. You then replace the syringe plug before the e-tube has completeley refilled. This should leave sufficient room for the air to expand without creating an overpressure inside the tube.

Note that by doing this, you are creating a bigger pressure difference, so your MOD (maximum operating depth) should be reduced.


#6

thxx for the tip, i was thinking about extracting some air, but, the question is, how do you do for fit the little plastic lead in the middle of the endcaps, without getting it totally filled up with the air?


#7

When you are pulling a vacuum on the main tubes, pull a higher vacuum than you need, this will give you enough time to fit the rubber plungers into end caps and still have a vacuum in the main tube. It takes about 5-10 seconds for the tube to refill with air so you can get the plungers in pretty easily.

Also, I have removed all of the nylon straps. I use 356mm x 7.6mm and 200mm x 7.6mm cable ties (2 each) to hold the main tube in place. I have upgraded to 2.8 battery tubes to remove the battery straps.


#8

Here is another solution. Run the ROV with the electronics on and one of the end cap plungers removed. Let the electronics heat the tube. Some air is forced out of the small hole. Running it for half an hour should be plenty. Then place the end cap plunger on the tube. When you switch off the ROV, the tube will cool and hold the end caps on very tightly. Do this at home the night before the dive perhaps.

Chris


#9

yeaaaaaaaaaaa that s brilliant!!!

thxx a lot


#10

And replace the straps with bungees! No more worries about them loosening, they continue tightening as you descend.