SS-581 Blueback

[SSN687]

3 August 2017

After I finish trimming it I’m ready to test the emergency blow system tomorrow in my buddy’s swimming pool. How much air pressure or volume of air is used in the emergency blow tank or just how is the tank normally filled?

Ernie

[trout]

I do not know how much. On my subs the key is put a small squirt in, then press the schrader valve down to allow the gas to escape quickly. This will pre-cool your gas tank to hold the next fill. Fill the take holding the gas can upside down until it seems to equalize, 5 - 10 seconds - i never counted. This is the way you trim your boat too! The tank should be filled and then trimmed out. You are getting there!

[SSN687]

3 August 2017

What are you using to fill the emergency blow tank, air compressor or a bicycle pump or can of compressed air? An empty scuba tank’s weight is less than a full (compressed) tank, the empty scuba tank will float, but the size of the emergency blow tank isn’t going to make a significant difference in the trimming process.

Ernie

[He Who Shall Not Be Named]

3 August 2017

What are you using to fill the emergency blow tank, air compressor or a bicycle pump or can of compressed air? An empty scuba tank’s weight is less than a full (compressed) tank, the empty scuba tank will float, but the size of the emergency blow tank isn’t going to make a significant difference in the trimming process.

Ernie

liquefied propane-butane. Air-brush propellant. Assumes a liquid state at only 70 psi at room temperature. Flashes to gas when the temperature rises significantly, or the pressure drops (opening the blow valve).




We've standardized on a one-size-bottle fits all SD sub-system. Otherwise this is the provided gas ballast blow sub-system.




Charging the gas ballast blow sub-system bottle with air-brush propellant.

David

[trout]

the size of the emergency blow tank isn’t going to make a significant difference in the trimming process.

You may be surprised. The weight of the liquid gas does impact the balance. On our subs, where several grams or fraction of an ounce can make the difference between sinking or not diving, it will play out to handling challenges. If you are using as a backup only, then you will want to be consistent on your fills. That is my experience for what it's worth.

[SSN687]

5 August 2017

Yesterday was another good day in the big testing tank, my buddy’s swimming pool. I got the boat very close to being trimmed and stayed cool on a hot and humid South Carolina afternoon. I need to add just over a ¼ oz of lead under the sail and a little more foam just prior to the after hatch. I’m running out of room to add foam around the engine room. I may have to add it at or below the water line in this area. It is setting correct on the surface but not level when submerged, ass end is heavy.
My friend’s young son was “helping” me. Every time I dove the boat he had to touch it or come over and be close to it helping me to retrieve it if needed. I had no problem with him helping me but his approached to the boat was tsunami like, tidal wave, rocking the boat while submerged about a foot. With my newly commissioned assistant we made a test depth dive, to the bottom of the pool about 5 feet. So after 3 hours of “trimming” with my assistant it was time for him to take his nap, then I got it dialed in or close. I had less than a teaspoon of water in the engine room and a couple drops in the battery compartment. I feel good about the amount of in leakage of water and the new snorkel valve working properly.

After getting it close to being trimmed, I tried my first test drive around the testing tank. I didn’t have set screws in the rudder and stern planes locked down but they were tight enough to drive it a little on the surface and submerged to the fair water planes. It’s quick and fast even on 3 hour old batteries. Those 5 bladed screws are fast. I need to figure how to reprogram my Futaba radio throttle control, making it slower for the first half of the throttle stick movement. I did a lot of cavitating and back emergencies as not to hit the tank walls. I think I see another learning curve here.

The emergency blow tank has been empty during all these trimming. Yesterday before going to the big test tank I tried a couple of stores looking for a can of air brush propellant. I didn’t find any but will continue to look or order a couple of cans of it for the next Friday’s visit to the big test tank.

This week add lead, foam, find an emergency air supply, and start final hull work preparing for painting, back to the big test tank next Friday.

Ernie

[SSN687]

19 August 2017

Well yesterday was a good day and a bad day. Got to the big test tank and had adjust the vent valve servo holder. Now I'm ready to finish trimming, had to add just over a ¼ oz to the engine room, put 2 - ¼ tire weights just aft of the WTC. It was just barely heavy. Decided to make a couple of laps around the pool to start the learning curve for maneuvering it. The stern plane servo was dead but I continued with the laps using the fairwater planes, which I have on the Futaba radio using the VR or flap trim control knob. Since I’m not very good at maneuvering it using the VR knob for depth control isn’t going to hinder me one bit. Well after about two laps I successfully parked the Blueback on the bottom on the test tank, about 5 to 6 feet deep. I got in the pool to retrieve it since it’s about 99°F to cool off also.

Good news, No water in the people tank, battery or engine room.

Started disassembling the boat on the side of the pool to verify that the stern planes servo had gone bad. Got the WTC torn down to parade rest, swapped a couple of the servo connections on the receiver and verified my assumption. I was holding the WTC in one hand and the engine room in the other hand, explaining to my friend’s young son, my commissioned helper, what I was doing or had done. The WTC exploded. First I thought the batteries had exploded, but they were ok. After inspecting the ballast tank area, the plastic hose from the emergency blow tank prior to the orifice had split. The split is in the flex hose in David's picture post #66. As I said earlier the air temperature was 99°F, with the humidity factor it was probably 105 - 107°F.

I had pressurized the emergency blow tank last week for the first time to help trim it as suggested in the forum, the pressurized air was leaking a little figured it all leaked out. I didn’t attempt to pressurize it again while trimming yesterday. I didn’t or haven’t tune the emergency blow system to work correctly as I'm testing in a swimming pool and can see the boat if something happens. I was planning to use the blow system when I was going to run in the lake or somewhere that it cannot be seen or really got lost.

During the load exploding noise I tossed the WTC but held the engine room. This caused the main battery wires to the engine room to pull the brass tubing from the bulk heads. I have or was able to slide the brass tube back into place between the two bulk heads. Today I'm going to add some dielectric grease to the o-rings and pressure test the WTC.

Any other suggestions on the brass tubing repair and retest?

Today remove the emergency blow system and change out the stern plan servo.

If the WTC brass tube pressure retest is successful I will reassemble everything and make one more unpainted run prior to disassembling and prepping for painting. I'm having my body shop friend’s son mix my paint and so I can start airbrushing it after the body work is completed and can plan some time in his paint booth.

Ernie

[trout]

Ernie,
I never leave any pressure in my blow tank when I am done with a run or test. After a run or after testing, just hold a screwdriver to the schrader valve nipple (or what ever it is called) to release any gas inside. In the earlier days, these tanks were made with PVC pipe and worked well, but after a while whether from a deteriorating pvc (because of the gas or age) or getting careless from comfort leaving gas in while on display, some began splitting with disastrous results. David, I believe, was the first to come out with the copper/brass tank we have today. The one area that is still plastic is that hose.

That being said, for the hose to fail, the pressure in your tank must have been getting pretty high! The specs for Clippard hose is

0 to 105 psig at 100°F (max. 120°F)

This is from Clippard's site (which I believe is where the hose is from). At 105 psig (which translates to 119.7 psi) at 100 degrees temperature it is almost double the storage psi of the gas. Was there any chance the hose was nicked or did you demonstrate gas coming out that might have frozen the tube? Just looking for a cause. There is only one other time I heard of this, but that was 10+ years ago and I believe a different hose. I will let David correct me on errors.

i am really glad you are safe and it all is recoverable.

[HardRock]

I had the same thing happen in 2014. Picked the sub up after it had been in the pool for a test trim. It had been out of the water for about ten minutes and just went "bang".

[HardRock]

One more from a slightly different angle.

[SSN687]

Can the brass fittings just be pushed back to replace the hose?

[SSN687]

My ruptured hose

[vital.spark]

Yes, the brass fitting can be pushed back to replace the hose. I had a hose blow off once due to thermal shock while placing the sub in the bath for trimming. Scared the hell out of me!

[SSN687]

22 August 2017

Ditto, I was lucky or should I say my friend was lucky that I didn’t leave a brown floating substance in the pool when it ruptured. It was as loud as shooting a 45 pistol without wearing hearing protection. The hose was within the WTC ballast tank area so there was little to no hose whipping to hurting anyone or cause damage.

Ernie

[He Who Shall Not Be Named]

Burst pressure of that tube (which is the sub-systems safety-valve) is around 500 psi. Working pressure of most propellants is around 70 psi at moderate room temperature. Your tank got hot. The propellant increased in pressure ... and pop!

No big deal. Replace the busted hose and sin no more. Your sin was not venting off the propellant as the model/SD sat in the sun.

David